The Structure Stability And Elastic Properties Of Low Elastic Modulus Ti Alloys From First-principles

Ti alloys have been widely applied to the aviation industry and medicinal plant field due to their excellent mechanical properties, biocompatibility and shape memory properties. Therefore, developing new β-type Ti alloys with high strength and low elastic modulus has been one of the most important aspect in research. In this thsis, the structures properties, pahse stability, elastic properties and crystal lattice vibration properties of β, a" and ω phase in Ti-Nb, Ti-Mo and Ti-Ta binary alloys were investigated by the calculation from first-principles.Firstly, the calculation of cohesive energy showed that with the increase of alloying elements Mo, Nb and Ta contents, the phase stability increased. The stability in descending order is:Mo>Nb>Ta.Besides, the phonon calculation showed that Ti-Mo alloys were stable in Mo content at 50 at.%, for Ti-Nb alloys that was in 75 at.%, but it was unstable for Ti-Ta even in 75 at.%. However, it was stable for a" and ω phase in Ti-25at.%Nb binary alloys.Density of states (DOS) calculation for Ti-Nb, Ti-Mo and Ti-Ta binary alloys showed that the total DOS of β, a" and co phase mostly came from d electron orbital, and with increased content of alloying elements, Ti alloys were more stable.Elastic properties calculations showed that with the increase of Nb, Mo and Ta content of alloying elements, C11-C12 increased in P-type binary titanium alloy, and that meant more stable. The Young’s moludus of the Ti binary alloys have the minimum valus in the vicinity of TM=25at.%. We found that the value of C11-C12 becomes nearly zero with the valence electron number e/a=4.10 for Ti-Nb, e/a=4.16 for Ti-Mo and e/a=4.11 for Ti-Ta.The calculation of Ti-15Nbat.%-xSn Ternary alloys showed that with the increase of Sn, the lattice parameters increased linearly, and the stability of P phase increased.