Fatigue properties of a medium-strength γ-TiAl alloy with different surface conditions

Effects of surface condition on fatigue properties of a medium-strength gamma-TiAl alloy Ti-45Al-5Nb-1W (at%) were investigated. It is found that the maximum stresses of fatigue samples are lower than the yield stresses of the medium-strength gamma-TiAl alloy. Meanwhile, the local plastic deformation is unconspicuous to occur at the crack tip. In this case, the fatigue strength is mainly decided by surface conditions of maximum-stressed surface, but compressive stress and deformation especially resulted from shot peening play an important role in the improvement of the condition fatigue strength. The affecting depth of shot peening is about 250 mu m. As a result, the relatively weak microstructures and phases become the preferential initiation sites and propagation routes. They are observed to be equiaxed gamma grains, B2 + omega grains, and alpha(2)-gamma lamellar interface in soft orientations. The existence of V-notch can significantly reduce the fatigue properties of the samples.