Analysis and design of materials and fluids requires understanding of the fundamental relationships between structure, composition, and properties. Dislocations and grain boundaries influence microstructure evolution through the enhancement of diffusion and by facilitating heterogeneous nucleation, where atoms must overcome a potential barrier to enable the early stage of formation of a phase. Adsorption and spinodal decomposition are known precursor states to nucleation and phase transition; however, nucleation remains the less well-understood step in the complete thermodynamic sequence that shapes a microstructure. Here, we report near-atomic-scale observations of a phase transition mechanism that consists in solute adsorption to crystalline defects followed by linear and planar spinodal fluctuations in an Fe-Mn model alloy. These fluctuations provide a pathway for austenite nucleation due to the higher driving force for phase transition in the solute-rich regions. Our observations are supported by thermodynamic calculations, which predict the possibility of spinodal decomposition due to magnetic ordering.

中文翻译：

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在Fe-Mn合金中，通过有限的旋节线波动对晶体缺陷进行相形核。

材料和流体的分析和设计需要了解结构，组成和特性之间的基本关系。位错和晶界通过增强扩散和促进异质成核而影响微观结构的演变，原子必须克服势垒才能形成相的早期阶段。吸附和旋节线分解是成核和相变的已知前体状态。然而，成核在形成微观结构的完整热力学序列中仍然是一个不太容易理解的步骤。在这里，我们报告相变机理的近原子尺度观察结果，该机理包括溶质吸附到晶体缺陷，然后在Fe-Mn模型合金中发生线性和平面的旋节线波动。这些波动为富溶质区域中较高的相变驱动力提供了奥氏体成核的途径。我们的观察得到热力学计算的支持，热力学计算预测了由于磁有序而发生旋节线分解的可能性。