Dislocation glide in alloys: chemistry/microstructure coupling – DeGAS

The goal of this young researcher project is to study the origin at the atomic scale of interstitial solute effects on mechanical properties in metals and alloys. This requires a coupling between chemistry and microstructure to understand how the dislocations, which are linear defects of the crystalline lattice responsible for the plastic deformation in materials, interact with solute atoms. The research project DeGAS is based on a multiscale approach combining various skills both in experiment, theoretical modeling and atomistic simulations in order to improve our fundamental comprehension of plasticity in alloys. To begin with, the study will focus on carbon in body-centered cubic iron. Recent results based on ab initio electronic structure calculations suggest a strong attraction of carbon solutes with screw dislocation cores inducing a spontaneous reconstruction of the core structure towards a low-energy configuration where, unexpectedly, the dislocation core adopts the hard core configuration, unstable in pure metals. The solute atoms are at the center of regular trigonal prisms formed by the iron atoms inside the dislocation core, a local configuration similar to the building unit of cementite, Fe3C. The proposed approach in this project couples ab initio calculations of interaction energies and energy barriers, a thermodynamic modeling of solutes and kinks, a line-tension description of pinning of dislocations by solutes, as well as the experimental evidence by in-situ straining experiments of dislocation glide mechanisms in the presence of solutes. This experimental part will be completed by the study of segregation on dislocation core by atom probe tomography and by electron energy loss spectroscopy. Then the developed approach will be generalized on the one hand, to other solutes (boron, nitrogen, oxygen) in iron and on the other hand, to carbon in other body-centered cubic metals such as tungsten.