Cao Peiyu, Tian Fuyang, Wang Yandong
State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, People's Republic of China.
J Phys Condens Matter. 2017 Nov 1;29(43):435703. doi: 10.1088/1361-648X/aa87d3.
Ti-Mo alloys are promising materials for shape memory alloys and biomedical materials. Whereas, the appearance of metastable ω phase can cause embrittlement and destroy the shape memory effect. In order to avoid the ω phase, the effect of Mo on the temperature dependent lattice parameters, phase stability and elastic mechanical properties of β, α, and ω Ti Mo (x = 0-2.0) random alloys was systematically investigated by using the exact muffin-tin orbitals method in combination with the coherent potential approximation. The theoretical predictions for the lattice parameters are in good agreement with the available experiments. Results show that β TiMo can almost transform to ω phase without lattice deformation and volume change, which suggests that the athermal ω phase is easier to precipitate and grow near 4 at.% Mo content in the β Ti Mo alloys. The critical content of Mo for the competed stabilization of β phase at T = 300 K is ~11.2 at.%. Its valence electron concentration of 4.224 is viewed as a necessary criterion for the competed phase stability. The calculations of formation energy are used to explain successfully why the partitioning of Mo can be found in TiMo alloy after annealing. Through the analysis of formation energy, both Mo addition and increasing temperature can stabilize the β phase. The calculated Cauchy pressure, Pugh's ratio, Poisson ratio, and Young's modulus suggests that ω phase is intrinsically brittle and has large Young's modulus compared with β and α phases.
钛钼合金是形状记忆合金和生物医学材料的理想材料。然而，亚稳ω相的出现会导致脆化并破坏形状记忆效应。为了避免ω相的出现，采用精确的 muffin-tin 轨道方法结合相干势近似，系统地研究了钼对β、α和ω TiMo（x = 0 - 2.0）随机合金的温度依赖晶格参数、相稳定性和弹性力学性能的影响。晶格参数的理论预测与现有实验结果吻合良好。结果表明，β TiMo 几乎可以在无晶格变形和体积变化的情况下转变为ω相，这表明在β TiMo 合金中，在钼含量接近 4 at.%时，无热ω相更容易析出和生长。在 T = 300 K 时，β相完全稳定所需的钼临界含量约为 11.2 at.%。其价电子浓度为 4.224 被视为相完全稳定的必要判据。通过对形成能的计算成功地解释了为什么在退火后的 TiMo 合金中会发现钼的偏聚现象。通过对形成能的分析可知，添加钼和升高温度都能使β相稳定。计算得到 的柯西压力、普格比、泊松比和杨氏模量表明，ω相本质上是脆性的，与β相和α相相比具有较大 的杨氏模量。
