Morphological and calorimetric studies on the
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I.
INTRODUCTION
U N T I L recently, amorphous metallic alloys were exclusively prepared by rapid quenching from the liquid or vapor states with very high cooling rates ranging from 10 6 to 1012 Ks -~. In 1983, the phenomena of solid-state amorphizing reactions induced by the solid-state interdiffusion of multilayered thin films, t~l hydrogen absorption, tz] and mechanical alloying (MA) 131 have been investigated as a unique technique for preparing several amorphous alloys. In fact, the MA process dates back to 1970, when Benjamin 141 used this process for producing composite metal powders with controlled microstructures. So far, the MA process has been employed for producing many dispersion-strengthened superalloys. [5-9] In 1983, Koch et al. t3j established the synthesis of amorphous Ni6oNb40 powders by MA of elemental Ni and Nb powders using a high-energy ball mill. Since then, the MA process via ball-milling L~~ and/or rodmilling I~z'j2'~3j techniques has been used for preparing various amorphous alloy powders. 1~4 23] Recently, E1Eskandarany e t a l . have employed this process for producing metal nitrides, such as Fez N[241 and nonequilibrium TiN, I251under purified nitrogen gas flow at room temperature. The present study reports morphological and calorimetric studies on the amorphization and subsequent crystallization processes of mechanically alloyed A15oZrs0 powders produced by the rod-milling technique. The rodM. SHERIF EL-ESKANDARANY, Research Associate, Department of Chemical Physics of Non-Crystalline Materials, KIYOSHI AOKI, Associate Professor, Department of Non-Equilibrium Materials, and KENJI SUZUKI, Professor, Department of Chemical Physics of NonCrystalline Materials, are with the Institute for Materials Research, Tohoku University, Sendai 980, Japan. Manuscript submitted October 28, 1991. METALLURGICAL TRANSACTIONS A
milled alloy powders have been characterized by means of optical metallography, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, differential thermal analysis (DTA), and differential scanning calorimetry (DSC).
II.
EXPERIMENTAL DETAILS
Pure elemental powders of AI (-325 mesh, 99.999 pct) and Zr (-200 mesh, 99.5 pct) were mixed to give the desired average composition of AlsoZrs0 in a glove box under a purified argon atmosphere (02 and HzO are less than 1 ppm) and sealed in a cylindrical stainless steel shell (SUS 304, 120 mm in diameter) together with ten stainless steel rods (SUS 304, 10 mm in diameter). The rod-to-powders weight ratio was 30:1. The milling processing was carried out at ambient temperature by mounting the rod mill on a rotator at the rate of 1.4 s -~. The MA experiments were interrupted at regular intervals (starting with 1.8 ks), and a small amount of the rod-milled alloy powders was removed from the vial in the glove box. The morphology of the alloy powders were studied by optical microscopy, SEM operated at 20 kV, and TEM/ energy dispersive X-ray analysis (TEM/EDX) using a 200 kV microscope. The samples for TEM o
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