Effect of in-Situ Intrinsic Heat Treatment in Metal Additive Manufacturing: A Comprehensive Review

Metal Additive Manufacturing (MAM) produces high-strength and complex shape components through a layer-by-layer metal deposition approach for aerospace, automobile, and structural applications. The heat is accumulated and subjected to reheating in the metal layers by depositing material from the feedstock with the help of a heat source on the existing metal layer. Generally, the reheating in the MAM process consists of multiple annealing, multilevel normalizing, and long tempering processes. The material morphology and mechanical properties of MAM products are affected due to the stored heat in the layers while the component is manufactured with the heat source of laser energy, electron energy, or conventional arc welding techniques. The grain structure is refined by reheating the layers by the heat source and without post-heat treatment techniques. The mechanical properties and morphological characteristics of the as-built MAM components due to the effect of in-situ intrinsic heat treatment (reheating) are measured through various materials testing methods such as Electron Back Scatter Diffraction (EBSD), Scanning electron microscopy (SEM), X-ray diffraction (XRD), tensile test, hardness test, compressive test and etc. The review aims to study the mechanical and morphological characteristics due to the effect of in-situ intrinsic heat treatments on low carbon steel, maraging steel, and Al alloys, which were fabricated by direct energy deposition (DED) and laser powder bed fusion (LPBF) techniques.