Structure study on rapidly solidified hydrogen storage alloy Zr(NiM)(2.1)

Molten alloy Zr(NiM)(2.1) (M=Mn, Cr, V) is rapidly solidified by melt spinn ing method with cooling rates of alloy ribbons between 4.35x10(5) Ks(-1) an d 5.33x10(6) Ks(-1). The structure is analyzed by means of XRD and TEM. The data from XRD are further analyzed by the Rietveld method. The results sho w that all the rapidly solidified alloys with different cooling rates are c omposed only of micro-crystalline C14 Laves and C15 Laves phases, different from the appearance of the non-laves phase constituents Zr7M10 and Zr,Ni,, together with the C14 and C15 Laves phase in the slowly cooled master allo y. The C14 Laves phase in rapidly solidified alloys assumes a laminar struc ture, in which the dimensions of C14 Laves micro-crystallites are almost co nstant, 1 nm along the c direction and 3-4 nm along the a and b directions. The abundance of C14 Laves phase increases in rapidly solidified alloys as the cooling rate increases, and on the contrary, the abundance of C15 Lave s phase decreases. When the cooling rate increases from 4.35x10(5) Ks(-1) t o 5.33x10(6) Ks(-1), the abundance of C15 Laves phase decreases from 88.29 wt.% to 43.63 wt.%, and the crystallite size of C15 phase decreases from 54 .1 nm to 17.8 nm. (C) 1999 Elsevier Science S.A. All rights reserved.