In this project, we aim to enhance the mechanical properties of an equiatomic CoCrNi medium-entropy alloy (MEA) by interstitial alloying. Carbon and nitrogen with varying contents have been added into the face-centred cubic structured CoCrNi MEA. The introduction of interstitial atoms results in considerably more pronounced strengthening effect in the MEA compared to that without interstitial addition. The underlying mechanisms are mostly associated with the interactions between interstitials and dislocations.
Equiatomic CoCrNi MEA attracted considerable attention due to its excellent combination of mechanical strength, ductility and fracture toughness. We explore the idea of incorporating additional interstitial elements to further boost its properties. The mechanisms responsible for the strengthening effect are related to the different manner interstitials interact with dislocations, as compared to larger substitutional atoms. While the latter are able to interact only with edge dislocation (due to symmetrical spherical distortion they produce), the interstitials interact with both types of dislocations, i.e. edge and screw dislocations, as a consequence of tetragonal distortion and resulting shear stress. Other phenomena of interstitial atoms presence like the change in stacking fault energy (SFE) may also come into play, changing the way plastic deformation is mediated. Also, the interstitial alloying can significantly alter the recrystallization kinetics according to the fact that the interstitial-free CoCrNi MEA can be fully recrystallized while the interstitial MEA containing 0.5 at. % C retains deformed microstructure after an identical annealing process.
International researcher team presents a novel microstructure design strategy for lean medium-manganese steels with optimized properties in the journal Science
The atomic arrangements in extended planar defects in different types of Laves phases is studied by high-resolution scanning transmission electron microscopy. To understand the role of such defect phases for hydrogen storage, their interaction with hydrogen will be investigated.
Femtosecond laser pulse sequences offer a way to explore the ultrafast dynamics of charge density waves. Designing specific pulse sequences may allow us to guide the system's trajectory through the potential energy surface and achieve precise control over processes at surfaces.