The influence of building direction and conventional heat treatment on the microstructure, physical, and mechanical characteristics of direct metal laser sintered Inconel 718 alloy

Abstract

ABSTRACTDMLS fabricated IN718 alloy samples with various build orientations are analysed with heat-treatment dependent mechanical and microstructural properties. The multiple heating and cooling cycles formed a complex micro-heterogeneous microstructure composed of columnar and equiaxed subgrains in the alloy. Solution treatment resulted in a partially dissolved δ phase, and the metastable γ” phase while ageing treatment eliminated the dendritic substructure. In contrast, δ-phases precipitated mainly in the interdendritic regions, and significantly eliminated the micro-segregation and Laves phases in the γ matrix after homogenised (HSA). . The tensile test showed that tensile strength decreased with increasing building orientation but ductility increased. Heat-treatment significantly improved the microhardness, ultimate tensile strength, and yield strength compared to the as-fabricated samples, but their ductility decreased. The tensile properties recorded an improvement of nearly 31.32% as compared to 0° as-built and 0° heat-treated direct aged samples. The higher microhardness (507.25 HV) was observed for the direct aged 0° build samples. The microhardness values were increased by nearly 45% after heat-treatment comparing to as-build 0° and 0° DA treated samples. The density was observed to be about 99.52% of the as-built samples, but performing the heat-treatment, no significant improvement in the density was observed and it was found similar to the as-fabricated sample.