■ Title: Severe Lattice Distortion in Medium-entropy FCC Single-phase Alloys
■ Speaker: Prof. Seok Su Sohn (Dept. of MSE, Korea Univ.)
■ Date and time: 5/28(Tue) 16:00
■ Venue: Applied Engineering Building (W1) 1st Floor, Multimedia Lecture Room
■ Host : Prof. Kibum Kang
■ Abstract :
Severe lattice distortion is a core effect in the design of multi-principal element alloys with the aim to enhance yield strength, a key indicator in structural engineering. Yet, the yield strength values of medium- and high-entropy alloys investigated so far do not substantially exceed those of conventional alloys owing to the insufficient utilization of lattice distortion. Here, based on a combined theoretical and experimental approach, I’ll introduce that the degree of lattice distortion is indeed a key parameter in controlling strengthening mechanisms for the design of hitherto unexplored ultrastrong medium-entropy single-phase alloys. Vanadium (V) is exploited as a very efficient element in a disordered VCoNi solid solution alloy. It is demonstrated that a wide fluctuation of the atomic bond distances in such alloys, i.e., severe lattice distortion, improves both yield stress and its sensitivity to grain size. Due to this enhanced Hall-Petch dependency, the VCoNi alloy could present 1.3 GPa of yield strength at 1mm of average grain size. In addition, the dislocation-mediated plasticity effectively enhances the strength–ductility relationship by generating nanosized dislocation substructures due to massive pinning.