Microstructures and Hydrogen Permeability of the Cold Rolled-Annealed Nb52Ti25Co23 Multiphase Alloy

Microstructures, crystal structures and hydrogen permeation properties of the Nb52Ti25Co23 alloy after cold rolling and subsequent annealing were investigated. This alloy could be cold rolled up to 60% reduction without annealing. The thin alloy membrane (25 μm) was easily prepared by cold rolling and subsequent annealing above 1000°C. The mixed microstructure of the primary (Nb, Ti) phase and eutectic {(Nb, Ti)+TiCo} phase in as-cast alloy changed to the lamellar structure of the (Nb, Ti) and TiCo phases by several cycles of rolling and annealing. The alloys having the primary (Nb, Ti) phase or the lamellar microstructure which the (Nb, Ti) phases are connecting each other along the hydrogen permeation direction showed higher hydrogen permeability than 2.0×10-8(molH2/m/s/Pa0.5) at 400°C. Grain growth of the (Nb, Ti) phase and the suppression of coarsening of the Ti2Co phase which is brittle and easy to crack are achieved under the final annealing of 1000°C×100 h. The Nb52Ti25Co23 alloy membrane with 25 μm thickness prepared by the above annealing conditions showed higher hydrogen flux J than 1.5 times of Pd77Ag23 alloy membrane with the same thickness.