Mechanical properties of zirconium alloys and zirconium hydrides predicted from density functional perturbation theory.

The elastic properties and mechanical stability of zirconium alloys and zirconium hydrides have been investigated within the framework of density functional perturbation theory. Results show that the lowest-energy cubic Pn (3) over barm polymorph of delta-ZrH1.5 does not satisfy all the Born requirements for mechanical stability, unlike its nearly degenerate tetragonal P4(2)/mcm polymorph. Elastic moduli predicted with the Voigt-Reuss-Hill approximations suggest that mechanical stability of alpha-Zr, Zr-alloy and Zr-hydride poly-crystalline aggregates is limited by the shear modulus. According to both Pugh's and Poisson's ratios, alpha-Zr, Zr-alloy and Zr-hydride polycrystalline aggregates can be considered ductile. The Debye temperatures predicted for gamma-ZrH, delta-ZrH1.5 and epsilon-ZrH2 are theta(D) = 299.7, 415.6 and 356.9 K, respectively, while theta(D) = 273.6, 284.2, 264.1 and 257.1 K for the alpha-Zr, Zry-4, ZIRLO and M5 matrices, i.e. suggesting that Zry-4 possesses the highest micro-hardness among Zr matrices.