Cyclic Strength of the Zr–1% Nb Alloy after Equal Channel Angular Pressing

The effect of equal channel angular pressing (ECAP) on the structure, static, and cyclic strength of zirconium alloy E110 (Zr–1% Nb) is studied. The ECAP procedure is applied to samples with a diameter of 20 mm and a length of 100 mm along the BC route with an angle of 110° between the channels in six passes with a stepwise decrease in temperature from 400 to 300°C. A highly inhomogeneous ultrafine-grained microstructure that is comprised of regions filled with cells and fragments with low misorientation and a high density of dislocations and regions with predominantly equiaxial structural units is formed in the alloy after ECAP. As a result of ECAP, the tensile strength of the alloy increases by 40%, the yield point increases by 22%, and the relative elongation decreases by a factor of 2. Equal channel angular pressing leads to a decrease in the endurance fatigue limit based on 107 cycles from 225 to 150 MPa and to a change in the fracture mechanism from a quasi-ductile microgrooved mechanism to a predominantly brittle one with secondary cracking. With high stresses in the cycle (above 280 MPa), the durabilities of the alloy both in the initial state and after ECAP are comparable.