Effect of local lattice distortion on the core structure of edge dislocation in NbMoTaW multi-principal element alloys and the subsystems

Refractory multi-principal element alloys (MPEAs) have attracted much attention as promising candidate materials for structural applications at elevated temperatures. Several studies have demonstrated that edge dislocation takes an important role in controlling high-temperature strength in refractory MPEAs. Here in order to understand the contribution of edge dislocation to strength, we have studied the effect of local lattice distortion on the core structure of edge dislocation in NbMoTaW MPEAs and the subsystems using atomistic simulations. We found the magnitude of lattice distortion is strongly dependent on the constituent elements and their concentrations. The lattice distortion reaches the maximum at around equiatomic composition. Binary alloys with large atomic size mismatch have a lattice distortion comparable with ternary and quaternary systems. We then have analyzed the core structure of 1/2<111>/{110} edge dislocation in NbMoTaW MPEAs and the subsystems in the framework of Peierls-Nabarro model. The dislocation core half-width decreases with increasing lattice distortion exponentially. As a consequence, the critical shear stress for dislocation motion normalized by shear modulus exhibits a linear increase as the lattice distortion increases. This may help understand the linear correlation of yield strength normalized by Young's modulus with lattice distortion in various refractory MPEAs reported in experiments. Our present work provides insights into the origin of the essential contribution of edge dislocation to strength in refractory compositional complex alloys.