Dynamic mechanical behaviour and dislocation substructure evolution of Inconel 718 over wide temperature range

A compressive split-Hopkinson pressure bar and transmission electron microscope (TEM) are used to investigate the mechanical behaviour and microstructural evolution of Inconel 718 at strain rates ranging from 1000 to 5000s^-1 and temperatures between -150 and 550°C. The results show that the flow stress increases with an increasing strain rate or a reducing temperature. The strain rate effect is particularly pronounced at strain rates greater than 3000s^-1 and a deformation temperature of -150°C. A significant thermal softening effect occurs at temperatures between -150 and 25°C. The microstructural observations reveal that the strengthening effect in deformed Inconel 718 alloy is a result primarily of dislocation multiplication. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. By contrast, the dislocation cell size decreases with increasing strain rate, but increases with increasing temperature. It is shown that the correlation between the flow stress, the dislocation density and the dislocation cell size is well described by the Bailey-Hirsch constitutive equations.