Atmosphere effects of the amorphization reaction in NiZr by ball milling
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A. Memezawa Graduate School, Tohoku University, Sendai 980, Japan
T. Masumoto Institute for Materials Research, Tohoku University, Sendai 980, Japan (Received 2 September 1992; accepted 14 September 1992)
An intermetallic compound c-NiZr and a mixture of elemental powders of nickel and zirconium [Ni5oZr5o (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-NiZrN 0 .i5 was synthesized in a nitrogen atmosphere, while a crystalline hydride c-NiZrH 3 was formed in a hydrogen atmosphere. On the other hand, ZrN and ZrH 2 were formed by MA in a nitrogen and a hydrogen atmosphere, respectively. The amorphization reaction was observed between ZrH 2 and Ni by further MA in a hydrogen atmosphere, and a mixture of a-NiZr^Hj, (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.
I. INTRODUCTION 1
Nonequilibrium phases such as amorphous, quasicrystalline,2 and nanocrystalline3 can be prepared by mechanical alloying (MA) and mechanical grinding (MG). The amorphization reaction by MA of a mixture of elemental powders with a large negative heat of mixing such as Ni—Zr has been extensively investigated,4"9 and the mechanism of amorphization is considered to be closely related to the formation of amorphous alloys by the solid-state interdiffusion reaction in artificially modulated multilayer composites.8"11 However, the mechanism of amorphization by MG of intermetallics is still not well understood. MA and MG are usually carried out using a high-energy ball mill in an inert gas atmosphere. Recently, the present authors have demonstrated that an amorphous nitride a-TiZrN 0 .3 is synthesized by MA and the chemical reaction between N 2 and Ti and Zr in a controlled nitrogen atmosphere.12 On the other hand, it has been shown that amorphous metallic hydrides are prepared statically by hydrogenation of the intermetallics.13"15 From such backgrounds, it is particularly interesting to know what phases are formed by ball milling of the zirconium base alloys in a nitrogen and a hydrogen atmosphere because of a large negative heat of formation of ZrN ( - 1 8 3 kJ/mol) and ZrH 2 ( - 8 2 kJ/mol). J. Mater. Res., Vol. 8, No. 2, Feb 1993 http://journals.cambridge.org
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In the present work, an intermetallic compound NiZr and a mixture of elemental powders of nickel and zirconium (Ni5oZr5o) were ball milled in an N 2 and an H 2 atmosphere and products were characterized as a function of the milling time. The phase formations during MG and MA are discusse
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