On the Estimation of Thermal Activation Parameters for Portevin–Le Chatelier Effect from Nanoindentation Data

Abstract

The development of methods to ascertain the activation enthalpy, $\Delta E_{\text{a}}$, for Portevin–Le Chatelier (PLC) effect is of interest as it facilitates understanding of the underlying mechanisms and the identification of solute species that age dislocations during deformation. Currently, most models for estimating $\Delta E_{\text{a}}$ are based on the critical strain, $\varepsilon_{\text{c}}$, for the onset of PLC during macroscopic uniaxial tests. However, an $\varepsilon_{\text{c}}$ is not always observed, and some of the models incorporate unverified dependences. In this work, we present a nanoindentation-based approach for estimating $\Delta E_{\text{a}}$ and the activation volume for the phenomenon. The approach is based on a more theoretically sound foundation and obviates the need for $\varepsilon_{\text{c}}$. The derived parameters are in good agreement with reported values for the Al-Mg alloy studied herein. The results are discussed in terms of strain rate, indentation depth, and indenter geometry, and reveal the utility of the technique for investigations of PLC more generally.