Phase-Field Simulation of δ Hydride Precipitation with Interfacial Anisotropy

Previous studies of delta hydride in zirconium alloys have mainly assumed an isotropic interface. In practice, the difference in crystal structure at the interface between the matrix phase and the precipitate phase results in an anisotropic interface. With the purpose of probing the real evolution of delta hydrides, this paper couples an anisotropy function in the interfacial energy and interfacial mobility. The influence of anisotropic interfacial energy and interfacial mobility on the morphology of delta hydride precipitation was investigated using the phase-field method. The results show that the isotropy hydride precipitates a slate-like morphology, and the anisotropic 8 hydride precipitates at the semi-coherent and non-coherent interfaces exhibited parallelogram-like and needle-like, which is consistent with the actual experimental morphology. Compared with the coherent interface, the semi-coherent or non-coherent interface adjusts the lattice mismatch, resulting in lower gradient energy that is more consistent with the true interfacial state. Simultaneously, an important chain of relationships is proposed, in the range of I-x < I-y < 1.5I(x)(I-y < I-x or I-y > 1.5I(x)), with the increase of the anisotropic mobility I-y in the y-axis, the gradient energy increases (decreases), the tendency of the non-coherent (semi-coherent) relationship at the interface, and the precipitation rate of hydride decreases (increases). Furthermore, the inhomogeneous stress distribution around the hydride leads to a localized enrichment of the hydrogen concentration, producing a hydride tip. The study of interfacial anisotropy is informative for future studies of delta hydride precipitation orientation and properties.