Influence of ultrasonic vibrations on the phase transformation and strain hardening of a Zr18Nb alloy in tension

It is established that, in tension of specimens of a Zr18Nb alloy in an ultrasonic field, a decrease in the conventional yield strength σ 0.2 caused by the application of ultrasonic deformations ends with increase in their amplitude as a result of hardening by the disperse ω -phase. It is shown that the strain hardening exponent of the quenched alloy ( n = 0.67) is higher than that for materials with a stable bcc lattice ( n = 0.5) and increases both after preliminary drawing (to n = 0.85) and after the action of ultrasonic deformations in tension (to n = 0.93). These effects are caused by the deformation-induced β→ ω transformation and the size and number of ω -precipitates identified by X-ray phase analysis, the results of which correlate with the data of measurements of the electric resistivity. We discuss possible mechanisms of influence of ultrasonic vibrations on the β→ ω transformation and size of the ω -phase. The formation of the large amount of the ultradisperse ω -phase located in slip planes of the bcc lattice (the β -matrix) leads to blocking of dislocation, formation of dislocation pile-ups, and increase in the strain hardening exponent and deformation stresses in tension of specimens.