316L不锈钢激光快速成形过程中熔覆层的热裂机理

The Hot Cracking Mechanism of 316L Stainless Steel Cladding in Rapid Laser Forming Process

采用微观测试分析方法,针对316L不锈钢粉末,深入研究了激光快速成形过程中熔覆层的开裂行为及其形成机理。研究结果表明,316L不锈钢激光熔覆层裂纹多发生在树枝晶的晶界,呈现出典型的沿晶开裂特征。裂纹断面上有明显的氧化彩色,扫描电镜照片显示裂纹断面上树枝晶的方向与轮廓清晰可见,树枝晶晶界相当圆滑,表明裂纹是在高温下产生的。熔覆层中的裂纹是凝固裂纹,属于热裂纹范畴。裂纹产生的主要原因是熔覆层组织在凝固温度区间晶界处的残余液相受到熔覆层中的拉伸应力作用所导致的液膜分离的结果。

The forming mechanism for the crack produced in the process of laser forming 316L stainless steel powder alloy has been studied in the paper by micro measurements. The results show that the cladding cracks were formed in grain boundary with dendritic structure commonly and presented a characteristic of cracking along grains. There was obvious oxidation color on the fracture section of the cracks. SEM photos show that the orientation and profile of dendrite grains are distinct and the dendrites are rather round on the crack surface. All these show that the cracks were formed at high temperature. The crack formed in the cladding layers is the solidification crack, which belongs to the domain of hot crack, mainly due to the separation of the liquid films in the grain boundary under the action of tension stress existed in the cladding layers which was produced in RLF process.