Tensile creep behavior of heat-treated TC11 titanium alloy at 450-550 ℃

摘要

The effect of heat treatment on the tensile creep behavior of duplex titanium alloy Ti-6.3Al-l.6Zr-3.4Mo-0.3Si (TC11) at 500 ℃, 300 MPa, as well as the tensile creep of heat-treated TC11-2 alloys over the temperature range 450-550 ℃ at stress range 300-450 MPa have been investigated in detail, by means of curve measurements and microstructure observation. At 500 ℃ and 300 MPa, the TC11 alloys with duplex microstructure exhibited less creep deformation and strain rates than basket-weave micro-structure, and heat treatment at condition of 970 ℃/1 h/AC+530 ℃/6 h/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 65 kJ/mol and 188 kJ/mol, and stress exponents in the range 1-3.8 were obtained. At 450 ℃, 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 ℃ and 550 ℃, the higher stress exponents and apparent activation energies indicated that creep is controlled by climb of dislocation. The second phases, mainly (Ti,Zr)_5Si_3, inhomogeneously precipitated from both primary α grain and α/β lath interface, which has limited effects on hindering the movement of dislocations during creep.