2021 Volume 70 Issue 2 Pages 111-117
The low cycle fatigue (LCF) properties of the TiAl alloy Ti-43Al-5V-4Nb (at.%) with triplex microstructure have been investigated. The LCF tests were conducted at room temperature, 600 °C and 760 °C. The result shows that test temperature has a small influence on the LCF life evaluated by the total strain range. On the contrast, the LCF life evaluated by stress range had a good correlation with ultimate tensile strength at each temperature. Though the elongation at 760 °C was relatively ductile, the material parameter of Coffin’s low fitted to experimental data means brittle fracture. In TiAl alloys, the brittle-to-ductile transition temperature which is around 700 °C is also affected by strain rate. Therefore the difference of strain rate between tensile tests and LCF tests may result in the brittle fracture. The fracture mode was brittle irrespectively of test temperature. The fatigue crack at room temperature was initiated in the globular γ phase. On the other hand, at the temperature of 600 °C, straight fatigue crack was initiated at β phase. This suggested that the oxidation of β phase decreased the LCF life in high temperature.
