Microstructure evolution and mechanical properties of heat treated LCB titanium alloy
(1. Central Metallurgical R&D Institute-CMRDI, P.O. Box 87 Helwan, Cairo, Egypt;
2. TU-Clausthal, IWW, Agricolastr. 6, Clausthal-Zellerfeld, Germany)
2. TU-Clausthal, IWW, Agricolastr. 6, Clausthal-Zellerfeld, Germany)
Abstract: 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.
Key words: beta Ti alloy; Ti-6.6Mo-4.5Fe-1.5Al alloy; fatigue crack; ageing; secondary α; primary α; β-grain; tensile strength; fatigue limit