A critical review of powder-based additive manufacturing of ferrous alloys: Process parameters, microstructure and mechanical properties

Highlights: • Critical overview of different additive manufacturing (AM) process parameters on the quality of ferrous alloys. • Introduction of new effective energy density numbers combined with the penetrated heat depth, hatch spacing and spot size. • Critical overview of solidification and phase transformation of AM-processed ferrous alloys with mechanical properties. Additive manufacturing (AM) is an advanced manufacturing technology, enabling production of complex shapes by adding material layer-upon-layer, as distinct from conventional subtractive, forming and other manufacturing approaches. Thus far, several metallic materials including different types of ferrous alloys have been additively manufactured to full density with better or equivalent properties compared to counterparts made by conventional methods. In this perspective, this review article presents different powder-based additive manufacturing processes deployed to ferrous alloys, their key process parameters, phase transformation and microstructure development during solidification, all of which impact on mechanical behavior. The article enlightens the basics of Laser Powder-Bed (LPB, also known as selective laser melting), Laser Powder-Fed (LPF) and Binder Jetting (BJ) AM processes. These processes involve a sequence of complex/rapid thermal cycle and solidification behavior that influence the development of microstructure and eventually control the mechanical properties. A thorough discussion on mechanical behaviors, i.e., hardness, tensile, and cyclic/fatigue properties of AM manufactured steels is also presented based on several combined process parameters.