Formation of metastable cellular microstructures in selective laser melted alloys

Selective Laser Melting (SLM) is one of the additive manufacturing techniques used to fabricate three-dimensional metal parts from a computer aided design. SLM is gaining more and more attention due to its ability to produce parts with intricate shape and added functionalities. Moreover, materials fabricated by SLM show an unique microstructure and in some cases a metastable cellular microstructure is observed. However, its formation during the SLM process is not fully understood, yet. Hence, the present manuscript attempts to explain the development of metastable cellular microstructures during the SLM solidification process by considering the Bernard Marangoni driven instability (BMI) and particle accumulated structure formation (PAS) mechanisms, where both thermodynamics and kinetics play a role. According to the considered theories it is proposed that the cellular microstructure forms only when the following conditions are satisfied: (1) A binary alloy system is preferred. If a multicomponent system is chosen, then only two phases should form in the respective alloy; (2) the solute should be immiscible with the solvent or have at least negligible solubility around the solidification temperature of the solvent phase; (3) the solute phase should possess a higher melting point than the solvent, and (4) the solute and the solvent should have a melting point difference of at least 673 K.