Fatigue and fracture behavior of ultrafine-grained near β titanium alloy produced by radial shear rolling and subsequent aging

The fatigue and fracture behavior of an ultrafine-grained near β Ti-5Al-5V-5Mo-1Cr-1Fe alloy produced by radial shear rolling and subsequent aging was investigated by very high cycle fatigue (VHCF) testing with the stress ratio R = −1. It was shown that the formed structure contributes to a high fatigue strength of the alloy in tests with a stress amplitude of 850 MPa and the number of cycles to failure 2.78 · 107. Fractographic analysis revealed an internal mode of fatigue crack development with ΔK values higher than 27 MPa m1/2. The fatigue crack initiation region was an area about 25 μm in diameter showing the presence of up to 10 μm long microcracks and micron-sized microvoids. The fatigue microcracks initiated at the interfaces between the primary α (α") phase particles and the transformed β matrix. A fatigue fracture model of the ultrafine-grained titanium alloy under VHCF loading was proposed which agrees well with the obtained experimental data.