Fatigue Crack Propagation Behavior of an Inertia Friction Welded α/β Titanium Alloy

The inertia friction welding process is being extensively investigated for the joining of high strength titanium alloys for aerospace applications. Although it offers solid state joining, the thermal cycle and deformation involved results in microstructural inhomogeneity across the weld interface. In this paper, the fatigue crack propagation behavior in an inertia welded microstructure in a high strength, high temperature α/β titanium alloy is considered. The fatigue crack propagation behavior in corner notched weld specimens at varying stress ratios is studied at room and elevated temperatures and compared with that of the parent material. Fatigue crack growth rates at lower stress intensity ranges are comparable with those in the parent material. However, in weld specimens tested at room temperature, unstable crack growth occurs at lower stress intensity range values compared to that at high temperature. Fracture surface observations show that this difference is related to a change in fracture mode from transgranular to intergranular/mixed mode during room temperature tests. This change in fatigue crack growth mechanism is deduced to be due to low ductility intergranular failure of grain boundary α in the refined transformed beta microstructure across the weld interface.