Tribological Behaviors Of(Cr,V)N Coatings In Wide Temperature Range

With the rapid development of high-tech industries such as modern aerospace,nuclear power as well as resources and power,the roller bearings,gears and various satellite components used in these fields need to undergo low temperature startup to high temperature stable operation stage or low/high temperature cycle running stage.High friction and wear caused by harsh temperature conditions directly affect the longevity and highly reliable operating characteristics of mechanical parts.Most of the currently researched lubricating materials are only for a specific temperature range,and the system is sophisticated.It is difficult to clarify the lubricating mechanism.Therefore,the development of a wide temperature range lubricating material with a simple system and good friction properties from room temperature to high temperature is the focus of current research.Starting from a simple ternary system,taking the synergistic effect of basic phase,reinforced phase and lubricating phase into account,the design of(Cr,V)N(chromium vanadium nitride)coating is carried out.The coating system uses Cr N as the basic phase,Cr-V solid solution system and the oxidized Cr₂O₃ as the reinforced phase,and V-based oxide as the lubricating phase.While satisfying the excellent anti-friction and abrasion resistance,the coating is endowed with excellent mechanical strength,high oxidation resistance and outstanding adhesion strength between the coating and substrate,in a wide temperature range.(Cr,V)N coatings are prepared by vacuum cathodic arc ion plating technology.The influence of load on tribological properties of VN coating at room temperature is studied.On this basis,the tribological characteristics of(Cr,V)N system in a wide temperature range is explored,and the friction and wear mechanisms are clarified.Studying the contact stress and physicochemical changes caused by the load is of great significance for the exploration of the coating's tribological properties.Coupled with an excellent adhesion strength,the VN coating also presents good tribological properties.With an increasing load,the friction coefficient decreases,while the wear rate increases,and the wear rate is up to 10^-6 mm³N^-1m^-1 order of magnitude.It is found that the heavier the load,the greater the interface contact pressure,and the tribo-chemical reaction caused by the heavy load is more intensity.This is benefit of reducing the shear stress and inducing more V element to oxidize as well as generating V₂O₅ lubricating phase,which lead to the decreased friction coefficient.Moreover,due to insufficient toughness and poor resistance to plastic deformation,the wear rate of the coating increases with increasing load.The single VN coating is not enough to meet the requirements of friction reduction and wear resistance.V-containing solid solution is considered to be a promising way to improve the mechanical and tribological properties of hard coatings due to the solid solution strengthening mechanism as well as the induced V-based Magnéli lubricant during friction process.By adjusting the position of the substrate and the target,a controllable preparation of the Cr-V-N coating with a variation V content in the range of 0.32-31.14 at.%is achieved.Due to the solid solution strengthening effect,Cr-V-N coatings exhibit excellent adhesion strength as well as toughness,and also represent good wear resistance.Tribological tests at room temperature indicate that the friction coefficient is relatively low(0.25-0.35),and the wear rate is as low as 10^-7 mm³N^-1m^-1 order of magnitude.As the V content increases,the friction coefficient and wear rate both show a slight increase,and the wear rate of the coatings with high V content is almost four times larger than that of low V content coatings.Based on the tribological study of Cr-V-N coating at room temperature,the Cr_0.58V_0.14N_0.28coating with a constant V content is selected to explore the high-temperature friction performance at500-900?,and the relationship between oxidation,mechanical behavior and friction mechanism is established.As the temperature increases,the oxidation rate of the coating increases,accompanied by a decrease in mechanical properties.The mechanical friction dominates at 500-600?.Due to the lack of oxidized lubricating phase,the friction coefficient(0.58-0.63)and wear rate are high.At700-900?,it is mainly predominant by oxidative lubricating friction.The formation of soft V-O phase reduces the friction coefficient(0.27-0.38).However,the damage of mechanical properties increases the wear rate.Combining the results of the friction coefficient and wear rate,the best tribological properties of the Cr_0.58V_0.14N_0.28 coating are obtained at 700-800?.