Evaluating the Wear of Polycrystalline Diamond Compact Drill Bit Cutters using Indentation and Scratch Tests

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1 46 Evluting the Wer of Polycrystlline Dimond Compct Drill Bit Cutters using Indenttion nd Scrtch Tests Rfid K. As 1 nd Ali Hssnpour 2 1 Deprtment of Chemicl Engineering, Fculty of Engineering, University of Al-Qdisiyh, Al-Diwniy, 58002, F.R. Irq 2 Institute of Prticle Science nd Engineering, School of Chemicl nd Process Engineering, University of Leeds, LS2 9JT, United Kingdom, Englnd Astrct Polycrystlline dimond compct (PDC) drill its re widely used in oil nd gs drilling. The wer of PDC cutters is mjor prolem during drilling. It leds to severe time losses which ffect the overll drilling opertion cost. Therefore, it is essentil to evlute the wer tendency for these cutters using predictive pproches. The present reserch is focused on studying the wer mechnisms of PDC cutters nd the effect of their mechnicl properties on the extent of wer. The volume of wer for the PDC cutters ws determined experimentlly using micro- nd nnoscrtch tests y implementing n pproch sed on the geometry of the removed mteril fter micro- nd nno-scrtch tests. The experimentl wer results were compred to the predictions from current models in the literture. Vrious wer models re evluted for micro- nd nno-scrtch tests on oth lyers of the PDC smples. The study shows tht the wer of the PDC cutters cn e predicted from the mteril mechnicl properties, pplied lod, sliding distnce, nd hrdness of the PDC cutters. The study could e extended for the evlution of wer intensity of PDC cutters from vrious mnufctures without using the previous techniques of rsion testing. Index Terms Bit wer, Indenttion, Micro-scrtch test, Nno-scrtch test, Polycrystlline dimond compct. I. Introduction Drilling for oil nd gs is still very demnding in mny res round the world. The use of polycrystlline dimond compct (PDC) its is widely spred nowdys due to their high performnce nd durility in hrsh environments. Synthetic dimond cutters or inserts tht re plced on the PDC it represent the most significnt prt of these its. PDC cutters hve significntly incresed drill it efficiency nd drilling performnce to point where PDC its hve overtken tricone its in mny oil nd gs drilling ARO-The Scientific Journl of Koy University Volume VI, No.1(2018), Article ID: ARO.10278, 9 pges DOI: /ro Received 22 July 2017; Accepted 12 April 2018 Regulr reserch pper: Pulished 31 My 2018 Corresponding uthor s, e-mil: Rfid.As@qu.edu.iq Copyright 2018 As RK, Hssnpour A. This is n open-ccess rticle distriuted under the Cretive Commons Attriution License. pplictions. Since the first commercil introduction of PDC its in 1976, mny chllenges ppered tht sometimes hlted their pplicility, especilly in hrd geologicl formtions, where rsive wer nd impct dmge previl. Wer of drilling its is due to mcroscopic or microscopic removl or frcture of mteril, especilly t the cutter surfce. Mouritz nd Hutchings (1991) investigted the wer rtes of the mterils used in the teeth of the rotry drilling its nd the rsive wer mechnisms of these mterils. Richrdson (1968) showed tht rsive wer rte of ny ductile mteril depended on the rtio of its hrdness (Hm) to tht of the rsive (H). When H/Hm <1, this mens tht the rsive cnnot scrtch the mteril nd the wer rte is extremely low. However, when H/Hm >1.2, the rsive cn scrtch the mteril nd cuse high wer rte (Mouritz nd Hutchings, 1991). Geoffroy (1999) showed tht more thn 50% of the energy of the drilling y PDC its is dissipted y the wer of cutters under norml drilling conditions, ssuming stedy motion nd voiding excessive heting. Fng, et l. (2001) descried tht the min filure modes of PDC cutters re due to frictionl het nd rsiveness of the rock s shown in Fig. 1. Tze-Pin, et l. (1992) nd Zcny (2012) postulted four primry filure modes of PDC cutters ccording to the type of wer mechnism: 1 - smooth wer, 2 - microchipping, 3 - gross frcturing or splling, nd 4 - delmintion. Vrious tests hve een crried out on PDC its nd, especilly, their cutters to ssess their performnce nd pplicility in diverse drilling conditions including hrsh environment nd high-temperture conditions. Bellin, et l. (2010) mentioned tht the mjority of the previous tests re rodly destructive. Arsion test is the well-known one, where the rsion resistnce of the cutter ginst rsive rocks is evluted. It depends minly on the hrdness of the minerls in the rock. Highly rsive rocks like grnite or hrd sndstone re normlly used in the rsion test. The wer of the PDC inserts hs een evluted nd reported in the literture (Bellin, et l., 2010); nevertheless, the precise ssessment of the mteril loss remins chllenge. Therefore, the current study is focused on this topic, tht is, determining the wer volume of the dimond lyer s well

2 47 s the sustrte of the PDC cutters fter pplying micro- nd nno-mechnicl testing. II. Methodology A series of micro- nd nno-indenttion tests were crried out to determine the mechnicl properties of the mterils forming the PDC smples. The smples re in the form of cylindricl disks with different dimensions. The imges of four PDC cutters tht hve een used in the experiments re shown in Fig. 2. The specifictions of the PDC cutters supplied from two different mnufcturers re given in Tle I. The upper prt of the PDC cutters is mde of dimond lyer in the form of PDC with colt s inder, wheres the lowest lyer (sustrte) consists of tungsten cride emedded in colt s inder. PDC specimens were finely polished to reduce the effect of surfce sperities nd consequently to reduce the mesurement error of hrdness nd Young s modulus. Furthermore, well-polished surfces will produce clerer imprints from micro- nd nnoindenttions nd enle etter mesurements of the digonls Commercil order TABLE I Specifictions of the PDC specimens Cutter dimeter (mm) Cutter height (mm) Dimond thickness (mm) M (±0.03) 8.0 (±0.1) 2.2 (±0.2) M (±0.03) 13.2 (±0.1) 2.2 (± 0.2) K (±0.05) 8.0 (±0.1) K (±0.05) 8.0 (±0.1) PDC: Polycrystlline dimond compct of the otined indents. Following the ove chrcteriztion work, micro- nd nno-scrtch tests were crried out, nd the results were compred with the predictions from the wer models in the literture. III. Experimentl Work A. Micro- nd nno-indenttion tests Micro- nd nno-indenttion mesurements of hrdness nd Young s modulus of mny mterils hve een performed y numerous reserchers; nevertheless, mny previous ttempts for indenting the dimond lyer of the PDC cutter hve filed. Mny reserchers mentioned the filure to e due to the rekge of the indenter, nd especilly, the Berkovich type (Sumiy nd Irifune, 2004). Nevertheless, the use of Berkovich proe ws successful under very low lods, tht is, <3 mn (Couvy, et l., 2011). In our work, nno-indenttion hrdness nd Young s modulus of the dimond lyer re mesured using Berkovich indenter using the NnoTest mchine mnufctured y Micro Mterils Ltd., Wrexhm, UK. A typicl lod-penetrtion plot for the indenttion is shown in Fig. 3. Hrdness nd Young s modulus of the smple were otined using the pproch reported in the literture (Couvy, et l., 2011) ut t different settings. After completing the nno-indenttion tests of the dimond lyer, it is crucilly importnt to check tht the Berkovich proe hs not een dmged. To do this, nnoindenttion tests were crried out on cermic smple efore nd fter the indenttion process of the dimond lyer. It ws oserved Fig. 1. Typicl filure modes of PCD inserts for rock drill it (Fng, et l., 2001). Fig. 2. Oil polycrystlline dimond compct cutters mnufctured y two different mnufcturers.

3 48 Fig. 3. () Applied force ginst displcement for tungsten cride-colt t fixed lod of 350 mn, () lod versus the indenttion depth for the polycrystlline dimond compct-co t fixed lod of 50 mn. tht the hrdness nd Young s modulus of cermic efore nd fter were nerly the sme nd this indicted tht the tip of the nnoindenter ws intct nd not dmged. The previous reported vlue of the hrdness nd Young s modulus of PDC ws within the rnge GP nd GP, respectively, depending on the dimond grin size nd the percentge of the colt inder which vried from 5% to 20% (Durovinski, 2006), (Osipov, et l., 2010), nd Ndlovu (2009). To prevent lrge fluctution in the mesurement of mteril properties, microindenttion experiments were crried out. A series of microindenttion tests were performed on the dimond nd the sustrte lyers of the PDC smples using INSTRON 5566 equipment using Vickers indenter t vrious lods. Microindenttions on dimond cotings require highly polished test surfce to discrd the effect of the sperities tht might cuse undesirle results such s producing uncler indents. Fig. 4 illustrtes the indents left fter using Vickers proe on the sustrte lyer of smple K1908 fter pplying lod of 50 N. Tle II demonstrtes the verge results of the hrdness nd Young s modulus determined from micro- nd nno-indenttion tests on oth lyers of the PDC smples. It is ovious tht the stndrd devition of the nnoindenttion results is much higher thn tht of microindenttion due to the forementioned reson. Frcture toughness ws determined from the microindenttion tests for the dimond nd the sustrte lyers of the PDC inserts. B. Microstructurl properties nd the colt content of PDC cutters This prt of the work is crried out to study the effect of the microstructurl properties of the cutters on the mechnicl properties of the dimond nd sustrte lyers. The microstructurl properties hve een chrcterized y energy dispersive X-ry (EDX) imges. The prticles size of the coting (dimond) nd the sustrte (tungsten-cride) hs een quntified y the Imge J softwre, wheres the weight percentge of the inder (colt) in the PDC smples hs een determined from EDX element tle content nd from longitudinl mesurement of the inder (colt) cross the interfce etween the dimond nd the sustrte lyers using (EDX-Quntline). Bckscttered detector (BSD) imges re used for displying the est resolution of the prticle distriution Fig. 4. Vickers imprints on the sustrte of smple K190 fter pplying 50 N lod. compred to norml scnning electron microscope (SEM) imges. EDX mps re used for determining the colt content in the dimond nd the sustrte lyers of the PDC cutters. The circulr equivlent dimeter of the dimond prticles nd sustrte is determined y imge J softwre fter nlyzing the BSD imges. It should e noted tht mjor drwck of this technique is tht the size chrcteristics re sed on two-dimensionl (2D) imge nlysis nd my not represent the prticles third dimension. Fig. 5 (top) shows the dimond prticles (lck res) emedded in the colt inder (white res) for smples M1313 () nd K1908 (). The prticle size distriution of the dimond grins of smples M1313 nd K1908 is shown in Fig. 5 (ottom). Fig. 6 (top) illustrtes the tungsten-cride prticles emedded in colt (lue) for () smple M1313 nd () smple K1908, wheres Fig. 6 (ottom) demonstrtes the tungsten-cride grin size distriution for (c) specimen M1313 nd (d) smple K1908. The colt content represented s weight percentge is determined from EDX element content t vrious spectrum res of the dimond nd sustrte lyers, nd then, verged results with stndrd devition re presented in Tle III. To summrize the microstructurl otined results, Tle III shows the microstructurl properties of two PDC smples from different mnufcturers.

4 49 c d Fig. 5. (Top) Bckscttered detector imges. () smple M1313, () smple K1908 of the dimond lyer displying the dimond grins (lck) nd the colt (white), (ottom) dimond prticle size distriution of smple M1313, nd (c) smple K1908 (d). TABLE II Mechnicl properties of PDC smples from micro- nd nno-indenttion tests PDC smple Vickers hrdness (GP) Yong s modulus (GP) Frcture toughness (MP.m 1/2 ) Lyer M1313 (Nno indenttion) 16.69± ± N/A Sustrte M1313 (Microindenttion) ± ± ±2.152 Sustrte K1908 (Microindenttion) ± ± ±2.146 Sustrte M1313 (Nnoindenttion) 49.36± ± N/A Dimond M1313 (Microindenttion) 50.85± ± ±1.219 Dimond K1908 (Micro indenttion) ± ± ±1.064 Dimond PDC: Polycrystlline dimond compct TABLE III Structurl properties of PDC inserts from different mnufcturers Microstructurl properties M1313 Dimond prticle size (µm) 12.03±4.9 min<4.52 mx>23.25 WC prticle size (µn) 2.52±2.11 min<0.38 mx>8.23 PDC smples K ±3.96 min<6.9 mx> ±1.69 min<0.3 mx>7.73 Co wt. % (in (dimond) 3.26± ±0.51 Co wt. % (in WC-Co) 7.37± ±0.32 PDC: Polycrystlline dimond compct Incresing the colt content for given prticle size cuses the frcture toughness to increse, ut it usully reduces the hrdness (Bellin, et l., 2010c). It is lso reported tht fine tungsten cride grin size nd low level of colt content led to higher hrdness nd good wer resistnce, wheres corse prticles nd high colt content produce low hrdness nd high wer rte (Mori, et l., 2003; Ndlovu, 2009). Yhioui, et l. (2013) stted tht the grin size nd the content of colt re the most significnt prmeters of PDC cutters s high wer rte is ssocited with lrge prticle size. Bellin, et l. (2010) reported tht the incresing the colt content in the dimond lyer nd the sustrte will increse the frcture toughness, wheres the wer resistnce increses with lower colt content. The prticle size of the sustrte lyer of smples M1313 nd K1908 is round µm, wheres the colt content in the sustrte of smple M1313 is slightly lower thn smple K1908. Accordingly, it is expected from these results tht the rsion (wer) resistnce of smple M1313 is slightly greter thn smple K1908, wheres smple K1908 hs etter frcture toughness thn smple M1313 (s cn e seen from Tle II). The hrdness of the dimond lyer of smple M1313 found to e greter thn the hrdness of the smple K1908 s shown in Tle II. This is minly due to lower level of inder content (3.26%) in smple M1313 compred to smple K1908 (4.4%), wheres the grin sizes re not tht different.

5 50 c d Fig. 6. (Top) BSD imges () smple M1313, () smple K1908 of the sustrte lyer displying the tungsten-cride prticles (gry) nd the colt (lue), (ottom) sustrte grin size distriution, (c) Specimen M1313, nd (d) specimen K1908. For the sustrte lyer, the hrdness of the tungstencride lyer of smple M1313 is found to e higher thn smple K1908 s shown in Tle II, nd this is ttriuted to the difference in the colt content of the sustrte for the two PDC cutters. The colt mss weight percentge in smple M1313 is ner 7%, wheres smple K1908 hs colt content of out 9%. The men grin size of smples M1313 nd K1908 is very similr. C. Microscrtch testing The work presented in this section is focused on quntifying the wer of PDC cutters nd the effect of their mechnicl properties on the extent of wer. The volume of wer for the PDC cutters ws determined experimentlly using microscrtch nd lter from nnoscrtch tests on different lyers of PDC cutters, tht is, the dimond lyer nd tungsten-cride (sustrte lyer) y implementing n pproch sed on the geometry of the removed mteril fter the tests. In ddition, this section illustrtes how the experimentl wer is compred to the predicted wer sed on current pproches in the literture. Vrious wer models re evluted for micro- nd nno-scrtch tests on oth lyers of the PDC smples: Sustrte nd dimond. The scrtch cused y shrp indenter produces rsion wer tht would e crucilly importnt for wer mechnism nd evlution. A series of microscrtch tests were crried out y pplying vrious lods on the surfce of the mteril nd moving the proe to sufficient sliding distnce to produce scrtch. Scrtch length nd width re the most points of interest for evluting the wer of the mteril. The microscrtch tests were performed using n INSTRON 5566 mechnicl testing mchine nd dimond indenter. Vickers nd spheroconicl dimond indenters were used during the microscrtch tests on oth lyers of the PDC smples. The otined microscrtches were exmined y SEM, EDX, 2D Tlysurf, nd three-dimensionl interferometer to determine the scrtches width nd depth s well s for nlyticl study. A series of microscrtch tests using Vickers indenter were conducted on oth lyers of the PDC specimens under vrious lods. The smples were mounted on n nvil tht hs mnul controller to lter the sliding distnce, wheres the pplied lod ws kept constnt. The sustrte of the PDC smple ws scrtched using lods rnging N. Mesured wer from microscrtch tests ws compred to the predicted wer sed on models in the literture. The height of the scrtch is mesured y the 2D profilemeter. Creful mesurements were crried out using Ultr Precision Tlysurf PGI800 with resolution up to 0.8 nm. The volume of wer (V w ) is determined experimentlly from the geometry of the removed mteril using the following eqution: ws. hs Vw = X (1) 2 Where w s is the width of the scrtch nd is mesured y imge nlysis of SEM records, X is the sliding distnce, nd h s is the height of the scrtch. Specil cre ws tken in scrtching the surfce of the dimond lyer, where low lods 10 N-20 N were pplied to void wrecking the tip of the indenter due to the high resistnce of the mteril surfce nd high degree of sperities. Mesured wer form microscrtch test is compred to the predicted wer sed on pproches in the literture y Rinowicz (1996), Hutchings (1992), nd Ning nd

6 51 Ghdiri (2006) s descried y Equtions (2), (3), nd (4), respectively: ( ) F.tn. X Vw = (2). H 2 F. X Vw =. H.tn (3) ( ) Fig. 7. () Groove otined using spheroconicl indenter t 50 N lod on WC-Co, () scrtch otined using spheroconicl lyer t 10 N on the dimond lyer. V w F H F = (2 L+ ) 5 1 (4) 17.1Kc K 4H 4 c Where F is the pplied lod (N), X nd L re the sliding distnces (m), β is the rsion ngle (degrees), H is the hrdness of the softest or rded mteril (N/m 2 ), α is the hlf ngle of the rsive prticle (degrees), nd K c is the frcture toughness of the mteril (MP.m 1/2 ). Due to the high risk of wrecking the dimond indenter, especilly when conducting the micro- nd nno-scrtch testing on the dimond lyer of the PDC smples, dditionl scrtch tests were performed using spheroconicl indenter. The use of sphericl tip of the proe is n effective wy to reduce the risk of rekge s compred to the use of shrp indenters, prticulrly when scrtching hrd cotings (Beke, et l., 2011). Fig. 7 shows the produced groove fter pplying 50 N on the tungsten-cride-colt (WC-Co) lyer of smple K1908 using spheroconicl indenter. The scrtch width nd sliding distnce were µm nd 200 µm, respectively, wheres Fig. 7 illustrtes scrtch otined fter pplying 10 N on the dimond lyer of smple K1908. The scrtch width nd sliding distnce were 29.9 µm nd 2300 µm, respectively. The SEM imges showed tht the deris resulted from the ploughing ction due to the microscrtching of smple K1908. The wer produced using spheroconicl indenter from microscrtch nd lter nnoscrtch test is determined from the following eqution which is found to quntify the wer volume of the x-trck s follows (CSM Ltd., 2002): Vw = Asegment * L (5) Where A segment is the re of the circulr segment s seen from Fig. 8 nd could e determined from the following eqution: 1 * 2 * [ ] Asegment = R si n (6) 2 Fig. 8. Sketch of the circulr segment of the conicl tip tht indents the dimond lyer. Where θ is the ngle opposing the segment of the circle, nd it cn e computed from Eqution (8): 1 h = 2 cos 1 R (7) Where R is the rdius of the circle nd h is the residul depth of the micro- or nno-scrtch s shown in Fig. 8. D. Nnomechnicl testing Nnomechnicl testing is technique tht hs een used recently for the evlution of mechnicl filure of cermics nd notly the nno-triologicl mesurements. Nnoscrtch testing pproch hs preference s it cn overcome prolems regrding the wreckge of the indenters nd the contriution of the mchine complince nd surfce roughness of the smple (Beke, et l., 2006; 2009; 2013). In this study, the multiscrtch test ws conducted on the sustrte nd the dimond lyers of two PDC cutters from different mnufctures under specific conditions of fixed lod t 500 mn fter 200 µm scrtch length, loding rte of 20 mn/s, nd scrtch rte of 10 µm/s. The Micro Mterils Nno Test device hs een used for the nnoscrtch test. The tip of the spheroconicl indenter hs rdius of 25 µm. The specimen s surfce hs een polished efore lunching the nnoexperiments to minimize surfce sperities.

7 52 IV. Results nd Discussion The experimentl wer s result of the microscrtch tests using Vickers indenter ws compred to the predicted wer from vrious models s shown in Fig. 9. It is clerly seen from Fig. 9 tht the predicted wer from Hutchings model is the closest to the experimentl wer sed on Eqution (1). Rinowicz model gve lower wer vlues thn the experimentl wer, wheres Ning nd Ghdiri model displys higher vlues thn the experimentl one. This might e due to the influence of frcture toughness on the eqution of Ning nd Ghdiri. This finding is pplicle for oth lyers of the PDC Dimond when Vickers indenter ws used to crete microscrtches on oth lyers of the PDC inserts. The otined wer from nnoexperimentl scrtch test together with those of microscrtch test of the sustrte lyer for smples K1908 nd M1313 is shown in Fig. 10. It cn e seen tht the wer of sustrte lyer for smple K1908 is slightly higher thn tht of smple M1313. Similrly, for the dimond lyer, wer results otined from micro- nd nno-scrtch tests were plotted in Fig. 10. Similrly, the wer of the dimond lyer of smple K1908 is slightly higher thn tht of smple M1313. Fig. 9. () Wer y vrious models for the tungsten-cride lyer for smple M1313, () wer for vrious models of wer for the dimond lyer for smple M1313. Fig. 10. () Experimentl wer for the sustrte lyer of smples K1908 nd M1313, () experimentl wer for the dimond lyer of smples K1908 nd M1313.

8 53 V. Conclusions The mteril properties nd wer tendencies of oth lyers (dimond nd sustrte) of two PDC it cutters from different mnufcturers (smples M1313 nd k1908) were studied using micro- nd nno-test techniques. Hrdness of the dimond lyer of smple M1313 found to e greter thn tht of the smple K1908. This is minly due to lower level of colt content in smple M1313 (3.26%) compred to tht of smple K1908 (4.4%) s well s slightly smller grin size of smple M1313 (12.03 µm) compred to tht of smple K1908 (12.73 µm). For the sustrte lyer, the hrdness smple M1313 is found to e higher thn tht of smple K1908 ttriuted minly to the difference in the colt content of the sustrte of the two PDC cutters. In this work, the wer of PDC smples hs lso een ssessed using micro- nd nno-scrtch techniques. The tests were crried out on oth lyers of PDC smples. The results suggest tht smple M1313 hs higher wer resistnce thn smple K1908. This is ttriuted to higher hrdness of smple M1313 s compred to smple K1908 which is result of different inder (colt) content nd grin sizes. Furthermore, the quntittive results suggest tht wer of ech smple is proportionl to the pplied force nd sliding distnce nd inversely to the hrdness of the mteril, ccording to the model of Archrd. It ws shown tht ll the dt for oth smples cn e unified on curve considering the three prmeters mentioned ove (lod, sliding distnce, nd hrdness), suggesting tht wer tendency of smples could e predicted sed on the mechnicl properties, notly hrdness. The findings of this study could e pplied to vrious types of PDC cutters from different mnufcturers to evlute the intensity of wer s qulity index rther thn using the previous trditionl rsion tests. Nomenclture A segment : Are of the circle s segment (µm 2, nm 2 ) Co: Colt (inder) CED: Circulr equivlent dimeter F: Applied lod (mn, N) F(A): Function in Archrd eqution H, H m : Hrdness of the mteril (N/m 2, GP) H : Hrdness of the rsive (N/m 2, GP) H: Residul depth (nm, µm) h s : Scrtch height (µm) K: Constnt for the system or wer coefficient K C : Frcture toughness of the mteril (MP.m 1/2 ) N: Index of incrementl depth nd sliding distnce R: Rdius of the circle (nm, µm) r: Height of the tringle (nm, µm) SHN: Scrtch hrdness numer (GP) V w : Volume of wer (µm 3, mm 3 ) WC: Tungsten-cride w s : Scrtch width (µm) X, L: Sliding distnce (µm) α: Hlf ngle of the rsive prticle (degrees) β: Arsion ngle (degrees) θ: Angle opposing the segment of the circle (degree). VI. Acknowledgments Specil word of thnks is given to Dr. Umir Zfr (Postdoc.) in Ghdiri group for his ssistnce in crrying out nnoscrtch tests t the Institute of Prticle Science nd Engineering t the University of Leeds, UK. Furthermore, the uthors must not forget the precious informtion given y Prof. Ben Beke (Micromterils, UK) for his help regrding the nnoscrtch test. References Archrd, J.F., Contct nd Ruing of Flt Surfces. Journl of Applied Physics, 24(8), pp Beke, B.D., Vishnykov, V.M., Vlizdeh, R. nd Colligon, J.S., Influence of mechnicl properties on the nno-scrtch ehviour of hrd nnocomposite TiN/Si 3 N 4 cotings on Si. Journl of Physics D: Applied Physics. 39(7), pp Beke, B.D., Goodes, S.R. nd Shi, B., Nnomechnicl nd nnotriologicl testing of ultr-thin cron-sed nd MoST films for incresed MEMS durility. Journl of Physics D: Applied Physics. 42(6), pp Beke, B.D., Hrris, A.J. nd Liskiewicz, T.W., Review of recent progress in nno-scrtch testing. Triology - Mterils, Surfces nd Interfces. 7(2), pp Beke, B.D., Shi, B. nd Sullivn, J.L., Nnoscrtch nd nnower testing of TiN cotings on M42 steel. 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USA. Geoffroy, H., Minh, D.N., Bergues, J. nd Putot, C., Interction etween Rock nd Worn PDC Bit: Theory nd Experiments. In: The 9 th Interntionl Society for Rock Mechnics Congress. Pris. Frnce. Hutchings, I.M., Triology: Friction nd Wer of Engineering Mterils. Edwrd Arnold, London. Mori, N., Moriguchi, H., Ikegy, A., Shioy, Y. nd Ohi, K., Development of Highly Durle Mterils for Drilling Hrd nd Arsive Rocks. In: The SPE Asi Pcific Oil nd Gs Conference nd Exhiition April 200, Jkrt. Indonesi. Mouritz, A.P. nd Hutchings, I.M., The Arsive Wer of Rock Drill Bit Mterils. Society of Petroleum Engineers, Pper SPE Ndlovu, S., The wer properties of Tungsten Cride-Colt Hrdmetls from the Nnoscle up to the Mcroscopic Scle. A PhD Disserttion Sumitted

9 54 to the Mterils Science nd Engineering, University of Erlngen-Nuremerg, Germny. Ning, Z. nd Ghdiri, M., Distinct element nlysis of ttrition of grnulr solids under sher deformtion. Chemicl Engineering Science. 61(18), pp Osipov, A.S., Bondrenko, N.A., Petrush, I.A. nd Mechnik, V.A., Drill its with thermostle PDC inserts. Dimond Tooling Journl. 70(625), pp Aville from: pdf. [Lst ccessed on 2012 Sep 16]. Rinowicz, E., Friction nd Wer of Mterils. 2 nd ed. John Wiley nd Sons, Toronto, ON. Richrdson, R.C., The wer of metls y reltively soft rsives. Wer. 11(4), pp Sumiy, H. nd Irifune, T., Indenttion hrdness of nno-polycrystlline dimond prepred from grphite y direct conversion. Dimond nd Relted Mterils. 13(10), pp Tze-Pin, L., Hood, M., Cooper, G. nd Xiohong, L., Wer nd filure mechnisms of polycrystlline dimond compct its. Wer. 156(1), pp Yhioui, M., Gerud, L., Pris, J.Y., Denpe, J. nd Dourfye, A., A study on PDC drill its qulity. Wer , pp Zcny, K Frcture nd ftigue of polycrystlline-dimond compcts. SPE Drilling nd Completion 27, pp