Understanding thermally-activated glide of [formula omitted] screw dislocations in UO2 – A molecular dynamics analysis

Abstract

As shown experimentally, the interplay between screw and edge dislocations in uranium dioxide (UO2) determines the low-temperature plasticity in this material. For the latter, neither the mobility of screw dislocations nor the mechanisms of their glide had been assessed – up until now. It is particularly interesting to evaluate the mobility of 1/2〈110〉{110} screw dislocations, supposedly the least mobile in UO2 due to the allegedly extremely high Peierls barrier of their motion. To address this issue, molecular dynamics simulations of dislocation glide are conducted on Lomonosov/MVS-10P supercomputers with LAMMPS software, and post-processing is done using DXA/OVITO. Under changing temperature and stress, the following variations of thermally-activated glide are found: nucleation and expansion of double kinks, formation and recombination of 1/6〈112〉 Shockley partials, self-pinning and production of debris, formation of sessile 1/3〈111〉 Frank loops. Velocity function of 1/2〈110〉{110} dislocations calculated at temperatures T=500–2000 K and shear stresses σ=10–1000 MPa shows a weak temperature dependence and becomes higher than the velocity of 1/2〈110〉{001} edge dislocations at temperatures T<1250 K.