Primary damage production in the presence of extended defects and growth of vacancy-type dislocation loops in hcp zirconium

Abstract

Production rates in long-term predictive radiation damage accumulation models are generally considered independent of the material's microstructure for reactor components. In this study, the effect of pre-existing microstructural elements on primary damage production in α-Zr -and vice-versa-is assessed by molecular dynamics (MD) simulations. -type dislocation loops, -component dislocation loops and a tilt grain boundary (GB) were considered. Primary damage production is reduced in the presence of all these microstructural elements, and clustering behavior is dependent on the microstructure. Collision cascades do not cause -type loop growth or shrinkage, but they cause -component loop shrinkage. Cascades in the presence of the GBs produce more vacancies than interstitials. This result, as well as other theoretical, MD and experimental evidence, confirm that vacancy loops will grow in the vacancy supersaturated environment near GBs. Distinct temperature-dependent growth regimes are identified.Also, MD reveals cascade-induced events where -type vacancy loops are absorbed by GBs. Fe segregation at the loops inhibits this cascade-induced absorption.

Two-dimensional vacancy platelets as precursors for basal dislocation loops in hexagonal zirconium

“…The number density of dislocation <a> loops is about to 2.6 × 10 15 m −2 at 350 °C and 3.4 × 10 15 m −2 at 400 °C, respectively. The density of vacancy <a> loops at both temperatures is less than 1 × 10 15 m −2 , which are insufficient to produce <c> dislocation loops by mechanism of coalescence and collapse 31 . Notably, profuse tiny <c> dislocation loops were also detected in the sample irradiated at 400 °C, as shown in Fig.…”

“…From atomic-scale modeling, a mechanism for <c> loop generation based on the collapse of irradiation-produced pyramids has been proposed 30 . Unlike the prior proposals, the formation of <c> loops in this case would be independent of the formation of <a> vacancy loops, and would instead require the collapse of a stacking fault pyramid that has grown beyond a critical size [30][31][32] . However, to date, these irradiation-induced pyramidal defects in Zr have not been observed.…”

“…The absence of vacancy <c> loops less than 10 nm on the basal planes and the presence of only interstitial <a> loops on the prismatic plane cannot explain the observed contraction along the c-axis of the irradiation growth phenomenon 1,11 . Being no smaller than 10 nm has suggested that the <c> loops require an incubation period in which point defects must cluster to a critical size before a <c> loop can be produced. The possible mechanisms for <c> loop formation have received much attention, and over the years, several hypotheses have been proposed 5,[29][30][31][32] . The formation of the <c> loops has been associated with the coalescence and subsequent collapse of <a> vacancy dislocation loops 5 .…”

Molecular Dynamics Simulations of Displacement Cascades in BCC-Fe: Effects of Dislocation, Dislocation Loop and Grain Boundary

“…The number of residual point defects was evaluated and compared with that in the pristine material under the same irradiation conditions. Dai et al [14] used molecular dynamics simulations to reveal that the primary damage production was reduced due to the presence of a-type dislocation loops, c-component dislocation loops and a tilt grain boundary. Fu et al [15] found that the residual vacancy number usually exceeded the residual interstitial number when the displacement cascades interacted with straight edge dislocation in tungsten via a molecular dynamics simulation.…”

Recoil energy dependence of primary radiation damage in tungsten from cascade overlap with voids

“…This was later demonstrated using computer simulations of cascade overlap, where the number of new defects was reduced as a consequence of overlap [8] . Since then, simulations of cascade overlap have been carried out in a number of materials, including Ni and Ni-based alloys [9] , Fe and Fe-based alloys [10][11][12] , equiatomic multicomponent alloys [13,14] , Zr [15][16][17] and recently also in In x Ga 1 −x N [18] .…”