激光冲击对E690高强钢激光熔覆修复微观组织的影响

Effect of Laser Shock on Microstructure of the Repair Layer of E690 High Strength Steel by Laser Cladding

为研究激光冲击对E690高强钢激光熔覆修复层微观组织的影响,选用专用金属粉末对E690高强钢试样预制凹坑进行激光熔覆修复,并使用脉冲激光对激光熔覆层进行冲击强化处理,同时采用扫描电镜、透射电镜和X射线应力分析仪分别对激光冲击前后激光熔覆层的微观组织和表面残余应力进行检测。结果表明:激光熔覆修复后,激光熔覆层组织为等轴晶,熔覆层与E690高强钢基体之间冶金结合良好,其表面残余应力为均匀分布的压应力。经激光冲击后,激光熔覆层截面晶粒得到细化,并观察到大量的形变孪晶,互相平行的孪晶界分割熔覆层粗大晶粒,在激光熔覆层的晶粒细化过程中发挥着重要作用;试样表层位错在{110}滑移面上发生交滑移,在晶界周围形成了位错缠结。经激光冲击后,激光熔覆层冲击区域表面残余压应力数值相较于冲击前提升了1.1倍。

In order to study the effect of laser shock on microstructure of the repair layer of E690 high strength steel by laser cladding,a special metal powder was selected to perform laser cladding on readymade pits of E690 high strength steel,and the laser cladded layer was subjected to surface mechanical strengthening treatment by laser shock processing.The microstructure and surface residual stress of the repair layer were characterized by a scanning electron microscope,transmission electron microscope and Xray stress analyzer.The results show that,after laser cladding repair,the repair layer presents an equiaxed grain structure.There is a good metallurgical bond between the laser cladded layer and the substrate.The residual stress on the surface of the repair layer is in a state of compressive stress.Following the laser shock processing,the cross-sectional grains on the repair layer are refined and a large number of deformation twins are observed.Coarse grains of the cladded layer are separated by parallel twin boundaries,which plays an important role in grain refinement process of the laser cladded layer.The dislocations on the surface of the sample experienced a slip on the{110}slip surface,forming dislocation entanglements around the grain boundaries.After laser shock,the value of surface residual compressive stress of laser cladded layer increases by 1.1 times compared with that prior to the laser shock processing.