Study On Preparation And Properties Of In-Situ Particle Reinforced Metal-Based Composite Coating On Titanium Alloy

TC4 titanium alloy has been widely used in many fields,but the properties of titanium alloy at high temperature is not perfect.In this paper,in order to improve the wear resistance and oxidation resistance of TC4 titanium alloy at high temperature,plasma spray welding technology is used to prepare in-situ particle reinforced metal-based composite coating on the surface of TC4 titanium alloy.The microstructure,wear properties and oxidation properties of the composite coating are studied.The spray welding powder for preparing the composite coating is a mixed powder of Ti,Cr,Ni,and Nb.After orthogonal optimization of the test parameters,the final test parameters are 65A welding current,0.8mm/s welding speed,10g/min powder feeding rate,4L/min plasma gas flow rate,and 6.5L/min shielding gas flow rate,the powder feeding gas flow rate is4.5L/min.The composite coating is well formed and has a dense structure.The composite coating was analyzed by various characterization methods,and the main phase composition of the composite coating determined to be Ti,Ti N,Ni Ti and Cr N.The strengthening phase is Ti N,and there are Ni Ti and Cr N in the area between the strengthening phase and the matrix,and the Nb element is dissolved in the Ti matrix.The microhardness of the composite coating can reach 900HV_0.5,the hardness of the substrate is only about 320HV_0.5,and the hardness of the composite coating is about 2.8 times that of the substrate.In the area near the fusion line,the hardness of the composite coating is lower due to the dilution of the substrate and the convection of the molten pool.Friction and wear tests at room temperature and high temperature show that the wear loss of the composite coating is far less than that of the substrate,indicating that the wear resistance of the composite coating is better than that of the substrate.In addition,the wear loss of the composite coating and the substrate is increasing with the increase of the load or the increase of the rotate speed.At high temperature and room temperature,the friction coefficient of the composite coating is smaller than that of the substrate.At room temperature,the wear mechanism of the composite coating and the substrate is abrasive wear and adhesive wear,and the wear morphology of the composite coating is better than that of the substrate.Under high temperature conditions,the wear mechanisms of the composite coating and the substrate are oxidative wear,adhesive wear and abrasive wear.The wear morphology of the composite coating is still better than that of the substrate.In the constant temperature oxidation experiment,the composition of the oxide film of the composite coating is Ti O₂,Ti N,Ni O and Cr₂O₃,and composition of the substrate oxide film is Ti O₂ and Al₂O₃.The increase in the oxidation quality of the composite coating is parabolic,while the increase in the quality of the substrate is linear.This also shows that the oxide film has a good protective effect on the composite coating,and its oxidation resistance is better than that of the substrate.In the cyclic oxidation test,the increase in the oxidation quality of the composite coating is still smaller than that of the substrate.The oxide film of the substrate generates internal stress under the action of heat and cold cycles,causing the oxide film to crack or even fall off.The oxide film of the composite coating is dense due to its compactness.The oxide film structure has good protection for the composite coating,and the oxidation resistance of the composite coating is better than that of the substrate.