Study On Cracking Mechanism And Control Method Of Al₂O₃-ZrO₂ Laser Cladding Layer On Titanium Alloy Surface

In view of the problem that Al₂O₃-ZrO₂ceramic coating on Ti-6Al-4V titanium alloy surface is prone to cracking,porosity and other defects,the research on the crack suppression mechanism of ceramic cladding layer and the analysis of cladding process are carried out,and the theoretical analysis,finite element simulation and experimental research are used to reveal the crack characteristics and cracking mechanism of Al₂O₃-ZrO₂ceramic cladding layer on Ti-6Al-4V titanium alloy surface.The study will clarify the influence of laser cladding process on the susceptibility of ceramic cladding layer to cracking,and propose a strategy to suppress the cracking and growth of ceramic cladding layer on titanium alloy surface,which will provide theoretical and experimental support to improve the cladding quality of ceramic coating on titanium alloy surface and strengthen the friction and high temperature performance of titanium alloy surface.In this paper,from the perspective of suppressing crack initiation,the optimization experiment of laser process parameters was carried out to explore the influence of the main laser process parameters on the cladding layer crack.The optimal laser processing parameters were determined by studying the microstructure and properties of the cladding layer.It is found that the laser energy density is 150J/mm²and the macroscopic crack is reduced obviously.The average microhardness of the cladding layer is 980HV,which is 180%higher than that of the Ti-6Al-4V matrix of 350HV.Meanwhile,the fracture toughness of the cladding layer is 4.7MPa·m^1/2,indicating the best wear resistance.Secondly,the matrix preheating experiment was carried out on the basis of the optimal process parameters,and the initial temperature of the matrix was increased by preheating Ti-6Al-4V.The optimum preheating temperature of the substrate was determined to be 200℃by observing the microstructure and properties of the cladding layer.When the preheating temperature is 200℃,the fracture toughness of cladding layer is 8.1MPa·m^1/2,70%higher than that of substrate without preheating.According to the thermodynamic coupling results at different preheating temperatures,it is found that the residual stress in the cladding decreases and the cracking tendency decreases with the substrate preheating.Finally,in order to prevent the subsequent growth of cracks,the toughness of the cladding layer was enhanced by adding CeO₂into the ceramic powder by adjusting the composition system of the cladding powder.The experimental results show that by adding CeO₂into the powder system,the crack propagation mode changes from transgranular fracture to crack bridging,which consumes the crack energy and stops the crack.At the same time,the content of CeO₂has a good effect in a certain range.In this series of experiments,the optimal content of CeO₂is 0.8wt%,under which the wear resistance of the cladding layer obtained by the cladding is greatly improved,the brittle shedding of the cladding layer at the crack is reduced,and the wear amount is significantly reduced.The wear amount of the cladding layer with CeO₂content of0.8wt%is about 75%lower than that of the cladding layer without CeO₂.