Abstract:The fatigue crack propagation behavior was investigated for the TC4-DT titanium alloy with bimodal and lamellar microstructure, developed by (a+b) annealing treatment and b annealing treatment, respectively. The effect of microstructure on fatigue crack growth rates of TC4-DT titanium alloy has been discussed by SEM analyses of fracture morphology and crack propagation paths in the two different microstructures. The results show that for the bimodal microstructure, the fatigue crack growth rate lowers with decrease in the content of primary a phase, and the turning point in the curve tends to move to the right. The lamellar microstructure exhibits tortuous crack paths and fatigue crack propagation resistance, which indicates that the lamellar structure has better damage tolerance compared with bimodal structure.