Abstract The low temperature phase (LTP) compound of MnBi is a promising, rare-earth metal free, and permanent magnetic material. However, it is difficult to obtain pure LTP MnBi, which results from a peritectic reaction between Mn and Bi atoms. In this study, the microstructural evolution and phase transformation kinetics of MnxBi100-x (x = 50, 55, 60) alloys were systematically investigated. Choosing an appropriate Mn content (Mn55Bi45) was found to promote the formation of the LTP MnBi. The results of the phase transformation kinetics indicated that the nucleation, growth and soft impingement processes are involved in the phase transformation process. In addition, in the initial stage of the LTP phase transformation, it was shown that the diffusional transformation was governed by two- and three-dimensional nucleation and growth, as well as a single mechanism of diffusion-controlled growth, which describes the entire transformation. At the final stage of the phase transformation, diffusion controlled growth, with soft impingement effects, dominates the process. The phase transformation kinetics analysis was confirmed with the X-ray diffraction and scanning electron microscopy results. This work implies that the local activation energy, Ec(α), and local Avrami exponent, n(α), can be applied to characterize the phase transformation behaviors of the LTP MnBi alloy.

中文翻译：

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MnBi合金的显微组织演变和相变动力学

摘要 MnBi 低温相（LTP）化合物是一种很有前途的无稀土金属的永磁材料。然而，由于Mn和Bi原子之间的包晶反应，很难获得纯LTP MnBi。在这项研究中，系统地研究了 MnxBi100-x (x = 50, 55, 60) 合金的显微组织演变和相变动力学。发现选择合适的 Mn 含量 (Mn55Bi45) 可促进 LTP MnBi 的形成。相变动力学的结果表明，相变过程涉及成核、生长和软碰撞过程。此外，在 LTP 相变的初始阶段，表明扩散转变受二维和三维成核和生长的控制，以及描述整个转变的单一扩散控制生长机制。在相变的最后阶段，具有软冲击效应的扩散控制生长在该过程中占主导地位。X射线衍射和扫描电子显微镜结果证实了相变动力学分析。这项工作意味着局部活化能 Ec(α) 和局部 Avrami 指数 n(α) 可用于表征 LTP MnBi 合金的相变行为。X射线衍射和扫描电子显微镜结果证实了相变动力学分析。这项工作意味着局部活化能 Ec(α) 和局部 Avrami 指数 n(α) 可用于表征 LTP MnBi 合金的相变行为。X射线衍射和扫描电子显微镜结果证实了相变动力学分析。这项工作意味着局部活化能 Ec(α) 和局部 Avrami 指数 n(α) 可用于表征 LTP MnBi 合金的相变行为。