Hydrogen and vacancy clustering in zirconium

Abstract

The effect of solute hydrogen on the stability of vacancy clusters in hexagonal closed packed zirconium is investigated with an ab initio approach, including contributions of H vibrations. Atomistic simulations within the density functional theory evidence a strong binding of H to small vacancy clusters. The hydrogen effect on large vacancy loops is modeled through its interaction with the stacking faults. A thermodynamic modeling of H segregation on the various faults, relying on ab initio binding energies, shows that these faults are enriched in H, leading to a decrease of the stacking fault energies. This is consistent with the trapping of H by vacancy loops observed experimentally. The stronger trapping, and thus the stronger stabilization, is obtained for vacancy loops lying in the basal planes, i.e. the loops responsible for the breakaway growth observed under high irradiation dose.

Solute strengthening in random alloys

“…(29), as it accounts for the exact misfitting displacement along glide direction instead of having an abrupt Heaviside function. On the other hand, inclusion of the interaction of solutes located in planes farther away from the glide plane is less obvious within this approach and would require additional modeling [76,79]. To conclude, simplified models to account for both elastic long-range effects and chemical-specific short-range interactions within the dislocation core allows us to tackle and understand the possible consequences of including core interactions, compared to the purely elastic case: (i) variation of w c with the solute type (seen in Al alloys [17], although changes are very weak), and (ii) strengthening/softening compared to the simplified misfit volume interaction model.…”

“…Note that interactions of substitutional solutes in planes farther away from the stacking fault can exists [37] and can be included in Eq. (29) by considering j = ±2, 3, .... Interstitial solutes and/or multiple solute sites not related by symmetry [76,77] are also straightforward to consider. However, in such cases, and even when considering only the two planes adjacent to the stacking fault energy, the Heavyside function may require some smoothing to avoid an abrupt transition in the energy contributions versus distance w. This does not change the general conclusions below.…”

“…However, in such cases, and even when considering only the two planes adjacent to the stacking fault energy, the Heavyside function may require some smoothing to avoid an abrupt transition in the energy contributions versus distance w. This does not change the general conclusions below. The solute/stacking fault interactions can be calculated using direct ab initio calculations, that are now routinely done for dilute alloys [76,77,78,79].…”

Взаимное влияние водорода и вакансий в alpha-цирконии на энергетику их взаимодействия с металлом

“…Деградация механических свойств конструкционных материалов, обусловленная водородным охрупчивани-ем [1], стимулирует интенсивные исследования влияния водорода на атомную и электронную структуру метал-лов и сплавов [2][3][4][5][6][7][8][9]. Исследования твердого раствора ниобий−водород методами электронно-позитронной ан-нигиляции, дифракции рентгеновского излучения и про-свечивающей электронной микроскопии [3,4] показали, что растворение водорода способствует образованию ва-кансий с последующим формированием сложных комп-лексов водород-вакансия, структура которых зависит как от концентрации водорода в металле, так и от спосо-ба его введения.…”

“…Исследования твердого раствора ниобий−водород методами электронно-позитронной ан-нигиляции, дифракции рентгеновского излучения и про-свечивающей электронной микроскопии [3,4] показали, что растворение водорода способствует образованию ва-кансий с последующим формированием сложных комп-лексов водород-вакансия, структура которых зависит как от концентрации водорода в металле, так и от спосо-ба его введения. Теоретические исследования металлов с кубической структурой [5][6][7], а также ГПУ металлов Ti [8] и Zr [9] выявили, что наличие водорода и вакансий в решетке металлов приводит к формированию различ-ных комплексов водород−вакансия. Очевидно, что на-копление этих комплексов может явиться дополнитель-ным фактором водородного охрупчивания материалов.…”