Effect of microwave hybrid heat treatment on the microstructure and hardness of 3D printed Inconel 718 superalloy

Abstract

ABSTRACT This study explores the potential of a microwave hybrid heating (MHH) technique as an efficient post-heat treatment route for an Inconel 718 (IN718) superalloy processed by laser powder bed fusion (LPBF). The LPBF-IN718 alloy is post-heat-treated using an industrial microwave (MW) oven and a conventional heat treatment route to eliminate the segregates and Laves phase. The MW treatment generates a relatively higher back diffusion rate of the segregated elements releasing more Nb into the γ-matrix compared to the conventional treatment. This results in lower fraction of intergranular δ-phase in the MW-processed microstructure (≈ 0.2%) relative to conventionally processed microstructure (≈ 0.81%). However, more precipitation of the MC-type carbides is observed in the matrix after the MW-treatment, indicating the supersaturation of the γ-matrix in the back-diffused elements. Both the MW and conventional treatments affect the hardness similarly owing to the combined effect of the precipitation hardening and the substructure strengthening. Compared to conventional heating, the MW processing time, to heat the sample to the set temperature, is reduced by a factor of 2, and the consumed energy is decreased by 80%. As a result, an MW-treatment can be considered as a cost-effective alternative to a conventional post-heat treatment for LPBF-IN718 components.