Guidelines for selective laser melting

This chapter introduces the metallurgical mechanism and physical characteristics of selective laser melting (SLM), a process in which a high-energy laser acts on metal powders that melt to form a tiny molten pool and then solidify again. When the laser acts on metal powders, such complex physicochemical phenomena as absorption and scattering of laser energy, heat transfer, phase change, and flow of melt in the molten pool occur during powder melting and rapid solidification, and the parts also experience very complicated stress and microstructure evolution in certain areas under the action of a laser-induced periodic and long-term intense thermal cycle. The state of powder materials, metallurgical behavior of the molten pool, and characteristics of the solidified structure are of key significance for SLM process control. In addition, metallurgical defects such as spheroidization, porosity, cracks, oxidation, and element evaporation also severely restrict the mechanical properties of the components. This chapter discusses SLM process control methods and guiding strategies in terms of material selection and characteristics, molten pool metallurgical behavior, metallurgical defect formation mechanisms, and solidification structure characteristics.