Study On Tribological Properties Of Transition Metal Nitride Nanocomposite Coating Synthesized By Physical Vapor Deposition

Reducing the friction and wear of mechanical parts is of great practical significance for the progress of modern industry level and social development.Transition metal nitride coatings are widely used in the fields of aerospace,machining,ship transportation and so on due to their excellent wear and corrosion resistance.However,with the continuous development of society,binary transition metal nitrides have been unable to meet the requirements of the increasingly stringent practical application because of their single performance,and the catalytic activity of transition metal nitride coatings has gradually been paid attention to the tribology field.Therefore,it is necessary to optimize the composition and microstructure of transition metal nitride coating to ensure the performance of the coating in the harsh engineering environment.The research objective of this paper is to obtain the controllable preparation of the strong-toughening transition metal nitride nanocomposite coating by means of element doping or multilayer structural regulation based on simple binary transition metal nitride（Ti N,CrN,MoN）.The tribological properties and tribo-induced catalytic effect of the nanocomposite coating are systematically studied to realize the multiple anti-friction and anti-wear effect on the coating,which provides the possibilities of mechanical parts for long service life.（1）Several transition metal nitride nanocomposite coatings are prepared on the surface of stainless steel by physical vapor deposition technology through element doping or multilayer structural regulation.X-ray diffractometry,X-ray energy dispersive spectroscopy,X-ray photoelectron spectroscopy,Raman spectroscopy,scanning electron microscopy,atomic force microscopy and transmission electron microscopy are used to characterize the chemical composition,phase structure,and microstructure of the composite coating in detail,including the type/content of doped elements,multilayer structure,nanocrystalline/amorphous interface structure,nanocrystalline/amorphous distribution,crystalline orientation and grain size of nanocrystals.It is found that the modulation period and element doping amount have significant effects on the microstructure of transition metal nitride nanocomposite coatings.The surface roughness of the TiAlN/W₂N multilayer coating decreases with the decrease of the modulation period,while the grain size of the coating decreases first and then increases as the decrease of the modulation period,and the TiAlN/W₂N multilayer coating with the modulation period of373 nm achieves the minimum grain size of 9.0 nm.The CrN coating presents an obvious loose columnar growth pattern with many microporous defects.With the doping of carbon elements,the columnar growth pattern of the coating is gradually interrupted,forming a polycrystalline composite structure composed of CrN phase,Cr₇C₃ phase and amorphous carbon,and the microstructure of the composite coating is more compact.（2）Furthermore,the hardness,elastic modulus,adhesion strength,tribological properties（room temperature,high temperature）and tribocorrosion behavior of the composite coating are tested,and it is found that the modulation period and the content of doping element have significant effects on the mechanical and tribological properties of the composite coating.The hardness,elastic modulus and tribocorrosion properties of CrCN nanocomposite coating improve first and then reduce with the increase of carbon content in the coating.The CrCN coating with the carbon content of 20.3 at.%exhibits the highest hardness and elastic modulus of 14.7 GPa and 197.7 GPa,respectively.However,the residual internal stress in the composite coating also increases with the increase of carbon content,leading to the decreasing of the adhesion strength of the composite coating.The MoN-Ag nanocomposite coating also has a similar strengthening mechanism.Its hardness,elastic modulus and tribological properties at room temperature show a trend of first increasing and then decreasing with the increase of Ag content.The MoN-Ag coating with Ag content of 2.2 at.%has the highest hardness（14.4 GPa）,elastic modulus（232.7 GPa）and the best tribological properties at room temperature,achieving the lowest wear rate of 1.27×10^-6 mm³（Nm）^-1.In addition,a large number of oxides(Mo O₃,Ag₂Mo O₄,Ag₂Mo₄O₁₃)with excellent lubricating effects are formed on the wear surface of the MoN-Ag coating under high temperature,which can maintain superb protection even at 700℃.（3）Finally,through the systematic study of the tribo-induced catalytic effect of transition metal nitride nanocomposite coatings in various lubricating medium and different friction conditions,it is found that several composite coatings present the tribo-induced catalytic effect,but there are differences in the tribo-induced catalytic effect of different kinds of composite coatings.The MoN-Cu nanocomposite coating has no tribo-induced catalytic phenomenon in more PAO10 lubricating oil.However,the MoN/Pt coating can tribo-induce the lubricating oil to degrade and form amorphous carbon film in situ with excellent solid lubrication effect under more oil and high load conditions,which greatly reduces the friction and wear of the coating.Molecular dynamics simulations show that oil molecules tend to dehydrogenate under the catalytic action of active metals,and further break into shorter carbon chains under the action of friction.It is found that lubrication medium and friction conditions have significant influence on the tribo-induced catalytic effect of the transition metal nitride nanocomposite coatings.For example,the MoN-Ag coating exhibits superb tribo-induced catalytic effect in octadecane containing only single bond,while it shows poor tribo-induced catalytic effect in 1-octadecene containing C=C double bond,and the increasing of loads can promote the tribo-induced catalytic effect of transition metal nitride composite coating.