Investigation of the yield region of concentrated Cu-Ge and Cu-Zn single crystals—II. Active slip volume, contribution to the flow stress and obstacle characteristics

Abstract

The measurements of the CRSS τ and of formation times t B of slip bands for Cu-30% Zn and Cu-3.8…7.3% Ge single crystals reported in part I are evaluated regarding the active slip volume V a and the obstacle characteristics (obstacle height ΔG 0, areal density N 2, activation volume V) for thermal activated dislocation motion (temperature T = 105–400 K, deformation rate i = 2.3 × 10 −4–1.8 × 10 −1 mm/s). The dependencies of V a on i, T, and alloy concentration c are discussed; the mean velocity of dislocation groups is estimated to about 10 −4–10 −2 cm/s for the above i-range ( T = 300 K, Cu-30% Zn). The obstacle characteristics determined by thermal activation analysis using two different interaction potentials are compared and confirm that 1. (i) groups of solute atoms act as effective obstacles, 2. (ii) a spectrum of obstacle sizes exists and 3. (iii) a considerable part of the external flow stress τ is due to an athermal contribution τ μ [≲ 75% of τ(400 K.)]. Similar obstacle characteristics are found from comparison with various theories of solid solution hardening.