Fabrication of TC4 and Ti48Al bimetals by plasma arc additive manufacturing： Microstructure and mechanical properties

Plasma arc additive manufacturing (PAAM) was applied to fabricate TC4 and Ti48Al (gamma titanium aluminide) bimetals in this work. The impact of deposition sequence on the microstructure and mechanical properties of two groups of bimetals (TC4-Ti48Al, first deposited TC4, then Ti48Al; Ti48Al-TC4, first deposited Ti48Al, then TC4) was investigated. The results show that the ultimate tensile strengths of two groups of bimetals exhibit significant differences, with 158.4 MPa for TC4-Ti48Al and 232.3 MPa for Ti48Al-TC4, the reason for this disparity is the difference in microstructure at the transition zone, which is attributed to heat input and Marangoni convection. The phase transformation evolution of TC4-Ti48Al transition zone is (major α2 + minor α)→ (major α2 + minor γ) → (major γ + minor α2), and (major α2 + minor α) → (major α + minor α2) for Ti48Al-TC4. The formation mechanism of transition zones and relationship between the microstructure characteristics and mechanical properties of two groups of bimetals were further discussed. Overall, the property of Ti48Al-TC4 was superior, and this work provides a promising new method for the preparation of TC4 and Ti48Al bimetals.