Phase reversion mediated the dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium-entropy alloy

IF 6.2 2区 材料科学 Q1 MATERIALS SCIENCE, MULTIDISCIPLINARY
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Abstract

An ultra-high strain rate (104 s−1) dynamic plastic deformation treatment at liquid nitrogen temperature (LNT-DPD) followed by annealing is carried out to obtain dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium entropy alloy (MEA). Such extreme loading conditions resulted in extensive phase transformation in this MEA. Subsequent annealing at 650 °C for 1 h further induced reverse phase transformation and partial recrystallization, forming a complex heterogeneous microstructure characterized by nested trimodal grain sizes and partitioned dislocation density. A superior yield strength of ∼800 MPa and a good ductility of ∼40% were simultaneously achieved in this heterogeneous alloy. In order to reveal the effects of grain size and dislocation density distributions on the mechanical property improvements, the underlying deformation mechanisms were systematically discussed. High density of geometrically necessary dislocations (GNDs) would be induced in complex heterogeneous structures during tensile deformation due to strain gradients or partitioning between different regions, which would lead to additional strengthening and work hardening. These results provide a novel approach to overcome the strength-ductility trade-off dilemma for FCC-structured MEAs.

在等熵铬钴镍中熵合金中,相变介导了晶粒尺寸和位错密度的双重异质性
在液氮温度下进行超高应变速率(104 s-1)动态塑性变形处理(LNT-DPD),然后进行退火,以获得等原子铬钴镍中熵合金(MEA)中晶粒尺寸和位错密度的双重异质性。这种极端加载条件导致这种中熵合金发生了广泛的相变。随后在 650 °C 下退火 1 小时,进一步诱导了反向相变和部分再结晶,形成了复杂的异质微观结构,其特点是嵌套的三odal 晶粒尺寸和分割的位错密度。这种异质合金的屈服强度高达 800 兆帕,延展性高达 40%。为了揭示晶粒尺寸和位错密度分布对机械性能改善的影响,系统地讨论了其基本变形机制。在拉伸变形过程中,由于应变梯度或不同区域之间的分割,复杂的异质结构中会诱发高密度的几何必要位错(GND),这将导致额外的强化和加工硬化。这些结果为克服 FCC 结构 MEA 的强度-电导率权衡难题提供了一种新方法。
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来源期刊
Journal of Materials Research and Technology-Jmr&t
Journal of Materials Research and Technology-Jmr&t Materials Science-Metals and Alloys
CiteScore
8.80
自引率
9.40%
发文量
1877
审稿时长
35 days
期刊介绍: The Journal of Materials Research and Technology is a publication of ABM - Brazilian Metallurgical, Materials and Mining Association - and publishes four issues per year also with a free version online (www.jmrt.com.br). The journal provides an international medium for the publication of theoretical and experimental studies related to Metallurgy, Materials and Minerals research and technology. Appropriate submissions to the Journal of Materials Research and Technology should include scientific and/or engineering factors which affect processes and products in the Metallurgy, Materials and Mining areas.
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