激光近凈成形SS316/Ni20復合材料的開裂機理

激光近凈成形SS316/Ni20復合材料的開裂機理Cracking mechanism of SS316/Ni20 composite fabricated by laser engineered net shaping

采用激光近凈成形制備梯度材料時異種材料的混合易產生缺陷，嚴重制約了梯度材料的應用。采用激光近凈成形技術制備不同成分比的SS316/Ni20復合材料薄壁結構，并利用OM、SEM、XRD、EDS等檢測手段研究不同成分比時復合材料的顯微組織、相組成及元素分布。對裂紋的微觀形貌、裂紋斷面的元素分布進行分析。結果表明：在給定工藝條件下，SS316質量分數為100%、20%~0時成形件形貌較好，無裂紋缺陷，SS316質量比在90%~30%時成形件發生開裂。裂紋沿晶界擴展，裂紋斷面上晶粒清晰可辨，屬于熱裂紋范疇。成形件開裂主要原因是凝固過程中雜質元素在晶界偏析形成連續的液膜，以及硬質相在晶界上的連續析出，降低晶粒間的結合強度，使其在殘余應力作用下產生開裂。

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.

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