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

• Published in: International journal of plasticity Vol. 110; pp. 294 - 305
• Main Authors: Lunev, A.V., Starikov, S.V., Aliev, T.N., Tseplyaev, V.I.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2018
• Subjects: Atomistic simulation; Ceramic material; Dislocations; Numerical algorithms; Atomistic simulation; Ceramic material; Numerical algorithms; Dislocations
• ISSN: 0749-6419; 1879-2154
• DOI: 10.1016/j.ijplas.2018.07.003

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. [Display omitted] •Modes of thermally-activated motion of the ½ {110} screw dislocations are examined.•Self-pinning on cross-kinks limits dislocation glide at T ≥ 1000 K and σ ≤ 1000 MPa.•Partial dissociation (Friedel-Escaig mechanism) is observed at T ≥ 500 K.•½ {110} screw dislocations are faster than ½ {100} edge dislocations at T < 1250 K.•Parameters for the glide velocity function are obtained from fitting to MD data.