npj: 高熵合金—畸变与相变的准确计算

高熵合金具有高强度、高熔点等优异的材料性能，是镍基高温合金的潜在替代品。但是，很多难熔性的高熵合金也面临延展性较低的缺点。对此，人们提出了相变诱导塑性，特别是通过bcc相到六方密堆积（hcp）相的结构转变，改善延展性。利用从头计算方法，可以有效地计算局域晶格畸变和相稳定性，但对于含有大量第4副族元素(Ti、Zr、Hf)的bcc合金而言，低温动力学不稳定性使得从头计算法失效，无法区分结构转变与化学诱导的局域晶格相变所引起的原子位移。

来自德国斯图加特大学材料科学研究所的Yuji Ikeda、荷兰代尔夫特理工大学材料科学与工程系的Konstantin Gubaev和德国马克斯普朗克研究所的Jörg Neugebauer等，针对体心立方无序合金，开发了一种利用对称性分析来检测晶体结构差异的方法，可用于区分bcc 相到ω相的转变和化学诱导的局域晶格畸变。结合从头计算，研究了多种含Ti、 Zr 、Hf元素的耐火高温合金的动力学和热力学相稳定性。他们发现，化学诱导的局域晶格畸变改变了bcc-hcp相平衡时的化学组分，使Ti、 Zr 、Hf元素含量增加，得到的平衡成分与实验报道的结果具有良好的一致性。该工作所介绍的方法将加深对耐热合金力学性能的理解，并对新型高熵合金的设计和应用有很好的指导意义。

该文近期发表于npj Computational Materials 7: 34 (2021)，英文标题与摘要如下，点击https://www.nature.com/articles/s41524-021-00502-y可以自由获取论文PDF。

Chemically induced local lattice distortions versus structural phase transformations in compositionally complex

Yuji Ikeda, Konstantin Gubaev, Jörg Neugebauer , Blazej Grabowski1 ＆ Fritz Körmann

Recent experiments show that the chemical composition of body-centered cubic (bcc) refractory high entropy alloys (HEAs) can be tuned to enable transformation-induced plasticity (TRIP), which significantly improves the ductility of these alloys. This calls for an accurate and efficient method to map the structural stability as a function of composition. A key challenge for atomistic simulations is to separate the structural transformation between the bcc and the ω phases from the intrinsic local lattice distortions in such chemically disordered alloys. To solve this issue, we develop a method that utilizes a symmetry analysis to detect differences in the crystal structures. Utilizing this method in combination with ab initio calculations, we demonstrate that local lattice distortions largely affect the phase stability of Ti–Zr–Hf–Ta and Ti–Zr–Nb–Hf–Ta HEAs. If relaxation effects are properly taken into account, the predicted compositions near the bcc–hcp energetic equilibrium are close to the experimental compositions, for which good strength and ductility due to the TRIP effect are observed.