Fatigue Resistance of the Sheets of Heat-Resistant Titanium Alloys

Abstract

The results of a study of the resistance to fatigue fracture of the sheets made of the heat-resistant titanium alloys VT18U (Ti–6.5Al–4.3Zr–2.4Sn–0.8Nb–0.7Mo–0.1Si, wt %), VT8 (Ti–6.4Al–3.4Mo–0.3Si, wt %), and VT25U (Ti–6.51Al–3.76Zr–1.71Sn–3.94Mo–0.5W–0.13Si, wt %) have been presented. Fatigue curves have been obtained in the initial state and in the oxidized one after isothermal annealing at a temperature of 560°C for 1000 h in air. It has been established that after annealing, the fatigue resistance of all oxidized alloys in the low-cycle region decreases by an order of magnitude. The fatigue limit of the oxidized alloys VT18U and VT25U does not change and is of about 320 MPa. The high-cycle fatigue limit of the VT8 alloy decreases from 300 MPa in the initial state to 230 MPa in the oxidized state. It has been established that after annealing, the phase composition of an oxide of 250 nm in thickness on the surface of the alloys is different and contains the phases of anatase and rutile for the VT18U and VT25U alloys and contains predominantly rutile for the VT8 alloys, which is why the fatigue limit of the oxidized alloys differs.