多道搭接激光熔覆镍基合金中裂纹断口形貌研究

利用预置法激光重熔在铁基材料上获得了Ni基合金多道搭接的熔覆层。利用光学显微镜和扫描电镜对熔覆层组织、裂纹走向以及裂纹面进行分析。多道搭接时，Ni基合金熔覆层极易出现贯穿裂纹。裂纹的扩展呈周期性，裂纹面上高温热裂断口和冷脆断口交替出现。高温下的裂纹沿树枝晶界韧性稳态扩展，穿过树枝晶时有斯裂棱：失稳扩展沿裂纹面进行、断口呈放射状的脆性特征。数值分析表明，多道搭接时热应力在整个开裂过程中起重要作用。裂纹于夹杂附近在最大热应力作用下起裂，起裂方向垂直于扫描方向。随后裂纹在热应力、组织因素及已有裂纹综合作用下进一步扩展、方向发生偏离。

Fractography Study on the Cracking Behavior of Laser-clad Multitrack Coatings

In this paper,large scale Ni|based laser|clad multi|track coatings were obtained by remelting the pre|located coatings.SEM observations showed that microstructures were composed of clad region and combined region. Microstructures in the overlapping region of Ni|based coatings showed a different characteristic.The microstructure in Ni|based overlapping region reveals radial direction.The fracture surface of multiple|clad coatings revealed periodically,where the hot crack surface and quenched crack surface appeared alternately.Numeric analysis results confirmed that the thermal stress played an important role during the crack initiating and propagting.