Plastic instabilities with propagating deformation bands in Cu–Al alloys

Abstract

A multizone laser scanning extensometric technique is used to measure, in parallel with sensitive and rapid stress recording, the sudden strain avalanches and accompanying stress drops during the Portevin–Le Châtelier (PLC) plastic instabilities of type B, which are characterized by jerky propagation in successive short jumps of a deformation band along the specimen axis during deformation with constant strain rate. For the example of Cu–15 at% Al polycrystals the breakaway process for the plastic avalanches is analysed from their strain rate and temperature dependence. It is concluded that local stress concentrations are essential in addition to the dynamic-strain-ageing effect in producing the PLC effect.