Effect of microstructural defects on hydrogen transport and embrittlement in V-Al hydrogen separation membranes

초록

In this study, the effects of microstructural defects on hydrogen transport properties and hydrogen embrittlement susceptibility were systematically investigated in a V-5Al (at %) alloy designed for hydrogen separation membranes. Cold rolling followed by annealing at 700-1000 degrees C under high vacuum produced progressive microstructural evolution, characterized by decreasing dislocation density and grain boundary area. Hydrogen diffusivity, apparent solubility, and permeability were determined using the time-lag method. The cold-rolled specimen with the highest defect density exhibited the lowest hydrogen transport properties, whereas the fully recrystallized specimen showed markedly higher diffusivity and apparent solubility, resulting in nearly doubled permeability at 300 degrees C. The results demonstrate that dislocations and grain boundaries act as trapping sites that reduce diffusivity and lower the apparent solubility of hydrogen. Hydrogen embrittlement susceptibility was evaluated by a mechanical stability test during hydrogen permeation and a tailored pre-charging protocol. Both approaches revealed that hydrogen embrittlement susceptibility increases as microstructural defects are removed. These findings show that microstructural defects exert a trade-off relationship, degrading hydrogen permeability while simultaneously mitigating embrittlement by limiting hydrogen uptake. This work establishes microstructure control as a critical design parameter for balancing hydrogen transport performance and mechanical stability during hydrogen permeation in vanadium-based hydrogen separation membranes.

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