First-principles study of phase stability and elastic properties in metastable Ti-Mo alloys with cluster structure

ABSTRACT

This paper provided a novel approach for evaluating phase stability and elastic properties in metastable Ti–Mo alloys with low Mo content by first-principles combined with cluster structure. In 54-atom body-centered-cubic supercell by substituting Ti atoms with 2–7 Mo atoms (7.1–23.0 wt% Mo), individual cluster structure of β-phase was constructed by ‘-Mo-Ti-Mo-’ cluster unit having the lowest cohesive energy. The distorted supercell was more stable than undistorted one at a low Mo content. With increasing Mo content, the density of state at Fermi level decreased, and bonding electron number increased, indicating β-phase stability was gradually promoted. Tetragonal shear elastic constant (C′ = (C₁₁ – C₁₂)/2), shear modulus (G₁₁₁) and anisotropy factor (A = C₄₄/C′) exhibited a fluctuation with Mo addition, while the change trend of A was opposite to C′ and G₁₁₁. Calculated Young’s modulus exhibited similar changing trend to the C′, implying that the softening of C′ resulted in low Young’s modulus of β-phase. Measured Young’s modulus exhibited significant difference from calculated one, which was mainly caused by formation of α″-martensite and ω-phase. The values of C′, G₁₁₁ and A were considered to associate with not only elastic properties of β-phase itself but also transition from β-phase to α″-martensite and/or ω-phase.

KEYWORDS:

• Metastable Ti–Mo alloys
• cluster structure
• first-principles
• phase stability
• elastic properties

Additional information

Funding

This work was financially supported by the National Natural Science Foundation of China (grant numbers 51471040 and 51771042), and the Fundamental Research Funds for the Central Universities of China (grant number DUT16LAB12).