Dislocation dynamics in Zr-1.6 wt% Cu alloy

A study of dislocation dynamics in Zr-1.6 wt% Cu alloy in the temperature range 77-543 K has been carried out. Owing to the presence of small amounts of retained β phase, the alloy showed ''pseudo yield points'' which made the accurate evaluation of the temperature dependence of yield and flow stresses by the conventional methods difficult. A new test procedure combining stress relaxation and temperature cycling was therefore devised and employed. As in zirconium, the experimental activation enthalpy for deformation at low temperatures was found not to follow the normally expected proportional variation with temperature. The activation free energies evaluated by including correction terms for the entropy of activation (for the case of linear elastic obstacles) and for the variation of the activation length (for the case of inelastic obstacles) also showed non-proportional variation with temperature. Values of mobile dislocation density evaluated from the activation energy values did not show any systematic variation with stress; quite often the values were abnormally high or ridiculously low. Log epsilonsub(p)vs sigma variation during stress relaxation was found to be linear in the temperature range 196-363 K while outside this range the curves had the expected negative curvature. It is concluded that the anomalies arise from the dynamic strain ageing attributable to hydrogen. (auth.)