Study On Quality Optimization Of Coaxial Powder Laser Cladding Of TC4 Titanium Alloy

In recent years,laser cladding forming technology has been widely used in the field of rapid forming and repair of metal parts because of its short forming period,high flexibility and direct forming of complex structural work pieces.However,because the laser coating process involves metallurgy,mechanics,heat transfer and other interdisciplinary interactions,including complex microstructure formation process and thermo physical process,it is difficult to use the existing instruments and equipment to study its mechanism.In this paper,the temperature field and stress field of coaxial powder feeding laser coating process are studied by numerical simulation and experiment with TC4 titanium alloy as the research material,and the forming quality of the laser coating part is optimized.The main research contents are as follows:(1)The temperature field of coaxial powder feeding laser coating process is simulated by finite element software ANSYS,and the influence of process parameters on temperature field is analyzed.The results show that the maximum temperature of the molten pool increases with the increase of laser power and decreases with the increase of scanning speed.(2)The temperature change law in the process of laser cladding is obtained by using the optimized process parameters to simulate the temperature field.The results show that the isotherm of temperature field is elliptical and there is temperature accumulation behind the spot.(3)The single-channel single-layer laser coating test with different process parameters was carried out with titanium alloy as material.The influence of process parameters on the height of the coating was analyzed.Then,the single-channel and multi-layer laser coating test is carried out.The "end protruding" phenomenon of the multi-layer coating formed by reciprocating scanning mode is simulated and the forming scheme is optimized,and the phenomenon of "lower narrow and upper width" is simulated and analyzed.The results show that the height difference and width difference of the end protruding can be reduced by 65.9%and 84.7%,and the width of the coating layer increases due to the accumulation of temperature before the five layers,but after the five layers,the temperature accumulation and heat dissipation gradually reach a relative balance,and the width of the coating layer remains stable.(4)The microstructure of multi-layer laser cladding parts of titanium alloy was observed.The results show that the microstructure is dendritic,and the main types of micro defects are incomplete defects and pore defects.(5)On the basis of the temperature field simulation results,the numerical simulation of the stress field in the multi-layer laser cladding process is carried out by using the indirect coupling method,and the equivalent stress distribution and the stress components in each direction are studied.The results show that there is a stress concentration phenomenon at the junction between the coating layer and the substrate,and the unidirectional stress along the scanning direction of the light source is the largest.