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,穿过树枝晶时有撕裂棱;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.
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