Plastic Flow Behaviour of Inconel 690 Super Alloy Under Compressive Impact Loading

Abstract

This paper studies the dynamic plastic flow behaviour, fracture characteristics, and microstructural evolution of Inconel 690 alloy under impact loading conditions. Compressive impact tests are performed using the compressive split-Hopkinson bar at strain rates ranging from 2.3 × 103 to 8.3 × 103 s−1 at room temperature. The effects of strain rate on the dynamic flow response, work hardening characteristics, strain rate sensitivity, and thermal activation volume are evaluated. A constitutive law based on the Zerilli-Armstrong model is proposed to describe the impact flow behaviour. The relationships between flow stress, dislocation, and twinning are analyzed and discussed in relation to the loading conditions. The evolutions of the dislocation and twinning substructures are investigated using transmission electron microscopy. Damage initiation and the fracture mechanisms are evaluated by scanning electron microscopy. The flow stress-strain response is shown to be significantly dependent on the strain rate, which not only causes obvious changes of the work hardening rate, strain rate sensitivity, and activation volume, but also influences the dislocation tangling and deformation twin substructures. The results indicate that the catastrophic failure at high strain rates results from the formation of localized shear bands. Finally, it is shown that the proposed constitutive law provides accurate predictions of the stress-strain relationship.