Effect of partial Ni substitution in V₈₅Ni₁₅ by Ti on microstructure, mechanical properties and hydrogen permeability of V-based BCC alloy membranes

Abstract

Vanadium-based alloy membranes with body-centred-cubic (BCC) structure are considered as one of the leading alternatives to Pd-based alloys for hydrogen separation applications due to their lower cost and higher permeability. As permeability and mechanical properties depend on what microstructure can be produced mainly by alloy composition under same processing conditions, the effect of alloy composition on microstructure, mechanical properties and hydrogen permeability has been investigated for the V 85 Ni 15 and V 85 Ni 10 Ti 5 (at%) alloys prepared by a same process route. All Ni atoms dissolve into the V-matrix to form a single highly supersaturated solid solution with dendritic segregation of Ni-solute atoms in the binary alloy. A part of Ni replacement with 5 at% Ti leads to the formation of small interdendritic phases NiTi and NiTi 2 in addition to major phase of V-based solid solution. The mechanical property testing shows that the ultimate strength of the ternary alloy is higher than that of the binary alloy, but the elongation and rollability are lower due to a combination of solid solution hardening and particle strengthening effect. The addition of Ti can greatly increase permeability about 4 times greater than the binary alloy at a permeation testing of 400°C. But the presence of small amounts of interdendritic compounds provides a barrier to hydrogen migration, resulting in a relatively lower hydrogen diffusion coefficient. In theory, the diffusivity and solubility of hydrogen atom in the presence of alloying element Ti is higher than that in the presence of alloying element Ni in vanadium. This is demonstrated using first principles calculation which further explains the mechanism of hydrogen permeation.

Influence of Nickel Addition on the Stability, Trapping, and Diffusion Behaviour of Hydrogen in Vanadium: A First-Principles Investigation

“…More specifically, decreased hydrogen solubility and restrained hydride formation are desirable. Experimental studies have shown that hydrogen solubility in transition metal alloys exhibits the following sequence: 13,15 ; adding Ni to V substantially reduces the hydrogen solubility of pure V, improving its resistance to H embrittlement 21,22,23 . Further, Ni, an effective catalytic component, is widely employed in hydrogen storage materials, chemical fuels, and organic chemical synthesis 24,25 .…”

Hydrogen Transportation Behaviour of V–Ni Solid Solution: A First-Principles Investigation

“…More specifically, alloying can decrease hydrogen solubility and restrain hydride formation. Experimental studies have shown that hydrogen solubility in transition metal alloys exhibits the following sequence: V–Ti > V–Cr > V–Mn > V–Fe > V–Co > V–Ni [ 11 , 14 ]; Ni doping substantially reduces the hydrogen solubility of pure V, improving its resistance to H embrittlement [ 22 , 23 , 24 ]. Further, Ni, an effective catalytic component, is widely employed in hydrogen storage materials, chemical fuels, and organic chemical synthesis [ 25 , 26 ].…”