Analysis of temperature and concentration dependence of flow stress in KCl–KBr single crystals with special reference to solute distribution

Abstract

Available data on the temperature and concentration dependence of critical resolved shear stress (CRSS) of KCl–KBr solid-solution crystals containing 9, 17, 27 and 45 mol% KBr in the temperature range 77–230 K have been analyzed within the framework of the kink-pair nucleation model of plastic flow in solid- solution crystals. It is found that CRSS τ decreases with increasing temperature T in accordance with the model relation lnτ = A − BT, where A and B are positive constants. The CRSS τ at a given temperature depends on solute concentration c as τ ∝ c^p , where exponent p has a value between 0.33 and 0.57 as temperature T rises from 0 to 230 K. The model parameter W _o, i.e. binding energy between the edge-dislocation segment L _o involved in the unit activation process and the solute atoms close to it (T → 0 K), which is inversely proportional to B, increases with solute concentration c monotonically as W _o ∝ c ^0.33 up to a critical value c _m = 35 mol% KBr, which is in reasonable agreement with the model prediction W _o ∝ c ^0.25. However, W _o decreases with an increase in c beyond c _m, which indicates somewhat ordered distribution of solute in the host lattice of concentrated KCl–KBr solid solutions with c > c _m.

Acknowledgement

One of us (M. Z. Butt) is grateful to the Pakistan Council for Science and Technology, Government of Pakistan, Islamabad for financial assistance under the Research Productivity Allowance Scheme.