Effects of post-processing on microstructure and mechanical properties of SLM-processed IN-718

Abstract

Nickel-based superalloys have been developed extensively and have proven attractive for various industrial applications over the past four decades, due to excellent mechanical properties that are maintained at high temperature. This study investigates selective laser melting (SLM) of the nickel-based superalloy IN-718 and documents the effects of post-processing treatments on the resulting microstructure and mechanical properties. Comprehensive microstructural characterization was performed on both as-deposited and post-processed materials using various techniques (e.g. EBSD, OM, BSE, CT). The as-deposited alloy exhibited fine and elongated grains that contribute to the mechanical anisotropy presented in a companion paper while post-processing produced a more equiaxed microstructure and reduced the mechanical anisotropy. Tensile, fracture toughness, and fatigue crack growth tests conducted at room temperature are reported in this work while elevated temperature properties are reported elsewhere. This work revealed the changes of the microstructure (γ morphology, γ crystallography, and precipitate distributions) and hence the mechanical behavior due HIP+HT which resulted in mechanical properties that approach wrought alloys after comparable heat treatment. The results are discussed in this light and focus on the differences in microstructure resulting from the AM process.