Microstraining in αCuAl single crystals

Abstract

The early stage of plastic deformation in αCu-Al single crystals has been studied at room temperature using a strain sensitivity of 1 × 10 −6. The stress corresponding to this strain increases from 75 g/mm 2 in a 0.5 at.% Al alloy to 394 g/mm 2 in a 14 at.% Al crystal; the easy glide stresses for the same alloys are 415 and 1550 g/mm 2, respectively. During microstraining, the stress is generally proportional to the square root of the plastic strain. Assuming a dislocation generation mechanism, independent calculations with the microstrain work-hardening behavior and the 1 × 10 −6 “yield stress” give approximately the same value for the unpinned length of dislocation for each alloy. If the pinning is due to forest dislocations, the forest density increases with solute concentration. The barrier density is calculated to be about an order of magnitude smaller than the forest density and this observation is explained with a model given by Meakin and Wilsdorf (formation of Cottrell-Lomer dislocations). Sub-grain boundaries may also be acting as barriers. Slip lines were examined with a light microscope in a 14 at.% Al crystal during various stages of microstraining. The coarse primary and cross slip lines characteristic of easy glide deformation in this “α-brass type” crystal are observed at a stress of about 2 3 the easy glide stress.