Fatigue crack growth thresholds of TiAl alloys

The growth behavior of fatigue cracks in TiAl alloys has been shown to depend on the crack size. Most of the naturally nucleated small fatigue cracks have been found to arrest after nucleation. Only a few do propagate at Delta K levels below the large crack threshold, Delta K-th The objective of this paper is to review the current understanding of this small crack behavior and to explore the validity of the concept of a growth threshold for small cracks, defined in terms of the applied stress range and the crack length at which crack arrest occurs, for treating the growth/no growth of small cracks. Crack growth threshold values for small cracks in TiAl alloys are presented and compared against the large crack value. The possible application of a size-dependent Delta K-th threshold for predicting of fatigue crack growth in TiAl alloys is discussed and evaluated against laboratory data.