PREPARATION OF MULTILAYERS FOR AMORPHIZATION BY SOLID-STATE REACTION

Abstract
Ni-Zr composite wires were prepared from 25 µm thick elemental Ni and Zr foils by a foi1 winding technique and codeformation using swaging and wire drawing. X-ray diffraction, differential scanning calorimetry, magnetization and resistivity measurements as well as crosssectional TEM were used to monitor the reaction progress during constantrate heating and to characterize the different reaction products. For kinetic reasons, an amorphous phase initially forms at the interface between the elemental layers. At a critical thickness of the amorphous interlayer the amorphous phase is no longer kinetically favoured and intermetallic phase formation sets in. Fully amorphous material is only obtained if the elemental layers are sufficiently thin, i.e. the interdiffusion reaction must be completed (or especially the Zr layers must be completely reacted) before intermetallic phase formation sets in. Similar multilayer composite powders are prepared during the initial stages of amorphization by mechanical alloying. For longer milling times TEM studies reveal the formation of the amorphous phase via interdiffusion at the interface between the elemental layers. Thus the reaction is quite similar to the solid-state reaction in layered composites.