Effect of heat treatment on microstructure and mechanical properties of laser deposited Ti60A alloy

A laser deposited near α titanium alloy Ti60A (Ti-5.54Al-3.38Sn-3. 34Zr-0.37Mo-0.46Si) was annealed near T_β at different temperatures for 1 h, followed by 700 C annealing for 2 h. The effect of duplex annealing on microstructure, room temperature and 600 C tensile properties and stress rupture life at 600 C/310 MPa was investigated. Fractography and microstructural characterisation were performed by optical microscopy, electron backscattered diffraction, scanning electron microscopy and transmission electron microscopy. Results indicate that as-deposited Ti60A alloy has a fine basket-weave microstructure. In the "T_β-30 C" state (1020 C/1 h/AC + 700 C/2 h/AC), the alloy has 65 vol.% coarsened lamellar α and transformed β. In the "T_β-10 C" state (1040 C/1 h/AC + 700 C/2 h/AC), the alloy has 25 vol.% "crab-claw- like" α and fine lamellar transformed β. Moreover, there are Ti₃Al precipitates described by [011̄1]α//[011̄2] Ti₃Al occurring without silicides in all three states of the alloy. The room-temperature tensile ductility and stress rupture life at 600 C/310 MPa is improved obviously in the "T_β-10 C" state, but the ductility at 600 C/310 MPa is reduced. The effect of near T_β duplex annealing on mechanical properties of laser deposited alloy Ti60A is discussed in detail as related to α morphology, continuous colony boundary α, fine lamellar transformed β and Ti₃Al precipitates.