(大连理工大学 精密与特种加工教育部重点实验室，大连 116024)
摘 要: 采用激光近净成形制备梯度材料时异种材料的混合易产生缺陷，严重制约了梯度材料的应用。采用激光近净成形技术制备不同成分比的SS316/Ni20复合材料薄壁结构，并利用OM、SEM、XRD、EDS等检测手段研究不同成分比时复合材料的显微组织、相组成及元素分布。对裂纹的微观形貌、裂纹断面的元素分布进行分析。结果表明：在给定工艺条件下，SS316质量分数为100%、20%~0时成形件形貌较好，无裂纹缺陷，SS316质量比在90%~30%时成形件发生开裂。裂纹沿晶界扩展，裂纹断面上晶粒清晰可辨，属于热裂纹范畴。成形件开裂主要原因是凝固过程中杂质元素在晶界偏析形成连续的液膜，以及硬质相在晶界上的连续析出，降低晶粒间的结合强度，使其在残余应力作用下产生开裂。
关键字: SS316/Ni20复合材料；梯度材料；激光近净成形；裂纹
（Key Laboratory for Precision and Non-traditional Machining Technology, Ministry of Education, Dalian University of Technology, Dalian 116024, China）
Abstract:The mixed gradient materials produced by the laser engineered net shaping (LENS) process are vulnerable, which restricts seriously the application of these materials. Different proportions SS316/Ni20 composite thin-walled structures were prepared using LENSTM and the microstructure, phase composition and distribution of elements under different compositions were studied by OM, SEM, XRD and EDS. Under the given process conditions, the results show that when SS316 mass fractions are 100%, 20%-0, the components appear well without crack. While, when the mass fractions ranges from 90% to 30%, the components crack. The morphology analysis of crack and elements distribution of the crack surface indicates that the cracks propagate along grain boundaries and the grains on the crack surface are visible, the cracking belongs to the hot crack domain. The main reason of cracking is the grain boundary segregation of impurity elements during solidification and hard phase continuous precipitation on the grain boundary, which reduces the bonding strength between the grains. It is prone to cracking under residual stress.
Key words: SS316/Ni20 composites; gradient material; laser engineered net shaping; cracks
