ABSTRACT
We performed atomic-scale ab initio calculations to investigate the stacking fault (SF) properties of the metastable ζ-Zr2H zirconium hydride. The effect of H near the SF was found to entail the existence of negative SF energies, showing that the ζ compound is probably unstable with respect to shearing in the basal plane. The effect of temperature on SFs was investigated by means of free energy calculations in the quasiharmonic approximation. This evidenced unexpectedly large temperature effects, confirming the main conclusions drawn at 0 K, in particular the ζ mechanical instability. The complex behaviour of H atoms during the shear process suggested ζ-hcp â Zr2H[Formula: see text]-fcc as a plausible shear path leading to an fcc compound with same composition as ζ. Finally, as shown by an analysis based on microelasticity, this Zr2H[Formula: see text]-fcc intermediate compound may be relevant for better interpreting the currently intricate issue of hydride habit planes in zirconium.
ABSTRACT
In order to better understand hydride formation in zirconium alloys, heterophase interfaces between α-Zr and γ-ZrH are investigated by means of ab initio atomic-scale simulations of multilayers coupled with continuous elasticity. Our approach allows us to separate out the elastic contribution, leading to basal and prismatic [Formula: see text] interface energies around 200 [Formula: see text] and 750 [Formula: see text] respectively, i.e. values noticeably higher than previously found for coherent particles such as ζ-Zr2H. By considering interfacial changes of H contents, the possibility of competing elasticity and chemistry effects for interface stability is analyzed. The effects of the strong anisotropy evident in [Formula: see text] interface energies on the important practical issue of preferential habit planes are discussed, allowing us to propose a plausible explanation for the experimental results.
