LOW TEMPERATURE YIELDING AND FLOW OF POTASSIUM AND ITS ALLOYS

The tensile deformation of a range of potassium-sodium and potassium-rubidium alloys has been examined at temperatures up to 77°K. There is little difference in yield stress at 77°K and 20.3°K, but below this latter temperature the yield stress increases nearly linearly with decrease in temperature. Extrapolation of the yield stress to 0°K shows that up to 0.01 at.% sodium (and for 0.86 at.% rubidium) the yield stress decreases with decrease in purity. The work-hardening coefficient is strongly temperature dependent and the temperature dependence of the flow stress is large. It is suggested that in this region a Peierls force mechanism may be responsible for yielding. Between 0.01 and 1 at.% sodium (and for 9 at.% rubidium) the deformation behaviour is nearly impurity independent. The work hardening rate and the flow stress both change comparatively slowly with temperature. It is suggested that in this region, dislocation-dislocation interactions may control the yielding. Above 1 at.% sodium, the yield stress increases strongly with both impurity and decrease in temperature. The work-hardening rate is independent of both impurity and temperature. It is possible that precipitation has occurred and that yielding is controlled by precipitation-dislocation interactions. © 1969.