Abstract The ferritic Fe-Ni-Al-Cr-Mo steel (FBB8) has good creep properties up to 700 °C due to B2-NiAl nanoscale precipitates and its creep resistance can be further improved by additions of 2 or 4 wt.% Ti, as a result of sub-precipitates within the main precipitates. Here, the hierarchical structure of the precipitates is studied in the light of phase separation via transmission electron microscopy (TEM) and atom probe tomography (APT). For FBB8-2Ti (with 2% Ti added) exhibiting B2-NiAl precipitates with L21-Ni2AlTi sub-precipitates, APT analysis shows strong partitioning of Ni, Al and Ti from the ferritic matrix into the B2/L21 precipitates and, within the precipitates, partitioning of Ti and Fe within the L21 sub-precipitates. Based on the published pseudo-binary phase-diagram between (Ni,Fe)Al and (Ni,Fe)Ti, this hierarchical precipitate microstructure is discussed based on the known miscibility gap between the B2 and L21 phases, due to partitioning of Ti into the L21 phase and ordering of Al and Ti on the Al sub-lattice of the B2 structure. For FBB8-4Ti (with 4% Ti added), by contrast, the L21 precipitates exhibit bcc sub-precipitates rich in Fe and Cr, with a composition close to that of the matrix; the absence of the B2 structure is consistent with an increase of Ti and Fe concentrations, to 18.2 and 19.3 at.% respectively, as measured via APT, in the L21 precipitates.

中文翻译：

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Fe-Ni-Al-Cr-Ti铁素体钢分层结构析出物的原子探针断层扫描研究

摘要 由于 B2-NiAl 纳米级析出物，铁素体 Fe-Ni-Al-Cr-Mo 钢 (FBB8) 在高达 700 °C 时具有良好的蠕变性能，通过添加 2 或 4 wt.% Ti 可以进一步提高其抗蠕变性，作为主要沉淀物中的亚沉淀物的结果。在这里，通过透射电子显微镜 (TEM) 和原子探针断层扫描 (APT) 根据相分离研究了沉淀物的分级结构。对于 FBB8-2Ti（添加 2% Ti），B2-NiAl 沉淀物和 L21-Ni2AlTi 亚沉淀物，APT 分析显示 Ni、Al 和 Ti 从铁素体基体强烈分配到 B2/L21 沉淀物中，并在沉淀物中，L21 子沉淀物中 Ti 和 Fe 的分配。基于已发布的 (Ni,Fe)Al 和 (Ni,Fe)Ti 之间的伪二元相图，由于 Ti 分配到 L21 相中以及 Al 和 Ti 在 B2 结构的 Al 亚晶格上的排序，基于 B2 和 L21 相之间已知的混溶间隙讨论了这种分层析出物微观结构。相比之下，对于 FBB8-4Ti（添加 4% Ti），L21 沉淀物表现出富含 Fe 和 Cr 的 bcc 亚沉淀物，其成分接近于基体；B2 结构的缺失与 L21 沉淀物中 Ti 和 Fe 浓度的增加一致，通过 APT 测量分别增加到 18.2 和 19.3 at.%。L21 沉淀物呈现出富含 Fe 和 Cr 的 bcc 亚沉淀物，其成分接近于基体；B2 结构的缺失与 L21 沉淀物中 Ti 和 Fe 浓度的增加一致，通过 APT 测量分别增加到 18.2 和 19.3 at.%。L21 沉淀物呈现出富含 Fe 和 Cr 的 bcc 亚沉淀物，其成分接近于基体；B2 结构的缺失与 L21 沉淀物中 Ti 和 Fe 浓度的增加一致，通过 APT 测量分别增加到 18.2 和 19.3 at.%。