Mechanistic insights into cracking suppression through process-induced microstructure relaxation in Ti-6242Si

Ti-6242Si processed via laser powder bed fusion (LPBF) presents challenges in achieving crack-free components with low occurrence of pore defects. In this study, processing diagrams and temperature prediction models were employed to investigate the influence of melting modes (conduction, transition, keyhole) on density, crack formation, and microstructural characteristics. The application of dimensionless processing diagrams enabled a reduction in porosity and achieving high density ranging from 99.55 % to 99.98 %; however, cold cracks were observed under processing via transition and keyhole melting modes. This work, demonstrates for the first time, that cracking was effectively suppressed by printing in conduction mode, while ensuring low occurrence of porous defects. This improvement was attributed to the effect of process-induced in-situ heat treatment (HT), which substantially reduced residual stresses in the conduction mode by suppressing acicular α ′ martensites within the basket weave microstructure. In-depth microstructure characterizations further revealed the presence of coarse α ′ martensite plates decorated with networks of fine Sn-rich particles formed during in-situ HT, indicative of a more relaxed and stabilized microstructure. This work demonstrates the strong sensitivity of Ti-6242Si microstructure to LPBF process parameters and highlights the importance of precise microstructure engineering during the process to achieve crack-free, high-performance Ti-6242Si components. • Melting modes critically governed cracking and residual stress behavior in Ti6242. • Conduction-mode LPBF enabled fully crack-free fabrication with 99.98 % density. • In-situ heat treatment during conduction mode promoted microstructural relaxation. • Coarse α ′ martensite and Sn-rich precipitates revealed intrinsic stress relief. • Tailored thermal cycles enable crack-free LPBF of near- α Ti alloys.