High temperature deformation behaviour of Haynes 188 alloy subjected to high strain rate loading

Abstract

The high temperature deformation behaviour of Haynes 188 alloy is investigated by means of a compressive split-Hopkinson pressure bar system at temperatures ranging from 25 to 800°C and strain rates in the range of 1×103–5×103s−1. It is found that the stress–strain curves obtained under high temperature conditions exhibit a flow softening effect. The maximum activation energy has a value of 51kJ/mol and occurs at a temperature of 800°C under a true strain of 0.3 and a strain rate of 1×103s−1. The Zerilli–Armstrong fcc model is shown to provide an adequate description of the stress–strain response of the Haynes 188 alloy specimens under the considered strains, strain rates and temperatures. An adiabatic shear band is formed in the specimen tested at room temperature under a strain rate of 5×103s−1. The dislocation density increases with an increasing strain rate or a decreasing temperature and leads to a greater flow stress. A linear correlation is observed between the square root of the dislocation density and the true stress. The dislocation hardening relation has the form σ=σ0+α1Gbρ, where α1 has a value of 0.58 for the present Haynes 188 alloy specimens.