Strain and stress: New insights into hydride growth of UNb alloys

To determine the contributions of elastic strain energy to chemical driving force of uranium hydride growth, an elastic fields model was set up by a spherical hydride particle growing at sub-surface of parent metal, which was used to interpret strain energy influence on the evolution of microstructure and kinetics characteristics of the hydride precipitates. The results showed that strain energy during hydride expansile growth in the matrix is considerably different for the three U materials. When hydride grows, the order of the strain energy value is U-5.7%Nb > U > U-2.5%Nb(mass fraction), which indicated that the U-2.5%Nb alloy is the most susceptible to hydrogen corrosion, followed by U, while U-5.7%Nb is the most resistant to hydrogen corrosion basing on reaction activation theory. Agreement of calculated strain energy with experimental results of hydride growth kinetics showed that the model in this work is correct, in which the large strain energy from volume change during hydride growth plays an important role in determination of growth kinetics. In addition to strain energy calculation, the stress distribution associated with hydride precipitate was used to interpret the interaction between hydride pattern and stress. The study provides quantificational evidences to understand the association of strain energy and stress with hydride of metals, which will lead to novel process opportunities.