Fatigue crack growth in lamellar microstructures of a γ-TiAl based intermetallic alloy

Fatigue crack growth behaviour of a TiAl-based alloy has been studied for lamellar microstructures. It has found here that the fatigue crack growth resistance is improved with reducing lamellae width, but can be degraded with increasing amounts of equiaxed gamma particles within colonies. These phenomena are; explained in terms of the degree and extent of intense plastic deformation occurring at the crack-tip and in terms of local fracture units. All lamellar microstructures studied exhibit a "bilinear" form of fatigue crack growth curves with a "transition point" at which crack growth rates accelerate sharply and changes in fracture mode and local fractographic appearance occur. As cracks encounter more equiaxed gamma grains, the "transition point" becomes less marked, together with reduced differences in microfractographic features between the corresponding regions.