Effect of post-treatment on the microstructure and tensile properties of Ni–Co-based superalloy manufactured by selective laser melting

Abstract

A newly designed Ni-Co-based superalloy was manufactured by selective laser melting (SLM) and the effect of hot isostatic pressing (HIP) and heat treatment on the microstructure and tensile properties was investigated. The as-built sample showed epitaxial grains including sub-structures, whereas recrystallisation occurred in the HIP-treated samples. Furthermore, carbide particles appeared at the grain boundaries, and the γ' phase formed extensively. The sample that was subjected to HIP-solution-treatment and aging (STA) contained a larger fraction of carbide and γ' phase compared to the HIP sample, with a needle-shaped topologically close-packed (TCP) phase also generated inside the γ matrix. The yield and tensile-strengths increased by approximately 60% after HIP, and the elongation increased by 0.8%. However, the HIP-STA sample underwent a significant decrease in elongation by TCP phase. The correlation between the microstructure and mechanical properties of the SLMbuilt superalloy is also discussed on the basis of the fractography results.