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<p>Hydrogen embrittlement (HE) presents a critical challenge for the application of superalloys in hydrogen-containing environments, such as future turbine systems. This study investigates the influence of the <i>β</i> phase and <i>γ</i>′ phase on HE sensitivity in the CoNiCr-based superalloy CoWAlloy6. A tailored heat treatment strategy was applied to vary the <i>β</i> and <i>γ</i>′ phase fraction while maintaining all other microstructural aspects constant. Tensile tests after high-pressure hydrogen charging (1000 bar, 300&#xa0;°C) reveal reduced HE susceptibility for CW6+<i>β</i>/−<i>γ</i>′ (CoWAlloy6 with higher <i>β</i> and lower <i>γ</i>′ content), compared to CW6−<i>β</i>/+<i>γ</i>′ (CoWAlloy6 with lower <i>β</i> and higher <i>γ</i>′ content). Thermal desorption spectroscopy measurements confirm that an increased <i>β</i> and the associated decreased <i>γ</i>′ phase fraction correlates with lower overall hydrogen solubility and slightly reduced diffusion rates. In addition, NanoSIMS mappings demonstrate the highest hydrogen uptake inside <i>β</i> phase precipitates. Consequently, the amount of diffusible hydrogen in the <i>γ</i>/<i>γ</i>′ compound is lower in CW6+<i>β</i>/−<i>γ</i>′, which in turn results in a modest work-hardening behavior. This work-hardening potential is essential for reducing the severity of HE. Furthermore, a slower strain rate during tensile testing increases HE severity, confirming the role of diffusible hydrogen content as a key aspect in the embrittlement mechanism. EBSD analyses of secondary cracks reveal predominantly transgranular cracking, indicating weakened <i>γ</i>/<i>γ</i>′ interfaces in the presence of hydrogen. The findings suggest that tuning the <i>β</i> and <i>γ</i>′ content by small modifications in heat treatment can positively affect the alloy’s resistance to hydrogen embrittlement, primarily by reducing the hydrogen solubility through a lower <i>γ</i>′ fraction and by lowering the amount of diffusible hydrogen in the microstructure through an increased <i>β</i> fraction.</p> Graphical Abstract <p></p>

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Hydrogen Embrittlement of a CoNiCr-Based Superalloy: The Role of the Intermetallic Precipitation Phases β and γ′

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年2月9日

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  • O. Nagel,
  • L. Strobel,
  • A. Stark,
  • M. Fritton,
  • C. Höschen,
  • P. Felfer,
  • R. Gilles,
  • S. Neumeier

摘要

Hydrogen embrittlement (HE) presents a critical challenge for the application of superalloys in hydrogen-containing environments, such as future turbine systems. This study investigates the influence of the β phase and γ′ phase on HE sensitivity in the CoNiCr-based superalloy CoWAlloy6. A tailored heat treatment strategy was applied to vary the β and γ′ phase fraction while maintaining all other microstructural aspects constant. Tensile tests after high-pressure hydrogen charging (1000 bar, 300 °C) reveal reduced HE susceptibility for CW6+β/−γ′ (CoWAlloy6 with higher β and lower γ′ content), compared to CW6−β/+γ′ (CoWAlloy6 with lower β and higher γ′ content). Thermal desorption spectroscopy measurements confirm that an increased β and the associated decreased γ′ phase fraction correlates with lower overall hydrogen solubility and slightly reduced diffusion rates. In addition, NanoSIMS mappings demonstrate the highest hydrogen uptake inside β phase precipitates. Consequently, the amount of diffusible hydrogen in the γ/γ′ compound is lower in CW6+β/−γ′, which in turn results in a modest work-hardening behavior. This work-hardening potential is essential for reducing the severity of HE. Furthermore, a slower strain rate during tensile testing increases HE severity, confirming the role of diffusible hydrogen content as a key aspect in the embrittlement mechanism. EBSD analyses of secondary cracks reveal predominantly transgranular cracking, indicating weakened γ/γ′ interfaces in the presence of hydrogen. The findings suggest that tuning the β and γ′ content by small modifications in heat treatment can positively affect the alloy’s resistance to hydrogen embrittlement, primarily by reducing the hydrogen solubility through a lower γ′ fraction and by lowering the amount of diffusible hydrogen in the microstructure through an increased β fraction.

Graphical Abstract