The Influence of Al Addition on Cracks, Microstructure and Properties of Laser Deposition Manufacturing TiAl Alloys

Aluminum volatilization during laser deposition manufacturing severely deteriorates the microstructure and service performance of TiAl alloys, causing aggravated brittleness, elevated crack sensitivity and structural degradation. To tackle this issue, this work proposes an aluminum composition compensation strategy based on Ti-48Al-2Cr-2Nb pre-alloyed powder, with three mass fractions of elemental Al (15 wt.%, 20 wt.% and 25 wt.%) added to systematically investigate their influences on the macroscopic cracking behavior, microstructure evolution, phase constitution and mechanical properties of the deposited alloys. The results demonstrate that 15 wt.% Al addition achieves crack-free laser deposition, yielding a uniform microstructure dominated by γ-TiAl phase with dispersedly distributed TiAl2 and minor B2 phases as well as low residual internal stress. No α2-Ti3Al phase is detected in all samples, as the Al-rich composition shift thermodynamically suppresses the stability of Ti-rich α2 phase. Excessive Al addition induces the massive formation of brittle Al-rich intermetallics (TiAl2 and TiAl3), which gradually evolve from isolated particles to a continuous network structure, leading to a sharp increase in crack susceptibility. Al addition continuously improves the microhardness of the alloys, and the 25 wt.% Al sample attains the maximum hardness of 522.3 HV, benefiting from the synergistic effects of grain refinement strengthening and second-phase strengthening. The 15 wt.% Al sample delivers the optimal comprehensive mechanical performance, with an ultimate tensile strength of 550.2 Mpa and a fracture elongation of 0.76%, where the finely dispersed TiAl2 precipitates exert a remarkable dispersion strengthening effect without causing severe embrittlement. This work provides a feasible experimental basis and technical reference for crack control and property optimization of laser deposition-manufactured TiAl alloys.