Strengthening mechanism of ω-Zr

The ω-zirconium (ω-Zr) is generally considered as the favorable strengthening phase in the application of Zr and its alloys. However, the intrinsic mechanism is still unclear. In this study, the elastic constants and anisotropic ideal shear strengths of ω-Zr and the common α-Zr phase are systematically studied by the first-principle calculations. Results reveal that the shear modulus of ω-Zr is 1.37 times that of α-Zr. The lowest shear strength of ω-Zr is 3.25 GPa along ( 1 0 1 ¯ 0 ) [ 0 0 0 1 ] , which is about 1.6 times the weakest shear strength (2.01 GPa) of α-Zr along ( 1 0 1 ¯ 0 ) [ 1 ¯ 2 1 ¯ 0 ] . In addition to the high strength, the critical strain of ω-Zr is 0.173, much larger than that (0.072) of α-Zr. The electron localization function (ELF) result shows that there are more electrons highly localized in ω-Zr than in α-Zr along their weakest shear directions, indicating the stronger metallic bonds of ω-Zr as the origin of the high shear strength and strain. In addition, based on the von Mises criteria, the dominating deformation mode for the polycrystalline material of ω-Zr is proposed along the { 1 0 1 ¯ 0 } 〈 0 0 0 1 〉 / { 1 0 1 ¯ 1 ¯ } 〈 1 ¯ 2 1 ¯ 0 〉 or { 1 1 2 ¯ 0 } 〈 0 0 0 1 〉 / { 1 0 1 ¯ 1 ¯ } 〈 1 ¯ 2 1 ¯ 0 slips, which is helpful to the understanding of deformation behavior in polycrystalline ω-Zr.