激光功率对激光熔覆Ni基涂层温度场和应力场的影响

Effect of laser power on temperature field and stress field of laser cladding Ni-based coating

为得到对H13钢表面进行激光熔覆制备Ni基涂层时的最佳激光功率值,利用COMSOL仿真软件对不同激光功率下的温度场和应力场进行数值模拟,得到1400和1600 W两组满足熔覆层基本要求的激光功率值,绘制了温度梯度和不同方向的热应力变化曲线,并通过实验验证了仿真结果的准确性,进而得到最佳激光功率值。仿真结果表明,温度梯度随激光功率的增大而增大,进而产生较大的热应力,热应力是裂纹产生的主要原因之一。在激光功率为1400和1600 W条件下进行实验验证并观察熔覆层形貌得知,激光功率为1400 W时截面未见明显的气孔和裂纹等缺陷,而激光功率为1600 W时截面裂纹明显;观察熔覆层微观组织发现,激光功率为1600 W时熔覆层中树枝晶明显增加,这是因为激光功率较大时温度梯度较大,使得晶体长大更快。宏观形貌和微观组织结果均证明了仿真结果的准确性。

To obtain the optimum laser power when preparing Ni-based coating on H13 steel surface by laser cladding,the temperature field and stress field with different laser powers were simulated by COMSOL simulation software.The laser power values of 1400 and 1600 W meeting the basic requirements of cladding layer were obtained,the curves of temperature gradient and thermal stress in different directions were plotted,and the accuracy of the simulation results was verified by experiments,and then the optimal laser power value was obtained.The simulation results show that the temperature gradient increases with the increase of laser power,resulting in a large thermal stress,which is one of the main causes of crack formation.Experimental verification and observation of cladding layer morphology at laser power of 1400 and 1600 W show that no obvious defects such as porosity and cracks are found in the cross section at laser power of 1400 W,while obvious cracks are found at laser power of 1600 W.By observing the microstructure of the cladding layer,it is found that the dendrite in the cladding layer increases obviously when the laser power is 1600 W,for the temperature gradient is larger at higher power which makes the crystal grow faster.The accuracy of simulation results is verified by both the macroscopic morphology and microstructure results.