Effect of Heat Treatment on Microstructure and Mechanical Properties of Nickel-Based Powder Metallurgy Superalloy Processed by Selective Laser Melting

Nickel-based powder metallurgy superalloys have the characteristics of uniform structure, fine grains and no macrosegregation. Due to their excellent mechanical properties, such as excellent fatigue resistance, creep resistance, excellent high-temperature strength and crack propagation resistance, they have become the preferred materials for critical hot-end components such as aero engine turbine disks. Selective laser melting (SLM) has a high ability to form complex shape of parts, reducing post-machining procedures and completing efficient productions with low component volumes, so it has become a new technical route for the preparation of superalloys. In this work, the FGH4096M alloy was prepared by SLM technique with pre-powders prepared by vacuum induction argon atomization method. The microstructure and mechanical properties of the as build and heat-treated (HTed) alloys were investigated by OM, SEM, EBSD and so on. The as build alloy with a small number of gamma' and carbide, mainly composed of austenite matrix gamma' phase, has the highest elongation. After heat treatment, a large amount of gamma' phase precipitated in the alloy, which is one of the main factors affecting the mechanical properties of the alloy. The uniform and dense distribution of gamma' precipitates in the alloy can significantly improve the strength. A higher lattice distortion between the gamma' phase with cubic or petaloid shape and matrix can increase the strength of the alloy to some extent. Fine dendritic and equiaxed structures in SLM FGH4096M can improve the property of the alloy as fine grain strengthening. The higher solution temperature promotes the recovery and recrystallization of the SLM alloy, and eliminates the intra-crystal dendritics and equiaxed structures. The average elongation of the as build alloy is 24.97%. The yield strength and ultimate strength of the SLM FGH4096M alloy after direct ageing treatment are the highest, and the average values are 1459.46 and 1595.56 MPa, respectively.