The Transition Between Thermally Activated and Athermal Flow in Polycrystalline Alpha-Zirconium

Abstract

The deformation of α-zirconium has been studied between 375 and 625°C and at strain rates from 5 × 10⁻⁶ to 10⁻¹ s⁻¹ by compression testing. The yield stress at the lower temperatures was relatively insensitive to strain rate and temperature, whereas at the higher temperatures, it was highly sensitive to strain-rate and temperature.

Various mechanisms are considered as being responsible for the athermal range of behaviour and it is concluded that the Orowan stress required to bow out segments of the Frank network is most likely to be controlling in this region. Similar considerations applied to the rate-sensitive range of behaviour suggest that the unpinning of nodes in the dislocation network is ratecontrolling above the transition temperature. In the transition region between the athermal and thermally activated ranges of flow, a maximum in flow stress was observed that is attributed to a dynamic strain-ageing effect caused by the presence of interstitial oxygen.