Influence of the zinc content and pre-cold work on the plastic properties of polycrystalline alpha-brasses

Abstract

The Petch equation σ v = σ 0 + K yl −1 2 , connecting the yield stress σ y, to the grain diameter, l, proved to be valid for polycrystalline alpha-brasses. The stress required to propagate a plastic nucleus across a grain-boundary in a pre-cold worked sample was found to be insensitive to zinc concentrations in the starting range. But in all cases the boundary stiffened when the zinc content increased to approach the beta-brass range. The friction stress, σ 0, increased with zinc content probably due to solution hardening. However, approaching the beta-brass range, σ 0 decreased because of the better accommodation of the zinc atoms in the beta-brass lattice. The work-hardening characteristics of alpha-brasses were also determined by the torsional deformation method of Kovács and Nagy. The rate of change of the microscopic shear strain, γ, characterizing the deformation, with respect to the macroscopic shear strain, θ = ND/ L, was found to be grain-size dependent and fitted the empirical relation (∂γ/∂θ) l,c = α + βƒ(c) · l 1 3 where α and β are constants, and ƒ(c) is some function of zinc content.