Microstructure evolution and mechanical properties of heat treated LCB titanium alloy

The influence of ageing time on microstructure and mechanical properties of low-cost beta （LCB） titanium alloy with a chemical composition of Ti-6.6Mo-4.5Fe-1.5Al was investigated. The correlation between microstructure and fatigue crack initiation and growth was also studied. Increasing ageing time tended to increase the volume fraction of the secondary α-precipitates, β-grain size and partial spheroidization of primary α-phase. The maximum tensile strength （1565 MPa） and fatigue limit （750 MPa） were obtained for the samples aged at 500 °C for 0.5 h, while the minimum ones of 1515 MPa and 625 MPa, respectively, were reported for the samples aged at 500 °C for 4 h. The samples aged at 500 °C for 4 h showed a transgranular fracture mode. However, the samples aged at 500 °C for 0.5 h revealed a mixture fracture mode of transgranular and intergranular. The formed cracks on the outer surface of the fatigue samples were found to propagate through the β-grains connecting the primary α-particles existing at the β-grain boundaries.

Mechanical characterization of cp-Ti produced by investment casting

The influence of hot swaging（SW） and annealing treatment on microstructure and mechanical properties of commercially pure titanium produced by investment casting was evaluated.The as-cast samples showed a typical microstructure consisting of a variety of α-morphologies,while the hot swaged samples exhibited a kinked lamellar microstructure.Annealing at 500 °C did not significantly change this microstructure while annealing at 700 and 870 °C led to recrystallization and formation of equiaxed microstructures.The cast bars exhibited a typical hard α-layer in near-surface regions with a maximum depth and maximum hardness of 720 μm and HV0.5 660,respectively.Due to SW,the tensile strength of the as-cast material drastically increased from 605 MPa to 895 MPa.Annealing at 500 °C decreased the tensile strength slightly from 895 to 865 MPa while annealing at 700 °C led to a further pronounced drop in tensile strength from 865 to 710 MPa.No additional decrease in tensile strength was noticed with increasing the annealing temperature from 700 to 870 °C.The true fracture strain of the as-cast and hot swaged samples was in the range of 0.05 to 0.12,while the annealed samples showed values in the range of 0.25 to 0.53.In addition,the as-cast and hot swaged samples revealed a brittle cleavage fracture surfaces.However,the annealed samples showed a transgranular ductile fracture with formation of dimples.