Heat treatment of laser metal deposited TiAl TNM alloy

For the manufacturing of low pressure turbine blades, titanium aluminides are used as structural materials, among them the alloy Ti-43.5Al-4Nb-1Mo-0.1B (at.-%) known as TNM™ alloy. In this study, laser metal deposition (LMD) was investigated as a potential technology to repair defective, damaged or worn blades, and process conditions were successfully optimized. However, post-process heat treatment is required to optimize the microstructure. In this work, different annealing treatments and the resulting microstructures were characterized for bulk LMD samples as well as for investment cast reference samples. Annealing temperatures were selected from 1245 to 1290 °C. The results show that annealing at 1290 °C for a duration of 60 min with subsequent furnace cooling can be used so that the LMD and cast micro-hardness nearly match, albeit with significant differences in microstructure. Nonetheless, yield strength mismatch can be mitigated and LMD can qualify as prospective additive repair technology, but also as a manufacturing technology for functional TiAl parts.