Numerical Simulation Of Temperature And Stress Field Of TiC/Fe-Based Gradient Coating By Laser Cladding

With the rapid development of science and technology in China,the requirements for the stability of mechanical products are more stringent.However,when the parts are operated in a harsh environment for a long time,many key parts will be corroded,worn and broken,resulting in parts failure and unable to continue stable operation.Strengthening the part surface can effectively reduce part failure,increase part stability and prolong the service life of parts,so as to reduce the cost of mechanical parts manufacturing industry and improve China's economic benefits.Therefore,it is imperative to strengthen the surface treatment of parts.In this paper,Fe-based gradient coatings with different TiC contents were prepared on 42CrMo by laser cladding technology in order to improve the hardness and wear resistance of the substrate.By adjusting the coating material ratio and optimizing the cladding process parameters,the TiC Reinforced Fe-based gradient coating with compact structure and no defects was prepared;The phase composition,microstructure,microhardness and wear resistance of the coating were analyzed;The temperature field and stress field of single and multi-layer coatings during laser cladding are simulated and analyzed by using finite element simulation software.The results show that the prepared gradient coating is mainly composed of Fe,Cr,Fe-Cr,(Cr,Fe)₇C₃ and TiC with powder ratio of 10%TiC+90%Fe,20%TiC+80%Fe,30%TiC+70%Fe,40%TiC+60%Fe and 50%TiC+50%Fe,process parameters:laser power 1200W,scanning speed 5mm/s,powder feeding speed 20g/min,and the phase composition of the prepared gradient coating is mainly Fe,Cr,Fe-Cr,(Cr,Fe)₇C₃ and TiC,in which(Cr,Fe)₇C₃ and TiC are dispersed,which plays a strengthening role and improves the mechanical properties of the gradient coating.The gradient coating structure is mainly composed of cellular crystal and dendrite.The dendrite structure mainly grows upward or diagonally upward.There is no obvious boundary between the bonding transition zone of the first layer and the second layer,indicating that the coatings have mutual melting,the growth direction of the second layer has changed,and no cracks,holes and other defects have not been found.Due to the preheating effect of the first layer,the second layer is composed of cellular crystals and dendrites,and the distribution of black TiC particles is significantly increased.At the same time,the first layer of coating is partially remelted,which makes the coating structure refined.In the bonding transition zone between the second layer and the third layer,due to the remelting of the second layer,there is no obvious boundary between the two coatings.The microstructure is similar to that of the second layer,and black TiC aggregates at the grain boundary.The grain size of the fourth layer is larger than that of the third layer,and the distribution is more uniform,and the dendrites are significantly reduced.The reason may be that the accumulated heat of the first three layers makes the cooling rate of the molten pool tend to be flat,the grains grow uniformly in all directions.In the bonding zone between the fourth and fifth layers,with the increase of TiC,the cooling rate at the top of the coating increases,the microstructure is obviously refined,and the black TiC particles are dispersed in the coating.The hardness of the base material is the lowest,close to the cladding layer area,and the hardness increases the fastest.With the increase of TiC content,the hardness of the coating presents a gradient upward trend.The average hardness of the first layer to the fifth layer is 541HV_0.2,641HV_0.2,653HV_0.2,665HV_0.2 and700HV_0.2 respectively,and the hardness of the outermost layer is 591.8HV_0.2,647.7HV_0.2,673.4HV_0.2,695.8HV_0.2 and 779.9HV_0.2 respectively,which is 2?3 times higher than that of the base material.With the increase of TiC content,the wear amount of the coating gradually decreases.The wear amount of the first to fifth layers is 0.8mg,0.62mg,0.55mg,0.31mg and0.2mg respectively,and the average friction coefficient is 0.71,0.99,0.62,0.91 and 0.75respectively.The wear mechanism of the first two layers is abrasive wear,and the wear mechanism of the third to fifth layers is abrasive wear and adhesive wear.The simulation of the cladding process is carried out by using the Simufact Welding finite element simulation software.The simulated weld pool is consistent with the actual weld pool morphology,and the coating height is consistent with the actual experimental data.Laser cladding is a steady-state heat transfer process,and the cooling rate reaches 10~6K/S,which is conducive to rapid solidification structure.The maximum temperature of laser cladding single coating is 1506.46?.The closer to the cladding layer,the greater the stress,and the maximum value is 58.87MPa.The size of the weld pool is proportional to the temperature.The shape of the weld pool of the latter layer is larger than that of the former layer,and the thermal cycle curve of the edge of the cladding layer jumps the most.The maximum temperature of the cladding layer is 2253.24?,and the maximum edge stress of the cladding layer is 559.20MPa.