Microstructure evolution during selective laser melting of metallic materials: A review

Selective laser melting (SLM) is an additive manufacturing technology that uses a laser beam to melt powder materials together layer by layer for solid part fabrication. Due to its superior rapid prototyping capability of three-dimensional structures, SLM has been used for widespread industrial applications including aerospace, automotive, electronics, and biomedical devices. As a state-of-the-art technology, ongoing investigations are being conducted to improve the efficiency and effectiveness of SLM. In particular, understanding of microstructure evolution during SLM is essential to achieve improved process control and ensure the performance of laser-fabricated components. This paper is to review the recent research and development progress in SLM of metallic materials with a focus on the process-microstructure relationship. The grain growth and porosity evolution as affected by laser processing parameters in the SLM process are discussed. Phase transformation in SLM of steel and titanium alloys is studied. The formation of precipitates in SLM of titanium, nickel, and aluminum/magnesium alloys is reviewed. The balling phenomenon and cracking behaviors during SLM are discussed. In addition, the recent development of computational modeling of microstructure evolution during SLM is investigated.