The role of competing mechanisms in the fatigue life variability of a nearly fully-lamellar ?-TiAl based alloy

Abstract The influence of competing mechanisms on the fatigue life behavior of a γ-TiAl based alloy was studied at room temperature and 600 °C. The alloy exhibited almost flat stress–life ( S–N ) behavior at both temperatures. This type of behavior was found to result from variability in life due to a probabilistic selection between two mechanisms, viz. failure by surface crack nucleation and that by subsurface crack nucleation. It is suggested that the S–N behavior of the alloy is actually composed of dual curves, over the same range of stresses, corresponding to each mechanism. This improved description of the S–N behavior (in terms of dual curves) of the alloy led to a significant reduction in the apparent uncertainty in life.