Effects of Hot Isostatic Pressing on the Microstructure and Mechanical Properties of K418 Alloys Fabricated by Selective Laser Melting

Selective laser melting (SLM) is a widely used process for manufacturing high-precision, structurally complex components. However, the existence of various defects poses significant challenges for the mechanical properties of products manufactured by SLM, particularly when fabricating the K418 nickel-based superalloy. In this study, the effects of hot isostatic pressing (HIP) treatment on the defect distribution, microstructure and mechanical properties were investigated, and the deformation and fracture mechanisms of the SLMed K418 alloy were analyzed. The results showed that the HIP treatment can effectively decrease the porosity of the K418 alloy from 13.7% to 2.1%. Most of the defects are eliminated after the HIP treatment, while a certain proportion of defects remain. Furthermore, the HIP treatment leads to a decrease in dislocation density, coarsening of the γ ′ phase, dissolution of the Laves phase and transformation of MC carbides into M 23 C 6 carbides. Besides, the HIP treatment enhances the ultimate tensile strength of the SLMed K418 alloy while having minimal influence on the fracture elongation. The coarsened γ ′ phase reduces the dislocation mean free path (Λ) and thus elevates the work-hardening rate (dσ/dϵ) of the samples subjected to HIP treatment, contributing to the improvement of the ultimate tensile strength.