Development of powders of Ti-Fe-Sn ultrafine eutectics for laser additive manufacturing

Abstract

Pre-alloyed powders of near-eutectic Ti66Fe27Nb3Sn4 (at.%) were produced by two standardised gas atomisation methods, named as Crucible-based Gas atomisation (CGA) and Crucible-Free atomisation (CFA), for powder bed fusion (PBF) techniques. PBF seems the ideal (and largely unexplored) processing route for bulk ultrafine eutectics because of their strict solidification criteria requiring fast and uniform cooling rates. CFA produced more desirable physical properties in powders, although the alloy's high oxygen affinity resulted in a dendritic oxide Fe2Ti4O. Electron Microscopy, X-ray Diffraction, image analysis and nanoindentation were used to understand the solidification behaviour in powder particles across different sizes, thus, different crystallisation kinetics. The alloy is quite sensitive to compositional fluctuations and solidified via different pathways in the two methods resulting in different microstructures. Presence of meta-stable phase and ultrafine inter-lamellar spacing (< 190 μm) of the eutectic matrix, which increases with powder particle size, highlight the potential of gas atomisation as a method to study rapid solidification.