Quantifying chemical homogeneity across the melt pool in laser powder-bed fusion of metallic glass matrix composites from blended elemental powders

Additive manufacturing (AM) with blended elemental powders offers an opportunity to reduce processing time and cost whilst increasing the range of alloys that AM can produce — it is possible to print alloys that are difficult to produce from pre-alloyed powders. Metallic-glass-matrix composites (MGMCs) are an example of such alloys. Their microstructures are complex, and printing parameters must balance the rapid cooling required for glass formation with achieving appropriate microstructural control to deliver favourable mechanical properties. Their uncommon compositions also mean that sourcing alloyed powder is challenging. Blended powder mixtures with overall composition Ti 58.5 Zr 31.5 Cu 10 (at.%) were processed using laser powder-bed fusion (L-PBF) to produce a β-(Ti, Zr) phase reinforced MGMC. The influence of volumetric energy density (VED) on powder mixing was investigated by experimental study and thermal fluid-flow simulations based on computational fluid dynamics. At low VED, a lack of complete melting and mixing in each melt pool is seen due to a lack of convective flow. To interpret this chemical inhomogeneity, a graphical method for interpreting heterogeneity is introduced, offering a broader application for AM processes utilising blended powders. The implications of requiring higher VED to enhance chemical homogeneity in blended powders are discussed, particularly concerning the production of metallic glasses and MGMCs via AM.