pin on disc wear nitrocarburising

8/3/2019 Pin on Disc Wear Nitrocarburising

1/8

Pin on disc wear investigation ofnitrocarburised H13 to ol steelP . c. K ing*l, R . w . R eyn old so n2 , A . B row nrigg" an d J . M . L on g"Nitrocarburised H13 disks were tested in dry, sliding wear against a stationary ruby ball (pin),Three different 4 h nitrocarburising treatments were compared, using N2/NH:yC02, N2iNH3I'natural gas and NiNH3 gas mixtures, resulting in compound layers of varying thickness,hardness, porosity and oxide morphology, During mild, Oxidative wear, with the formation ofabrasive wear debris, the most brittle and oxidised surfaces performed poorly, Polishing to abright, reflective finish greatly reduced wear. However, the NiNH3I'C02 sample also frequentlymaintained a 'very mild' wear regime, owing to the formation of a protective film between the wearsurfaces, and resulting in a lowering of the friction coefficient This treated surface was porousand covered in a complex layer of coarse oxide +e-carborutnde. Nitrocarburised samples andwear tracks were characterised by optical microscopy, SEM, atomic force microscopy and stylusprofilometry,~ .. ; P in o n dis c. W ea r 1e sti1g . N itro ca rbu ri$ i:> g, Compo!.nd layer, H I :! , T o oI _. Oxidative wear . F r ic ti on _ , FkJid_ bed.Cover layer,PoliShIng. P""""'Y, AFM, Prolilomatry, SEM

Introduct ionNitrocarburising is a common, inexpensive surfacetreatment that can be applied to Cr-Mo-V hot workingsteels such as H13, to improve their hardness andresistance to wear and fat igue. Forging dies and corepins for die casting! are two prime examples. H13 usedfor hot plastic working is successfully nitrocarburised tomi tigate against abrasive wear and thermal fatigue.Nitrocarburising is used to extend the life of extrusiondies. High temperature, un!ubrieated sliding contactwith aluminium causes wear of the die wall, whichresults in changes in the dimensions and surface finish ofthe product,"

The role of trea tmen I parameters on the surfacemicrostructure of nitrocarburised tool steels was dis-cussed in a previous paper. J Particular attention waspaid 10 the effect of secondary, carbon bearing gas onthe degree of carbon enrichment and compound layerp roperties, Itwas noted, for instance, that the choice ofcarbonaceous gas greatly influenced the degree ofporosity and oxidation at the compound layer surface.This is important, not only because components arefrequently put into service directly after nitrocarburis-ing, but also because, if the surface is to be polishedback, the amount of oxidised, porous rna terial thatneeds to be removed can be an important issue.Furthermore, it was shown that on some subst rates,such as H13 hot working die steel, carbon may be deeply

'ScI>ooI Gf Engi nee r in g and Technology, ~ University . 221 BurwoodHighway, Burwood, V i c. 3 1 25 , Australia'Reynoldson TecIv1olog.... , ISO _am> Rd. laooching 1 ' 1 a < > I , Vic.3139, AlJstraliaCorr~ng author. email pckinOyBl>oo_COITI

C 200'5 liI .tft!lt4 of lIa tt lriJ ,1 $. Mln Hlls . lid lU:tlflfPu li lhi hd by ' '' n4 iY 0 11"if. .IIof , t I _ Iftlltlhlt.R eu l,_" 12 ""'.!fUll 2 00 4i I cc cp t. d, D ec . .. b lt f : i i! ID Q .tD Ol 10 , it191 : L , . . . . 3,29.1l-50~0911

absorbed throughout the entire di ffusion zone. Thetotal di ffusion depth, the amount of grain boundarycementite below the compound layer, and even thesharpness of the compound layer-dilTusion zoneinterface, are all affected. Carbon may become highlyconcentrated in the compound layer when high levels ofnatural gas are used, resulting in a harder layer, ordecarburisation at the surface may occur with carbondioxide.Clearly, it is possible to produce a multitude ofdifferent nitrocarburised layers by altering the treatmentconditions. A variety of different commercial nitrocar-burising processes are also in existence.4-6 And yet, therehas been very little elTort to understand the role of thesedifferences in a wear situation. In this study, the effect ofcompound layer properties on wear behaviour wasinvestigated. Using a pin on disc apparatus, nitrocar-burised samples were tested in dry, sliding wearconditions. Porosity, hardness, layer adhesion andtoughness were the dominating factors.During sliding wear of metals, oxide formed byfrictional heating is known to prevent excessive adhesivedamage to the underlying metal, resulting inmild wear.Mild wear produces fine, oxidised wear debris. ' Uponclose metal!urgical examination, many authors havenoticed protective, raised patches of oxide on the wornmetal surface. 8,9 If oxide is removed faster than it isformed, severe wear results. Severe wear is characterisedby a rough, torn wear surface with ploughing by hardasperities, and the formation of large, metallic debris. Ithas been shown by Kato et al.8 that nitriding shifts theonset of severe wear to higher loads and sliding speeds,and reduces the wear rate compared wi th unni tridedsteel within the same wear mode.

Su~"'c.. En.. ilnlIarln r 2005 'YOL 21 NO 2 99


2/8

KI.g ot 01 . Nlt ,ou,bu,l ,ed H'3 tool s t. . 1

a N"INH,fCO,; b NoIN.H,lnai. gas; c N"INH,; top compound layer remained unetched apart from oxide (grey); middle dif-fusion z.onewas heavilyetched, and bottom substrate was unetchedM.lcrographe of nltrocarburtaed SIImpl . .. . , e tchad with n ItaI

Expe rimen ta l me thodDiscs 40 mm in diameter were machined from HI3 toolsteel (O38C-48CT-I2Mo-lISi-4l4Mn--{J2Ni (wt-%.The discs were quenched from 102S'C and temperedonce at 580C to a hardness of 48 HRC. A secondtemper was omitted, since some further temperingoccurs during nitrocarburising, The Hat surfaces werethen precision ground to a high finish (Table I).

Nitrocarburising was performed in an industrial160 mm dia. Huidised bed, with 120grit A1~OJ (meandiameter 1oo).lm) as the fiuidising medium. All treat-ments were 4 h long, at 570'C, and a total gas fiowrateof 1Sm1 h-1. Three different inlet ga s mixtures werechosen for comparison. These were N~125%NH;I8O/OC02, N,!2S%NH;l20' 'Ionatural gas, and N2I2S%NH). Samples were then quenched in another Huidisedbed, operating at ambient temperature on N2 How.Thetopography of nit rocarburised surfaces was charac-terised using atomic force microscopy (AFM) on aDME Dualscope DS 45-40 non-contact instrument.

Nitrocar burised samples were wear tested in the astreated condition or with a polish after treatment.Polishing was performed On a Struers RotoSysternautomatic polisher using IS 11mdiamond paste and asteady 20 N force applied to the samples, rotating in acounter direction to the pad. All samples were polished,with periodic visual inspections, to a bright, reflectivefinish. Different times were needed to achieve this, asshown in Table 1.Wear tests were performed using a CSEM pin on disctribometer. The pin was a 6 mm dia. singlecrystal Al203(ruby) ball. I t was held down stationary on the fiat faceof the testpiece disc under a 20 N load. The disc wasthen rotated at O ' I m s-1 relative to the pin, creating a

circular wear track. Tracks were made at variousdiameters, but the frequency of revolution was adjusted

to maintain the same sliding speed. All tests wereperformed unlubricated and in air. Lateral friction forcedata were sampled at 1 Hz.

Cross-sectional line scans of the wear t racks wereperformed using the Tencer Alpha step 200 profil-ometer. A 12'5 um radius stylus was moved across thesurface, and data sampled at I IUO intervals. Theprofilometer was also used for determining surfaceroughness R .. of the treated surfaces. Micrographs ofthe wear track area were taken by SEM using theLEICA S440 microscope on secondary electron mode at10-20 kV.Resul ts and d is cussionC h a ra ct er is at io n o f t re at ed s ur fa ce sFor a detailed study of nitrocarburised tool steel.diffusion profiles and microstructures, the reader i sreferred to King.' Al l treatments produced a hard, e-carbonitride compound layer immediately below thesurface. and a diffusion zone containing a heavydispersion of alloy nitrides within the tempered marten-site matrix (Fig. I).

The N2INH;lC02 treatment generated the thickestcompound layer, owing to rapid development ofe-Fe2-1(N,C) in the high oxygen potential associatedwith this gas mixture. The surface, which was originallybright and smooth with scratches in the grindingdirection, developed a thick external Fe)04 layer. As aresult, the treated surface had a dull blue grey finish. I twas found that this external oxide layer partially reducedback during treatment, nucleating coarse s-nitridecrystals above the original surface. This mixed Fe)O.JFe2.1N layer isthe so called 'cover layer ' and, as a resultof its nitride con t ent, it came up while in the opticalmicrograph.l" The topographical investigation (Fig. 2)

Table 1 Change in sur face roughn ...... due to nltrocarburislng and post-pollahlng procedureN"INH:lnalUraJ gas

R. before treatmentR, ener trealmentC om poo nd layer158.28 nm25060 nm1 5 1 1mthick, porous ,heavily oxldlsed27 min64nmPo li sh in g t im eR. alter polishing

16621 nm1311fTlthick, heavily oxldised,some porosity, high carbon1 3 m in16+17 nm

15929 nm9 I'm thick, non-porous6min24+ 14ru n

100 Surface Enllneerinl l 2005 \101. 21 NO 2


3/8

King ~I.I. Nltrocerburi d H13 tool st l

a NoINHoICO,; b NoINH:lnatural gas; c NoINH.2 Surface IOpography due 10 CDYllr layer build up In various nllrOc8rburialng IItmoaplw'esrevealed a rough, nodular surface. Gaps betweennodules resulted in the cover layer being microporous.

Simultaneously, as nitrogen levels reached criticallevels below the original surface, pores began to form,eventually resulting in a region of extremely fine scaleporosity in the outer compound layer (porosity has beenshown to be unavoidable beyond a certain layerthickness). II The fresh sur face created by these poresalso oxidised. The porous zone therefore appeared dullgrey in the polished cross-section, owing to the 'filling in'of the pore volume by MC)04 alloy oxides.The N21NH,Inatural gas compound layer was thinner,more dense and slightly less oxidised, It contained ahigher carbon content than the other compound layersand was harder as a result. However, the same processesat work in the N~,1C02 compound layer were alsobeginning to alter the surface at the 4 h mark of thistreatment. There was some porosity at the surface, andsigns within the external oxide layer of some reductionto e-nitride, In contrast, no porosity was found after theNIINH) treatment, and the layer has been shown to bemore ductile as a result. The exterior surface wasbrighter and smoother, and scratches from the surfacegrinding process were still clearly visible (see roughnessdata in Table I and surface topograpby in Fig. 2),Table I also sbows the surface roughnesses measuredafter polishing back the nitrocarburised surfaces. Bykeeping the polishing conditions strictly constant, it wasfound that significantly less polishing rime was requiredfor the N:z/NH, sample, because of the minimal surfaceoxidation that had occurred. Polishing only needed toremove the thin external oxide layer and expose the

original ground surface before a bright, reflective finishwas achieved. Incidentally, the measured roughness ofthis sample after polishing was actually higher, owing togrinding marks on the original surface. For the N,INH,tC~ sample, the surface remained dark until (it wasassumed that) the porous zone below the originalsurface had also been removed. Later metaUographiealexamination revealed that, in fact, a very small amountof porosity had remained, despite the change inappearance.

Results of pin on disc wear testingFigure 3 shows the development of friction throughoutthe course of 500 m wear tests. Several phases ofincreasing or decreasing friction were seen between theruby pin and the as treated CO~ sample. Sucb large,sudden variations in friction behaviour were not afeature of wear testing against polished or untreatedsurfaces. Repeated tests on the same C~ sampleshowed some variat ion in the timing and shape of thefeatures seen in Fig. 3a . While sharp drops and steadyrises were common on the CO2 sample, tbey were notpredictable. In some cases, low friction was maintainedbetween the two surfaces for extended periods.

Profilorneter examination of the wear tracks aftervarious test dura lions (Fig. 4) revealed Ihat the CO2sample experienced two distinct levels of wear. Often,very lit tle material was lost, and Ibis corresponded to asustained, low coefficient offriction.1t seemed that, withthe given test parameters, the CO2 sample was at thethreshold between two wear regimes, and that the

Surf ... En,ln , ln, 2005 VOL21 NO2 101


4/8

King et ot H I tr oi :ar bu rl5 ed H13 t ee I 5t ll !! el

0 ----(0) N fI3 l C O2 1 N2

I!iD 1 1 :1 : 1 - 1 5 0 lO G ~ 3 0 C Ir.I--.;..~

. . .

~1~---------------------------1M tOO tlSO 2D(J 2B 3m~(" " " . . .u~--------- -,

~ t - - - - - - - - - - - - - - - - - - - - - - - - - - - _ ,".t--------:.L~.I.:--A,,-----------tlo'~"""""""""-o+------------to ~ t - - - - - - - - - - - - - - - - - - - - - - _ ,0.1 "1---------------------------...,

M ~ ~ ~ ~ _ ... "" ~ ~0I1IIIiI"Ic:tI~

a N,.IN~o.: b untreated H13; c N,lNH.,Inatuml gas3 FrIc tIon coeITIcIenI during wea r I88ting, ~ the

ruby pin and various treeIedIuntreated H13 substndel

occurrence of one Or the other was an entirely randomevent. The cause may have been subtle variations in theproperties of the nitroearburised surface, which were notdetected bymetaUographic examinat ion (the layersappeared to be perfectly even across the treatedsurfaces). Changes in ambient temperature and humidityduring the tests may have also played a part.For an explanation of this behaviour, the wearsurfaces were examined following each test. Figure 5shows opt ical micrographs of the wear scars (brightcircular and ell iptical patches) on the ruby ball af tervarious stages in the test and on different 8Ubstrates, Theball was wiped with ethanol prior to optical examinationto remove any loose, powdery debris. These micro-graphs can be matched with SEM images of theopposing wear tracks on the H13 discs (Fig. 6) Thesliding direction was from left to r ight in Fig. 5and fromtop to bottom in Fig. 6.During the very ear ly s tages of the test, a shiny fi lmdeveloped on the surface of the ruby ball (Fig. S,,).There was also a smooth layer on the H13disc (Fig. 00).These micrographs were taken after test ing of the as

102 SuTfu. Enrlne-trhJI 2005 'IOL 21i NO2

. . .

treated CO2 sample was stopped following a sharp dropof the friction coefficient to 0'25. Gaps in the film inFig. 00 reveal patches of the original, ground surface.Machining maries at an oblique angle to the slidingdi rection were dearly visible. The nodular covering layerhad fractured and exfoliated in these areas. Other gapsin the film reveal only the oxide layer of the treatedsurface.

After longer wear distances, the filmon the ruby hall(Fig. 5b ) and the H13 disc (Fig. 6b ) became heavilyscored. However, scratches in the gaps in Fig, 6b were inthe grinding direction only. Apart from removal of thecovering layer, the nitrocarbunsed surface was unda-maged at this point. These micrographs were takenduring the low friction regime.If, in. contrast, the friction coefficient experienced asteady upturn, wear tracks revealed material fromdeeper below the surface. In Fig. 6c , the protective filmhad been squeezed out to the sides of the wear track,owing to the pressure beneath the ruby ball, Throughoutthe majonly of the wear track area, the filmwas absent,as were the machi ning marks of the original surface.Deeper wear was also accompanied by the appearance

of fin.e,powdery red wear debris. This usually adhered tothe bal l, behind the wear scar, as in Fig. 5d and e, andcould not be wiped off easily. Powdery debris thataccumulated adjacent to the wear track was collected,and X-ray diffraction examination showed il to belargely Fe:z~. Therefore, during the faster wearingmode of the as t reated CO2 sample, and in all wear testsof the other nitrocarburised samples, an abrasivemechanism tool:: place. It appears that removal of theprotect; ve oxide film was related to the appearance ofwear debris. - -The two types of behaviour discussed so far arereferred to here as 'mild' (abrasive) and 'very mild' (non-abrasive) wear. Mild wear corresponded 10 the oxida tiveprocess described by many authors for the sliding wearof metals. However, the formation of a protective oxideplateau, which almost eliminated wear of the underlyingsurface, is a new observation for nitrocarburisedsteels,

Severe, adhesive wear and the generation of large,metallic wear particles were not seen on any of thenitrocarburised samples under the given conditions.During deep penetration, broad ridges and groovesdeveloped On both mating surfaces. Fragmented, com-pacted wear debris w as found lodged within grooves, asseen in Whittle and Scott. I The. CO:! sample, after2000 m of wear showed this clearly (Fig. 5d) However, itwas the natural gas sample that developed the deepestgroove patterns of all the samples, possibly because ofthe harder compound layer, and associated harder weardebris produced during testing of this sample. Figure 4cshows the dramatic peaks and valleys following a2000 II.! test of the na turalgas sample, whose deepesttroughs penetrated well into the diffusion zone. Profilesof the NH) only and COl samples were comparativelyrounder (Fig. 4b and d). The wear scar on the ruby ballfollowing testing of the hard, natural gas sample wasmuch larger than the others, caused by hard debrislodged firmly within the deep grooves (Fig. Sj).Wear tracks on the NHj.only and natural gas sampleswere also covered in a dark film, which showed signs ofheavy shearing and plastic flow. Many places were bare,while in others the film was peeling otT (Fig. l ie).


5/8

King ~r at NltroCJIrburl,ed Ht3 1001,t1

I . :I. ,.(bl_100'2 HI2 2 0 0 C I m mId_. . . . . . . . . . . \ . . . . . . . . ,- t ,....... "I"

\ I\ I\,,/,..,. --1:+-------1---+---J .+-----+----f'-----_i

.aL_ =. ~--------------J .,. '- -:.~_--..,:----- . ..J~t_------------_i~--------------_1a N,lNH ....CO. 125 m; b NoINH"rC02 200 m, mild wear; c NoINH,tnatumi gas 200m: d NoIN.... 200m

4 Wear track cros....:tlonel prall'" after varlou8 _r dtat.ncea and substrat8 treatmenta

a CO. 22 m; b co . 125 m, very mild war, c unbeatad H13 500 m; d co, ltOOO m, mild war, e N.... only l t O O O m; r naIlnIgas 2000 m

5 Optical micrograph. of worn area on 8Ur tace 01ruby bal l

Sume. Ensln rlns 2005 VOl 21 N02 103


6/8

King ot t a/. N i tr o ta f 'b u ,l se d H 1 3 t o o l s t ee l

a co. sampIB 22 m: b co. sample 125 m . I I E I r Y mild w e a r : c co. ~ 125 m, mild w e a r : d CO. "","pia 2000m . mildwear; a N omH . 2 00 0 on; f untreated 50 0 m6 SEM micrograph. 01weer t racks on H13 discs

However, despite these obvious signs of oxidation, onlyraised film formed on the CO2 sample was of highenough integrity to result in very mild wear.The abili ty of the CO2 sample to maintain a protectivefilm without the formation of abrasive debris should berelated to the covering layer and/or underlying porousregion, as these were the features that distinguished thissample from the others. Similar situations, wherereduced wear has come as a result of an oxide layer as

part of a hardened sur face microstructure, have beenreported in the literature, For instance, it has been foundthat post-oxidation of plasma nitrided AISI 5140 steelresulted in a reduction in friction coefficient and wearrate compared with plasma nitrided only samples in anunlubricated pin on disc wear test against WC-Co,Wear debris was absent from the wear tracks of thepost-oxidised specimens. ' : ' Other systems where metaloxides act as solid lubricants are well documented,

104 '"rfac. Ensln rlns 2005 VOL 21 NO 2

Tribe-oxidation of W~o is known to produce oxideswhicb lower the friction parameters, In tests of WC-Coagainst various bard counterface materials , i t has beenshown that abrasive wear debris can break down theprotective oxide film, resull ing in increased frictioncoefficient. I.Metal oxide 'plateaus' or 'islands' have alsobeen found to lower friction and wear of Fe--5o/oCr 'laswell as titanium sliding against Ah03(sapphire), IS

In tests where the CO2 sample behaved according tothe mild, abrasive wear regime, the differences betweenthe various treatments followed a more recognisablepattern, The more oxidised, porous and bri!tle surfaceswore at a faster rate (Fig, 7), The advantage of theharder compound layer on the natural gas sample wasapparently nil (apart from considerably greater wear ofthe counterface material; Fig. 5/J . Nitrocarburisingresulted in a reduced wear rate compared with theunt reated material (Fig. 8). SEM examination of the


7/8

Ki.g ~r . ,. 10111 " '(,)" '1 .... II. 3 100 1 st 1

.. C O 2-a - Natural gas-e- NH3-only

o'+-----------~----------~----------~--------__,

7 Wear track area maaaured by profllometryo

worn surface of untrealed H 13 (Fig. 6j) showed rough,oxidised sections and smoother areas wi th scratchesrunning in the sliding direction. Some deep ploughinghad occurred. The wear scar on the ruby ball wascovered in well adhered wear debris (Fig. 5c). Therefore,there were features of severe, adhesive wear that werenot seen on the nitrocarburised samples. Polishing afternitroearburising further improved the wear resistance.There was lit tle difference between the natural gas andNH3 only samples, once the surfaces were fully polished.However, wear of the CO2 sample was still significant,owing to a small amount of porosity that was notremoved by polishing, despite the significantly longerpolishing period and the bright, shiny finish achieved.

The response of the as treated NlINH;JCOl specimento the given wear conditions was, at worst, unpredict-able and, at best, frequently superior to the otbers.Heavy oxidation is common with many commercialnitrocarburising (oxynitrocarburising) processes, and isnot usually seen as detrimental for many applications.However, in some cases bri ttleness must be avoided,such as in extrusion dies, where debris from excessivelythick compound layers isknown to cause downtime." Asmooth surface is often required for die components toensure a higb surface finish on the product. I t was seen

1000_dlblnoe(m)

1500

bere that, if nitrocarburised parts are to be polishedfollowing treatment, a non-porous, less oxidised surfaceis a better starting point. These microstructural featurescan be more influential than other, more often discusseddetails, such as tbe compound layer hardness.ConclusionIt has been shown that the porous and highly oxidisedsurface produced during nitrocarburising under a highoxygen potential may behave very differently from moredense layers under the given wear conditions. While thissample wore faster during oxidative, abrasive wear, itwas also prone to switch to a very mild wear regime.Very mild wear was characterised by a sudden loweringof the friction coefficient, the persistence of a protectivefilm between the wear surfaces, and a lack of weardebris. Future work could investigate a broader range ofconditions (force, sliding speed, counterface material)under which very mild wear is likely or certain to occur.The controlled engineering of an oxide layer, such as isdone commonly using steam or oxidising treatmentfollowing nitrocarburising for corrosion resistance,6.17-19offers an opportunity to exploit this behaviour fortribological purposes. However, i t has been shown here

. . . .cB3000E!! 2 O O O.,~.~1ooo. .

4000

oUntreated

. a s treated[Ipolished

CO 2 Natural gas NH3-0nly8 InfluenQa 01poU8hlngl lrealmenl conditions on wear track a......, measured by proIIlometry

Surfa.. Ensl rln, 2005 vOL21 "02 105


8/8

that a single step 'oxynitrocarburising' process is alsoeffective.AcknowledgementThe authors would like to thank Dr Ken Short, fromthe Australian Nuclear Science and TechnologyOrganisation (ANSTO), for his expert technical adviceand assistance with the wear testing equipment,References1. N. Krishnarej, P. B. Srinivasan. K. J. L lye, and S. Sunderesen:

Wear. 1998.115. 12J-130.2 . T . Bjork , R. Weste rga rd and S. Hogmark ; Wear .WOI. :149,316-323.3. P. C. K ing , R ..W. Reynoldson , A . B rowur ig g and J.M. LODg: S.rf

Eng . , 200S, 21 (2), 86-98.4. L. J. Ilpl"" G "" T e ch no t. , 2000, 2, 24-25.S. P. Psyllald e t a l. : Surf. Coal . Technot., 2003, 162(1),67-78.6. G. Wahl and S. Alwart in 'Heal treating', Proc:. 16th Ccuf . , 1996.

Cincinnati, OH, ASM.7. T. F. QUinn. J. L. Sulli van and D. M. Rcwsce: WMr. 1984.94.

175-191.

lOG SUrfl" EO.ln rlns 2005 VOL21 NO 2

8. H. Kato, T. S. Eyre and B. Ralph: ACl. Me/oil . MOler .. 1\194.41(5).170J-171).9. D. 1. Barnes, 1. E. Wilson, F. H. SI011 and G. C. Wood: w....1911. 45, 161-176.

1 0. S. Pi ee sch a nd S. Bohmer : M al ". S oL F or um , 1994. 163-165, 259-264.

11. C. D awes, D. F. Tranter and C. G. Smilh: H e al T re at: M e t . 1 9 81 1 ,7(1),1-4.12. R. D. T. Whit tle and V. D. seou: Me l. T e ch n ol ., 1984. II(June).231-241.

13. A. Alsaran, H. Allan., M. Karakan and A. Celik: Surf. COOl.Tedmol. , 2 0 04 . 1 7 6 . 3 4 4- 3 48 .14. 1 . M. Guilemany , J, M. Miguel , S. Vizcaino and F. C lime. l: Surf.COOl.T

pin on disc wear nitrocarburising

Documents