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

The influence of competing mechanisms on the fatigue life behavior of a (gamma)-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.