Predicting the chemical homogeneity in laser powder bed fusion (LPBF) of mixed powders after remelting

An advantage of laser powder bed fusion (LPBF) of metals is that one can create topologically complex components with comparative ease. Most LPBF studies use commercial pre-alloyed powders and less attention has been given to new alloy design for LPBF. Physical mixing of powders with different chemistries can be an effective way to access new alloy compositions for LPBF without the need for custom pre-alloyed powders. In this work, a previously published model to describe the chemical distribution of LPBF material from mixed powders is extended to the process of remelting and is quantitatively compared with experiment. A mix of Ni and stainless steel powders is used to assess the effect of remelting on the chemical homogeneity and the model is shown to agree well with experiment once evaporation of selected species and changes in melt pool size during remelting are incorporated. Strategies to improve the chemical homogeneity of prints from mixed powders are discussed. Remelting is one approach but the chemical homogeneity improves only marginally after three remelts. The critical role of the melt pool size compared to the minority powder particle spacing is emphasised. Finally, an example of using spatially controlled chemical homogeneity to create architectured materials using LPBF is shown.