Study On The Tribological Behaviors Of Physical Vapor Deposition (PVD) Coatings

The coatings deposited by Physical Vapor Deposition(PVD)techniques have found a wide industrial application as protective coatings in the fields of tools,dies, automobile,aerospace,etc.for their attractive properties such as high hardness,good wear resistance and chemical stability.Carrying a foundational research in tribological behaviors of the PVD coatings would provide technological reference for deposition and industrial applications of the coatings,and deepen the basic theory in coating tribology.Sliding wear tests of the PVD CrN(prepared by Filtered Cathodic Vacuum Arc (FCVA)and Multi-arc Ion Plating(MAIP)techniques),AlCrN and AlTiN(prepared by MAIP)and WC/C(prepared by magnetron sputtering)coatings against Si₃N₄ ceramic balls and titanium balls have been carried out on a CETR UMT-2 multifunctional test system under reciprocating(bidirectional)and ball-on-disc (unidirectional)sliding conditions.Microhardmeter,nanoindenter,profilometer, scanning electron microscopy(SEM),energy dispersive spectroscopy(EDX),X-ray diffractometer(XRD),X-ray photoelectron spectroscopy(XPS)and electron probe micro-analyser(EPMA)were used to study the tribological behaviors of the PVD coatings systematically.Main conclusions are drawn as follows:1.CrN coating was prepared by FCVA technique.The sliding tribological properties of the FCVA CrN coating and MAIP CrN coating were comparatively studied.The results showed that the tribological properties of the FCVA CrN coatings were significantly dependent upon the coating deposition parameters,which were optimized accordingly.The FCVA CrN coating exhibited much better wear resistance than the MAIP CrN coating,which can be attributed to the smoother and denser coating surface of the FCVA CrN coating resulted from much fewer macroparticles and pitting defects.The differences on the wear debris removal behaviors and wear mechanisms of the PVD CrN coatings were caused by the different microstructure of the coatings.2.The sliding tribological behaviors of the CrN,AlCrN and AlTiN coatings were comparatively studied to reveal the influences of coating composition on tribological performance of the PVD coatings.It was showed that:1)The CrN coating exhibited better wear resistance than the AlCrN coating under normal wear conditions,whereas suffered local severe wear damage in the central zone of the wear scars when higher normal loads were imposed.The AlCrN coating formed by the CrN coating alloying with aluminum would show significantly improvement in load-carry capacity.2)The difference between the tribological performances of the AlTiN and AlCrN coatings was caused by their different wear debris removal and tribo-chemical reaction behaviors.The AlTiN coating exhibited low wear debris removal efficiency,and the wear debris accumulated inside the friction interface would accelerate the wear of the coating.The AlCrN coating exhibited high wear debris removal efficiency and the worn surface was characterized by a mild-polish-effect.In addition,the oxides(Cr₂O₃,Cr₂O₅ and Al₂O₃)formed by the tribo-chemical reactions of chromium and aluminum could protect the AlCrN coating against wear admirably for their high hardness,high oxidation resistance and good thermal stability.3)The AlCrN coating with good load-carry capacity and high wear debris removal efficiency exhibited high oxidative wear and abrasive wear resistance.In sum,the components of the PVD coatings had significant influence on the hardness,load-carry capacity,wear debris removal and tribo-chemical reaction behaviors of the coatings,and would finally affect the tribological properties of the coatings.3.The CrN coating presented better performance in anti-adhesion to titanium than the AlCrN and AlTiN coatings.The aluminum contained in the AlCrN and AlTiN coatings has a strong affinity to titanium element,which would lead to the adhesion of titanium to the coatings.Therefore,the aluminum-contained coatings were unsuitable for the tribological applications related to titanium counterparts.4.The WC/C solid lubrication coating exhibited good lubricating effectiveness for the graphite transfer film formed on the counterparts.When sliding against titanium ball,the wear of the WC/C coating was characterized by a combination wear mechanisms of ultra-mild abrasive and oxidative wear.When sliding against Si₃N₄ ball,the wear damage of the WC/C coating was characterized by a combination of plastic flow,abrasive and oxidative wear under reciprocating sliding condition,and a combination of delamination and oxidative wear under ball-on-disc condition.The delamination of the coating was originated from the pitting defects of the coating formed during the coating deposition.A relatively lower sliding velocity was found to be good for the formation of transferred films on the two counterparts. The WC/C coating showed good anti-adhesion properties against titanium and thus is potential candidate in the fields of the tribological applications related to titanium counterparts.