General statistical mechanics theory for fluctuating dislocation resistances in complex concentrated alloys

Abstract

Dislocations have wavy shapes in solute-solution alloys from solute interactions and thermal agitations at finite temperatures. From dislocation shapes simulated by molecular dynamics at different temperatures, the Fourier harmonics of the dislocation shapes are found to follow two trends: while the energies of long wave-length harmonics obey power-law distribution characteristic of random-walk, self-affine shapes, the energies of short-wavelength harmonics follow an exponential law corresponding to maximum entropy with mean energy $1/\beta =1/{\beta }_T+1/{\beta }_M$$1/\beta =1/{\beta }_T+1/{\beta }_M$ comprising a thermal component $1/{\beta }_T$$1/{\beta }_T$ and a mechanical component $1/{\beta }_M$$1/{\beta }_M$. The mechanical beta ${\beta }_M$${\beta }_M$ is a key indicator for dislocation-solute interactions: Fe₇₀Ni₁₁Cr₁₉ with weak interactions has low and weakly temperature-dependent $1/{\beta }_M$$1/{\beta }_M$; NiCoV with high interactions has high and almost constant $1/{\beta }_M$$1/{\beta }_M$ over a wide temperature range; NiCoCr and NiCoCrFeMn with intermediate interactions have intermediate $1/{\beta }_M$$1/{\beta }_M$ decreasing sharply on increasing temperature as the solutes fail to pin dislocations in wavy and energetic configurations at high temperatures. This work establishes a new theoretical framework to classify solute-solution alloys according to their dislocation-solute interactions and to predict the CRSS required for depinning of edge dislocations at finite temperatures.