Basal Oriented Columnar Microstructure Formation in Laser Powder Bed Fusion Prepared α Titanium Alloy

Laser powder bed fusion (LPBF) titanium alloys are known to have a strong crystallographic texture; however, this is limited to β-titanium alloys, while α-titanium alloys usually show an acicular microstructure resulting from martensitic transformation. In contrast, a strong <0001>//BD texture in CP-Ti was successfully formed by optimizing the LPBF conditions. In this study, we investigated the mechanism of such a strong texture formation through detailed microstructural analysis and experimental verification. It was clarified that <0001>//BD textured grains formed as a result of grain growth in the heat-affected zone around the melt pool. The acicular grains originated from martensitic transformation are integrated by lower grain, and formed columnar grain with <0001>//BD orientation. By optimizing the LPBF conditions based on this mechanism, specifically by increasing the holding time at high temperatures and the temperature of the grain growth area, a strong crystallographic texture was also promoted in case of Ti-9 wt% Al alloy.