Observations on the Generality of the Grain-Size Effect on Fatigue Crack Growth in Alpha Plus Beta Titanium Alloys

摘要

Results obtained through analysis of the literature agree with those of our own as regards the effect of grain size (l) on region-II fatigue crack growth rates (da/dN) of alpha + beta titanium alloys in ambient air, viz. that for a given value of stress-intensity range (delta kappa), da/dN decreases as (l) is increased. The analysis indicates that when microstructural modification of a given alloy affects a reduction in da/dN, the reduction appears attributable to an increase in (l); conversely, when microstructural modification fails to affect a significant change in da/dN, the result appears attributable to a negligible change in (l). Comparison of fatigue crack growth behavior at stress-intensity ranges of 15, 21 and 40 MPa square root m indicates a diminution of the grain-size effect with increased delta kappa. As elucidated in terms of the reversed plastic zone size model, diminution of the grain-size effect follows as a consequence of the reduced portion of the structure-sensitive mode of crack growth present as delta kappa is increased.