The Change of Yielding Behavior Observed in α Brass Single Crystal by Low Temperature Annealing Treatment

Abstract

In order to clarify the mechanism of anneal-hardening, the change of yielding behavior of tensile prestrained 70/30 brass single crystal was studied. On reloading, after annealing, the yield stress was observed to increase higher than the final flow stress (σ_p) just before unloading, and the yield stress increment (Δσ) ratio (defined as (100Δσ⁄σ_p) showed two maxima against the prestrain values. One of the two maxima was observed in the prestrain range at the initial part of stage 1 hardening (<0.1 in shear strain) and correlated with a simple strain aging mechanism. The other was observed in the prestrain range at the initial part of stage 2 hardening and explained by the characteristics of Lomer-Cottrell sessile dislocation. With increasing the annealing time, these two values showed a single maximum, but if an arbitrary prestrain was taken the ratio (100Δσ⁄σ_p) showed oscillating behaviors against annealing time. Especially at a prestrain of about 0.3 in shear strain the ratio (100Δσ⁄σ_p) showed an under damped oscillation. These behaviors were discussed from the viewpoint of the stability of dislocation structure and the work hardening mechanism.