A study of δ-hydride precipitation behavior in Zr alloys by phase-field method

A phase-field model combined with CALPHAD thermodynamic database was employed to investigate the microstructure evolution of δ-hydride in Zr alloys during isothermal aging. The results showed that under the elastic strain energy, a small δ-hydride forms a plate-like structure which deviates from the (0001)α base plane 39°. With the δ-hydride growth, the competition between elastic strain energy and interfacial energy gradually reaches a balance. The tilt angle between δ-hydride and the basal plane decreases to ∼15°, which is consistent with experimental results. As the hydrogen content increases, the volume fraction and number density of the δ-hydrides increase, while their size decrease. Increasing temperature results in a decrease in volume fraction and number density of the δ-hydrides, but an increase in their size. As the shear stress around the δ-hydride increases, the hydrogen-depleted region gradually expands from the tips of δ-hydride to the surrounding of the entire δ-hydride. The elastic interaction energy between different δ-hydride variants is the main factor leading to the formation of different stacking structures and coarsening structures in the experimental results.