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

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 gamma ' 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 gamma ' 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 celcius), the secondary gamma ' precipitates decreased with the increase of solution temperature, while the tertiary gamma ' precipitates from the subsequent aging process gradually increased; for higher solution temperature over 1100 celcius, exceeding the complete dissolution temperature of the gamma ' phase, only tertiary gamma ' precipitates from the subsequent aging process were uniformly distributed in the alloy. After double solid solution (1170 celcius + 1050 celcius) + aging heat treatment (DSSA), there were three sizes of gamma ' precipitates in the alloy. In general, the SLM + SSA (1130 celcius) alloy obtained the best comprehensive properties, which could be related to the homogenized microstructures and the uniform and dense distribution of single sized tertiary gamma ' precipitates in the alloy. Graphic