Mp

Sa

b

a

ARRAA

KDCMTL

1

t(ttdbfLNvC(potult

Uf

0d

Materials Science and Engineering A 528 (2011) 2309–2318

Contents lists available at ScienceDirect

Materials Science and Engineering A

journa l homepage: www.e lsev ier .com/ locate /msea

icrostructural evolution of AISI 4340 steel during Direct Metal Depositionrocess

. Bhattacharyaa,∗, G.P. Dindab, A.K. Dasguptab, J. Mazumdera

Center for Laser Aided Intelligent Manufacturing, University of Michigan, Ann Arbor, MI 48109, USACenter for Advanced Technologies, Focus: HOPE, Detroit, MI 48238, USA

r t i c l e i n f o

rticle history:eceived 23 September 2010eceived in revised form 2 November 2010ccepted 9 November 2010

a b s t r a c t

In the current investigation AISI 4340 steel was laser deposited on a rolled mild steel substrate by DirectMetal Deposition (DMD) technology. The microstructural investigation of the clad was performed usingoptical and electron microscopes and X-ray diffraction techniques. The microstructure consisted of ferrite,martensite and cementite phases. Two types of martensite, lathe-type and plate-type, were observed in

vailable online 16 November 2010

eywords:irect Metal Depositionlad

the microstructure. Decrease in microhardness values from the top layer to the alloy layer proves that thedegree of tempering of the martensite phase increases in the same direction. The lattice parameters ofthe identified phases were found to be shorter than those reported in literature. The reported parametersin literature are from samples processed under equilibrium conditions.

icrohardnessemperingattice parameters

. Introduction

Direct Metal Deposition (DMD) technology [1–3] developed athe University of Michigan Ann Arbor is a solid free form fabricationSFF) technology. SFFs are a group of manufacturing technologieshat include rapid prototyping (RP) and rapid manufacturing (RM)o produce near-net shape components from their computer aidedesign (CAD) files. Other SFF technologies, similar to DMD haveeen developed at other laboratories and have been named dif-erently; Directed Light Fabrication (DLF) at Los Alamos Nationalaboratory [4], Laser Engineered net Shaping (LENS®) at Sandiaational Laboratory [5] and Selective Laser Sintering (SLS®) at Uni-ersity of Texas, Austin (commercialized by Desktop Manufacturingorporation) [6] to name a few. DMD and other SFF technologiesexcept SLS) work on same basic principle that involves a highower laser to create a melt pool in the substrate and simultane-

usly deposit fused pure metal (or alloy) powders (or wires) intohe melt pool, forming a metallurgical bond with the substrate. SLSses a powder bed where laser melts a layer of powder and a fresh

ayer of powder is provided each time a new layer is melted whilehe table moves downward to accommodate the new layer.

∗ Corresponding author at: 2350 Hayward Street, 2040 G.G. Brown Laboratories,niversity of Michigan, Ann Arbor, MI 48109, USA. Tel.: +1 734 764 2177;

ax: +1 734 763 5772.E-mail address: sudipb@umich.edu (S. Bhattacharya).

921-5093/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.msea.2010.11.036

© 2010 Elsevier B.V. All rights reserved.

In DMD, RP of the 3D object to be created starts with a CADdesign. The entire CAD model is first sliced into several parallel lay-ers, each with a build height of approximately 25–33% of the beamdiameter, and then a tool path is created to build each layer. Thetool path data is processed by converting them into conventionalCNC G and M codes and feeding into the DMD computer. RM thenfollows by focusing a high power laser beam onto a substrate tocreate a melt pool and simultaneously delivering metal powdersinto the melt pool through a specially designed coaxial nozzle thatconverge the powder at the same point on the focused laser beam.The 3D object is created layer by layer (and/or pixel by pixel) byusing a CNC machine or a Robot that controls the part geometryand layer height according to the tool path data fed to the DMDcomputer [7].

DMD process can be used to manufacture near-net shape com-ponents with complex geometries, coat surfaces, repair parts andbuild graded materials which is otherwise difficult to accomplish byconventional manufacturing processes [7].The closed loop opticalfeedback system used in DMD process reduces the manufacturingtime by eliminating intermediate steps from design to product. Theclosely controlled process parameters produces clad with uniformthickness and extremely fine and controlled microstructure [2,3,7]with the ability to extend the solid solubility of certain elementsinto another [8]. However during DMD residual stresses are gen-

erated in the clad layer due to (i) plastic deformation caused bythermal mismatch among the deposited clad and substrate becauseof rapid solidification and (ii) volumetric change induced by solid-state phase transformation in the clad which could result in crackformation [9,10].

2310 S. Bhattacharya et al. / Materials Science and Engineering A 528 (2011) 2309–2318

owin

lavtascaiwrsc

m4woewptpsais

2

2

mtcpguo

TA

ple matrix was made to perform a statistical design of experiment(DOE) based on a L9 orthogonal array of Taguchi method [17] inorder to optimize parameters to produce samples with minimumporosity and maximum deposition rate. Table 3 shows the opti-mal parameter combination drawn from this trial sample matrix

Fig. 1. SEM micrograph of AISI 4340 steel powder sh

AISI 4340 steel is a medium carbon, heat treatable, high strengthow alloy (HSLA) steel used for critical structural applications, suchs building components, automobile components, high pressureessels for nuclear power plants, and aircraft components, due to itsoughness, high strength and ability to retain good fatigue strengtht elevated temperatures [11–13]. The microstructure of carbonteels primarily consists of a mixture of ferrite with some cementitearbides, tempered and untempered martensite, and some retainedustenite depending on the processing conditions. Primary alloy-ng elements (nickel, chromium and molybdenum) addition along

ith carbon makes it the material of choice for corrosion and wearesistant applications, e.g. for making medical devices (along withtainless steels) and submarine components used under submergedonditions [13,14].

The current research effort was undertaken to evaluate theicrostructure evolution during the repair of some high value AISI

340 steel components by DMD process. AISI 4340 steel has beenell researched. However, reported literature on laser processing

f AISI 4340 steel primarily discuss laser surface treatment and itsffect on the mechanical properties of the alloy. Few publishedorks have also reported the microstructural characterization ofost laser treated AISI 4340 steel surfaces [12,13,15]. In this inves-igation complete microstructural characterization and mechanicalroperties (based on microhardness measurements), of AISI 4340teel deposited by DMD process has been reported, which is notvailable in open literature. The paper also investigates the changen lattice parameters of the microstructural phases due to rapidolidification.

. Experimental

.1. Materials

Gas atomized prealloyed AISI 4340 steel powder (−140/+325esh), manufactured by Carpenter Powder Products, PA, was used

o prepare reported DMD samples. Table 1 shows the chemical

omposition of the as-received powder. Fig. 1(a) shows as-receivedowder particles morphology. Powder was also mounted in epoxy,round and polished to examine the powder particle cross-sections,sing scanning electron microscopy (SEM), for particle morphol-gy, size and porosity measurements. As-received powder particles

able 1ISI 4340 steel powder composition (wt.%).

Fe C Ni Cr Mn Mo Si

Bal. 0.42 2.63 0.90 0.74 0.45 0.29

g (a) particle morphology (b) particle cross-section.

cross-section can be seen in the SEM micrograph of Fig. 1(b). Thepowder particles were mostly spherical with an average parti-cle size of 75 �m and 85% of the particles within the 60–120 �mrange. Approximately 100 particles per micrograph were selectedfor measurements and always the largest diameter and the diame-ter in the direction perpendicular to the long axis were measured.The average powder particle porosity was found to be approxi-mately 0.45%.

2.2. Sample preparation

Fig. 2 shows the schematic of DMD process. DMD system primar-ily consisted of the laser generation system, the powder deliverysystem, feedback control system, and CNC motion stage [16]. TheDMD process could be performed either in air or under controlledatmosphere. DMD samples for this investigation were preparedat Focus: HOPE using a 1 kW fiber coupled diode laser (LaserlineGmbH, Germany) POM DMD 105D system with a 2 mm diam-eter laser beam. A combination of DMD processing parameters:laser powers 500, 550 and 600 W, processing speeds 400, 450, and500 mm/min, and powder feed rate 5, 6 and 7 g/min and 50% over-lap between two adjoining passes, were used to build a trial samplematrix (Table 2), and later experimental samples. Argon was usedas both carrier and shielding gases during deposition. The trial sam-

Fig. 2. Schematic diagram showing the DMD process.

S. Bhattacharya et al. / Materials Science and Engineering A 528 (2011) 2309–2318 2311

Table 2DOE sample matrix used for developing process parameters for AISI 4340 steel on mild steel substrate using diode laser.

Run order Power (W) Scanning speed (mm min−1) Powder feed rate (g min−1) Deposition quality Average porosity (%)

L1 500 400 5 Good 0.20L2 500 450 6 Good 0.40L3 500 500 7 Good 0.20L4 550 400 6 Good 0.20L5 550 450 7 Non-bonding at interface 1.98L6 550 500 5L7 600 400 7L8 600 450 5L9 600 500 6

Table 3Optimal parameter combination for depositing DMD samples for microstructuralcharacterization.

Sample Power (W) Scanning speed(mm min−1)

Powder feedrate (g min−1)

fcslwftZlp3

3 mm diameter discs were punched out of these slices and thesediscs were further ground to approximately 100–110 �m. These

Fs

AISI 4340 steel 500 450 5

or depositing the experimental samples used for microstructuralharacterization. Rolled mild steel plates were used as the sub-trates for all samples. Both trial and experimental samples had 8ayers, alloy (or dilution) layer plus 7 layers on top of it. The layers

ere deposited in a cross hatched pattern, i.e. deposition directionor every layer was perpendicular to the previous layer. Fig. 3 showshe schematic of the cross hatched pattern deposition scheme. Theincrement between layers was approximately 0.5 mm. The alloy

ayer was deposited with slightly different DMD parameters; laserower 800 W, processing speed 500 mm/min and powder feed rategm/min.

ig. 3. Optical micrograph showing the longitudinal cross-section of the experimental sateel DMD sample.

Good 0.60Good 0.53Voids 4.13Good 0.20

2.3. Characterization

The microstructure along the longitudinal (x–z), transverse(y–z) cross-sections, and horizontal (x–y) (or top view) of theas-deposited experimental sample were examined by opticalmicroscopy (OM) (NikonTM), and SEM (PhilipsTM, XL30 FEG scan-ning electron microscope). The crystal structure and the latticeparameter determination were performed by X-ray diffraction(XRD), (Rigaku rotating electrode X-ray diffractometer) and trans-mission electron microscope (TEM) (JEOL 3011 high resolutiontransmission electron microscope (HRTEM)) operating at 300 kV.

XRD was performed with Cu K� radiation at 40 kV and 100 mA,scanned in the standard �–2� ranges of 30–100◦ and data collectedat every 0.01◦ interval. TEM samples were prepared from thin slices,(approximately 300–400 �m thick), taken out of the bulk sample.

discs were then further thinned to make them electron transparentusing a FischioneTM Model 110 twin-jet electropolisher. Electropol-ishing was performed at 18–20 V and 45–50 mA using 33% nitric

mple and a diagram showing the laser scanning direction and layers in AISI 4340

2 ce and Engineering A 528 (2011) 2309–2318

aiptTaw

3

3

dNm

3

csibvfi0dmal

Table 4AISI4340 DMD® clad composition (wt.%) from EDAX.

F

312 S. Bhattacharya et al. / Materials Scien

cid–methanol solution as the electrolyte, maintained at approx-mately −15 to −20 ◦C. Microhardness (MH) measurements wereerformed on the polished samples with a Vickers microhardnessester (Clark, CM-400AT) using 500 g load and dwell time of 15 s.he final hardness measured along each layer was calculated as theverage of six data values while the final hardness across the layersas calculated as the average of three data values.

. Results

.1. Microstructure

Specimens for OM, SEM and MH measurements were cut fromifferent parts of the experimental sample and etched with 2.5%ital (97.5% ethanol and 2.5% nitric acid) solution to reveal theicrostructure.

.1.1. Optical microscopyFig. 3 shows the optical micrograph of the longitudinal (x–z)

ross-section of the as-deposited experimental sample, and achematic of the laser deposition and laser scanning directionsn different clad layers. Total thickness of the clad was found toe approximately 3.400 �m. Thickness of each layer was found toary approximately between 300 �m and 500 �m. However, noeedback control was used during these experiments. Since the Zncrement for each layer during deposition was kept constant at

.5 mm (500 �m), it shows that there is some interlayer overlapuring deposition. The laser band width measured from opticalicrograph (Fig. 3) was found to be approximately 943 �m. Also

s the laser beam diameter was 2 mm (2000 �m), percentage over-ap measured from optical micrograph was approximately 50%. The

ig. 4. SEM micrographs showing the three-dimensional view of the AISI 4340 steel DMD

Fe C Ni Cr Mn Mo Si

Bal. – 2.57 1.40 0.55 – 0.30

percentage overlap corresponds to the experimental parameters.The specific energy (or fluence) applied to the sample, calcu-lated from processing parameters, was found to be approximately33 J/mm2.

3.1.2. Scanning electron microscopyFig. 4 shows three-dimensional view of microstructures at three

different locations along the clad; (a) first few layers, (b) middlelayers, and (c) top layers. Fig. 5(a–h) shows the longitudinal (x–z)view microstructures of clad layers 7 through alloy layer. Fig. 5(i)shows the interface microstructure, and Fig. 5(j) shows the sub-strate microstructure.

Fig. 6 shows the plan (x–y) view microstructure of the clad.The longitudinal view microstructures clearly show needle shapedmartensite in the top few layers (layer 7–5), and they appear to gettempered or rounded in middle through lower layers (layer 4–1),towards the interface. The grain size also appears to increase inthat direction. Plan view (Fig. 6(b)) also shows microstructure withprobably some retained austenite along the grain boundaries. How-ever, XRD and TEM analysis did not detect any retained austenitephase.

Fig. 5(j) shows typical rolled microstructure with large grains inthe substrate. Interface and alloy layer also show some fine tem-pered martensite and larger grains. Fig. 7 shows the EDAX® analysisof the clad layers and Table 4 gives the chemical compositionof the clad obtained from the analysis. The chromium composi-

sample at three different locations (a) first few layers, (b) middle layers, (c) top.

ce and

tc

3

FtXe

F(

S. Bhattacharya et al. / Materials Scien

ion in the clad was found to be slightly higher than the powderomposition.

.1.3. X-ray diffraction analysis

Fig. 8 shows the XRD plot of the AISI 4340 steel DMD clad.

errite (�-Fe), martensite, and cementite (Fe3C) phases were iden-ified from the plot. No retained austenite was observed in theRD plot. The equilibrium microstructure of hypo-eutectoid steel isxpected to be primarily ferrite and pearlite (ferrite + cementite) at

ig. 5. SEM micrographs showing longitudinal (y–z) view microstructures of the AISI4340i) interface, and (j) substrate marked in Fig. 3.

Engineering A 528 (2011) 2309–2318 2313

room temperature. Since DMD is a non-equilibrium process somemetastable phases such as martensite could be certainly expectedin the microstructure.

3.1.4. Transmission electron microscopyFigs. 9(a), 10(a) and 11(a) shows the bright field (BF) images of

microstructural phases and Figs. 9(a), 10(a) and 11(a) shows theircorresponding selected area diffraction (SAD) patterns. SAD pat-terns identified these microstructural phases, i.e. ferrite, martensite

DMD® sample layers (a) through (h) corresponding to layer 7 through alloy layer,

2314 S. Bhattacharya et al. / Materials Science and Engineering A 528 (2011) 2309–2318

(Conti

aiiwzi2S2Sct

Fig. 5.

nd cementite and corroborated the XRD results. Retained austen-te phase was not detected in TEM investigation as well. The phasedentified from the SAD pattern of Fig. 9(b) was ferrite (�-iron),

ith a body centered cubic (BCC) crystal structure and a [0 1 1]one axis (ZA). Lattice parameter a of the ferrite phase match-ng the XRD pattern peaks (PDF #04-004-2482) was reported as.8676 A. The corresponding lattice parameter calculated from the

˚

AD pattern was found to be 2.810 A, which was approximately.0% shorter than the reported values. The phase identified from theAD pattern of Fig. 10(b) was a lathe type martensite with a bodyentered tetragonal (BCT) crystal structure and a [1 1 1] ZA. Lat-ice parameters a, and c of the martensite phase matching the XRD

Fig. 6. SEM micrographs showing the plan (x–y) views m

Fig. 7. EDAX analysis showing chemical com

nued.)

pattern peaks (PDF #00-044-1290) were reported as 2.859 A and2.937 A,respectively. The corresponding calculated lattice parame-ters from SAD pattern were 2.856 A and 2.902 A, respectively, whichwere approximately 0.1% and 1.2% shorter than the reported val-ues. The phase identified from the SAD pattern of Fig. 11(b) wascementite (Fe3C), with an orthorhombic crystal structure and a[0 0 1] ZA. The reported lattice parameters a, b and c of the cemen-

tite phase matching the XRD pattern peaks (PDF #01-074-3832)were 4.5119 A, 5.0825 A, and 6.7330 A, respectively. The corre-sponding calculated lattice parameters from the SAD pattern were4.4800 A, 5.0509 A, and 6.7291 A, which are approximately 0.7, 0.62and 0.058%, respectively shorter than the reported values. The lat-

icrostructure of the AISI 4340 steel DMD® sample.

position of the AISI4340 DMD® clad.

S. Bhattacharya et al. / Materials Science and

t(estc

Fig. 8. XRD scan of AISI 4340 steel DMD® sample.

ice parameter information obtained from powder diffraction files

PDF) of phases matching the XRD pattern peaks are obtained fromquilibrium microstructures. The bright field image in Fig. 12(a)hows the plate type martensite and Fig. 12(b) shows the disloca-ion networks surrounding the martensite phase observed in thelad.

Fig. 9. (a) Bright field image showing the area marked for SAD in the

Fig. 10. (a) Bright field image showing the area marked for SAD in the m

Engineering A 528 (2011) 2309–2318 2315

3.2. Microhardness measurement

Microhardness measurements were taken across the sampleand along each layer to determine the mechanical response ofvarious phases on the microstructure. Fig. 13 shows microhard-ness plotted against distance from the interface and Fig. 14 showsa histogram of microhardness measurements along each layer.Microhardness decreases from layer 7 to alloy layer. The averagemicrohardness along each layer, layer 7 through alloy layer, variesfrom 681–480 VHN. Decrease in hardness from the upper to thelower layers indicates increase in amount of tempered martensiteacross the samples which were also observed from SEM micro-graphs (Figs. 5 and 6).

4. Discussion

The microstructure of steel is well researched over the years.Several known microstructural phases in steel are austenite, fer-rite, pearlite, martensite and bainite. Fig. 15(a) shows the portionof the Fe–C phase diagram highlighting the eutectoid region andFig. 15(b) shows the continuous cooling transformation (CCT) dia-gram of alloy steels [18]. Fig. 15(b) clearly shows that the cooling

rates can significantly alter the microstructure. Under equilibriumprocessing condition, on cooling from austenite region to belowthe eutectoid temperature, expected microstructure for the givenAISI 4340 steel powder composition (Table 1) should primarily con-sists of ferrite and pearlite phases. However, the cooling rates for

ferrite phase (�) and (b) corresponding indexed SAD pattern.

artensite phase (m) and (b) corresponding indexed SAD pattern.

2316 S. Bhattacharya et al. / Materials Science and Engineering A 528 (2011) 2309–2318

Fig. 11. (a) Bright field image showing the area marked for SAD in the cementite (Fe3C) and (b) corresponding indexed SAD pattern.

nsite

DaelDm

F

Fig. 12. Bright field image showing (a) marte

MD usually are as high as 103–105 K/s [7,13] and result in devi-tion from equilibrium microstructure. CCT diagram shows that

xtremely rapid cooling rates place the DMD process to the extremeeft hand side of the diagrams, below the martensite finish line. TheMD microstructure of an alloy steel is thus expected to be pri-arily martensitic. The microstructure of the alloy steels may also

ig. 13. Plot showing variation microhardness with distance from interface.

and dislocation networks around martensite.

consists of secondary phases, such as several alloy carbides [19]depending on the composition.

The microstructural investigation of DMD AISI 4340 steel, using

SEM and TEM, reveals that the clad primarily consists of ferriteand martensite and some cementite phases. According to Costaand Vilar [20] extremely rapid cooling rate during DMD suppressesthe diffusive microstructural transformations and results in major-

Fig. 14. Plot showing microhardness measured along each layer.

S. Bhattacharya et al. / Materials Science and Engineering A 528 (2011) 2309–2318 2317

F phasec F = fer

ipodoTt(ctdcmwsi

oosootfattsTtS7slmaf

ac

ig. 15. (a) Portion of the Fe–C equilibrium phase diagram showing the equilibriumooling transformation (CCT) diagram for alloy steel [18] (A = austenite, B = bainite,

ty of carbon atoms to remain in the solution in austenite (�-Fe)hase and form metastable martensite phase. The carbon atomsccupying the interstices in the BCC lattice in ferrite phase causesistortion of the lattice in one direction while contraction in thether two normal directions and thus resulting in a BCT structure.he strength of the martensitic structure in steels depends on theempering temperature, carbon content and the martensite startMs) and finish (Mf) temperatures [21]. Lee and Su [22] related thehange of martensite morphology with carbon content. They statedhat low-carbon content results in lathe type martensite with highensity of dislocation, as observed in rolled structure, high carbonontent results in plate type martensite with very fine twins andedium carbon content results in a complicated microstructureith a mixture of lathe and plate type martensite. Figs. 11 and 12

hows that the both lathe and plate types of martensite are presentn the current DMD AISI 4340 steel samples

Heat treatments can alter the distribution, size and morphol-gy of the metastable phases and also results in the precipitationf secondary phases [22,23] in as-cast structure. Lee and Su [22]howed that the cast microstructure of AISI 4340 steel consistedf lathe martensite and tempering process resulted in the growthf the lathes and precipitation of several types of carbides aroundhese lathes. During DMD a considerable amount of heat is trans-erred to the bulk, hence starting from substrate every layer actss a heat sink for the subsequent layers above it. Thus accordingo Costa and Vilar [20] every solidified layer undergoes successivehermal cycles as new layers are deposited and results in solid-tate microstructural transformation in these resolidified layers.his could significantly change the matrix microstructure, distribu-ion of secondary phases and eventually material properties [22].EM micrographs (Fig. 5) show that the martensite phase in layeris fine needle shaped and it gets tempered and rounded in sub-

equent layers towards the interface. The microstructure of lowerayers is etched darker as compared to upper layers. Decrease in

icrohardness values (Figs. 13 and 14) from layer 7 to alloy layer

lso proves that the degree of tempering of the martensite phaseollows same direction.

Extremely rapid cooling during DMD results in residual stressccumulation in clads [9]. These residual stresses could affect therystal structure of microstructural phases in the clad. The mechan-

s present at the sample composition indicated by an arrow [18] and (b) continuousrite, M = martensite, P = pearlite).

ical properties of the material could be directly related to the crystalstructure of each phase [24]. Researchers have [25,26] investi-gated the effect of residual stress on the mechanical behavior ofmicrostructural phase in materials. The effect of cooling rate on themicrostructural phases is observed in the TEM SAD patterns. Thelattice parameters of the phases identified using TEM SAD patternswere shorter as compared to the lattice parameters for the samephases reported in literature. The reported lattice parameters wereobtained from the samples with equilibrium processing. This showsthe effect of residual stresses present in DMD clads on the crys-tal structure of the microstructural phases. No information on theeffect of residual stresses on lattice parameter of microstructuralphases is available in open literature.

Fastow et al. [15,27] reported the presence of traces ofretained austenite phase along with martensite phase in themicrostructure of laser surface alloyed AISI 4340 steel. Researchers[28,29] have also reported the presence of retained austenitephase on prior austenite grain boundaries in cast and lasersurface treated AISI 4340 steel samples. Sastry and Wood[28] showed that the orientation between retained austen-ite and martensite exhibited a Kurdjumov–Sachs relationship,(1 1 1)�//(1 1 0)� in a laser surface treated AISI 4340 steel sam-ple. Molian [29] showed that cementite particles precipitatedduring heat treatment of cast AISI 4340 steels displayed Bha-garyatskii orientation relationship with martensite such as,[0 1 1]�//[1 0 0]Fe3C, [1 1 1]�//[0 1 0]Fe3C and (2 1 1)�//(011)Fe3C.SEM micrographs (Fig. 6) also show some retained austenite alongthe grain boundaries in the current sample. However, they wereneither detected in XRD scans nor in TEM analysis. These orien-tation relationships between austenite (�), ferrite (�), martensite,�-carbide and Fe3C phases in DMD AISI 4340 steel deposited usinga CO2 laser have been explored in detail by our group in anotherpublication [30].

It was found that the formation of martensite from �followed the conventional Kurdjumov–Sachs relationship. Orien-

tation relationship between �-carbide and Fe3C also followed theconventional orientation relationships reported in literature. How-ever, the relationship between �- and �-carbide did not follow anyof the conventional orientation relationships reported in literature[30].

2 ce and

5

wopmhltttlar

A

oto

R

[

[[

[

[[[[[

[[[[[[[

[

[27] M. Fastow, M. Bamberger, N. Nir, M. Landkof, Mater. Sci. Technol. 6 (1990)

318 S. Bhattacharya et al. / Materials Scien

. Conclusions

AISI 4340 steel were successfully deposited using a DMD systemith diode laser on a mild steel substrate. The samples consisted

f an alloy layer and 7 more layers on top. The microstructuralhases identified in the clad using SEM, XRD and TEM were ferrite,artensite and cementite. It was observed that the clad micro-

ardness decreases from the top (layer 7) to the bottom (alloy)ayer. This corresponds to the SEM micrographs which show thathe degree of tempering of the martensite phase increases fromop to the bottom layers. The lattice parameters of the phases iden-ified from TEM SAD patterns were found to be shorter than theattice parameters reported in literature, ferrite a = 2.0%, martensite= 0.1% and c = 1.2%, and cementite a = 0.7%, b = 0.62% and c = 0.058%,

espectively.

cknowledgements

The current investigation was financially supported by the Officef Naval Research. Authors would like to thank Dr. Kai Sun fromhe Electron Microscope Analysis Laboratory (EMAL) at Universityf Michigan for his help in the work.

eferences

[1] J. Mazumder, J. Choi, K. Nagarathnam, J. Koch, D. Hetzner, JOM 49 (1997) 55–60.[2] J. Mazumder, A. Schifferer, J. Choi, Mater. Res. Innov. 3 (1999) 118–131.[3] J. Mazumder, D. Dutta, N. Kikuchi, A. Ghosh, Opt. Lasers Eng. 34 (2000) 397–414.[4] J.O. Milewski, G.K. Lewis, D.J. Thoma, G.I. Keel, R.B. Nemec, R.A. Reinert, J. Mater.

Process. Technol. 75 (1998) 165–172.

[[[

Engineering A 528 (2011) 2309–2318

[5] http://www.sandia.gov/mst/pdf/LENS.pdf.[6] D.E. Bunnell, D.L. Bourell, H.L. Marcus, Advances in Powder Metallurgy and

Particulate Materials, Part 15, Metal Powers Industries Federation (MPIF),Princeton, NJ, 1996, pp. 93–106, Section 15.

[7] G.P. Dinda, A.K. Dasgupta, J. Mazumder, Mater. Sci. Eng. A 509 (2009) 98–104.[8] J. Singh, J. Mazumder, Acta Metall. 35 (1987) 1995–2003.[9] M. Pilloz, J.M. Pelletier, A.B. Vannes, J. Mater. Sci. 27 (1992) 1240–1244.10] P.B. Kadolkar, T.R. Watkins, J.Th.M. De Hosson, B.J. Kooi, N.B. Dahotre, Acta

Mater. 55 (2007) 1203–1214.11] N. Ozdemir, Mater. Lett. 59 (2005) 2504–2509.12] M.P. Nascimento, R.C. Souza, W.L. Pigatin, H.J.C. Voorwald, Int. J. Fatigue 23

(2001) 607–618.13] R.L. McDaniels, S.A. White, K. Liaw, L. Chen, M.H. McCay, P.K. Liaw, Mater. Sci.

Eng. A 485 (2008) 500–507.14] A. Ragab, H. Alawi, K. Sorein, Mech. Mater. 18 (1994) 69–77.15] M. Fastow, M. Bamberger, Scr. Metall. Mater. 22 (1988) 183–186.16] J.L. Koch, J. Mazumder, U.S. Patent Number 6,122,564, September 19, 2000.17] http://www.itl.nist.gov/div898/handbook/pri/section5/pri56.htm.18] D. William, Callister Jr., Materials Science and Engineering: An Introduction,

sixth ed., John Wiley & Sons, Inc., New York, 2003, pp. 281 and 317.19] S. Kheirandish, A. Noorian, J. Iron Steel Res. Int. 15 (2008) 61–66.20] L. Costa, R. Vilar, Rapid Prototyping J. 15 (2009) 264–279.21] K. Shimizu, Z. Nishiyama, Metall. Trans. B 3 (1972) 1055–1068.22] W.-S. Lee, T.-T. Su, J. Mater. Process. Technol. 87 (1999) 198–206.23] G.P. Dinda, L. Song, J. Mazumder, Metall. Trans. A 39 (2008) 2914–2922.24] Y. Liu, J. Mazumder, K. Shibata, Metall. Trans. A 25 (1994) 37–46.25] R. Dakhlaoui, A. Baczmanski, C. Braham, S. Wronski, K. Wierzbanowski, E.C.

Oliver, Acta Mater. 54 (2006) 5027–5039.26] A.J. Perry, D.E. Geist, K. Narasimhan, J.R. Treglio, Surf. Coat. Tech. 86–87 (1996)

364–371.

900–904.28] C.N. Sastry, W.E. Wood, Mater. Sci. Eng. 45 (1980) 277–280.29] P.A. Molian, Mater. Sci. Eng. 51 (1981) 253–260.30] G. Sun, S. Bhattacharya, G.P. Dinda, A. Dasgupta, J. Mazumder, Unpublished

results, 2010.