Microstructure-driven enhancement of malleability and hydrogen transport properties in V-Cu-Ni-Al hydrogen separation membranes

Abstract

Vanadium-based alloys offer excellent hydrogen permeability but suffer from hydrogen embrittlement and poor malleability, limiting their industrial application. In this study, two alloys, V76Cu15Ni7Al2 (7Ni2Al) and V76Cu15Ni2Al7 (2Ni7Al), were designed to improve mechanical stability by tailoring the microstructure through preferential partitioning of Ni to the V matrix and Al to the Cu-rich phase. Microstructural analyses revealed that 7Ni2Al formed a sigma phase and exhibited an inhomogeneous Cu-rich phase distribution with isolated pockets, which promoted brittle fracture and crack formation at V-Cu interfaces. In contrast, 2Ni7Al developed a continuous Cu-rich network, suppressed sigma phase formation, and exhibited a reduced hardness difference between the V and Cu phases due to the preferential partitioning of Ni and Al, thereby achieving significantly improved malleability. Cold-rolled sheets exhibited that 2Ni7Al possessed far fewer edge cracks than 7Ni2Al, successfully overcoming the workability limitations of conventional vanadium-based alloys. Both alloys demonstrated high hydrogen permeability (similar to 2.0 x 10(-8) mol H-2<middle dot>m(-1)<middle dot>Pa--1(/)2<middle dot>s(-1) at 673 K), exceeding Pd-based membranes. Furthermore, neither alloy exhibited hydrogen blistering nor embrittlement during cooling, confirming stable permeability under non-steady-state conditions. These findings highlight that optimizing the Cu phase distribution and Ni/Al ratio is a promising strategy for designing hydrogen separation membranes with superior malleability and resistance to hydrogen embrittlement.