Micromechanical Characterization of Rapidly-Solidified Nb-TiNi Hydrogen Permeation Alloy Membranes

The micromechanical tests have been performed for melt-spun Nb-TiNi ribbons, and the relation between the mechanical properties and microstructural change with heat treatment has been investigated. Micro-cantilever specimens with dimensions of 10(B)×20(W)×50(L)μm3 were prepared by focused ion beam (FIB) machining. Fracture tests were carried out at room temperature in air using a mechanical testing machine developed for micro-sized specimens. The fracture toughness value (KQ) of as-melt spun ribbon which consists of an amorphous phase was 5.3 MPam1/2. In contrast, the KQ of the melt-spun ribbon annealed at 773 K for 3.6 ks decreases to 2.8 MPam1/2. With annealing above 973 K fracture toughness increases again. This is due to the nanocrystallization of the amorphous phase and the formation of aggregates which are composed of B2-TiNi and bcc-Nb(Ti) phase with the cube-on-cube orientation relationship. These results suggest that the high temperature annealing is required for the application to the hydrogen permeation membrane.