Fatigue behavior of Nb doped titanium aluminides

Tensile fatigue tests at both ambient and high temperatures have been conducted using Nb doped titanium aluminides, and the results have been compared with that of IN718. Fatigue behavior at ambient temperature shows no clear limit stress of fatigue life, which varies from short to more than 10⁵ cycles within the very narrow range of stress amplitude. TEM observations reveal that dislocation structures of fatigued specimens show an inhomogeneous dislocation density at the adjacent grains. In the case of high temperature fatigue tests, the fatigue life increase with decreasing the stress amplitude, the limit stress amplitude of the fatigue life has been determined to be 400 MPa. After the high temperature fatigue tests, TEM observations reveal that specimens show relatively stable dislocation structures which are composed of the dislocation wall, di-pole and polygonization inside the grains.