Fatigue crack propagation rate of lamellar microstructure for TC4-DT titanium alloy

The fatigue crack propagation rates of different lamellar microstructures in TC4-DT titanium alloy were studied. Different lamellar microstructures were obtained by different heat treatment processes, and the effect of lamellar microstructure parameters on fatigue crack growth rate was investigated. Results show that the thin lamellar microstructure by duplex treatment and air cooling possesses a higher fatigue crack propagation resistance than the coarse lamellar microstructure by furnace cooling. The crack propagation mechanism of multi-heat treatment is different from that of the duplex heat treatment, since the multi-heat treatment generates secondary α lamellar. Under the same first heat treatment, the crack propagation rate in a mid-rate range by multi-heat treatment is higher than that by the duplex heat treatment. The secondary α lamellar microstructure has good deformation compatibility, and accelerates the crack propagation; as a result, the multi-heat treatment causes a higher fatigue crack propagation rate than the duplex heat treatment+air cooling.