LATTICE EXPANDING BEHAVIOR AND DEGRADATION OF LANI5-BASED ALLOYS

Lattice expansion, contraction and degradation were investigated in tw o types of LaNi5-based alloys to identify the dominant factors in the mechanism of intrinsic degradation. Alloys were subjected to hydriding -dehydriding cycling tests up to 1000 cycles in pure hydrogen. Lattice expanding behaviour was studied by in-situ X-ray powder diffractometr y, focusing on discrete lattice expansion of the crystal lattice betwe en the alpha phase and the beta phase in the plateau region. The alloy with a wider plateau region showed larger discrete expansion and latt ice strain. The difference in degradation behaviour between the two al loys was related to the discrete expansion, especially in the c axis d irection. This phenomenon is considered to be the dominant factor in t he intrinsic degradation mechanism. (C) 1998 Elsevier Science S.A.