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

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.