Mitigating cracking in laser powder bed fusion of Ti-48Al-2Cr-2Nb via introducing massive β phase

The application of Ti-48Al-2Cr-2Nb (TiAl-4822) produced by laser powder bed fusion (LPBF) is hindered by its severe cold cracking susceptibility caused by the intrinsic brittleness of α2 and γ phase. Although the high cooling rate of LPBF is normally deemed detrimental for brittle materials, the present study proposed a counterintuitive strategy to mitigate cold cracking, by taking advantage of the high cooling rate rather than suppressing it. By reducing laser input energy, the cooling rate of LPBF increased, which led to the formation of a massive ductile β phase. The unique β and α2 phase distribution and the transition of β → α2 were also revealed, further proving the presence of the massive β phase. Compared with the sample without β phase, the β-containing sample successfully mitigated cold cracking. This study shows a novel method to alleviate the cracking problem of LPBF-processed TiAl-4822, providing new insights into the future LPBF process design of TiAl-4822 and other TiAl-based alloys.