Yang Xiaolan, Shang Jiaxiang
School of Materials Science and Engineering, Beihang University, Beijing 100191, China.
School of Physics and Electronic Science, Zunyi Normal College, Zunyi 563006, China.
ACS Omega. 2021 Aug 19;6(34):22033-22038. doi: 10.1021/acsomega.1c02601. eCollection 2021 Aug 31.
The effect of Nb on the crystal structures and electronic mechanism of martensitic transformation in NiTi Nb alloys is investigated by first principles. The lattice parameters, the formation energy, the middle eigenvalue of the transformation stretch tensor (λ), and the energy difference between the parent and martensite (Δ) as a function of Nb content ( = 0, 2.08, 6.25, 8.33, 10.42, 12.5, 18.75) are calculated. Lattice parameters increase with the increase of Nb content. The formation energies of the parent B2 phase, martensite orthorhombic B19, and monoclinic B19' increase with the increase of Nb content. It is also found that at ≤10.42 at. % Nb, the martensite stable phase is monoclinic structure B19'; at >10.42 at. % Nb, the orthorhombic crystal structure B19 is formed. The energy difference between the parent and martensite means that the transformation temperature decreases with increasing Nb concentration at Nb ≤ 10.42 at. % and increases at >10.42 at. % Nb. The λ of the NiTiNb alloys have the same value of about 0.95 with low Nb content. Furthermore, the electronic structure mechanisms behind the martensitic transformations are discussed in detail based on the density of states.
通过第一性原理研究了铌（Nb）对NiTi Nb合金马氏体相变晶体结构和电子机制的影响。计算了晶格参数、形成能、相变拉伸张量的中间本征值（λ）以及母相和马氏体之间的能量差（Δ）随铌含量（= 0、2.08、6.25、8.33、10.42、12.5、18.75）的变化关系。晶格参数随铌含量的增加而增大。母相B2相、马氏体正交B19相和单斜B19'相的形成能随铌含量的增加而增大。还发现，当铌含量≤10.42原子百分比时，马氏体稳定相为单斜结构B19'；当铌含量>10.42原子百分比时，形成正交晶体结构B19。母相和马氏体之间的能量差意味着，在铌含量≤10.42原子百分比时，相变温度随铌浓度的增加而降低，而在铌含量>10.42原子百分比时则升高。低铌含量时，NiTiNb合金的λ值约为0.95。此外，基于态密度详细讨论了马氏体相变背后的电子结构机制。
