Micromechanical characterization of rapidly-solidified Nb-TiNi hydrogen permeation alloy membranes

Abstract

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) μm 3 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 (K Q) of as-melt spun ribbon which consists of an amorphous phase was 5.3 MPam 1/2. In contrast, the K Q of the melt-spun ribbon annealed at 773 K for 3.6 ks decreases to 2.8 MPam 1/2. 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. © 2008 The Japan Institute of Metals.