ATMOSPHERE EFFECTS OF THE AMORPHIZATION REACTION IN NIZR BY BALL MILLING

An intermetallic compound c-NiZr and a mixture of elemental powders of nickel and zirconium [Ni50Zr50 (at. %)] have been mechanically ground (MG) and mechanically alloyed (MA), respectively, using a high-energy ball mill in various atmospheres. The products were characterized by x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and chemical analysis as a function of milling time. An amorphous a-NiZr alloy was prepared by both MG and MA in an argon atmosphere. By MG of NiZr, an amorphous nitride a-NiZrN0.15 was synthesized in a nitrogen atmosphere, while a crystalline hydride c-NiZrH3 was formed in a hydrogen atmosphere. On the other hand, ZrN and ZrH2 were formed by MA in a nitrogen and a hydrogen atmosphere, respectively. The amorphization reaction was observed between ZrH2 and Ni by further MA in a hydrogen atmosphere, and a mixture of a-NiZr(x)H(y) (x < 1) and ZrH2 was obtained. However, no amorphization was observed by MA between ZrN and Ni in a nitrogen atmosphere. The effects of the milling atmosphere on the phase formations during MG and MA are discussed based on the gas absorption rate.