Microstructure evolution and mechanical properties of additively manufactured Ni-based GH4099 superalloy via hot isostatic pressing and heat treatment

Abstract

In this study, GH4099 alloys with over 99.99 % density were produced by laser powder bed fusion (LPBF) and followed by hot isostatic pressing (HIP) and heat treatment (HT). The effects of HIP and HT on the microstructure evolution and mechanical properties of the additively manufactured GH4099 superalloy were examined systematically. The as-deposited columnar crystals were effectively transformed into equiaxed crystals via HIP and HT. During HIP, the elimination of defects and elemental segregation in the deposited samples occurs. However, uneven precipitation of the γ′ phase within grains causes the emergence of minor gaps in the γ matrix, which adversely affects mechanical properties. The microstructure resulting from HIP + solution treatment (ST) consists entirely of equiaxed recrystallized grains. The presence of twin and long-period stacking-ordered (LPSO) phases at twin boundaries strongly hinders dislocation behavior, and the remelting of precipitates and carbides greatly improves plasticity. Moreover, during the loading process at 900 °C, γ′ phase and carbides were re-precipitated, and the strain concentration was minimized during the precipitation process, resulting in the highest high-temperature strength. Conversely, in the HIP + solution and aging treatment (SAT) process, the progression of γ′ phase precipitation, condensation, annexation, and growth contributes to a reduction in strength. Coupled with an increase in the plasticity of the LPBF GH4099 alloy.