Microstructural and mechanical characterizations of rapidly solidified Nb-TiNi hydrogen permeation alloy

The microstructural and mechanical characterizations of the rapidly solidified Nb₂₀Ti₄₀Ni₄₀ (at%) hydrogen permeation alloy have been performed. An as-melt spun ribbon consists of an amorphous phase with sound bending ductility. The successive crystallization of B2-TiNi and bcc-Nb solid solution phases takes place during heating. The amorphous phase is stable in the specimens annealed below 773 K. The specimens annealed from 798 to 923 K are quite brittle, although those consist of fine equiaxed grains less than 50 nm. With annealing above 948 K for prolonged periods the grain size is increased to about 150 nm or more and the hardness is decreased about 260 Hv or less. Consequently, the ductility is recovered. The fracture toughness of as-melt spun and annealed ribbons is also investigated by the micromechanical test.