随动进给脉冲电流增强激光熔覆制备镍基合金涂层试验

Ni-Based Alloy Coating Prepared by Laser Cladding Strengthened by Follow-up Feed Pulse Current

基于随动进给脉冲电流增强激光熔覆技术在42CrMo合金结构钢基体表面制备了Ni60A镍基合金涂层,研究了脉冲电流对熔覆涂层的影响。结果表明:采用随动进给电极,利用脉冲电流的趋肤效应,将大部分电流引入熔池,提高了电流利用效率,且较近的电极距离大大提高了电流密度,增强了改善效果,有利于制备缺陷少、质量高的熔覆涂层;相对于传统激光熔覆,脉冲电流增强激光熔覆既能提高熔覆效率,又能细化熔覆层晶粒,降低孔隙率,并均匀熔覆层组织,使其由常规激光熔覆形成的枝晶转变成等轴晶;脉冲电流增强激光熔覆试样的孔隙率为0.39%,平均晶粒尺寸约为4μm,优于常规激光熔覆的0.62%和6μm;同时采用随动进给电极可以减少熔覆层残余热应力和开裂敏感性,特别是小电极距离特有的高能量密度脉冲电流在熔覆层裂纹尖端形成的绕流效应和焦耳热效应能够实现熔覆层裂纹的在线自愈合,获得无裂纹的熔覆层,从而解决了激光熔覆层易开裂问题。

In this study,Ni60 A-based alloy coating was prepared on a 42 CrMo alloy structured steel substrate surface using laser cladding strengthened by follow-up feed pulse current.Moreover,the effect of pulse current on laser cladding coating is investigated.Results demonstrate that the follow-up feed electrode can increase the utilization efficiency of the pulse current by exploiting its skin effect,directing most of the current into a melting pool.However,the relatively close electrode distance can significantly increase current density and strengthen the improvement effect,which is beneficial for preparing high-quality cladding coatings with few defects.Besides demonstrating higher efficiency than conventional laser cladding,the pulse current-strengthened laser cladding also refines the crystal grain size of the cladding layer,reduces porosity,and increases the uniformity of microstructures in the cladding layer.Hence,dendritic crystals in conventional laser cladding are transformed into isometric crystals.The porosity of the pulse current-strengthened laser cladding is 0.39%and the average grain size is approximately 4μm,which are better than the corresponding values of 0.62%and 6μm,respectively,for a conventional laser cladding.Moreover,the residual thermal stress and cracking sensitivity on the cladding layer are lowered by using the follow-up feed electrode.In particular,the streaming effect and Joule thermal effect produced by the unique high-energy density pulse current across a small electrode distance at the crack tip of the cladding layer can facilitate self-healing of cracks in the cladding layer.Therefore,a crack-free cladding layer can be obtained.Thus,the proposed method solves the easy-cracking problem of the laser cladding layer.