Formation of an amorphous (a-) Nb(20)Ti(40)Ni(40) alloy by rapid quenching and its crystallization behavior were investigated by X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. The B2-TiNi phase was firstly crystallized and the remaining amorphous (a-) phase subsequently decomposed into the bcc-(Nb, Ti) + B2-TiNi phases. The crystallized (c-) Nb(20)Ti(40)Ni(40) samples obtained by annealing above 1173 K were ductile and insusceptible to hydrogen embrittlement between 598 and 673 K. Hydrogen permeability at 673 K (Phi(673 K)) for the a- and c-Nb(20)Ti(40)Ni(40) alloys were 8.1 x 10(-9) and (3.0-4.8) x 10(-9) mol H(2)/m/s/Pa(0.5), respectively. Phi(673) (K) increased with the increase in the diameter of the bcc-(Nb, Ti) phase, although this led to poor resistance to hydrogen embrittlement. The lower hydrogen permeability of the c-Nb(20)Ti(40)Ni(40) alloy was due to its lower hydrogen diffusivity. The present work demonstrated that rapid quenching and subsequent annealing are useful to prepare thermally stable Nb-TiNi hydrogen permeation alloy membranes. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.