Abstract Control of discontinuous and continuous precipitation of L12-ordered γʹ precipitates is crucial for tailoring microstructure and mechanical properties of coherent precipitation-strengthened high-entropy alloys (HEAs). In this study, we show that the appropriate addition of Nb not only suppresses discontinuous γʹ precipitation through grain boundary segregation but also promotes continuous γʹ precipitation through nanoscale solute partitioning, leading to substantially improved mechanical properties of the HEAs. Specifically, we explore the effects of Nb on the discontinuous and continuous precipitation microstructures, grain boundary segregation, and mechanical properties of (CoCrFeNi)94-xAl3Ti3Nbx (x = 0, 0.4, 0.8, 1.6, and 2.3 at.%) HEAs. Atom probe tomography reveals that Nb exhibits preferential segregation at grain boundaries of HEAs, which substantially inhibits the grain boundary precipitation and migration due to the reduction of grain boundary energy and solute drag effect, thereby suppressing discontinuous γʹ precipitation at the grain boundaries. Moreover, Nb partitions to the continuous γʹ nanoparticles in grain interiors, which leads to a high chemical driving force for continuous γʹ precipitation. Because of these beneficial effects, Nb-modified HEAs with a uniform distribution of γʹ nanoparticles throughout the matrix were developed, and the correlation between the precipitate microstructure and mechanical properties of these HEAs is discussed.

中文翻译：

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通过纳米级 Nb 偏析和分配控制 γʹ-强化高熵合金的不连续和连续析出

摘要 控制 L12 有序 γʹ 析出相的不连续和连续析出对于调整相干析出强化高熵合金 (HEAs) 的显微组织和力学性能至关重要。在本研究中，我们表明，适当添加 Nb 不仅通过晶界偏析抑制不连续的 γʹ 沉淀，而且通过纳米级溶质分配促进 γʹ 连续沉淀，从而显着改善 HEAs 的机械性能。具体而言，我们探讨了 Nb 对 (CoCrFeNi)94-xAl3Ti3Nbx（x = 0、0.4、0.8、1.6 和 2.3 at.%）HEAs 的不连续和连续沉淀显微组织、晶界偏析和机械性能的影响。原子探针断层扫描显示 Nb 在 HEAs 的晶界处表现出优先偏析，由于晶界能量的降低和溶质拖曳效应，大大抑制了晶界的析出和迁移，从而抑制了晶界处不连续的γ′沉淀析出。此外，Nb 分配到晶粒内部的连续 γʹ 纳米粒子，这导致连续 γʹ 沉淀的高化学驱动力。由于这些有益效果，开发了 γʹ 纳米粒子在整个基体中均匀分布的 Nb 改性 HEA，并讨论了这些 HEA 的析出物微观结构与机械性能之间的相关性。此外，Nb 分配到晶粒内部的连续 γʹ 纳米粒子，这导致连续 γʹ 沉淀的高化学驱动力。由于这些有益效果，开发了 γʹ 纳米粒子在整个基体中均匀分布的 Nb 改性 HEA，并讨论了这些 HEA 的析出物微观结构与机械性能之间的相关性。此外，Nb 分配到晶粒内部的连续 γʹ 纳米粒子，这导致连续 γʹ 沉淀的高化学驱动力。由于这些有益效果，开发了 γʹ 纳米粒子在整个基体中均匀分布的 Nb 改性 HEA，并讨论了这些 HEA 的析出物微观结构与机械性能之间的相关性。