Effect of Ti/Ni Ratio and Annealing on Microstructure and Hydrogen Permeability of Nb-TiNi Alloy

Abstract

A series of Nb₄₀Ti_30+xNi_30−x alloys are characterized in terms of microstructure, crystal structure, ductility, susceptibility to hydrogen embrittlement, and hydrogen permeability as non-palladium-based hydrogen permeation alloys. The maximum hydrogen permeability and ductility of the alloy is exhibited by the alloy with composition of x=2 (Nb₄₀Ti₃₂Ni₂₈). The enhancement of hydrogen permeability correlates well with an increase in the volume fraction of the primary (Nb, Ti) phase. After cold rolling and annealing, the hydrogen permeability of the Nb₄₀Ti₃₄Ni₂₆ (x=4) alloy becomes superior to that of the Nb₄₀Ti₃₀Ni₃₀ (x=0) composition previously reported to be the best in the Nb₄₀Ti_30+xNi_30−x series. The present results indicate that the hydrogen permeability of the Nb-TiNi alloy can be optimized by annealing and appropriately adjusting the Ti/Ni ratio for a given niobium content.