Thermodynamic analysis on the effect of H in the formation of vacancy clusters in Cu.
ORAL
Abstract
Stress-induced voiding (SIV) is amongst the most commonly reported defects in metallic systems [1]. Supersaturation of vacancies is considered an initial stage of voiding in metals [2]. It is generally known that H promotes the formation of vacancies, thus, it is anticipated that H will play a significant role in voiding phenomena [3, 4]. However, since measuring experimentally the amount of H incorporated in metals remains challenging, a theoretical analysis is needed.
To efficiently describe the effects of H on the mechanical properties of Cu, large-scale simulations are required. In this work, we combined Density Functional Theory (DFT) with Bond Order potentials (BOP) Molecular Dynamics (MD) simulations. Our MD simulations of polycrystalline Cu under tensile strain demonstrated that grain boundaries and triple junctions aggregate high stresses which they release via the emission of twin dislocations. Dislocation analysis showed that the presence of H facilitates the formation of Shockley dislocations close to the grain boundary region, leading to a reduction of the yield strength of the crystal. Using statistical mechanics the equilibrium concentration of vacancy clusters in pure Cu was determined. We determine the synergy effect between H atoms and Cu vacancies. H concentration for up to 100 bar partial pressure values and temperatures close to the melting point of Cu was found to be orders of magnitude lower than the estimated concentration of vacancies. Due to this low H concentration, the synergy effect between H atoms and Cu vacancies was found to be negligible. This synergy effect was significant only for hydrogen partial pressures of 1 GPa or above. Thus, under such conditions, H presence in the grain boundaries is expected to increase locally the concentration of vacancies and facilitate the growth of larger vacancy clusters.
References
[1] Wu, Z. et al. 2008. Microelectronics Reliability, 48(4), pp.578-583.
[2] Zarnas, P.D. et al. 2021. International Journal of Solids and Structures, 213, pp.103-110.
[3] Djukic, M.B. et al. 2019. Engineering Fracture Mechanics, 216, p.106528.
[4] Barrera, O. et al. 2018. Journal of materials science, 53(9), pp.6251-6290.
To efficiently describe the effects of H on the mechanical properties of Cu, large-scale simulations are required. In this work, we combined Density Functional Theory (DFT) with Bond Order potentials (BOP) Molecular Dynamics (MD) simulations. Our MD simulations of polycrystalline Cu under tensile strain demonstrated that grain boundaries and triple junctions aggregate high stresses which they release via the emission of twin dislocations. Dislocation analysis showed that the presence of H facilitates the formation of Shockley dislocations close to the grain boundary region, leading to a reduction of the yield strength of the crystal. Using statistical mechanics the equilibrium concentration of vacancy clusters in pure Cu was determined. We determine the synergy effect between H atoms and Cu vacancies. H concentration for up to 100 bar partial pressure values and temperatures close to the melting point of Cu was found to be orders of magnitude lower than the estimated concentration of vacancies. Due to this low H concentration, the synergy effect between H atoms and Cu vacancies was found to be negligible. This synergy effect was significant only for hydrogen partial pressures of 1 GPa or above. Thus, under such conditions, H presence in the grain boundaries is expected to increase locally the concentration of vacancies and facilitate the growth of larger vacancy clusters.
References
[1] Wu, Z. et al. 2008. Microelectronics Reliability, 48(4), pp.578-583.
[2] Zarnas, P.D. et al. 2021. International Journal of Solids and Structures, 213, pp.103-110.
[3] Djukic, M.B. et al. 2019. Engineering Fracture Mechanics, 216, p.106528.
[4] Barrera, O. et al. 2018. Journal of materials science, 53(9), pp.6251-6290.
–
Presenters
-
Vasileios Fotopoulos
University College London
Authors
-
Vasileios Fotopoulos
University College London
-
Ricardo Grau-Crespo
University of Reading
-
Alexander Shluger
University College London