Abstract: TC18 titanium alloy was subjected to single-phase zone heat treatment with different processes (temperature of T_β+(15-35) ℃, and time of 0.5, 1, 2, 4 h) to obtain the initial microstructure with different grain sizes. The effect of grain size on the properties of the duplex annealed TC18 titanium alloy bar was investigated, and the heat treatment process with consistent microstructure and serviceability was obtained. The results show that with the increase of average grain size, the tensile strength of the TC18 titanium alloy increases first and then decreases, while the elongation after fracture, percentage reduction of area and fracture toughness show the opposite trend. To ensure that the TC18 titanium alloy components have both high tensile strength and good plasticity and toughness, the grain size should be controlled within the range of 300-430 μm, with the corresponding single-phase zone temperature and holding time being T_β+(25-35)℃ and 2-4 h, respectively.

Key words: TC18 titanium alloy, single-phase temperature, holding time, grain size, serviceability