Effect Of Mo Element On Properties And Tribological Properties Of CoNiV Medium-entropy Alloy

This experiment is based on the Co Ni V medium entropy alloy with a single face centered cubic structure and high plastic toughness.By adding Mo element,the yield strength and wear resistance of the alloy are improved.The optimal ball milling process for preparing Co Ni V alloy powders by mechanical alloying was systematically studied.On this basis,the high entropy powders of Co Ni V series with different molar ratios of Mo element were prepared.Then,the bulk high entropy alloys with different Mo contents(X=0?0.25?0.5?0.75?1)were prepared by SPS sintering.The effects of different molar ratios of Mo on the microstructure,fracture toughness,bending strength and tribological properties of Co Ni VMox alloy at room temperature were studied,and the effects of different molar ratios of Mo on the high temperature hardness,high temperature compression properties,high temperature oxidation resistance and high temperature tribological properties of Co Ni VMox high temperature alloy at high temperature were explored.1.The effect of ball milling time on the properties of Co Ni V alloy powders was investigated.The alloy powders of Co Ni V alloy can be obtained by appropriately increasing the mechanical alloying time.When the milling speed is 250 r/min and the milling time is 40 h,the best properties of Co Ni V ternary alloy powders and Co Ni VMox alloy powders with different Mo contents are obtained.Co Ni VMo alloy blocks with uniform structure and high density can be obtained by optimizing the sintering temperature.2.By adjusting the Mo content in Co Ni VMo _Xalloy,the crystal structure and tissue composition in the crystal can be changed,thus realizing the optimization of mechanical properties.When the content of Mo is 0.25,the hardness of the material can reach 819.99±11 HV at room temperature,the compressive strength can reach2384.47±4.3 MPa,the fracture toughness and bending strength can reach 2427.43±2.2MPa and 36.43±1.2 MPa·m^1/2,respectively.At 800?,the mechanical properties of Co Ni VMo_0.25alloy can be maintained at 2000±10 MPa,and shows the characteristics of non-brittle fracture.3.In the friction and wear experiments at room temperature,when X?0.5,the wear resistance of Co Ni VMox alloy increases with the increase of Mo content,but the plasticity of the material becomes worse.When X?0.5,the friction coefficient of the alloy increases,the wear resistance decreases.In conclusion,the mechanical properties and tribological properties of Co Ni VMo_0.25alloy at room temperature are the best in the Mo content system.The experimental investigation in this section shows that the mechanical properties and wear resistance of the matrix material can be effectively improved by combining proper amount of intermetallic compounds with FCC matrix.4.At the temperature of 800?,when the molar ratio of Mo content is 1,the alloy highest high temperature hardness is 828±50.5HV.By adding Mo element to the entropy alloy in Co Ni V,the solid solution strengthening mechanism of the alloy can be adjusted to make the material have high hardness and oxidation resistance.In the cyclic oxidation test at 800?,Co Ni V alloy and Co Ni VMo alloy belonged to the antioxidant level,while GH4169 alloy was in the sub-antioxidant level.5.At 800?,the friction coefficient of Co Ni VMox alloy with different Mo content(X=0.25?0.75 and 1)is almost stable at about 0.3,and the increase of Mo content will improve the self-lubrication effect of Co Ni VMox alloy.In the medium temperature range of 200??400?,the friction coefficient and wear rate of Co Ni VMo_0.75/Al₂O₃friction pair are low,and abrasive wear and adhesive wear mainly coexist.In the high temperature range of 600??800?,oxidation wear and abrasive wear mainly coexist.The wear rate of Co Ni VMo_0.75alloy and Co Ni VMo alloyis an order of magnitude lower than that of Co Ni VMo_0.25alloy.In the friction test at 800?,the wear rate of Co Ni VMo_0.75alloy is the lowest,only 1.40×10^-5mm³?N^-1?m^-1.