Cyclic solid-state transformations during ball milling of aluminum zirconium powder and the effect of milling speed
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M. SHERIF EL-ESKANDARANY, formerly Visiting Professor, Institute for Materials Research, Tohoku University, is Associate Professor of Materials Science and Physical Metallurgy, Mining and Petroleum Engineering Department, Faculty of Engineering, Al Azhar University, Nasr City 11371, Cairo-Egypt. K. AOKI, Professor, is with the Department of Materials Science, Kitami Institute of Technology, Hokkaido 090, Japan. K. SUMIYAMA, Associate Professor, is with the Institute for Materials Research, Tohoku University, Sendai 980-77, Japan. K. SUZUKI, formerly Dean, Institute for Materials Research, Tohoku University, is Senior Executive Advisor, Sumitomo Metal Industries, Ltd., Amagasaki 660-0891, Japan. Manuscript submitted August 31, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
hydrocarbon compounds to form ZrC or ZrH2 at nearly room temperature. Thus, no lubricating agents were employed during the ball milling experiments. During the first few hours of MA time (0 to 6 hours), most of the Al and Zr powders adhered to the surfaces of the milling tools. The adhered powders are fractured off upon further MA time (6 to 12 hours). The MA experiments were performed in a high-energy planetary ball mill (Fritsch P5) equipped with a rotation speed dial controller varying from 1 to 8. The maximum rotation speed of this mill is 360 rpm (onset speed, I 5 8), whereas the minimum rotation speed is 45 rpm (onset speed, I 5 1). In order to understand the effect of the milling speed on the cyclic phase transformations, several samples were prepared, using milling speeds 90 rpm (I 5 2), 180 rpm (I 5 4), 270 rpm (I 5 6), and 360 rpm (I 5 8). In all the experiments, the temperature of the vial, Tv , was measured every 30 minutes. It is worth noting that when the samples were milled with low milling speed (I 5 2 and 4), Tv did not increase remarkably (Tv # 307 or less). For those experiments run at I 5 6 and 8, however, Tv increased rapidly with increasing MA time and was found to be about 320 K after 30 minutes of MA time. In order to minimize the temperature effect in our study of the cyclic transformations, the ball-milling experiments were stopped periodically (every 30 minutes) and then resumed when the temperature of the vial decreased to about 300 K. This on/off mode was also applied even for those samples milled at low milling speed. It is worth noting that when the vial was charged with milling media only and operated at I 5 8 for 30 minutes, the vial’s temperature increased to about 310 K.[9] In order to study the reproducibility of work, all the milling experiments were repeated under the same experimental conditions three times. The structural changes with the milling time of the powder were followed by X-ray diffraction (XRD) (Cu Ka radiation). The samples were thermally analyzed with a differential thermal analyzer (DTA) at a constant heating rate of 20 K/min. The induction coupled plasma emission method was used to analyze the concentration of Al and Zr and the degree of Fe contamination in the milled powders. The gas contami
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