Department of Materials Science and Engineering, University of North Texas, Denton, TX, 76191, USA.
Sci Rep. 2017 Jan 17;7:40540. doi: 10.1038/srep40540.
The extraordinary creep-resistance of Mg-Nd-based alloys can be correlated to the formation of nanoscale-platelets of β-MgNd precipitates, that grow along 〈110〉 in bulk hcp-Mg and on dislocation lines. The growth kinetics of β is sluggish even at high temperatures, and presumably occurs via vacancy migration. However, the rationale for the high-temperature stability of precipitate-matrix interfaces and observed growth direction is unknown, and may likely be related to the interfacial structure and excess energy. Therefore, we study two interfaces- {112}/{100} and {111}/{110}- that are commensurate with β/hcp-Mg orientation relationship via first principles calculations. We find that β acquires plate-like morphology to reduce small lattice strain via the formation of energetically favorable {112}/{100} interfaces, and predict that β grows along 〈110〉 on dislocation lines due to the migration of metastable {111}/{110}. Furthermore, electronic charge distribution of the two interfaces studied here indicated that interfacial-energy of coherent precipitates is sensitive to the population of distorted lattice sites, and their spatial extent in the vicinity of interfaces. Our results have implications for alloy design as they suggest that formation of β-like precipitates in the hcp-Mg matrix will require well-bonded coherent interface along precipitate broad-faces, while simultaneously destabilizing other interfaces.
Mg-Nd 基合金的非凡抗蠕变性能可归因于纳米级 β-MgNd 析出物薄片的形成，这些析出物沿 hcp-Mg 的〈110〉方向和位错线上生长。即使在高温下，β 的生长动力学也很缓慢，可能通过空位迁移发生。然而，沉淀-基体界面的高温稳定性和观察到的生长方向的原理尚不清楚，可能与界面结构和过剩能有关。因此，我们通过第一性原理计算研究了与 β/hcp-Mg 取向关系相一致的两个界面{112}/{100}和{111}/{110}。我们发现β通过形成能量有利的{112}/{100}界面来获得板状形态以减小小晶格应变，并预测β由于亚稳{111}/{110}的迁移而沿位错线生长。此外，我们研究的两个界面的电子电荷分布表明，相干沉淀的界面能对畸变晶格位的分布及其在界面附近的空间范围敏感。我们的结果对合金设计具有启示意义，因为它们表明在 hcp-Mg 基体中形成β 样沉淀将需要沉淀宽面具有良好结合的相干界面，同时使其他界面失稳。
