Abstract: The low-cycle fatigue curves (Δεt) of titanium alloy TC11 (Ti-6.5 Al - 3.5Mo - 1.5Zr - 0.25Si alloy) at 500℃ are determined under different conditions of heat treatment. The linear empirical formulas between the fatigue life Nf and the tensile ductilities, i. e. and (?), are given under different values of total strain range Δε. The important experimental results show that under different conditions of heat treatment the Nf of titanium alloy TC11 at 500℃ decreases with the reduction of tensile ductilities of the alloy as these samples approach to same magnitude of tensile strength, it is especially pointed out that the Nf of Widmanstatten strueture at 500℃ is generally shorter than equiaxed grain α structure which has a higher tensile ductjlity, but the Af of Widman-statten structure at 500℃ between them decreases if the thickness of α needles is thiner and the size of colonies is finer in the widmanstatten structure.

Key words: titanium alloy, fatigue, luctihty, microstructure