Length scales and scale-free dynamics of dislocations in dense solid solutions

Abstract

The fundamental interactions between an edge dislocation and a random solid solution are studied by analyzing dislocation line roughness profiles obtained from molecular dynamics simulations of Fe0.70Ni0.11Cr0.19 over a range of stresses and temperatures. These roughness profiles reveal the hallmark features of a depinning transition. Namely, below a temperature-dependent critical stress, the dislocation line exhibits roughness in two different length scale regimes which are divided by a so-called correlation length. This correlation length increases with applied stress and at the critical stress (depinning transition or yield stress) formally goes to infinity. Above the critical stress, the line roughness profile converges to that of a random noise field. Motivated by these results, a physical model is developed based on the notion of coherent line bowing over all length scales below the correlation length. Above the correlation length, the solute field prohibits such coherent line bow outs. Using this model, we identify potential gaps in existing theories of solid solution strengthening and show that recent observations of length-dependent dislocation mobilities can be rationalized.

Microelasticity model of random alloys. Part II: displacement and stress correlations

“…It will allow to assess the influence of stress correlations on the dislocation roughness (i.e. the shape of the dislocation line) and to clarify recent results obtained with atomistic calculations [53] and continuous modeling [35]. More importantly, it will allow to investigate the solid solution strengthening in concentrated alloys by estimating the critical stress to unpin a dislocation from the underlying correlated stress.…”

Edge dislocations in multi-component solid solution alloys: Beyond traditional elastic depinning

“…Traditional elastic depinning theory [9,10] has been long thought to be the core basis of the description of the behavior of single dislocations in general disordered environments [10][11][12], and more specifically in solid solutions [13,14] where chemical disorder proliferates. The key prediction of such elastic depinning theories is the onset of a characteristic length scale, the dislocation correlation length ξ, below which the dislocation line displays fractal characteristics with non-trivial roughness.…”

“…The choices of the studied materials are motivated by prior studies that provided benchmarks for traditional depinning behavior (Fe 0.7 Ni 0.11 Cr 0.19 [13], FeNi [14]), and also by motivating experimental findings on equiatomic multicomponent alloys (CrCoNi, CrMnCoNi, CrFeCoNi, CrMnFeCoNi, Fe 0.4 Mn 0.27 Ni 0.26 Co 0.05 Cr 0.02 ) that point towards exceptional strength [17][18][19][20][21]. Equiatomic fcc HEAs with low stacking fault energy showed an excellent balance between strength and ductility, particularly at cryogenic temperatures [3,4].…”

“…Our focus is the depinning behavior of a model configuration of single edge dislocations under shear stress that drive ideal dislocation glide at the low temperature of 5K. MD simulations can successfully describe the complicated interaction between stacking faults and chemical disorder during loading, at the atomic scale [13,14]. There are several MD based studies that explained the core structure of dislocations as well as the interaction of dislocations with solutes in fcc traditional alloys [13,14,24].…”

“…MD simulations can successfully describe the complicated interaction between stacking faults and chemical disorder during loading, at the atomic scale [13,14]. There are several MD based studies that explained the core structure of dislocations as well as the interaction of dislocations with solutes in fcc traditional alloys [13,14,24]. Consistently with these prior studies, our simulations are characterized by a simulation cell with fcc crystal and random distribution of constituent elements, created along X = [110](l x = 252 Å), Y = [ 111](l y = 122 Å), and Z = [1 12](l z = 2002 Å) containing 5,432,700 atoms (see Fig.…”