Preparation And Tribological Properties Of Cr₃C₂-NiCr Matrix High-temperature Wear Resistant Materials

With the development of modern industry,many high-tech fields such as equipment manufacturing and aerospace require materials to be stably operated in extreme environments.Typical service environments such as high temperature,heavy load,high speed,high vacuum and other extreme environments result in high-temperature friction and wear.The failure of mechanical equipment and its components caused by high-temperature wear is becoming more and more prominent.In this study,the Cr₃C₂-NiCr coating and the Cr₃C₂-NiCr matrix self-lubricating composite were prepared by High Velocity Air-Fuel?HVAF?and spark plasma sintering?SPS?.Firstly,the relationship between microstructure,microhardness and tribological properties of the Cr₃C₂-NiCr coatings was studied through optimizing the HVAF process parameters and heat treatment under argon atmosphere.Secondly,the effect of Mo and BaF₂ addition on the high-temperature tribological behavior of the Cr₃C₂-NiCr composite was also studied.Four types of Cr₃C₂-NiCr coatings with different fuel inlet pressures were prepared by HVAF.It was found that when the inlet pressure was551.6 kPa,the porosity was the lowest and the retained carbide content was high.Meanwhile,the Cr₃C₂-NiCr coating showed the highest microhardness(1064 HV_3N)and the best wear resistance(0.35×10^-53.24×10^-55 mm³/Nm)from root temperature to 600oC.The binder phase of the as-sprayed coatings was inclined to brittle fracture during the sliding wear at room temperature,resulting in macroscopic cracks and eventual material loss by chipping of chunks.Heat treatment cause precipitation and growth of secondary chromium carbides.The accompanying precipitation hardening improved the microhardness and the wear resistance at room temperature.After 500oC heat treatment,no brittle fracture and macro crack was observed during the sliding wear at room temperature.The Cr₃C₂-NiCr coating has the highest hardness(1130 HV_3N),and the best tribological properties at room temperature(0.32×10^-5 mm³/Nm)after 500oC heat treatment for 60 minutes.The Cr₃C₂-NiCr and Cr₃C₂-NiCr-Mo-BaF₂ composites were prepared by SPS.Incorporation of Mo and BaF₂ dispersion led to a slight decrease in the hardness and relative density,but BaMo₄ and MoO_x formed on the wear tracks through tribochemical reactions together with BaF₂ helped form a glaze layer,which substantially decreased the wear rate and friction coefficient.In particular,the wear rate of the Cr₃C₂-NiCr-Mo-BaF₂composite was approximately one order of magnitude lower than that of the Cr₃C₂-NiCr composite from 700°C to 900°C when sliding against Si₃N₄ balls.The Cr₃C₂-NiCr composite showed poor tribological properties compared with the Cr₃C₂-NiCr-Mo-BaF₂ composite because Cr₂O₃ wear debris failed to generate an effective glaze layer.The glaze layer is damaged by hard Cr₃C₂ particles.The predominant wear mechanism is abrasive wear rom 600°C to 800°C and oxidation wear at 900°C.