On the role of effective temperature and dislocation microstructures on the mechanochemical effect in corrosion cracking

Abstract

In this paper, we bring together the mechanochemical effect in corrosion cracking with the thermodynamic theory of plasticity. The incorporation of effective temperature (or its dual variable — the configurational entropy of dislocations), which has been previously overlooked in the modelling, enables the derivation of thermodynamically consistent formulations for both the chemical potential of dislocations and the mechanochemical effect. This approach enables consideration of the influence of different dislocation distributions. If the change in effective temperature (quantifying the configurational disorder of dislocations) is ignored, the formulation of the mechanochemical effect simplifies to the widely-used model proposed by Gutman (1994). The key quantities to evaluate the mechanochemical effect can be obtained within the framework of thermodynamic dislocation theory (TDT); using a few physical parameters extracted from plane strain testing at different strain rates, numerical simulations have been conducted and compared with experimental results for 316L stainless steel, showing good agreement with both stress–strain mechanical and corrosion current density tests. In this study, rather than being used to pass parameters into the corrosion model, the mechanical response is employed to validate the model’s ability to capture the coupled mechanochemical behaviour. Furthermore, different heterogeneous dislocation microstructures are constructed to examine their effect on the mechanochemical behaviour. It is found that, despite producing similar hydrostatic stresses, the mechanochemical effect varies depending on the underlying microstructural configuration, which demonstrates the importance of incorporating dislocation distributions into models of stress corrosion cracking.