Effect of Heat Treatment on Structure and Properties of Laser Powder Bed Fusion Inconel 939

Abstract

Additive manufacturing of high gamma prime (γ’) Nickel-based superalloys are challenging due to their hot cracking tendency. This study comprises an understanding of microstructural evolution and mechanical properties of Inconel 939 (IN939) alloy processed via laser powder bed fusion (LPBF). The as-printed samples comprised of columnar grains along the build direction with a pronounced <100> texture resulting in ∼17% lower elastic modulus along the build direction as compared to the builds in transverse orientation. The microstructure consists of cellular and columnar dendrites with segregation of Nb, Ta and Si in the inter-dendritic regions (decorating the cell boundaries). Occurrence of fine (< 50 nm) intra granular carbides in the as printed condition is a unique feature of this microstructure. Heat treatment resulted in dissolution of the dendritic microstructure with precipitation of semi-coherent γ’ (Ni3(Al,Ti)) precipitates (150–200 nm) homogeneously from the matrix resulting in ∼16% enhanced yield strength. The <100> texture is retained even after the solution and aging heat treatment indicating thermal stability of this structure.