Distinct Microstructure and Hardness of Zr-2.5Nb Alloy Annealed in Lower and Upper Dual-Phase Regions: the Role Played by Nb

IF 3.3 3区材料科学 Q2 MATERIALS SCIENCE, MULTIDISCIPLINARY

Metals and Materials International Pub Date : 2024-08-20 DOI:10.1007/s12540-024-01788-5

Lan Qi, Linjiang Chai, Tao Yang, Fangli Zhang

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Abstract

A 50%-rolled Zr-2.5Nb alloy sheet was annealed in lower (700 °C) and upper (800 °C) α-Zr + β-Zr dual-phase regions, respectively, followed by water quenching. Microstructural features were meticulously characterized and analyzed using electron channeling contrast imaging and electron backscattering diffraction techniques. After annealing at 700 °C, the alloy obtains a mixed structure of recrystallized α grains and granular β phase, and the preservation of β phase can be associated with the enrichment of Nb. For the 800 °C sample, its microstructure comprises recrystallized α grains and ultrafine plates produced by martensitic transformation. There exist numerous nanotwins inside these martensitic plates, which are related to the Nb-induced reduction of martensite start temperature (M_S). Hardness tests reveal that compared to the as-rolled sample (249.8 ± 11.0 HV), the hardness of the 700 °C sample slightly drops (240.9 ± 6.7 HV) due to increased α-grain sizes and the reduced deformation defects. In contrast, there appears a notable increase in hardness for the 800 °C sample (290.0 ± 5.5 HV), which is attributed to synergistic effects of multiple mechanisms including grain refinement strengthening of martensitic laths, nanotwin boundary strengthening, and solid-solution strengthening.

Graphical Abstract

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在上下双相区退火的 Zr-2.5Nb 合金的不同显微组织和硬度：Nb 的作用

将 50%轧制的 Zr-2.5Nb 合金薄片分别在下部（700 °C）和上部（800 °C）α-Zr + β-Zr 双相区退火，然后进行水淬火。利用电子通道对比成像和电子反向散射衍射技术对微观结构特征进行了细致的表征和分析。在 700 °C 退火后，合金获得了再结晶 α 晶粒和颗粒状 β 相的混合结构，而 β 相的保留可能与 Nb 的富集有关。800 °C 样品的微观结构包括再结晶的 α 晶粒和马氏体转变产生的超细板。这些马氏体板内存在大量纳米细丝，这与铌引起的马氏体起始温度（MS）降低有关。硬度测试表明，与轧制前的样品（249.8 ± 11.0 HV）相比，700 °C 样品的硬度略有下降（240.9 ± 6.7 HV），原因是 α 晶粒尺寸增大，变形缺陷减少。相比之下，800 °C试样的硬度明显提高（290.0 ± 5.5 HV），这归因于多种机制的协同效应，包括马氏体板条的晶粒细化强化、纳米孪晶边界强化和固溶强化。

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来源期刊

Metals and Materials International 工程技术-材料科学：综合

CiteScore

7.10

自引率

8.60%

发文量

197

审稿时长

3.7 months

期刊介绍： Metals and Materials International publishes original papers and occasional critical reviews on all aspects of research and technology in materials engineering: physical metallurgy, materials science, and processing of metals and other materials. Emphasis is placed on those aspects of the science of materials that are concerned with the relationships among the processing, structure and properties (mechanical, chemical, electrical, electrochemical, magnetic and optical) of materials. Aspects of processing include the melting, casting, and fabrication with the thermodynamics, kinetics and modeling.