About the formation of vacancy clusters in fcc metals: an atomistic approach

Vacancy clusters have a major contribution in multiple mechanisms as oxidation, precipitation and creep and can lead to material premature cracking. It is thus essential to have a deep understanding of the stability of these defects under a wide range of stress and temperature. Multiple factors influence the formation of the clusters, yet the preponderant factor seems to be the presence of a gaseous environment, like H [1,2,3].

For this purpose, we investigate at the atomic-scale the formation of such clusters. Using empirical force fields derived from EAM potentials we show that the interaction between point-defects is very attractive which favor the formation of voids. We found that the absorption of point-defects by the clusters is slightly anisotropic. It occurs at the cluster poles in {100} directions for vacancies and {110} directions for H interstitial atoms. We determine their stable shape for various fcc metals: Al, Pd, Ni, Cu, Au, Ag. Finally, we show that H not only drastically decrease the formation energy and influence the stable shape of the defects but has also an influence in the long range elastic distortion. Hence that have a direct consequence on the interaction between the voids with dislocations and the other material defects and those impact the mechanical properties in term of elastic and plastic behavior [4,5].

[1] L. Clarebrough et al., Acta Metall. 15 (6) (1967)

[2] B. Eyre, J. Phys. F: Met. Phys. 3 (2) (1973)

[3] Y. Fukai (2006) The metal-hydrogen system: basic bulk properties

[4] G. Hachet et al., Acta Mater. 148 (2018) 280-288

[5] K. Arakawa, et al. ISIJ International, 61 (2021) 2305-2307