Study On Microstructure And Wear Resistance Of Laser Cladding Ni₃Al/Cr₃C₂ Composites

In order to improve the wear resistance of key components of diesel engine,Cr3C2 particles-reinforced Ni3Al-based composites materials were prepared to be used as high-temperature wear-resistant coatings with excellent comprehensive performance.Laser cladding of Ni3 Al alloy and Ni3Al/Cr3C2 composites were carried out on of 304 stainless steel.The laser cladding parameters suitable for Ni3 Al alloy and Ni3Al/Cr3C2 composites were clarified by analyzing laser spot type,laser power and scanning speed.Microstructures,mechanical properties and wear resistance at room temperature and high temperature of the cladding materials were investigated.Based on the experimental results,the main conclusions in this work are as follows:(1)In this study,a 5 mm × 5 mm rectangular spot was selected as the test spot mode with laser power of 1.6 k W,scanning speed of 0.24 m/min,and powder feeding rate of 0.87 kg/h,1.18 kg/h,and 1.43 kg/h.As the powder feeding rate increases,the thickness of the cladding layer gradually increases,and the dilution rate of the substrate gradually decreases.When the powder feeding rate is 1.43 kg/h,average thickness of the cladding layer reaches about 1.5 mm.When the powder feeding rate is over 1.18 kg/h,the dilution of the substrate is less than 10%.(2)The Ni3Al/Cr3C2 cladding composites consist of matrix γ’-Ni3 Al phase and in-situ dispersed M7C3(M=Fe,Cr)carbide.The size of carbide increases with increasing the powder feeding rate and Cr3C2 addition.When the powder feeding rate is 1.43kg/h and Cr3C2 addition is 45 wt.%,coarse Cr3C2 carbides occur in the cladding layer.The micro-hardness of the cladding materials increase with an increasing of the powder feeding rate and Cr3C2 addition.(3)At room temperature,with increasing the Cr3C2 addition,the wear loss of the cladding materials at first decreases and then slowly increases.For the case of 1.43kg/h powder feeding rate and Cr3C2 addition is 25 wt.%,the wear loss is the minimum.As the temperature increases,the wear loss of the cladding materials decreases.At 650 °C,both the wear loss and friction coefficient of Ni3Al-25%Cr3C2 composites reach the minimum.(4)At room temperature,the main wear mechanisms of Ni3 Al alloy cladding materials are adhesive wear and abrasive wear,and that of Ni3Al/Cr3C2 cladding composites is abrasive wear.At high temperature,the main wear mechanisms of Ni3 Al alloy cladding materials are adhesive wear,abrasive wear and oxidative wear,whereas those of Ni3Al-25 wt.%Cr3C2 cladding composites are abrasive wear and oxidative wear.(5)A friction and wear test of exhaust valves was carried out at actual working conditions simulated for engineering application.The results indicate that,the total sinking of the exhaust valve with Ni3Al-25%Cr3C2 composite coating and valve seat decreases about 45% compared with the original valve.