Abstract Metastable solidification of undercooled Co60Si40 melts was investigated by microstructural studies and in-situ high-energy X-ray diffraction. Five solidification paths were identified. Three of them were observed at low undercoolings, which show uncoupled and coupled growth of stable β-Co2Si and CoSi compounds. The other paths were observed at high undercoolings, which show peritectic and primary crystallization of a metastable Co5Si3 compound. The β-Co2Si and Co5Si3 compounds crystallize into a hexagonal crystal structure and experience solid-state decomposition. Microstructure formation depends on solidification path. The coupled and uncoupled growth of the stable compounds produces a regular lamellar eutectic structure and an anomalous eutectic structure, respectively. The crystallization and solid-state decomposition of the metastable Co5Si3 compound brings about a fine-grained two-phase mixture, which represents another type of anomalous eutectic structure. The results provide proof of two rare mechanisms of anomalous eutectic formation and shed light onto metastable phase relations in the undercooled region of the Co Si system.

中文翻译：

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过共晶 Co 2 Si - CoSi 成分的亚稳态凝固：微观结构研究和原位观察

摘要 通过显微结构研究和原位高能 X 射线衍射研究了过冷 Co60Si40 熔体的亚稳态凝固。确定了五个固化路径。其中三个在低过冷度下观察到，这表明稳定的 β-Co2Si 和 CoSi 化合物的非耦合和耦合生长。在高过冷度下观察到其他路径，显示亚稳态 Co5Si3 化合物的包晶和初级结晶。β-Co2Si 和 Co5Si3 化合物结晶成六方晶体结构并发生固态分解。微观结构的形成取决于凝固路径。稳定化合物的耦合和非耦合生长分别产生规则的层状共晶结构和异常的共晶结构。亚稳态 Co5Si3 化合物的结晶和固相分解产生细晶粒的两相混合物，它代表了另一种异常共晶结构。结果提供了两种罕见的异常共晶形成机制的证据，并揭示了 Co Si 系统过冷区域中的亚稳态相关系。