Crystallization and microstructure changes in rapidly solidified Nb₂₀Ti₄₀Ni₄₀ hydrogen permeation alloy

The crystallization behaviors and microstructure changes by heat treatments in the rapidly solidified Nb₂₀Ti₄₀Ni₄₀ hydrogen permeation alloy have been investigated. There are two exothermic peaks at 872 and 914 K in DSC heating curve. The first and second peaks correspond to the crystallization of B2-TiNi and bcc-Nb phases, respectively. The orientation relationship of these two phases is cube-on-cube relation. The specimens annealed from 773 to 923 K are quite brittle, although those microstructures consist of fine equiaxed grains less than 50 nm. With prolonged annealing above 948 K the grain size is increased to about 150 nm or more and the hardness is decreased around 250 Hv, thus the ductility is recovered. These results suggest that the high temperature annealing is required for the application of the melt-spun ribbon to the hydrogen permeation membrane.