Understanding thermally-activated glide of 1/2〈110〉{110} screw dislocations in UO2 – A molecular dynamics analysis

Abstract As shown experimentally, the interplay between screw and edge dislocations in uranium dioxide (UO 2 ) 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 UO 2 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.