Crack suppression in wire-arc directed energy deposition of a γ-TiAl alloy

It was a big challenge to effectively eliminate cracks in wire arc directed energy deposition of TiAl alloys. Crack-free γ-TiAl alloy deposition layers were fabricated by a combining technique of preheating and heat preservation. A coupled thermo-mechanical model was developed to calculate the thermal stress evolution in the deposited layer. A first-principle model was employed to calculate the free energy and ductility of the γ and α2 phases. Based on the numerical and microstructural analyses, the crack suppressing mechanism was revealed. The α2 phase had a higher residual stress state at the boundary, and was more stable and brittle than the γ phase. The cracks were suppressed by decreasing the thermal stresses and brittle α2 phase formation.