A review on metallurgical aspects of laser additive manufacturing (LAM): Stainless steels, nickel superalloys, and titanium alloys

Additive Manufacturing (AM), likewise branded as 3D printing, is a field of significant interest that has been recognized as an advanced process for production of engineering components in a layer-by-layer approach. It both offers an alternative fabrication route for existing designs, as well as enables new designs with complexity unattainable using conventional techniques. Amongst different AM processing routes, Laser Additive Manufacturing (LAM) is one of the supreme encouraging additive manufacturing means due to the potential to fabricate products at low cost with high quality and productivity. Considering many studies are in progress in this new and exciting field, this review paper argues the present state of the art and considers new avenues for future research studies. It explores the key metallurgical phenomena during LAM and the differences between various routes of LAM technology in terms of powder bed fusion (PBF) or directed energy deposition (DED) involving different forms of powder-bed, powder-fed, and wire-fed assembly. The reported microstructural aspects, functional, and mechanical properties of advanced and high applicable materials classified as stainless steels, nickel-based and superalloys, titanium-based alloys, and metal matrix composites (MMCs) for various practical applications are highlighted along with the effects of different pre- and post-treatment characteristics. Hereafter an evaluation of the field is provided; the gaps in the scientific understanding are underlined, which may limit the growth of LAM technology for the design of metallic parts.