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<p>The integrity and performance of Zr-2.5Nb alloy pressure tubes in nuclear reactors are significantly influenced by the behavior of hydrides within the material. A comprehensive understanding of the hydride distribution, orientation relationship, and precipitation mechanism is crucial for predicting and mitigating potential degradation in these critical components. This study presents a multi-scale characterization approach, integrating scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy, to investigate the mesoscale, microscale, and atomic-scale features of hydrides in Zr-2.5Nb alloy pressure tubes. The results reveal that hydrides predominantly form along α/α grain boundaries and α/β phase boundaries, with minimal intragranular presence. Distinct crystallographic orientation relationships between interfacial and intragranular hydrides and the α-Zr matrix are identified. Interfacial hydrides (γ-ZrH, δ-ZrH<sub>1.66</sub>, and ε-ZrH<sub>2</sub>) exhibit a strong hereditary orientation relationship with the α-Zr matrix, characterized by &lt;11<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\bar{2}\)</EquationSource> <EquationSource Format="MATHML"><math> <mover accent="true"> <mrow> <mn>2</mn> </mrow> <mrow> <mo stretchy="false">¯</mo> </mrow> </mover> </math></EquationSource> </InlineEquation>0&gt;<sub>α</sub>//&lt;110&gt;<sub>γ</sub>//&lt;110&gt;<sub>δ</sub>//&lt;111&gt;<sub>ε</sub> and {0001}<sub>α</sub>//{111}<sub>γ</sub>//{111}<sub>δ</sub>//{101}<sub>ε</sub>. Intragranular hydrides maintain the relationship of &lt;11<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\bar{2}\)</EquationSource> <EquationSource Format="MATHML"><math> <mover accent="true"> <mrow> <mn>2</mn> </mrow> <mrow> <mo stretchy="false">¯</mo> </mrow> </mover> </math></EquationSource> </InlineEquation>0&gt;<sub>α</sub>//&lt;110&gt;<sub>γ</sub>//&lt;110&gt;<sub>δ</sub>//&lt;110&gt;<sub>ε</sub> and {0001}<sub>α</sub>//{200}<sub>γ</sub>//{200}<sub>δ</sub>//{200}<sub>ε</sub>. High-resolution transmission electron microscopy observations uncovered a continuous slip of Shockley partial dislocations within the α-matrix, originating from 60° mixed-type &lt;a&gt; perfect dislocations on each basal plane. This slip, coupled with an atomic shuffle mechanism, facilitates the B-type phase transition, leading to the precipitation of δ-ZrH<sub>1.66</sub> with a face-centered cubic structure.</p>

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Multi-scale Microstructural Characterization and Precipitation Mechanism of Hydrides in Zr-2.5Nb Alloy Pressure Tube

  • 期刊论文

  • 发表日期：

    2026年2月17日

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  • Bo Li,
  • Changxing Cui,
  • Yanchao Li,
  • Hui Wang,
  • Shuo Sun,
  • Huanzheng Sun,
  • Zheng Feng,
  • Wen Zhang,
  • Guojun Zhang

摘要

The integrity and performance of Zr-2.5Nb alloy pressure tubes in nuclear reactors are significantly influenced by the behavior of hydrides within the material. A comprehensive understanding of the hydride distribution, orientation relationship, and precipitation mechanism is crucial for predicting and mitigating potential degradation in these critical components. This study presents a multi-scale characterization approach, integrating scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy, to investigate the mesoscale, microscale, and atomic-scale features of hydrides in Zr-2.5Nb alloy pressure tubes. The results reveal that hydrides predominantly form along α/α grain boundaries and α/β phase boundaries, with minimal intragranular presence. Distinct crystallographic orientation relationships between interfacial and intragranular hydrides and the α-Zr matrix are identified. Interfacial hydrides (γ-ZrH, δ-ZrH1.66, and ε-ZrH2) exhibit a strong hereditary orientation relationship with the α-Zr matrix, characterized by <11 \(\bar{2}\) 2 ¯ 0>α//<110>γ//<110>δ//<111>ε and {0001}α//{111}γ//{111}δ//{101}ε. Intragranular hydrides maintain the relationship of <11 \(\bar{2}\) 2 ¯ 0>α//<110>γ//<110>δ//<110>ε and {0001}α//{200}γ//{200}δ//{200}ε. High-resolution transmission electron microscopy observations uncovered a continuous slip of Shockley partial dislocations within the α-matrix, originating from 60° mixed-type <a> perfect dislocations on each basal plane. This slip, coupled with an atomic shuffle mechanism, facilitates the B-type phase transition, leading to the precipitation of δ-ZrH1.66 with a face-centered cubic structure.