Microstructure and cracking behavior analysis of gradient transition layer in TC4/AlSi12 bimetallic structure

To enhance the integrated additive manufacturing of titanium alloy structural components in the missile field, this study investigated the feasibility of fabricating TC4/AlSi12 bimetallic structure (Ti/Al BS) samples using a gradient transition approach via Laser Melting Deposition (LMD). The cracking tendency of deposition layers formed from mechanically mixed powders with xTC4 + (1-x)AlSi12 (x = 10%, 20%, 90%) was analyzed, using 10% TC4 mass fraction increments. A three-layer gradient transition LMD Ti/Al BS (90% TC4+10% AlSi12, 80% TC4+20% AlSi12, and 10% TC4+90% AlSi12) was fabricated. The results indicate that due to the thorough mixing of Ti and Al atoms, lamellar Intermetallic Compounds (IMCs) precipitated within all three gradient transition layers of the LMD Ti/Al BS. Progressing from the TC4 side to the AlSi12 side within the three-layer gradient transition zone, the IMCs formed in the sequence: Ti3Al → Ti2Al → Ti3Al2+Si → Ti5Si3 → TiAl3. The formation of numerous lamellar IMCs induced longitudinal metallurgical cracks within the gradient transition layer. The aluminum alloy, owing to its lower solidification temperature and good fluidity, partially healed these cracks.