In-situ annealing temperature effect on variant selection within β grains of TA15 alloy by electron beam powder bed fusion

Within titanium alloys produced via additive manufacturing processes, the phenomenon of variant selection is both prevalent and intricate. Hereby, the electron back-scatter diffraction (EBSD) technique was employed to examine the variant selection of Ti-6.5Al-2Zr-1Mo-V (TA15) alloy, which was fabricated by electron beam powder bed fusion (EB-PBF) at different in-situ annealing temperatures of 700 °C and 800 °C. The EBSD results indicated that all twelve α phase variants were present at both temperatures; To quantitatively describe the variation in variant selection, the α/α boundary length fractions classified by angle/axis pair types were further analyzed. The study discovered that IV-type (63.26°/[10̅5 53̅]) α/α boundary length fraction was higher than that of other types at 700 °C; II-type (60°/[112̅0]) α/α boundary was dominant at 800 °C. This phenomenon can be attributed to the influence of factors such as residual stress and cooling rate on the self-regulation mechanism during the β→α phase transformation, influenced by varying annealing temperatures. Results on effect of in-situ annealing temperature on α variant selection will facilitate a deeper comprehension of microstructure evolution of EB-PBF fabricated titanium alloys and offer a crucial reference for more precise microstructural customization in future product manufacturing.