Tensile creep behavior of heat-treated TC11 titanium alloy at 450–550 °C

Abstract

The effect of heat treatment on the tensile creep behavior of duplex titanium alloy Ti–6.3Al–1.6Zr–3.4Mo–0.3Si (TC11) at 500°C, 300MPa, as well as the tensile creep of heat-treated TC11-2 alloys over the temperature range 450–550°C at stress range 300–450MPa have been investigated in detail, by means of curve measurements and microstructure observation. At 500°C and 300MPa, the TC11 alloys with duplex microstructure exhibited less creep deformation and strain rates than basket-weave microstructure, and heat treatment at condition of 970°C/1h/AC+530°C/6h/AC has the best creep performance. TEM analysis indicates that the creep in duplex structure alloy is controlled by dislocation climb (Metal-type or Class II alloy creep), and changes to a jogged-screw creep model in basket-weave structure. For heat-treated TC11-2 alloy, the corrected activation energies between 65kJ/mol and 188kJ/mol, and stress exponents in the range 1–3.8 were obtained. At 450°C, small apparent stress exponent (equal ∼1) as well as low activation energies suggested that the creep is controlled by double mechanisms of Harper–Dorn dislocation creep and diffusion type creep. At 500°C and 550°C, the higher stress exponents and apparent activation energies indicated that creep is controlled by climb of dislocation. The second phases, mainly (Ti,Zr)5Si3, inhomogeneously precipitated from both primary α grain and α/β lath interface, which has limited effects on hindering the movement of dislocations during creep.