Simulation Of Temperature Field And Stress Field Of Laser Cladding Carbon-based Antioxidation Coating And Laser Ablation Process

Carbon materials are limited in their application prospects in high temperature fields due to their sensitivity to oxygen.Anti-oxidation coatings are usually used to protect them.The commonly used coating preparation techniques have a long molding cycle and low bonding strength,while the laser surface cladding technology perfectly overcomes these two shortcomings.However,due to the characteristics of rapid temperature rise and fall of laser cladding,it is easy to produce large temperature gradients and stresses,which lead to coating cracks.In this work,numerical simulation method is used to investigate the change law of temperature field and stress field in the process of laser cladding anti-oxidation coating on carbon surface,so as to determine suitable laser process parameters for three different anti-oxidation coating systems and improve coating quality,and provide reference for practical laser cladding.Moreover,on the basis of the simulation results of temperature field and stress field,the formation mechanism of porosity,cracks and other defects in the anti-oxidation coating during laser ablation was explored.First,the finite element model of single-pass and multi-pass laser cladding was established with ANSYS software,and the control of various process parameters was realized with APDL language.Suitable process parameters for three anti-oxidation coatings were determined:among them,the optimal scanning rate,spot radius,scanning interval and preheating temperature of HfB₂-SiC-Si-MoSi₂ coating,HfC-NbC-TaC-TiC-ZrC coating and HfN-NbN-TaN-TiN-ZrN coating are the same,which are 10mm/s,0.1mm,0.1mm and 600?respectively.The optimum laser power is 64W,128W,and96W respectively,and the optimum coating thickness is 0.075mm,0.05mm and0.05mm respectively.During the laser cladding process,the cladding zone will affect the temperature field and stress field distribution of the entire coating and the substrate.The temperature gradient distribution in each area during the cladding process is explored.The temperature gradient on the Y-axis in the cladding area is the largest,while those on the X-axis and Z-axis were smaller.In addition,the temperature gradient in the adjacent path area of the cladding area is larger on the X-axis and Y-axis and smaller on the Z-axis,while the temperature gradient in the farther path area is the largest on the X-axis and smaller on the Y-axis and Z-axis.The shear stress of the cladding zone is the largest along the 45°scanning path,and the coating cracks are most likely to appear in this direction,which is consistent with the actual cladding results.The residual stress of coating is compressive stress,which is beneficial to reduce the tendency of coating cracking.The increase of the scanning interval has little effect on the overall distribution of the temperature field and the stress field,but will increase the temperature gradient and stress in the X-axis.The increase of the coating thickness will reduce the efficiency of laser energy transfer to the interface and increase the temperature difference between the surface and the interface;but under the condition that the temperature at the interface reaches the lowest melting point of the composite coating composition,further thinning the coating will increase the Z-axis temperature gradient at the interface and may cause excessive burn.The results show that the cladding temperature of HfC-NbC-TaC-TiC-ZrC coating is higher,the temperature gradient and thermal stress are higher in the laser cladding process,and the possibility of inner bending and falling off of the coating is greater.Due to the low thermal conductivity of the HfN-NbN-TaN-TiN-ZrN coating,the temperature gradient and thermal stress produced in the laser cladding process are larger,and the cladding area only affects the adjacent path area,and the influence of scanning interval on the x-axis stress distribution is smaller.In addition,the temperature and stress fields of the two coatings are basically consistent with those of HfB₂-SiC-Si-MoSi₂ coatings.The laser cladding model is used to simulate the laser ablation temperature field of HfB₂-SiC-Si-MoSi₂ coating,and it is found that the highest temperature of the coating surface is only 829?and 1351?under the line ablation of 64 and 96W,which does not cause major damage to the coating body.In the actual experiment,the coating can't be damaged under the line ablation of 128W power.Under the action of 64W and96W point ablation,the maximum surface temperature of the coating reaches 1150?and 1700?,and the maximum interface temperature reaches 920?and 1380?,which does not cause great damage to the main body of the coating.But in actual situation,the coating has been eroded after 4 seconds of ablation at 96W point.In addition,the actual ablation results are consistent with the simulation results.