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<p>Accurate high-temperature coefficients of thermal expansion (CTE) are essential for the thermal design and thermodynamic modeling of refractory metals under extreme conditions, as well as for the validation of materials simulations. This study employs a high-speed shadowgraph method combined with a multi-stepwise pulse-heating technique to determine the relative linear thermal expansion, <i>ε</i>, of pure niobium as a function of specimen temperature, <i>T</i>. Repeated pulsed current heating increased <i>T</i> in a stepwise manner from near room temperature to 95&#xa0;% of the melting point within 3&#xa0;s, providing 22–24 temperature points per run. At each step, the current was briefly interrupted (~ 20&#xa0;ms) to determine <i>T</i> from the electromotive force of a welded thermocouple, while high-speed silhouette images acquired during this interval were used to evaluate <i>ε</i> from the specimen width. The measured <i>ε</i> increased with <i>T</i> in all three runs, corresponding to a total expansion of approximately 2.2&#xa0;% up to 2580&#xa0;K. The resulting instantaneous CTE, <i>α</i>(<i>T</i>) = <i>dε</i>/<i>dT</i>, exhibited high reproducibility and showed a nonlinear temperature dependence. The expanded relative uncertainty (<i>k</i> = 2) of <i>α</i>(<i>T</i>) was estimated to be 4.2&#xa0;% at 1500&#xa0;K and 8.5&#xa0;% at 2500&#xa0;K. These results demonstrate that the present approach provides a practical and efficient method for determining the CTE over a wide temperature range within a few seconds in a single high-speed heating experiment.</p>

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High-Speed Shadowgraph Imaging for Measuring the Temperature-Dependent Thermal Expansion of Niobium up to Near Its Melting Point Using a Multi-stepwise Pulse-Heating Technique

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  • 发表日期：

    2026年7月8日

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  • Isamu Orikasa,
  • Hiromichi Watanabe

摘要

Accurate high-temperature coefficients of thermal expansion (CTE) are essential for the thermal design and thermodynamic modeling of refractory metals under extreme conditions, as well as for the validation of materials simulations. This study employs a high-speed shadowgraph method combined with a multi-stepwise pulse-heating technique to determine the relative linear thermal expansion, ε, of pure niobium as a function of specimen temperature, T. Repeated pulsed current heating increased T in a stepwise manner from near room temperature to 95 % of the melting point within 3 s, providing 22–24 temperature points per run. At each step, the current was briefly interrupted (~ 20 ms) to determine T from the electromotive force of a welded thermocouple, while high-speed silhouette images acquired during this interval were used to evaluate ε from the specimen width. The measured ε increased with T in all three runs, corresponding to a total expansion of approximately 2.2 % up to 2580 K. The resulting instantaneous CTE, α(T) = dε/dT, exhibited high reproducibility and showed a nonlinear temperature dependence. The expanded relative uncertainty (k = 2) of α(T) was estimated to be 4.2 % at 1500 K and 8.5 % at 2500 K. These results demonstrate that the present approach provides a practical and efficient method for determining the CTE over a wide temperature range within a few seconds in a single high-speed heating experiment.