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I.

INTRODUCTION

R E C E N T L Y , a considerable number of studies on various alloy systems by mechanical alloying (MA) have been carried out, and nonequilibrium phases, such as amorphous phases and supersaturated solid solutions, in some alloy systems have been reported. ~1,2,3~ In this article, the result of microstructural change and metastable phase formation by MA of elemental aluminum and copper powders is presented. II.

EXPERIMENTAL

PROCEDURE

Elemental powders of aluminum (purity 99.99 pct and particle size less than 350 mesh) and copper (purity 99.99 pct and particle size less than 200 mesh) were used as starting materials. These powders were mixed to give nominal starting compositions of AI-10, 20, 33, 50, 67, 75, and 80 at. pct Cu. In this experiment, a conventional horizontal, low-energy ball-milling apparatus was used. Both the vial and balls were made of SUS304 stainless steel. The size of the vial was 120 mm in inner diameter and 140 mm in height, and the diameter of the balls was 9 mm. The vial was rotated at an angular velocity of 9.4 rad/s (90 rpm). The total weight of the balls was 4 kg, and the weight ratio of the balls to the powder mixture was kept at 1:90. The powder mixture was sealed in the vial under an argon atmosphere with 3 mass pct methanol in order to prevent excessive sticking of the sample to the balls and to the vial wall. An experiment without the addition of methanol was performed. The results obtained showed no notable difference from the experiment with methanol addition. To follow the process of ball milling, small amounts of powder were taken out at fixed time intervals in a glove box with an argon atmosphere for analysis. Powder X-ray diffraction analysis was performed on a Rigaku RAD-B diffractometer with Cu K~ radiation to identify the phases formed during the ball-milling process. The changes in the lattice parameter of aluminum and copper were estimated from the shifts of the X-ray FENG LI, Graduate Student, K.N. ISHIHARA, Assistant Professor, and P.H. SHINGU, Professor, are with the Department of Metal Science and Technology, Kyoto University, Kyoto 606-01, Japan. Manuscript submitted March 30, 1991. METALLURGICAL TRANSACTIONS A

diffraction peaks. Pure silicon powder was used as the standard in the precise measurement of the lattice parameter. Microstructures of ball-milled powders were observed by scanning electron microscope (SEM) with electron probe microanalyzer and transmission electron microscope (TEM). The samples for SEM observation were prepared using the standard metallographic technique. The samples for TEM observation were made by slicing the powder particles which were embedded in epoxy resin using a diamond blade. III.

RESULTS

A. Formation of Fcc Solid Solution A face-centered cubic (fcc) solid solution of copper in aluminum which coexisted with a nonequilibrium phase was obtained in the compositions of AI-10 at. pct Cu and A1-20 at. pct Cu. Figure 1 shows the X-ray diffraction patterns of AI-20 at. pct Cu samples for various ballmilling times. The