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Superior high-temperature properties and deformation-induced planar faults in a novel L12-strengthened high-entropy alloy
Acta Materialia ( IF 9.4 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.actamat.2020.02.028
Y.L. Zhao , T. Yang , Y.R. Li , L. Fan , B. Han , Z.B. Jiao , D. Chen , C.T. Liu , J.J. Kai

Abstract We developed a novel high-performance L12-strengthened high-entropy alloy (HEA) in the multicomponent Ni-Co-Fe-Cr-Al-Nb system. The phase transformation, mechanical properties and associated deformation behaviors were systematically investigated through combinational analyses involving the three-dimensional atom probe tomography (3D-APT), transmission electron microscopy (TEM) and first-principles calculations. In contrast to conventional alloys that generally strengthened by Ni3(Al, Ti)-type precipitates, a high density of coherent L12 nanoprecipitates with a new chemical constitution of (Ni, Co, Fe, Cr)3(Al, Nb) can be controllably introduced via elaboratively tuning the content of Al and Nb, resulting in a large lattice misfit of ~0.78% that rarely achieved in previous HEAs. The newly developed (Ni2Co2FeCr)92Al4Nb4 HEA enables excellent tensile properties at a large temperature window from room temperature to 870 °C. More remarkably, an anomalous growth in yield strength can be observed at the temperatures above 600 °C, showing a peak yield stress over 720 MPa when deformed at 760 °C, which surpasses most of the previous L12-strengthened HEAs, as well as the commercial superalloys. Detailed TEM analyses revealed that the multicomponent L12 precipitates are mainly sheared by the super-partial dislocations, forming superlattice intrinsic stacking fault (SISF) loops coupled with antiphase boundaries (APBs). Such an interesting deformation substructure enables sustained work hardening and produces high tensile strengths at the high temperatures. The underlying mechanisms of those SISF loops were carefully discussed, which could be possibly ascribed to the local elemental segregation on the planner faults.

中文翻译:

新型 L12 强化高熵合金的优异高温性能和变形诱导平面断层

摘要 我们在多组分 Ni-Co-Fe-Cr-Al-Nb 系统中开发了一种新型高性能 L12 强化高熵合金 (HEA)。通过涉及三维原子探针断层扫描 (3D-APT)、透射电子显微镜 (TEM) 和第一性原理计算的组合分析,系统地研究了相变、机械性能和相关的变形行为。与通常通过 Ni3(Al, Ti) 型沉淀物强化的传统合金相比,具有 (Ni, Co, Fe, Cr)3(Al, Nb) 新化学成分的高密度相干 L12 纳米沉淀物可以可控通过精心调整 Al 和 Nb 的含量引入,导致约 0.78% 的大晶格失配,这在以前的 HEAs 中很少实现。新开发的 (Ni2Co2FeCr)92Al4Nb4 HEA 在从室温到 870 °C 的大温度范围内具有出色的拉伸性能。更值得注意的是,在高于 600 °C 的温度下可以观察到屈服强度的异常增长,在 760 °C 变形时显示出超过 720 MPa 的峰值屈服应力,这超过了之前大多数 L12 强化的 HEAs,以及商业高温合金。详细的 TEM 分析表明,多组分 L12 析出物主要被超局部位错剪切,形成与反相边界 (APB) 耦合的超晶格本征堆垛层错 (SISF) 环。这种有趣的变形子结构能够实现持续的加工硬化并在高温下产生高拉伸强度。仔细讨论了这些 SISF 循环的潜在机制,
更新日期:2020-04-01
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