Effect of Heat Treatment on Microstructure and Properties of FGH4096M Superalloy Processed by Selective Laser Melting

Abstract: A self-designed nickel-based superalloy, designated as FGH4096M, was prepared by selective laser melting (SLM). Different heat treatments were performed to improve the mechanical properties of the SLM alloy through optimizing the microstructures and the features of γ′ precipitates. Compared with the as-deposited alloy, the columnar grains with dendritic structures and equiaxed structures were retained in the alloy after direct aging, but a large amount of tertiary γ′ phase precipitated, especially around the sub-grain boundaries, resulting in the highest tensile strength but the lowest elongation. During solid solution and aging treatment (SSA), the recovery and recrystallization occurring in the alloy facilitated the grains to be equiaxed with the increase of solution temperature. For lower solution temperature (below 1100 ℃), the secondary γ′ precipitates decreased with the increase of solution temperature, while the tertiary γ′ precipitates from the subsequent aging process gradually increased; for higher solution temperature over 1100 ℃, exceeding the complete dissolution temperature of the γ′ phase, only tertiary γ′ precipitates from the subsequent aging process were uniformly distributed in the alloy. After double solid solution (1170 ℃ + 1050 ℃) + aging heat treatment (DSSA), there were three sizes of γ′ precipitates in the alloy. In general, the SLM + SSA (1130 ℃) alloy obtained the best comprehensive properties, which could be related to the homogenized microstructures and the uniform and dense distribution of single sized tertiary γ′ precipitates in the alloy. Graphic Abstract: [Figure not available: see fulltext.].