Stress-Dependent Elastic Behaviour of a Titanium Alloy at Elevated Temperatures

In this study the influence of stress and temperature on the elastic modulus during fully-reversed low cycle fatigue of the titanium alloy Ti6242 is examined. The change of the elastic properties with stress manifests itself in a crescent-like shaped hysteresis loop of stress vs. plastic strain at very low amplitudes, i.e. below the technical yield stress. A quadratic extension of Hooke’s law with a second constant “k” is applied. The parameters are determined all along the unloading curve in tension and compression. The approach results in the alignment of the hysteresis loop so that they become vertical, i.e. the elastic strain is accurately described. The value and sign of “k” depend on whether the deformation occurs in tension or compression. Like the Young’s modulus E ₀, “k” also depends on temperature. At temperatures up to 550°C the values of “k” in tension and compression do not change during fatigue life. However, at 650°C thermally activated slip processes lead to changes of both, E ₀ and “k”.