Effects of post-heat treatment on anisotropic mechanical properties of laser additively manufactured IN718

Abstract

In this presented work, the effects of different heat treatments on the anisotropic mechanical properties of Inconel 718 (IN718) fabricated by laser powder bed fusion (LPBF) and laser directed energy deposition (LDED) were comparatively investigated. Samples prepared in build direction (BD) and transverse direction (TD) for tensile and creep tests were heat-treated with Solution + double aging (SA) and Homogenization + solution + double aging (HSA) procedures, separately. Experimental results indicate that both SA-treated LPBF-IN718 and LDED-IN718 show strong anisotropy in tensile and creep properties. TD samples have higher tensile strength and relatively better creep performance. After HSA treatment, LPBF-IN718 samples still show strong anisotropic tensile and creep properties. In contrast, anisotropy in mechanical properties of LDED-IN718 samples is mitigated significantly. The columnar grains in as-built LDED-IN718 recrystallized after HSA treatment, resulting in similar tensile and creep properties in both directions. The difference in residual stresses of LPBF-IN718 and LDED-IN718 is the main reason that causes the totally different conditions after HSA treatment. This work can provide a deeper understanding of the difference in anisotropic mechanical properties of LPBF-IN718 and LDED-IN718, which may guide the design of proper heat treatment of laser additively manufactured nickel-based superalloy potentially.