a review of developments towards dry and high speed machining of inconel 718 alloy

International Journal of Machine Tools & Manufacture 44 (2004) 439–456www.elsevier.com/locate/ijmactool

A review of developments towards dry and high speed machiningof Inconel 718 alloy

D. Dudzinskia,∗, A. Devillez a, A. Moufki a, D. Larrouque`re b, V. Zerroukib, J. Vigneaub

a Laboratoire de Physique et Mecanique des Materiaux, UMR CNRS 7554, ISGMP, Universite de Metz, Ile du Saulcy, 57045 Metz Cedex 1,France

b SNECMA Moteurs, Route Nationale 7, BP 81, 91003 Evry Cedex, France

Received 21 March 2003; received in revised form 9 June 2003; accepted 10 June 2003

Abstract

The increasing attention to the environmental and health impacts of industry activities by governmental regulation and by thegrowing awareness in society is forcing manufacturers to reduce the use of lubricants.

In the machining of aeronautical materials, classified as difficult-to-machine materials, the consumption of cooling lubricantduring the machining operations is very important. The associated costs of coolant acquisition, use, disposal and washing themachined components are significant, up to four times the cost of consumable tooling used in the cutting operations. To reducethe costs of production and to make the processes environmentally safe, the goal of the aeronautical manufacturers is to movetoward dry cutting by eliminating or minimising cutting fluids. This goal can be achieved by a clear understanding of the cuttingfluid function in machining operations, in particular in high speed cutting, and by the development and the use of new materialsfor tools and coatings. High speed cutting is another important aspect of advanced manufacturing technology introduced to achievehigh productivity and to save machining cost. The combination of high speed cutting and dry cutting for difficult-to-cut aerospacematerials is the growing challenge to deal with the economic, environmental and health aspects of machining.

In this paper, attention is focussed on Inconel 718 and recent work and advances concerning machining of this material arepresented. In addition, some solutions to reduce the use of coolants are explored, and different coating techniques to enable a movetowards dry machining are examined. 2003 Elsevier Ltd. All rights reserved.

Keywords: Inconel 718; High speed cutting; Dry cutting; Cemented tools; Ceramic tools; Coatings; Minimum lubrication application; Surface integ-rity

1. Introduction

The development of governmental pollution-pre-venting initiatives and increasing consumer focus onenvironmentally conscious products has placed increasedpressure on industries to minimise their waste streams.In this way, the ISO 14000 international environmentalmanagement system standards have been developed tohelp industries to manage better the impact of theiractivities on the environment. Particularly concerned isthe metal-working sector which includes automotive andaerospace industries. Attention is being directed to the

∗ Corresponding author.E-mail address: [email protected] (D. Dudzinski).

0890-6955/$ - see front matter 2003 Elsevier Ltd. All rights reserved.doi:10.1016/S0890-6955(03)00159-7

role of cutting fluids in machining, machine tool energyefficiency and the impact of process wastes on theenvironment.

The ADEME, French Agency for Environment andEnergy Management, supports a project with the goalof improving the machining processes of difficult-to-cutmaterials for the aerospace industry, in order to movetowards dry cutting operations that are more friendly forenvironment and health, and in the same way, to reduceenergy consumption.

The advantages of dry machining are:

� non-pollution of atmosphere or of water whichreduces the danger to health, in particular, skin andrespiratory damage,

� no residue of lubricant on machined components

440 D. Dudzinski et al. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456

which reduces or eliminates cleaning costs and asso-ciated energy consumption,

� no residue of lubricant on evacuated chips whichreduces disposal costs and the associated energy con-sumption.

At high cutting speeds, it is well known that the lubri-cation in the cutting zone is not evident and not reallyeffective. That is why high speed machining and drymachining are often associated. High speed machiningleads to lower cutting forces, higher removal rates andtherefore to lower energy consumption. The project isconcerned with these two aspects of machining to realisethe ecological importance and high performance machin-ing of hard-to-cut aerospace materials. In the first step,the dry machining of the Inconel 718 alloy used bySnecma-Moteurs will be studied.

Before introducing dry machining, it is important tosummarise the functions of cutting fluids and to searchhow the effects of cutting fluids may be substituted. Gen-erally, the use of cutting fluid leads to an increase oftool life by the reduction of cutting forces (lubricationeffect) and temperatures in the tool (cooling effect).However, these effects are not evident in high speedmachining, in particular, when ceramic inserts areemployed [1]. The energy consumed in performing amachining operation is mainly converted into heat. Cut-ting fluids are employed to remove heat from the work-piece, the tool, the fixtures and the machine tool (coolingeffect). The heat generated is mainly dissipated in thechip and in the workpiece, a rather small part of heatflows to the tool. However, the highest temperature isobtained at the tool–chip interface which leads to dif-fusion wear and cutting edge degradation. The otherimportant functions of the cutting fluids are to flush awaythe chips from the cutting zone (flushing effect) and toprovide corrosive resistance to the machined component.

In addition, it is necessary to understand well themechanisms that contribute to tool wear and to work-piece surface integrity when working with Inconel 718.Hence, this paper is a general review of the recent devel-opments in the machining of this material and an explo-ration of the possible ways to dry cutting. In the firstpart, the characteristics of Inconel 718 that are respon-sible for its poor machinability are reviewed and theassociated problems are listed. Then, the latest researchcarried out on the use of uncoated and coated carbidetools under wet and dry conditions is summarised. Theconstant demand to increase productivity and quality hasled to the development of ceramic tools. They are usedfor machining nickel-based alloys at higher cuttingspeeds and some of their results are given. When sur-faces are produced, they need to meet functional servicerequirements, in particular for the aerospace compo-nents. As a consequence, attention is focussed on theparameters influencing the surface quality during mach-

ining Inconel 718. Finally, to examine the move towardsdry cutting of Inconel 718, interesting alternatives toconventional flooding coolant supply that are minimumquantity lubrication technologies, are reported and recentinnovations of tool coatings for dry machining are dis-cussed.

2. Machinability of Inconel 718

Nickel-based superalloys are widely employed in theaerospace industry, in particular in the hot sections ofgas turbine engines, due to their high-temperaturestrength and high corrosion resistance. They are knownto be among the most difficult-to-cut materials. Attentionis focussed on the Inconel 718 family in the followingparagraphs.

The properties responsible for the poor machinabilityof the nickel-based superalloys, especially of Inconel718, are [2–6]:

� a major part of their strength is maintained duringmachining due to their high-temperature properties,

� they are very strain rate sensitive and readily workharden, causing further tool wear,

� the highly abrasive carbide particles contained in themicrostructure cause abrasive wear,

� the poor thermal conductivity leads to high cuttingtemperatures up to 1200 °C at the rake face [7],

� nickel-based superalloys have high chemical affinityfor many tool materials leading to diffusion wear,

� welding and adhesion of nickel alloys onto the cuttingtool frequently occur during machining causing sev-ere notching as well as alteration of the tool rake facedue to the consequent pull-out of the tool materials,

� due to their high strength, the cutting forces attainhigh values, excite the machine tool system and maygenerate vibrations which compromise the surfacequality.

The difficulty of machining resolves itself into twobasic problems: short tool life and severe surface abuseof machined workpiece [3,8]. The heat generation andthe plastic deformation induced during machining affectthe machined surface. The heat generated usually altersthe microstructure of the alloy and induces residualstresses. Residual stresses are also produced by plasticdeformation without heat. Heat and deformation gener-ate cracks and microstructural changes, as well as largemicrohardness variations [9]. Residual stresses haveconsequences on the mechanical behaviour, especiallyon the fatigue life of the workpieces [10,11]. Residualstresses are also responsible for the dimensional insta-bility phenomenon of the parts which can lead toimportant difficulties during assembly [12,13]. Extremecare must be taken therefore to ensure the surface integ-

441D. Dudzinski et al. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456

rity of the component during machining. Most of themajor parameters including the choice of tool and coat-ing materials, tool geometry, machining method, cuttingspeed, feed rate, depth of cut, lubrication, must be con-trolled in order to achieve adequate tool lives and surfaceintegrity of the machined surface [9,11].

3. Cutting tools for machining Inconel 718

The requirements for any cutting tool material usedfor machining nickel-based alloys should include [3]:

� good wear resistance,� high hot hardness,� high strength and toughness,� good thermal shock properties,� adequate chemical stability at elevated temperature.

Turning, milling and drilling are common operationscarried out in the manufacture of jet engine mounts andblades, while turning and drilling are the predominantmachining operations in the manufacture of disks for gasturbines. Most published work on the machining ofnickel-based alloys deal with turning, then with milling,while drilling has received little attention.

3.1. Machining Inconel 718 with carbide tools

Cemented carbide tools are still largely used for mach-ining the nickel-based superalloys, especially Inconel718. Over the years, the use of carbides for cutting toolshas been established. However, with the increasingdemand to achieve fast material removal and better sur-face quality, high speed machining was introduced andthe use of the cemented carbide tools has become moreproblematic. For nickel-based alloys, the concept of highspeed machining refers to speeds over 50 m/minapproximately. In order to achieve higher cutting speeds,coated cemented carbides have been developed. In thefollowing, the performance of coated and uncoated car-bide tools in machining Inconel 718 is presented.

Liao and Shiue [14] analysed the wear mechanism oftwo cemented carbide tools: K20 and P20 grades, in dryturning of Inconel 718. The feed rate and the depth ofcut were 0.10 mm/rev and 1.5 mm, respectively. Thecutting speed was either 35 or 15 m/min.

On the wear surface of the K20 carbide, they observeda sticking layer very close to the cutting edge. Built-up-edge (BUE) was formed at a cutting speed of 35 m/minwith chipping of the cutting edge. When P20 carbidewas used, the sticking layer also could be found, butcomparatively, the wear was more irregular, the flankwear length was larger and the groove was deeper.

Using the electron probe microanalyser (EPMA) toanalyse the concentrations of tool elements and work

elements beneath the rake face, they found for the cut-ting speed V = 35 m/min, that there were no change oftool elements but Ni and Fe diffused into the cutting toolfor the two cemented carbide tools. This diffusion of thework elements into the cutting tool may be explained bythe very high cutting temperature (about 1000 °C) duringthe experiments.

Alaudin et al. [15] performed extensive research onthe end milling of Inconel 718. They carried out testsunder dry conditions with uncoated tungsten carbideinserts (K20 grade). The tool life was investigated in thefull immersion and half immersion (both in up cut anddown cut). From the cutting tests, it was found that atool life range of 5–10 min can be obtained at cuttingspeed of 19.32 m/min, feed of 0.09 mm/tooth and axialdepth of cut of 1.0 mm. In addition, they concluded thatfull immersion increased tool life in comparison withhalf immersion and down cut gave better performancethan the up cut end milling.

Derrien and Vigneau [16] tested uncoated and coatedcarbide (K20 grade, CrN and TiN coatings) for millingoperations (contouring) at a high cutting speed of 200m/min, a feed rate of 0.04 mm/tooth and a depth of cutof 0.5 mm. They showed that TiN coated carbide hasthe lowest wear. In addition, the machining perform-ances with air assistance and micropulverisation werecompared with those of dry cutting. Dry cutting resultedin the best tool performance.

Rahman et al. [4] presented a work which discussesthe machinability of Inconel 718 subjected to variousmachining parameters including tool geometry, cuttingspeed and feed rate. Flank wear of the inserts, workpiecesurface roughness and cutting force components havebeen considered as the performance indicators for toollife. Turning experiments were conducted under wetconditions. Two types of inserts were used:

� K type substrate, TiN PVD coated cemented car-bide, and

� multi Al2O3 CVD coated cemented carbide.

They studied the effect of the side cutting edge angle(SCEA), Fig. 1, on the tool life for three feeds (0.2, 0.3and 0.4 mm/rev) and three cutting speeds (30, 40 and50 m/min), the depth of cut was fixed to 2 mm. For thetwo inserts, tool life increases as the SCEA increasesfrom �5 to 45°, see for example Fig. 2. For theseincreasing values of the SCEA, the temperature of thetool–chip interface related to the undeformed chip thick-ness t1 certainly decreases. Moreover, the heat generatedduring the cutting process is distributed over a greaterlength of the cutting edge lS. This improves heat removalfrom the cutting edge, distributes the cutting forces overa larger portion of the cutting edge, reduces tool notch-ing and substantially improves tool life.

Throughout the experiments, the PVD–TiN coated


Fig. 1. SCEA or approach angle.t1 is the undeformed chip thickness,f is the feed, w is the width of cut, lS is the length of the engagedcutting edge.

Fig. 2. Effect of SCEA on tool life for a cutting speed of 30 m/minand different feed rates using the Al2O3 CVD cemented coated tool.From Rahman et al. [4].

carbide insert exhibited excellent resistance to depth ofcut notch wear at the approach angles of 15° and 45°.The inserts performed satisfactorily even at the highestspeed of 50 m/min and at the highest feed rate of 0.4mm/rev at 45° approach angle. This type of insert perfor-med best at the speed of 30 m/min and the feed rate of0.2 mm/rev with an approach angle of 45°.

The Al2O3 CVD coated cemented carbide exhibitedmore severe notch wear at all three angles tested andmight not be suitable for cutting Inconel 718.

Itakura et al. [17] conducted dry turning experimentsto identify the tool wear mechanism clearly when a com-monly used coated cemented carbide tool cuts Inconel718. The tool was a square tip made of coated cemented(P20, TiN/TiC multilayered coating). The temperaturewas measured using the tool–workpiece thermocouplemethod. With this method, only the average temperature

of the contact area can be measured. The cutting speedswere 30, 100 and 150 m/min, the feed rate was 0.2mm/rev and the depth of cut was 0.25 mm. Continuousand interrupted experiments were conducted.

During continuous cutting at a speed of 30 m/min,Inconel 718 adhered to the rake face of the major cuttingedge and the adhering material became a stable BUEprotecting the face. For this reason, there was almost norake wear but only flank wear. The hard particles con-tained in the Inconel 718 alloy were certainly responsiblefor abrasive wear of the coating film on the flank face.In addition, the work material adhered to the surface ofthe worn area of the flank and tool material was repeat-edly being removed. The cutting temperature at 30m/min was 990 °K and at 100 m/min it was 1320 °K;at this temperature, stable adhesion of the BUE is nolonger possible and wear advances on both rake andflank faces. The coating film on the rake face wears off,and later, when the wear reaches the cemented carbidematerial, the rate of wear increases. In the same way,the flank wear progresses faster at a cutting speed of100 m/min. This is due to the high-temperature causingdiffusion and surface oxidation at high speeds.

During interrupted cutting, material adhering to therake face (BUE) is removed, causing the coating film toflake. Wear advances as the number of repetitionsincreases. It has been verified that gradually reducing theundeformed chip thickness at the end of cutting will helpto reduce the separation of BUE and, as a result, willreduce the separation of coating film from the rake face.

Jindal et al. [18] studied the relative merits of PVD–TiN,TiCN and TiAlN coatings on cemented carbide sub-strate (WC—6 wt% Co alloy) in the turning of Inconel718 with coolant. The tested cutting speeds were 46 and76 m/min, the feed rate and the depth of cut were main-tained constant and equal to 0.15 mm/rev and 1.5 mm,respectively. At both speeds, TiAlN and TiCN coatedtools performed significantly better than tools with TiNcoatings. The end of life for all the three coated toolswas dictated by maximum flank wear or nose wear. Atthe lower cutting speed of 46 m/min, an excellent per-formance of the TiAlN coated tools was noted, Fig. 3.The maximum flank wear was about 0.15 mm after acutting time of 5 min. Furthermore, the TiAlN toolsexhibit lower nose and crater wear than the TiCN andTiN coated tools.

Since the substrate material was the same for all thecoated tools, the observed differences in tool lives andwear behaviour were attributed to the coatings. Coatingsincrease wear resistance and may reduce cutting forcesand temperatures at the tool edge and thereby indirectlyaffect the deformation and fracture behaviour of the tool.TiAlN has a significantly higher hardness than TiCN orTiN above 750 °C which will translate into improvedresistance to abrasive wear. Also, it exhibits good high-temperature chemical stability. This high-temperature


Fig. 3. (a) Tool lives of PVD–TiN, TiCN and TiAlN coated insertsin turning Inconel 718 (feed = 0.15 mm/rev, depth of cut = 1.5 mm,cutting speed = 46 and 76 m/min); (b) maximum flank wear as afunction of time (cutting speed = 46 m/min), from Jindal et al. [18].

stability is a result of the tendency of TiAlN coatingto form a protective outermost layer of Al2O3 and anintermediate layer comprising titanium, aluminium, oxy-gen and nitrogen during the machining operation, lead-ing to higher oxidation resistance. Finally, TiAlN hasthe lowest thermal conductivity among the three coatingstested. This should result in lower tool tip temperaturesas much of the heat generated during machining wouldbe carried away by the chip. As a result, the TiAlN coat-ing imparts excellent crater resistance.

Prengel et al. [19] confirmed the conclusion of theprevious work but with a multilayer coated tool. Theyperformed Inconel 718 turning tests with a coolant anddifferent PVD coated carbide cutting tools at 61 and 76m/min, Fig. 4. The TiAlN-multilayer showed someadvantages over the TiAlN-monolayer andTiN/TiCN/TiAlN-multilayer coating particularly at ahigher speed of 76 m/min. The main failure mode inInconel 718 machining was abrasive nose wearaccompanied by plastic deformation. Depth-of-cutnotching was also observed. The notching was heavilyinfluenced by burr formation on the uncut diameter.Coated flaking was observed early in the cut at the depthof cut region for all the coated tools tested.

Fig. 4. Performance of TiAlN–monolayer and TiAlN–multilayercoated carbide tools in turning Inconel 718, from Prengel et al. [19].The two tested cutting conditions were: cutting speed = 61 m/min,feed = 0.125 mm/rev, depth of cut = 1.27 mm, cutting speed = 76.2m/min, feed = 0.15 mm/rev, depth of cut = 1.52 mm.

Sharman et al. [2] detailed experimental work usingTiAlN and CrN coated tungsten carbide (K10 gradecarbide) end mills for dry machining up to 150 m/minrectangular blocks of Inconel 718. A three factor, fullfactorial cutting experiment design at two levels was out-lined with the workpiece inclined at 45° and 60° fromthe horizontal, Fig. 5. All the tests resulted in low toollives; however, the longest one occurred with TiAlNcoated tools at 90 m/min with a workpiece angle of 45°,Fig. 6. One large notch located towards the high speedposition together with a smaller notch at the leading edgeposition was generally evident.

Finally, TiAlN coated tools performed better than CrNcoated tools due to their higher hardness and oxidationresistance. The extensive BUE and coating peeling seenwith CrN coated tools at a cutting of 90 m/min suggests

Fig. 5. Configuration of ball end milling tests performed by Sharmanet al. [2]. Axial and radial depths of cut: 0.5 and 1 mm, feed rate:0.1 mm/tooth.


Fig. 6. Dry ball end milling of Inconel 718 with coated carbide tools, results of the machining tests, from Sharman et al. [2].

that CrN has a higher chemical affinity to Inconel 718than TiAlN.

The work of Jawaid et al. [5] is concentrated on thewear behaviour of two different grades of single layerPVD–TiN coated and uncoated tungsten carbide insertwhen face milling Inconel 718 for various cutting con-ditions, Fig. 7. An emulsion with 6% concentration wasused as a coolant. The cutting speeds were 25, 50, 75and 100 m/min for the coated tools and 25 and 50 m/minfor the uncoated tool. The depth of cut was 1 mm andthe feed rates were 0.08 and 0.14 mm per tooth.

The uncoated carbide (WC 90.1%, 9.5% Co, 0.4%VC) tool performed better than the PVD–TiN layercoated tools at the lowest cutting speed of 25 m/min andfor both feed rates in terms of tool life and of volumeof metal removed. Flank wear developed either on themain cutting edge or on the nose, controlled the tool lifeat all cutting conditions for all the three types of inserts.

Premature removal of the coating layers from thetool–chip contact zone hindered the overall performanceof the PVD–TiN layer coated tools at a cutting speed of25 m/min.

Ducros et al. [20] studied TiN/AlTiN and CrN/TiNnanolayer coatings deposited on a K20 cemented carbideand its machining performance was tested by turningInconel 718 alloy. Lubricated tests were carried out; cut-ting speed, feed and depth of cut were 40 m/min, 0.2mm/rev and 1.5 mm, respectively. The performance of

Fig. 7. Average flank wear when face milling Inconel 718, (a) at feed rate 0.08 mm per tooth, (b) at feed rate 0.14 mm per tooth. A and B weretwo different grades of single layer PVD–TiN layer coated tools, C was an uncoated tungsten carbide insert (WC 90.1%, 9.5% Co, 0.4% VC).From Jawaid et al. [5].

the nanolayer coated tools was compared with that ofclassical mono- and multilayer coated and uncoatedinserts, Table 1. Abrasive nose wear and chipping at thecutting edge were the main failure modes observed. Thedepth-of-cut notch is considered as a determinant for toollife when machining Inconel 718. The notching is influ-enced by burr formation on the uncut diameter; this fail-ure mode is mainly due to the hardening of the materialduring machining. This phenomenon appeared for unco-ated or CrN/TiN coated tool and was attenuated withTiN/AlTiN nanolayer coated insert. According to theauthors, this was probably due to better chip sliding anda reduced cutting temperature with this coating. Abrasivewear is mainly due to carbide particles in Inconel 718.The high hardness of the TiN/AlTiN nanolayer coating(Hardness HV0.05 = 3900) provides better abrasion resist-ance than classical multilayer and monolayer structures.In addition, TiN/AlTiN nanolayer coating presents a bet-ter resistance to welding. High-temperature resistance ofAlTiN included in this coating allows better resistance tothe BUE phenomenon than CrN/TiN nanolayer coating.

As summary, it appears from previous studies thatadhesion and abrasion are dominant when machiningInconel 718. Work material adheres to the cutting edgeto form a BUE, depending on the cutting conditions. TheBUE is not always stable and is sometimes repeatedlyremoved with tool material leading to important notch-ing at the depth of cut and at the tool nose and coating


Table 1Cutting tool failures of different coatings used for turning Inconel 718. Tool life was determined by an average flank wear of 0.5 mm, a depth-of-cut notch width of 1 mm or a nose wear of 0.8 mm. Cutting conditions were: cutting speed V = 40 m/min; feed rate f = 0.2 mm/rev; depthof cut d = 1.5 mm

Cutting tool and coating Tool life Depth-of-cut notching after Flank wear VB (µm) after BUE after 4 min4 min machining (2 passes) 4 min machining (2 passes) machining (2 passes)

Uncoated 4 min +++ 500 +++Commercial multilayer TIN/TiAlN (26 6 min + 300 +layers)Multilayer CrN/TiN 5 min ++ 400 ++Nanolayer CrN/TiN 6 min 30 s ++ 250 +Multilayer TiN/AlTiN 6 min + 300 +Nanolayer TiN/AlTiN 7 min 30 s 0 100 0

The wear was: +++ very important, ++ important, + beginning, 0 not significant. From Ducros et al. [20].

peeling. The hard particles contained in Inconel 718 pro-duce severe flank wear. Flank wear and notching are themain failure modes which limit the tool life. Due to thehigh cutting temperatures, oxidation and diffusion alsooccur [17].

The cutting speeds usually employed, under dry con-ditions, are in the range of 20–30 m/min and up to 50m/min for coated tools, the feed rates are about 0.1–0.2 mm/rev in turning. Some authors [2,16] tested withsuccess higher cutting speeds, up to 200 m/min with car-bide tools.

The K20 grade (WC 93%, 7% Co) cemented carbideseems to be the best for cutting Inconel 718. This is dueto its high hot hardness and high compressive strength;in addition, its relative low cobalt content increases itsabrasion resistance. The high thermal conductivity andlow thermal expansion coefficient of the K20 grade alsoimproves performance by reducing the thermal shock[8].

It has been shown also that the cutting geometry,especially the SCEA, has a significant influence on thetool life [4] and for interrupted cutting such as end mill-ing, the down cut gives better results [15].

In comparison with the TiN and TiCN coatings, it hasbeen shown that the PVD (Ti,Al)N coating is most suit-able in dry machining of difficult-to-cut materials suchas Inconel 718. Superior oxidation resistance, high-tem-perature chemical stability, high hot hardness and lowthermal conductivity are the principal reasons of its per-formance [18]. Recently, a TiN/AlTiN nanolayer coatinggave good results when machining Inconel 718 with lowBUE phenomenon and reduced abrasion wear [20].

3.2. Machining Inconel 718 with ceramic tools

The advantages of ceramic tools are [8]:

� high-temperature resistance enables them to be usedat high cutting speeds,

� abrasion and corrosion resistance,

� hot hardness and low chemical affinity resulting inlonger tool life in comparison with carbide tools.

However, the major disadvantages of ceramic toolsare their low resistance to mechanical shock or low frac-ture toughness and their low thermal conductivity. Thelow toughness is the biggest problem when cuttingnickel-based alloys.

In the paper by Narutaki et al. [21], wear character-istics of three ceramics tools were examined:

� SiC whisker-reinforced alumina Al2O3 ceramic,� silicon nitride Si3N4 ceramic, and� TiC added alumina ceramic Al2O3–TiC

under high speed turning tests of Inconel 718 up to 500m/min, in the presence of 10% water-based coolant andthe use of these ceramics tools was discussed. Anotherinteresting point of this work was the discussion ontool geometry.

The SiC whisker ceramic showed the best perform-ance in respect of notch wear VN at the side cutting edgein the speed range of 100–300 m/min with a feed rateof 0.19 mm/rev and a depth of cut of 0.5 mm, Fig. 8.However, the notch wear VN and the flank wear VB withthe SiC whisker and the Si3N4 ceramics became verylarge at higher speeds or higher feed rates. The Al2O3–TiC ceramic showed very small flank wear VB under thesame testing cutting conditions but a maximal value forVN around a cutting speed of 100 m/min. In addition,the TiC added alumina ceramic tool showed very smallflank and notch wear at the cutting speed of 500 m/min.

Using a thermocouple method, the authors estimatedthe rake and the flank temperatures during the tests. Inthe cutting speed range of 400–500 m/min, the flanktemperature attained 1250–1300 °C, Fig. 9. The wearof the SiC whisker and of the Si3N4 ceramics increasesdrastically over the cutting temperature of 1300 °C (themelting point of Inconel 718 is 1550 °C). In addition,diffusion tests between the three chosen ceramics and


Fig. 8. Influence of cutting speed and of feed on notch wear VN and flank wear VB, when turning Inconel 718 with ceramic tools. From Narutakiet al. [21].

Fig. 9. Cutting temperature when machining Inconel 718 with Si3N4

ceramic tool, from Narutaki et al. [21].

Inconel 718 were carried out. With the SiC whisker cer-amic, the Ni diffused into the tool. With the Si3N4 cer-amic, Si diffused into Inconel 718 and Cr in the alloy.These tests showed that the Al2O3–TiC ceramic tool wasthe most stable to Inconel 718. Therefore, the Al2O3–TiC ceramic tool was the best cutting tool, as it has morethermal wear resistance than the other tools in high speed

machining. The same conclusion was also obtained byKitagawa et al. [7].

The maximum notch wear observed for the Al2O3–TiC ceramic tool around the cutting speed of 100 m/minwas a kind of transfer type wear generated by anadhesion of work material to the tool, this mechanismwas temperature dependent. The flank wear is generallyconsidered as a kind of mechanical wear, such as anabrasive wear. However, for the SiC whisker and theSi3N4 ceramic tools flank abrasive wear wasaccompanied by diffusion, which is a thermally acti-vated process.

Kitagawa et al. [7] investigated tool wear and cuttingtool temperature by means of turning experiments up to300 m/m, in the presence of 10% water-based coolant.Performances of two types of ceramic, Si3N4 and Al2O3–TiC, have been investigated. They confirmed that notchwear VN (at the side cutting edge) and VN� (at the endcutting edge) were the major types of wear observedwhen cutting Inconel 718. Flank wear VB remainedlower in the whole tested speed range, Fig. 10. Theypostulated that temperature has an important role in toolwear. They measured it in the rake face and in the flankof the tool. All the temperatures rose monotonically, upto about 1200 °C, with increasing cutting speed. How-ever, taking into account the decreasing of notch wearat higher cutting speed, they estimated that the wearcharacteristics observed cannot be explained by tempera-ture alone and that the wear is rather developed by anabrasive process than a thermally activated adhesionmechanism.

They observed also the chip morphology: withincreasing cutting speed, serrations in the chip becameobvious and the chip thickness decreased. In addition,large plastic flow towards the side of the chip could bedepicted at a speed of 150 m/min. Plastic flow took place


Fig. 10. Dependence of flank wear VC = VB and notch wear VN andVN� on cutting speed at cut distance of 50 m with an Al2O3–TiC cer-amic tool (depth of cut = 0.5 mm, feed rate = 0.19 mm/rev), fromKitagawa et al. [7].

on the work surface and a burr was generated by theside cutting with a maximum height at the same cuttingspeed. They confirmed the superiority of the Al2O3–TiCceramic on the Si3N4 one over a cutting speed of 250m/min.

To reduce the notch wear of the Al2O3–TiC at lowcutting speed, different tool geometry, Fig. 11, wastested by Narutaki et al. [21] corresponding to increasingvalue of the SCEA. A tool with a large cutting edgeradius (button type with nick) corresponding to a highvalue of the SCEA showed better performance in termsof tool wear.

The effect of tool geometry on cutting temperaturewas also discussed by El-Wardany et al. [22] when turn-ing hardened steel with an Al2O3–TiC ceramic cuttingtools. Different geometrical tool configurations (differentnose radii, angles of approach, widths of tool chamfer,

Fig. 11. Increasing the SCEA reduces the wear, from Narutaki et al.[21].

and rake angles) were tested. In addition, they estimatedthe cutting edge temperature during tests at cuttingspeeds up to 500 m/min by measuring the rake face tem-perature with a thermocouple located very close to thetool tip. The cutting edge temperature decreased with theincreasing tool nose radius. According to the authors,this can be explained by the fact that for smaller noseradius, the tool tip area available for heat conductiondecreases making the local temperature to rise.

Increasing the angle of approach (SCEA) reduced thecutting edge temperature. Increasing the angle ofapproach reduced the undeformed chip thickness t1 andincreases the width of cut w, see Fig. 1, leading to alower heat generation during cutting and, consequently,the tool cutting edge temperature is reduced. In addition,the authors showed that there exists an optimal negativerake angle for which the temperature is minimum dur-ing cutting.

In the same paper, El-Wardany et al. [22] presentexperimental results concerning turning Inconel 718with an Al2O3–TiC ceramic cutting tool. An interestingresult emerged, initially with an increase of cutting speedfrom 110 to 510 m/min, the cutting edge temperaturedecreases, but with a further increase in the cutting speedup to 720 m/min, the measured temperatures increase tothe range of 650–850 °C, Fig. 12. Although the raketemperature was found to increase with the increase ofthe cutting speed [21], the temperature at the tool tipdepends on the nature of the tool and workpiecematerials and on their thermal diffusivity. The thermaldiffusivity is a measure of transient heat flow and isdefined as the thermal conductivity divided by the pro-duct of specific heat times density. The thermal conduc-tivity of the Inconel 718 increases linearly with tempera-ture and its value at 1300 °C is 1.5 times higher than at1000 °C. The variations with temperature of density and

Fig. 12. Turning Inconel 718 with an Al2O3–TiC ceramic cuttingtool, effect of cutting speed on tool edge temperature, from El-Ward-any et al. [22].


specific heats for Inconel 718 are not thought to bemajor; hence, the increase of thermal diffusivity withtemperature is due to thermal conductivity variations.This high value of the workpiece’s thermal diffusivityis accompanied by lower values of the tool’s thermaldiffusivity; therefore, the dissipation of heat at high cut-ting speed is higher through the workpiece than throughthe tool and assures low values of tool tip temperature.

At the cutting speed of 720 m/min, the cutting edgewas covered with workpiece material caused by pressurewelding between the work and the tool. This pressurewelding appears when the rake temperature approachesthe melting temperature of Inconel 718. Therefore, thethermal diffusivity of the tool is affected by the weldedlayer. Hence, at 720 m/min, the tool tip temperatureattains a higher value, about 800 °C.

Elbestawi et al. [23] investigated the failure character-istics and the cutting performance of silicon carbide(SiC) whisker-reinforced ceramic tools during milling ofInconel 718. They performed cutting tests using roundand square inserts, at cutting speeds ranging from 200to 700 m/min, and feeds from 0.05 to 0.15 mm/tooth.Various immersion ratios were considered (from 0.25 to1.00). They observed three main types of tool wear: flankwear, depth of cut notch wear and trailing edge wear.The depth of cut notch wear was the dominant failuremode for tool at full immersion, and cutting speeds from200 to 400 m/min, Fig. 13a. For higher cutting speeds(400–700 m/min), lower immersion ratios and higherfeeds, trailing edge wear and/or flank wear were thedominant modes, Fig. 13b. Round inserts improved thecutting performance in comparison with square ones.They provided a stronger cutting edge aiding notch wearresistance. The optimum performance was obtained atcutting speed of 700 m/min or higher, axial depths ofcut in the range from 1 to 2 mm, and feeds of 0.10 to0.18 mm/tooth, increasing the immersion ratio improvedthe tool life.

El-Wardany and Elbestawi [24] extended their endmilling experiments of Inconel 718 up to 2000 m/minusing flood coolant. Some tests were performed underdry conditions, at cutting speeds of 1000 and 2000m/min, and feed of 0.2 mm/tooth. As in the previouswork, they used round inserts of SiC whisker-reinforcedceramic. The best combination of cutting conditions wasa speed of 1000 m/min, a feed of 0.2 mm/tooth and fullimmersion (the depth of cut was 0.75 and 1.5 mm). Forthese conditions, the mode of tool failure was flaking ofthe rake face caused by the sticking of the workpiece onit. The tool life in terms of volume of material removalwas three times that removed by cutting speeds higheror lower that this optimal speed and a surface finish of0.7 µm was produced. The cutting process was morestable during dry cutting tests at high speeds; only craterwear was developed on the tool accompanied by a small

Fig. 13. (a) End milling Inconel 718 with a SiC whisker-reinforcedceramic tool. Modes of Failure at 1.25 mm depth of cut and full immer-sion. (b) End milling Inconel 718 with a SiC whisker-reinforced cer-amic tool. Modes of Failure at 1.25 mm depth of cut and 0.5 and 0.25immersion, from Elbestawi et al. [23].

amount of plastic deformation on the tool rake face, andthe surface finish was about 0.5 µm.

Gatto and Iuliano [25] coated 20% SiC whisker-reinforced Al2O3 tools with CrN and TiAlN using PVDin order to minimise the temperature effect and to obtainan increase in tool life. They performed machining testson a vertical boring mill under dry conditions. The cut-ting speeds were 300, 400 and 530 m/min, the feed rateswere 0.08, 0.12 and 0.22 mm/rev and the depth of cutwas 1.5 mm for all the tests. Flank wear VB and notchwear VN were measured and statistical models were pro-posed. The coatings protected the ceramic tool as a ther-mal barrier and they increased the ceramic tool life.Maximum productivity was obtained with the TiAlNcoated ceramic, Fig. 14.

Li et al. [6] used Sialon (Si3N4–Al2O3) ceramic toolsfor turning tests of Inconel 718. Sialon ceramic tools areprone to notch wear, with minimum damage to the toolnose at lower speeds (120 m/min). A transition isobserved at 240 m/min. Further increasing the speed to300 m/min leads to a reduction in notching and anincrease in nose and flank wear.

Tool life of ceramic tools is severely limited byexcessive notching in the depth of cut region, caused bywelding and pull-out, which may be due to the relativelylow mechanical toughness of ceramic tools. In addition,ceramics are poor heat conductors which make them vul-


Fig. 14. Dry machining Inconel 718 with coated ceramic tools.Maximum productivity values Q, the values refer to a machined vol-ume of 40 cm3, from Gatto and Iuliano, [25]. Q = Vfd, where V is thecutting speed, f the feed and d the depth of cut.

nerable to thermal cracks. However, ceramic tools havelarge usage possibilities. They can withstand higher cut-ting speeds (above 200 m/min) than uncoated and coatedcarbide tools. Dry conditions are generally rec-ommended during machining with ceramic tools. Coat-ings may be used to improve the cutting performance ofceramic tools.

3.3. Assisted machining for Inconel 718

One approach to enhance the machining performance(in terms of material removal rate, tool life and surfacefinish) in hard-to-cut materials is hot machining. Local-ised heat sources such as laser and plasma [26,27] wereused to assist the machining of such materials. At hightemperatures above 750 °C, Inconel 718 exhibits sig-nificantly reduced yield stress, Fig. 15; therefore, local-ised heating may soften the material and reduce the shearstrength and strain hardening associated with chip for-mation. During plasma enhanced machining (PEM),Leshock et al. [27] showed that the cutting forcesdecrease with increasing the surface temperature, Fig.

Fig. 15. Yield stress of Inconel 718 vs. temperature from Leshock etal. [27].

Fig. 16. Resultant cutting force vs. surface temperature for variouscutting speeds (feed = 0.124 mm/rev), during PEM of Inconel 718with ceramic inserts (aluminium oxide reinforced with silicon carbidewhiskers) from Leshock et al. [27].

16, and the surface roughness is also improved. How-ever, beyond 530 °C, surface oxidation was observed;this problem should be resolved by a more accurate con-trol of the plasma arc. With PEM, the notching is elimin-ated and the tool life is increased, but the chip tempera-ture is a little higher than in conventional machining,leading to higher flank wear rates [27].

An alternative solution to enhancing the machiningperformance of hard-to-cut materials is to reduce the cut-ting temperatures by the application of a high pressurewaterjet coolant [28]. Another possibility is to use liquidnitrogen as coolant [29,30]. To minimise waste, cryo-genic fluid is applied directly to the cutting edge wherethe material is cut and heat is generated. The flow rateof the cryogenic fluid is proportional to the heat gener-ated in the cutting process, preventing the workpiecefrom becoming distorted due to extreme heating or coo-ling, Fig. 17. The cooling effect obtained with this

Fig. 17. Assisted machining of Inconel 718. Application of liquidnitrogen to the cutting zone. From Hong et al. [30].


method is stronger than with waterjet cooling and thetemperature dependent wear reduced significantly in thetests of machining titanium and Inconel 718 alloys.However, nitrogen is expensive and does not recycle.

Kim et al. [31] proposed a cooling system which usescompressed air. The drier air exchanges heat in an air-cooler system and its temperature decreases down toabout �2 °C. The compressed chilly air is jetted throughthe nozzle enabling adiabatic expansion and leading toa temperature in the jet of about �12 °C. This coolingtechnique was tested in ball end milling at cutting speedsof 90 and 210 m/min, feed rate of 0.1 mm/tooth, depthof cut of 0.5 mm with coated TiAlN carbide tool. Thetool life was significantly improved at 90 m/min; how-ever, at a speed of 210 m/min, the compressed air failedto infiltrate into the tool–chip interface or tool–work-piece and the advantage of the proposed cooling systemwas reduced.

4. Surface integrity when machining Inconel 718

For safety critical industries such as aerospace, surfaceintegrity is important for the components submitted tohigh thermal and mechanical loads during their use,Axinte and Dewes, [32]. Structures in aerospace appli-cations are subjected to severe conditions of stress, tem-perature and hostile environments. Section size is con-tinually reduced in order to minimise weight so thatsurface condition has an ever-increasing influence onits performances.

Service histories and failure analyses of dynamiccomponents show that fatigue failures almost alwaysnucleate on or near the surface of a component. By con-sidering stress corrosion resistance, it is again recognisedthat the surface of a component is a primary factor indetermining susceptibility to attack and subsequent fail-ure. Hence, much attention should be paid to surfacecharacteristics of components [33].

Overheating/burning, surface irregularities, BUEs ordeposits of debris, macro- and microcracks, cavities,microdefects such as laps and inclusions, metallurgicalalterations including microstructural distortion, phasetransformations, heat affected layers, tensile residualstresses are the main problems identified. Such changesoccur due to thermal and mechanical loads during mach-ining. Residual stresses are an effect from both heat gen-erated and mechanical work going into the surface andsubsurface. Thermal effects tend to give tensile stresses,while mechanical influences contribute to compressiveresidual stresses, [32]. Jacobson et al. [34] have notedthat when increasing cutting speed during hard turningof bainitic steels, one also increases the strain rate in theprocess which gives more mechanical work leading tocompressive stress. In the same way, increasing thestrain rate in the cutting zone introduces more generated

heat, which has a tendency to produce tensile stress atthe machined surface.

Residual stress strongly affects the fatigue life of acomponent. A tensile mean stress reduces the allowedalternating stress in service. Conversely, the introductionof a compressive mean stress will increase the allowedalternating stress for a given fatigue life. High tensilestresses generated by the machining of work hardeningalloys can be highly deleterious to fatigue performance.The effect is most significant in the high cycle fatigueregime where the applied stress magnitude is not suf-ficient to significantly relax the residual stresses pro-duced during manufacturing. Brinksmeier et al. [35] givea good overview of the subject of residual stresses, theirmeasurement and causes in machining processes.

Field and Khales [33] proposed a minimum surfaceintegrity data set, which involves surface finish(roughness and waviness), macro- and microstructureand hardness of the surface, microhardness variations,structural changes in the machined surface layer. Theyadded residual stresses and a minimal fatigue testing togive a ‘standard’ data set. In the following, we presentsome results about surface finish during machiningInconel 718 and the main parameters which affect thesurface integrity are identified.

Ezugwu and Tang [9] carried out turning tests onInconel 718 alloy using round- and rhomboid-shapedpure oxide (Al2O3 + ZrO2) and mixed oxide (Al2O3 +TiC) ceramic tools. Coolant was not used because of thelow thermal shock properties of ceramics. Inconel 718alloy was machined at a speed of 152 m/min, a feed rateof 0.125 mm/min and a constant depth of cut of 2.0 mm.They have shown that the geometry of cutting toolsplays an important role in determining the nature ofmachined surfaces. The round inserts produced bettersurface finish than the rhomboid inserts. All the rhom-boid-shaped ceramic tools failed after machining for 1min due to severe notching at the depth of cut. Underthe chosen conditions, long continuous chips were pro-duced due to the ductility of the work material. The hard-ness of the workpiece surface layer increased with pro-longed machining due to plastic deformation and to thehigh rate of work hardening of Inconel 718. Plasticdeformation was evident by the observation of the elong-ation of grains and orientation under the machined sur-face. Tearing of the surface layer of the Inconel 718 wasobserved in all machining trials. Tearing on themachined surface of a component reduces its fatiguestrength.

Bresseler et al. [36] and Kishawy and Elbestawi [37]studied the phenomenon of material side flow which rep-resents an important aspect of machined surfaces. Theyconducted experiments in order to study the effect ofcutting edge preparation, nose radius, feed and tool wearon surface material side flow quality during dry hardboring and hard turning. The work material was not the


Inconel 718 alloy but a hardened steel. However, theirwork is important to identify the generally parametersinfluencing surface quality. They verified that cuttingedge preparation has a significant effect upon thematerial side flow, especially during finishing oper-ations. Although cutting with a small feed improves sur-face finish, it leads to more material side flow on themachined surface, hence to a deterioration in surfacequality. In addition, an increase in the tool nose radiusleads to the ploughing of a large part of the chip and inconsequence to severe material side flow on themachined surface.

Near surface residual stress distributions in Inconel718 arising from a turning operation were studied bySchlauer et al. [38]. The cutting conditions were verysimilar to orthogonal cutting. The cutting tool used wasa SiC whisker-reinforced alumina Al2O3 ceramic. Thetool geometry was kept constant. Cutting speeds were10, 410 and 810 m/min and for the feed were 0.01, 0.06and 0.11 mm/rev. For the cutting speed of 10 m/min, lowresidual stresses were found. At higher cutting speeds of410 and 810 m/min, a thin layer exhibiting tensileresidual stresses was formed near the machined surface,with a maximum tensile stress at the surface, Fig. 18.Within 10 µm from the machined surface, the tensilestress dropped to 0. It was followed by a layer with com-pressive stresses that is several times thicker than thetensile layer. When the cutting speed was increased, thetensile and the compressive stresses increased and thedepth of the layer affected by machining increased too.

Similar stress profiles were found by Derrien and Vig-neau [16] and Guerville and Vigneau [11]. They carriedout high speed and dry milling tests (contouring andpoint milling) with uncoated cemented carbide K20mills. For contouring operations at V = 200 m/min (f= 0.04 mm/ tooth and depth of cut = 0.5 mm), residualstresses are tensile, affecting a layer of 400 µm with anextreme value of 1500 MPa. This maximum value wasthree times the one obtained using a conventional speed

Fig. 18. Turning Inconel 718 with a SiC whisker-reinforced aluminaceramic tool. Residual stress depth profiles for the feed 0.06 mm/revand the three tested cutting speeds (10, 410, 810 m/min). FromSchlauer et al. [38].

Fig. 19. Contouring Inconel 718 with a carbide K20 tool: comparisonof residual stresses profiles after high speed machining (200 m/min,dry conditions) and conventional machining (16 m/min, emulsion 5%),from Derrien and Vigneau [16], Guerville and Vigneau [11].

of 16 m/min and wet conditions, Fig. 19. On the otherhand, for the point milling tests, the level of the residualstresses was lower with a maximum tensile stress valueof about 750 MPa near the machined surface, amaximum compressive stress value of 500 MPa and a100 µm affected layer, Fig. 20.

Comparable residual stress profiles were also obtainedafter ball end milling by Ng et al. [39]. The tests wereperformed at a cutting speed of 90 m/min, feed of 0.2mm/tooth and an axial depth of cut of 0.5 mm in downmilling, the workpiece surface was inclined with anangle of 45° from the horizontal. High tensile stress

Fig. 20. Point milling Inconel 718 with carbide K20: comparison ofresidual stresses profiles after high speed machining (200 m/min, dryconditions) and conventional machining (18 m/min, dry conditions),from Derrien and Vigneau [16], Guerville and Vigneau [11].


values were measured parallel to the feed direction nearthe machined surface, followed by highly compressivestress at a shallow depth and the compressive layer wasmaintained to 150 µm.

Gas turbine components are complex in their shape.They are thin walled and call for very close dimensionaltolerances and good surface integrity. The Inconel 718used for jet engine component is not only known to bedifficult to cut but also to reveal dimensional instabilityafter machining [12,13]. Dimensional instability is achange of dimension with respect to time without anyfurther work being done on the component. Dimensionalinstability of components induces problems duringassembly. The two probable causes of this phenomenonare the residual stresses and microstructure changesintroduced by the machining process. Subhas et al.[12,13] compared the dimensional instability of Inconel718 with that of Ti–6Al–4V and mild steel. The speci-mens were machined at identical cutting conditions andthe dimensional changes were measured with respect totime up to 220 h after machining. Inconel 718 is moreprone to dimensional instability than either titaniumalloy or mild steel, dimensional changes being lowestfor the latter material. It can be noted that this phenom-enon is not observed in other nickel-based alloys. Micro-scopic observations showed that shear localised chipswere formed with the Inconel 718 alloy at various cut-ting speeds. These chips are very similar to thoseobtained with the Ti–6Al–4V alloy, see also the studyof Komanduri and Shroeder [40]. According to Subhaset al. [12,13], the dimensional instability of Inconel 718may be attributed to the presence of g� phase. They alsostudied the influence of cutting conditions on the plasticdeformation mechanism and then on residual stresses. Inparticular, they observed that negative rake anglesincrease the residual stresses. They finally proposed aprocess parameter optimisation technique to control thedimensional changes within acceptable limits.

5. The way to dry machining

The use of coolants, in addition to being undesirableto the environment and for the human health, entails highcosts in production and disposal. Depending on themachined workpiece, cost savings up to 17% of the totalworkpiece cost can be made by introducing dry machin-ing. This is mainly due to the elimination of coolant sup-ply, cleaning, maintenance and disposal costs [41,42].Reducing costs in the cutting process together withreduced environmental pollution by the use of dry mach-ining is the main key for the industry to remain competi-tive and profitable in the future [42]. Today, wet cuttingis still largely used in manufacturing industry, butresearch and development is being undertaken to mini-mise the use of coolant lubricants and new concepts of

minimum quantity cutting fluid application have beendeveloped, [42–47]. In the following, the concept ofminimum fluid application is developed and then theresults of some dry cutting experiments using hard coat-ings are presented.

5.1. Minimal quantity of cutting fluid application

The characteristic of the ‘minimal quantity’ appli-cation is to substitute all the effects of the coolant lubri-cant by using jet application to produce effects of equalvalues. Only a small amount of lubricant is needed if itis efficiently applied to the cutting zone. This lubricantis completely used and results in almost dry chips. How-ever, all the effects provided by the usual cutting fluidflood-type lubricant are not possible with minimal quan-tity application or dry cutting alone. For example, theflushing effect is not supplied and the cooling effect ispartially or not at all (with dry cutting) obtained. Then,additional use of minimum cooling system of the work-piece and a specially adapted blow-out technology forchip removal are required. Nevertheless, the resultsobtained with minimum quantities of cutting fluid appli-cation in drilling are excellent compared to the usualflood-type application, [45]. The ‘minimal quantity’lubrication is a suitable alternative for economically andenvironmentally compatible production. It combines thefunctionality of cooling lubrication with an extremelylow consumption of lubricant and therefore it has thepotential to close the gap between overflow lubricationand dry cutting [43].

Machado and Wallbank [44] conducted experimentson turning medium carbon steel (AISI1040) using a Ven-turi to mix compressed air (the air pressure was of 2.3bar) with small quantities of a liquid lubricant, water orsoluble oil (the mean flow rate was between 3 and 5ml/min). The mixture was directed onto the rake faceof a carbide tool against the chip flow direction. Theapplication of a mixture of air + soluble oil was able toreduce the consumption of cutting fluid, but it promoteda mist in the environment with problems of odours, bac-teria and fungi growth of the overhead flooding system.For this reason, the mixture of air + water was preferred.However, even if the obtained results were encouraging,the system needed yet some development to achieve therequired effects in terms of cutting forces, temperatures,tool life and surface finish.

In contrast, Varadarajan et al. [46] developed an alter-native test equipment for injecting the fluid and used itwith success in hard turning for which a large supply ofcutting fluid is the normal practice. The test equipmentconsisted of a fuel pump generally used for diesel fuelinjection in truck engines coupled to a variable electricdrive. A high speed electrical mixing chamber facilitatedthorough emulsification. The test equipment permittedthe independent variation of the injection pressure, the


frequency of injection and the rate of injection. Theinvestigations performed by the authors revealed that acoolant-rich (60%) lubricant fluid with minimal addi-tives was the ideal formulation. During hard turning ofan AISI 4340 hardened steel of 46HRC (460 HV), theoptimum levels for the fluid delivery parameters were:a rate of 2 ml/min, a pressure of 20 MPa and a highpulsing rate of 600 pulses/min. In comparison, for thesame cutting conditions, with dry cutting and wet cut-ting, the minimum quantity of cutting fluid method hasled to lower cutting forces, temperatures, better surfacefinish, longer tool life. In addition, it was observed thattightly coiled chips were formed during wet turning andduring minimal application, while long snarled chipswere prevalent during dry turning. It must be noted thatduring minimal application, the rate of fluid was only0.05% of that used during wet turning. The major partof the fluid used during minimal quantity application wasevaporated, the remnant was carried out by work andchips and was too low in volume to cause contaminationof the environment.

The paper of Klocke and Eisenblatter [47] deals withdrilling tests using minimum cooling lubrication systemswhich are based on atomising the lubricant directly tothe cutting zone. Small quantities of lubricant, in orderof 10–50 ml/h, were mixed with compressed air for anexternal feeding via a nozzle or for internal feeding viaspindle and tool. Internal feed systems with their abilityto deliver the mixture very close to the drill–workpiececontact point may achieve very good results in terms ofsurface finish and tool life.

Lahres et al. [42] presented dry machining ofsynchronising cones for automotive application. Thework material was austenitic 22Mn6 steel. In the firststep of their study, dry machining was compared tomachining with coolant and with minimal lubricant sys-tem. The used minimal lubricant system worked with aspecial oil which had food-grade quality. The air volumeflow was about 50 l/min and the air volume oil was about20 ml/h; hence, the produced chips were dry after leav-ing the contact zone of the cutting process. At this oilvolume flow, a single chip can carry a maximum of 1nl. Therefore, the chips could be declared as beingalmost dry and passed for metallic recycling withoutfurther treatment. The results exhibited an advantage forthe minimal lubricant technique and for the dry machin-ing.

In the second step, they investigated new tool coatingswith a potential for dry machining:

TiAlNOx,TiAlN + MoS2,single layer (Ti,Al)N,multilayer TiN + TiAlN.

A new series of experiments were performed under

minimal lubrication. The best performance was obtainedwith the double layer TiAlN + MoS2 coating. Metallo-graphical studies indicated that the solid lubricant MoS2

is worn after a few machined parts. However, a smallamount of solid lubricant exists further in the valleys ofthe tool surface profile and initiates a low friction at thetool–chip interface. Nevertheless, a small amount ofsolid lubricant exists perhaps also on the machined sur-face; this pollution is a problem for the aerospacecomponents.

The TiAlNOx consists of two layers: the first layeron top of the substrate surface is a thick TiAlN-coatingnecessary to achieve good adhesion, the second is a thinAl2O3-coating used to reduce oxidation and wear. Theperformance of this coating was almost as good as theone of TiAlN + MoS2 - coating.

5.2. Dry cutting

Elimination of coolants also involves the absence oftheir positive effects on the metal cutting processes. Fordry cutting operations, sufficient heat removal and theavoidance of heat build-up above a critical temperaturemust be guaranteed. The removal of chips from the cut-ting zone is another important aspect. The process mustpreserve the surface integrity of workpiece and producestable tool wear suitable for automatic manufacturingsystems. Tools with high hot hardness, high refractivityand low coefficients of friction are required and the useof tools with low-adhesion coatings can help greatly.Tool coatings play a major part in tool development, inparticular for dry machining, Schulz et al. [48]. The toolcoatings can at least partially substitute the eliminatedfunctions of the cutting fluids.

Tonshoff and Mohfeld [49] and Tonshoff et al. [50]presented an interesting paper on (Ti1�x, Alx)N coatingsfor wear protection in dry drilling operations of temperedsteel. Due to the complex thermal and mechanical loadsin drilling, cutting materials for dry drilling require highhot hardness and high toughness.

Coatings separate tools from the workpiece materialin cutting and offer a possibility of replacing coolants.Demands placed on coatings for dry machining includereduction of friction to decrease dissipated thermalenergy in tool–workpiece contact and protection of heatand diffusion to guarantee high wear resistance at hightemperatures. Because of the poor conditions for heatconduction from the drill, only thermally stable coatinglayers are applied. (Ti,Al)N possesses the lowest coef-ficient of thermal conduction and a considerablyincreased oxidation stability compared with other hardcoatings, particularly with TiN coating. Whereas TiNoxidises at temperatures higher than 600 °C, (Ti,Al)Nhas a high oxidation resistance up to 800 °C. The forma-tion of a dense Al2O3 top layer increases diffusion andoxidation resistance of the (Ti,Al)N film. Compared to


TiN, (Ti,Al)N has a high hardness even at elevated tem-peratures. For dry drilling operations, the ternary(Ti,Al)N system has remarkable advantages; comparedto uncoated carbide and TiN coated tools, it has asuperior wear behaviour. The best wear behaviour in drydrilling of tempered steel was obtained for an Al/Ti ratioequal to 1.

A further improvement in dry machining was achi-eved by adding oxygen to a (Ti,Al)N coating to formTiAlON [51]. Though the microhardness of TiAlON waslower than (Ti,Al)N, TiAlON offered a higher abrasionresistance during dry drilling due to the formation ofAl2O3. Alumina provides oxidation resistance and isthermally stable. In addition, a graded multilayer struc-ture of TiAlON with Al2O3 was developed by providinga stable oxide layer on layer on top of the nitride coating,Bouzakis et al. [52].

Schulz et al. [48] showed the performance of oxideAl2O3 and ZrO2 PVD-coatings in dry cutting operationsof high strength graphic cast iron. Commercial titanium-based hard coatings like TiN, TiCN and TiAlN with highhardness even at high temperatures provide a high wearresistance. Oxide PVD-coatings specially developed fordry machining additionally combine a reduction of fric-tion at elevated temperatures with high wear resistance.The changed contact conditions will decrease the heatgeneration. Then, the tendency for the work material toadhere on the rake face is reduced and the chip flow isimproved. The substrate of the drilling tool was a finegrain tungsten carbide with 10% of cobalt (K20–40).The advantage is a much better toughness and a reducedrisk of cutting edge chipping. Different oxide PVD-coat-ings were tested: TiAlN–Al2O3, TiAlN–ZrO2, TiZrN–ZrO2 and compared with the uncoated and the simpleTiAlN coated tool performances. Due to the high hard-ness, increased resistance and a low friction coefficienteven at elevated temperatures, the oxide-coated toolsshow notable advantages for dry drilling in high strengthmaterials. With the different oxide coatings, the tool lifewas remarkably improved. The TiAlN–ZrO2 coating hadthe best performance. A significant reduction of the cut-ting edge temperature by using the oxide coating wasalso observed.

Hard coatings such as TiAlN may increase tool per-formance and tool life by arresting or slowing down cer-tain types of wear. However, these coatings retain a highcoefficient of friction and require a lubricant. For drycutting applications, a solid lubricant such asMoS2/titanium composite coatings may be used toreduce the friction coefficient and then to decrease thecutting forces and temperatures which reduces the localwelding and, in consequence, improves surface finish.The MoS2/titanium composite coatings have a muchlower wear rate than the traditional hard coatings. Theyhave also a very low friction (0.02–0.1) which allowsthem to be used at high speeds. Beside the commercially

obtainable MoS2 coatings, other low-friction coatingssuch as tungsten carbide/carbon (WC/C) coatings areavailable. This type of hard/lubricant coating was pro-posed for dry machining, [53–56].

A new highly improved AlTiN film has beendeveloped and proposed by Arndt and Kacsich [57] fordry or minimum quantity lubrication and high speedmachining of stainless steel as well as hardened steel upto 63 HRC. The improvement of the deposition oper-ation has led, to the new coating, to possess bettercharacteristic properties such as high hardness associatedto an ultra-fine crystallinity. The cutting performancesof the new coating were compared with success to othercommercial (Ti,Al)N films.

Recent hard coatings are the superlattice structuredPVD hard coatings presented by Hovsepian and Munz[58]. They are dedicated to high-temperature perform-ance and for tribological applications. Abrasion resistantTiAlN was combined with VN to achieve a wear resist-ant low friction coefficient coated tool tested with suc-cess during dry machining of steels. In the same way,the hard coating TiAlCrYN was overcoated withlubricious and non-sticking coating C/Cr and tested onend mills for the machining of extremely abrasive highCo containing Ni-based alloys. However, no publishedresults from these tests have yet been found.

6. Conclusions

Inconel 718 is a high strength thermal resistantmaterial alloy. It is a highly strain rate sensitive materialwhich work hardens readily, and contains hard particlesmaking it a very difficult-to-cut material. The difficultyof machining Inconel 718 resolves into short tool lifeand poor surface integrity. The main wear mechanism isabrasion observed for all the tested tools. Welding andadhesion on the cutting tool frequently occur to form aBUE. The BUE is repeatedly removed leading to severenotching. Machining induces plastic deformation andheat generation, the consequences are metallurgicaltransformations and residual stresses in the machinedsurface layer. The residual stress distribution exhibits amaximum tensile stress near the machined surface andthen a compressive stress. The depth of affected layerand the tensile and compressive stresses increase whenthe cutting speed increases.

Cemented carbide tools are largely used for machiningnickel-based alloys at very low cutting speeds of 20–30m/min, the K20 grade appears to be the best for cuttingInconel 718. Higher cutting speeds, certainly up to 100m/min, under dry conditions may be achieved withcoated carbide tools. The PVD (Ti,Al)N coating seemsto be most suitable. It displays high oxidation resistance,high-temperature chemical stability, high hot hardnessand low thermal conduction. The nanolayer structureswith higher hardness appear to give encouraging results.


Much higher cutting speeds (from 200 to 700 m/min)are attained with ceramic tools. The Al2O3–TiC is thechemical most stable to Inconel 718; it has most thermalresistance in high speed machining. Round inserts of SiCwhisker-reinforced ceramic improve the cutting per-formance for milling of Inconel 718, in comparison withthe square ones. Ceramics are poor conductors and vul-nerable to thermal cracks and dry machining is rec-ommended with them.

The use of coolants is undesirable for environmentand human health; furthermore, it induces highadditional costs. New concepts have been introduced tominimise coolant lubrication and in the same way newcoatings with a potential for dry machining have beendeveloped.

In dry machining, the positive effects of coolants haveto be obtained by another way. For the removal of chipsfrom cutting zone, heat evacuation must be guaranteed.The process must preserve an acceptable surface integ-rity. Tools with high hot hardness, high refractivity, lowadhesion and low friction properties are required. OxidePVD-coatings combine a reduction of friction at elevatedtemperature with high wear resistance, they show excel-lent performance during drilling high strength materials.Solid lubricants such as MoS2/titanium composite coat-ings or WC/C coatings should give useful results whenmachining Inconel 718 under dry conditions.

Experiments and machining simulation now have towork together to find a way to the dry cutting of Inconel718. The objective is to find the suitable tool and appro-priate coating, to define the better geometrical tool con-figuration and the optimal cutting conditions in order toobtain more acceptable surface integrity and the longertool life.

Acknowledgements

The research work published in this paper was carriedout with the financial aid of ADEME, French Agency forEnvironment and Energy Management. It corresponds tothe first stage of the study concerning high speed anddry cutting of Inconel 718.

References

[1] J.M. Vieira, A.R. Machado, E.O. Ezugwu, Performance of cuttingfluids during face milling of steels, Journal of Materials Pro-cessing Technology 16 (2001) 244–251.

[2] A. Sharman, R.C. Dewes, D.K. Aspinwall, Tool life when highspeed ball nose end milling Inconel 718, Journal of MaterialsProcessing Technology 118 (2001) 29–35.

[3] E.O. Ezugwu, Z.M. Wang, A.R. Machado, The machinability ofnickel-based alloys: a review, Journal of Materials ProcessingTechnology 86 (1999) 1–16.

[4] M. Rahman, W.K.H. Seah, T.T. Teo, The machinability of

Inconel 718, Journal of Materials Processing Technology 63(1997) 199–204.

[5] A. Jawaid, S. Koksal, S. Sharif, Cutting performance and wearcharacteristics of PVD coated and uncoated carbide tools in facemilling Inconel 718 aerospace alloy, Journal of Materials Pro-cessing Technology 116 (2001) 2–9.

[6] L. Li, N. He, M. Wang, Z.W. Wang, High speed cutting ofInconel 718 with coated carbide and ceramic inserts, Journal ofMaterials Processing Technology 129 (2002) 127–130.

[7] T. Kitagawa, A. Kubo, K. Maekawa, Temperature and wear ofcutting tools in high speed machining of Inconel and Ti–6Al–6V–2Sn, Wear 202 (1997) 142–148.

[8] R. Arunachalam, M.A. Mannan, Machinability of nickel-basedhigh temperature alloys, Machining Science and Technology 4(1) (2000) 127–168.

[9] E.O. Ezugwu, S.H. Tang, Surface abuse when machining castiron (G-17) and nickel-base superalloy (Inconel 718) with cer-amic tools, Journal of Materials Processing Technology 55 (1995)63–69.

[10] S. Brunet, Influence des contraintes residuelles induites par l’us-inage sur la tenue enfatigue des materiaux metalliques aero-nautiques, These de doctorat, ENSAM, 1991.

[11] L. Guerville, J. Vigneau, Influence of machining conditions onresidual stresses, in: D. Dudzinski, A. Molinari, H. Schulz (Eds.),Metal Cutting and High Speed Machining, Kluwer Academic Ple-num Publishers, 2002, pp. 201–210.

[12] B.K. Subhas, Bhat Ramaraja, K. Ramachandra, H.K. Balakrishna,Simultaneous optimization of machining parameters for dimen-sionnal instability control in aero gas turbine components madeof Inconel 718 alloy, Journal of Manufacturing Science andEngineering, Transactions ASME A22 (2000) 586–590.

[13] B.K. Subhas, Bhat Ramaraja, K. Ramachandra, H.K. Balakrishna,Dimensionnal instability studies in machining of Inconel 718nickel based superalloy as applied to aerogas turbine components,Journal of Engineering for Gas Turbines and Power, TransactionsASME 122 (January 2000) 55–61.

[14] Y.S. Liao, R.H. Shiue, Carbide tool wear mechanism in turningof Inconel 718 superalloy, Wear 193 (1996) 16–24.

[15] M. Alaudin, M.A. El Baradie, M.S.J. Hashmi, Tool life testingin the end milling of Inconel 718, Journal of Materials ProcessingTechnology 55 (1995) 321–330.

[16] S. Derrien, J. Vigneau, High speed milling of difficult to machinealloys, in: A. Molinari, H. Schulz, H. Schulz (Eds.), Proceedingsof the First French and German Conference on High Speed Mach-ining, University of Metz, France, 1997.

[17] K. Itakura, M. Kuroda, H. Omokawa, H. Itani, K. Yamamoto, Y.Ariura, Wear mechanism of coated cemented carbide tool incoated tool in cutting of Inconel 718 super-heat resisting alloy,International Journal of Japanese Society for Precision Engineer-ing 33 (4) (December 1999) 326–333.

[18] P.C. Jindal, A.T. Santhanam, U. Schleinkofer, A.F. Shuster, Per-formance of PVD TiN, TiCN and TiAlN coated cemented carbidetools in turning, International Journal of Refractory Metals andHard Materials 17 (1999) 163–170.

[19] H.G. Prengel, P.C. Jindal, K.H. Wendt, A.T. Santhanam, P.L.Hedge, R.M. Penich, A new class of high performance PVD coat-ings for carbide cutting tools, Surface and Coatings Technology139 (2001) 25–34.

[20] C. Ducros, V. Benevent, F. Sanchette, Deposition, characteriz-ation and machining performance of multilayer PVD coatings oncemented carbide cutting tools, Surface and Coatings Technology163-164 (2003) 681–688.

[21] N. Narutaki, Y. Yamane, K. Hayashi, T. Kitagawa, High speedmachining of Inconel 718 with ceramic tools, Annals of CIRP42 (1) (1993) 103–106.

[22] T.I. El-Wardany, E. Mohammed, M.A. Elbestawi, Cutting tem-perature of ceramic tools in high speed machining of difficult-to-


cut materials, International Journal of Machine Tools and Manu-facture 36 (5) (1996) 611–634.

[23] M.A. Elbestawi, T.I. El-Wardany, Yan Di, Tan Min, Performanceof whisker-reinforced ceramic tools in milling nickel-based alloy,Annals of CIRP 42 (1) (1993) 99–102.

[24] T.I. El-Wardany, M.A. Elbestawi, High speed machining ofnickel based superalloys with silicon carbide whisker reinforcedceramics, paper MR 95-160 IN, First International Machining andGrinding Conference, September 1995, Dearborn, USA.

[25] A. Gatto, L. Iuliano, Advanced coated ceramic tools for machin-ing superalloys, International Journal of Machine Tools andManufacture 37 (5) (1997) 591–605.

[26] J.W. Nowak, Y.C. Shin, F.P. Incropera, Assessment of plasmaenhanced machining for improved machinability of Inconel 718,Journal of Manufacturing Science and Engineering 119 (1997)119–129.

[27] C.E. Leshock, Kim Jin-Nam, Y.C. Shin, Plasma enhanced mach-ining of Inconel 718: modelling of workpiece temperature withplasma heating and experimental results, International Journal ofMachine Tools and Manufacture 41 (2001) 877–897.

[28] J. Vigneau, Usinage des materiaux aeronautiques a faible usina-bilite, Techniques de l’ ingenieur, Traite de Genie Mecanique, BM1285, 1999.

[29] Z.Y. Wang, K.P. Rajurkar, Cryogenic machining of hard-to-cutmaterials, Wear 239 (2000) 168–175.

[30] S.Y. Hong, I. Markus, W.C. Jeong, New cooling approach andtool life improvement in cryogenic machining of titanium alloyTi–6Al–4V, International Journal of Machine Tool Manufacture41 (2001) 2245–2260.

[31] S.W. Kim, D.W. Lee, M.C. Kang, J.S. Kim, Evaluation of mach-inability by cutting environments in high-speed milling of diffi-cult-to-cut materials, Journal of Processing Technology 111(2001) 256–260.

[32] D.A. Axinte, R.C. Dewes, Surface integrity of hot work tool steelafter high speed milling—experimental data and empirical mod-els, Journal of Materials Processing Technology 127 (2002)325–335.

[33] M. Field, J.F. Khales, Review of surface integrity of machinedcomponents, Annals of CIRP 20 (2) (1971) 153–163.

[34] M. Jacobson, P. Dahlman, F. Gunnberg, Cutting speed influenceon surface integrity of hard turned bainite steel, Journal ofMaterials Processing Technology 128 (2002) 318–323.

[35] E. Brinkmeier, J.T. Cammet, W. Konig, P. Leskovar, J. Peters,K. Tonshoff, Residual stresses—measurement and causes inmachining processes, Annals of the CIRP 31 (2) (1982) 491.

[36] B. Bresseler, T.I. El-Wardany, M.A. Elbestawi, Material sideflow in high speed finish boring of case hardened steel, in: Pro-ceedings of the First French and German Conference on HighSpeed Machining, Metz, France, 1997, pp. 196–206.

[37] H.A. Kishawy, M.A. Elbestawi, Effects of process parameters onmaterial side flow during hard turning, International Journal ofMachine Tools and Manufacture 39 (1999) 1017–1030.

[38] C. Schlauer, R.L. Peng, M. Oden, Residual stresses in a nickel-based superalloy introduced by turning, Materials Science Forum404-407 (2002) 173–178.

[39] E.G. Ng, S.L. Soo, C. Sage, R.C. Dewes, R. Dewes, D.K. Aspin-wall, High speed ball nose end milling of Inconel 718 with vari-able tool geometry—experimental and finite element analysis, in:D. Dudzinski, A. Molinari, H. Schulz (Eds.), Metal Cutting andHigh Speed Machining, Kluwer Academic Plenum Publishers,2002, pp. 191–200.

[40] R. Komanduri, T.A. Schroeder, On shear instability in machininga nickel–iron base superalloy, Journal of Engineering for Industry108 (May 1986) 93–100.

[41] F. Klocke, Dry cutting, Annals of the CIRP 46 (2) (1997)519–526.

[42] M. Lahres, O. Doerfel, R. Neumuller, Applicability of differenthard coatings in dry machining an austenitic steel, Surface andCoatings Technology 120-121 (1999) 687–691.

[43] E. Brinksmeier, A. Walter, R. Janssen, P. Diersen, Aspects ofcooling lubrication reduction in machining advanced materials,Proceedings of the Institution of Mechanical Engineers 213 (PartB) (1999) 769–778.

[44] A.R. Machado, J. Wallbank, The effect of extremely low lubri-cant volumes in machining, Wear 219 (1997) 76–82.

[45] H. Popke, Th. Emmer, J. Steffenhagen, Environmentally cleanmetal cutting processes—machining on the way to dry cutting,Proceedings of the Institution of Mechanical Engineers 213 (PartB) (1999) 329–332.

[46] A.S. Varadarajan, P.K. Philip, B. Ramamoorthy, Investigationson hard turning with minimal cutting fluid application (HTMF)and its comparison with dry and wet turning, International Journalof Machine Tools and Manufacture 42 (2002) 193–200.

[47] F. Klocke, G. Eisenblatter, Machinability investigation of thedrilling process using minimal cooling lubrication techniques,Annals of the CIRP 46 (1) (1997) 19–24.

[48] H. Schulz, J. Dorr, I.J. Rass, M. Schulze, T. Leyendecker, G.Erkens, Performance of oxide PVD-coatings in dry cutting oper-ations, Surface and Coatings Technology 146-147 (2001) 480–485.

[49] K. Tonshoff, A. Mohfeld, PVD-coatings wear protection in drycutting operations, Surface and Coatings Technology 93 (1997)88–92.

[50] K. Tonshoff, A. Mohfeld, T. Leyendecker, H.G. Fuss, G. Erkens,R. Wenke, T. Cselle, M. Schwenck, Wear mechanisms of(Ti1�x,Alx)N coatings in dry drilling, Surface and Coatings Tech-nology 94-95 (1997) 603–609.

[51] K. Tonshoff, B. Karpuschewski, A. Mohfeld, T. Leyendecker, G.Erkens, H.G. Fuss, R. Wenke, Performance of oxygen-rich TiA-lON coatings in dry cuttings applications, Surface and CoatingsTechnology 108-109 (1998) 535–542.

[52] K.D. Bouzakis, N. Vidakis, N. Michailidis, T. Leyendecker, G.Erkens, G. Fuss, Quantification of properties modification andcutting performance of (Ti1�xAlx)N coatings at elevated tempera-tures, Surface and Coatings Technology 120-121 (1999) 34–43.

[53] N.M. Renevier, N. Lobiondo, V.C. Fox, D.G. Teer, J. Hampshire,Performance of MoS2/metal composite coatings used for drymachining and other industrial applications, Surface and CoatingsTechnology 123 (2000) 84–91.

[54] V. Derflinger, H. Brandle, H. Zimmerman, New hard/lubricantcoating for dry machining, Surface and Coatings Technology 113(1999) 286–292.

[55] B. Navinsek, P. Panjan, M. Cekada, D.T. Quinto, Interfacecharacterization of combination hard/solid lubricant coatings byspecific methods, Surface and Coatings Technology 154 (2002)194–203.

[56] N.M. Renevier, H. Oosterling, U. Konig, H. Dautzenberg, B.J.Kim, L. Geppert, F.G.M. Koopmans, J. Leopold, Performanceand limitation of hybrid PECVD (hard coating)–PVD magnetronsputtering (MoS2/Ti composite) coated inserts tested for dry highspeed milling of steel and grey cast iron, Surface and CoatingsTechnology 163-164 (2003) 659–667.

[57] M. Arndt, T. Kacsich, Performance of new AlTiN coatings indry and high speed cutting, Surface and Coatings Technology163-164 (2003) 674–680.

[58] P.Eh. Hovsepian, W.-D. Munz, Recent progress in large scaleproduction of nanoscale multilayer/superlattice hard coatings,Vacuum 69 (2003) 27–36.

a review of developments towards dry and high speed machining of inconel 718 alloy

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