Abstract In the present work, several long standing issues related to the formation of various carbides and transformation of Nb 2 C→NbC carbide in Nb-1Zr-0.1C alloy have been addressed. For this purpose, samples were processed by two routes. In the first route, as-solidified samples were extruded and recrystallized and in the second route, as-solidified samples were directly heat treated without imparting deformation. By combining detailed diffraction analyses and ab-initio calculations, identity of the Nb 2 C carbides in the as-solidified and extruded samples, among the various reported Nb 2 C crystal structures has been established as an orthorhombic crystal structure (α-Nb 2 C) having Pnma space group. Chemical analyses showed that the Nb 2 C carbides in extruded samples had higher Zr content as compared to the carbides formed in as-solidified samples. Experimental and theoretical results revealed that Zr destabilizes Nb 2 C phase which was shown as a possible reason for the precipitation of a more stable (Nb,Zr)C phase in recrystallized as well as in directly heat treated as-solidified samples. Detailed precession electron diffraction analysis of (Nb,Zr)C particles showed that if the nucleation of precipitates occurs prior to recrystallization and the growth of the precipitates occurs simultaneously with recrystallization, precipitates do not exhibit specific orientation relationship (OR) with the matrix phase. In contrast, if nucleation and growth of precipitates take place after recrystallization or in samples which do not undergo recrystallization, a specific (Baker-Nutting) OR is followed. Finally, by establishing atomic interrelationship by high resolution electron microscopy, the formation mechanisms of (Nb,Zr)C carbides in different morphologies in Nb alloy have been explained.

中文翻译：

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Nb-1Zr-0.1C(wt.%)合金中稳定的NbC碳化物相的形成机制

摘要 在目前的工作中，已经解决了与 Nb-1Zr-0.1C 合金中各种碳化物的形成和 Nb 2 C→NbC 碳化物转变相关的几个长期存在的问题。为此，样品通过两条路线进行处理。在第一条路线中，凝固的样品被挤压和再结晶，在第二条路线中，凝固的样品直接热处理而不产生变形。通过结合详细的衍射分析和 ab-initio 计算，在各种报道的 Nb 2 C 晶体结构中，凝固态和挤压态样品中 Nb 2 C 碳化物的身份已确定为正交晶体结构（α-Nb 2 C ) 具有 Pnma 空间群。化学分析表明，与凝固样品中形成的碳化物相比，挤压样品中的 Nb 2 C 碳化物具有更高的 Zr 含量。实验和理论结果表明，Zr 使 Nb 2 C 相不稳定，这被证明是在再结晶和直接热处理的凝固样品中析出更稳定的 (Nb,Zr)C 相的可能原因。(Nb,Zr)C 颗粒的详细旋进电子衍射分析表明，如果沉淀物的成核发生在再结晶之前，并且沉淀物的生长与再结晶同时发生，则沉淀物与基体相不表现出特定的取向关系 (OR)。相比之下，如果在重结晶后或在未经历重结晶的样品中发生沉淀的成核和生长，则遵循特定的 (Baker-Nutting) OR。最后，通过高分辨率电子显微镜建立原子相互关系，解释了铌合金中不同形貌的 (Nb,Zr)C 碳化物的形成机制。