The effect of room temperature deformation on the yield stress anomaly in Ni₃(AlHf) B

Abstract

This paper describes results on the variation with temperature T ₂ of the flow stress τ_yp(T ₂) in the yield stress anomaly regime of single crystals of Ni₃(AlHf)B, prestrained at T ₁ (mainly room temperature), where T ₂ > T ₁. The results are discussed in terms of a model in which the stress to operate Frank-Read sources is rate controlling. Workhardening is assumed to increase this stress, but not τ_s(T), the stress required to propagate screw dislocations dynamically through the crystal. In the temperature range T ₁ to T _2C, at which τ_yp(T _2C) equals the yield stress τ_y(T _2C) of the virgin crystal, τ_yp(T _2C) increases more slowly with increasing temperature T ₂ than τ_y(T ₂). In this range, the flow stress is thought to be controlled by the stress required to operate at T ₂ dislocation sources workhardened at T ₁ For T >T _2C, τ_yp(T ₂) is of the same order as or slightly less than τ_y ,(T ₂). In this range of temperatures, the yield stress is thought to be controlled by τ_s(T). For large prestresses at T₁, the yield stress anomaly effectively disappears. At high prestresses and temperatures, recovery effects become significant.