Measurement of solid solubility of germanium in aluminum
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I.
INTRODUCTION
THE AL-Ge system is a simple eutectic one consisting o f liquid, face-centered cubic (fcc) A1 solid solution, and diamond cubic Ge solid solution,m In the usual aging treatment o f the A1-Ge alloys, the stable Ge precipitates are formed from the early stage without the formation o f intermediate metastable phases. Hence, A1-Ge alloys are very suitable for the fundamental study o f nucleation growth t2j and Ostwald ripening t3] o f precipitates in solid matrices. Moreover, metastable and amorphous phases are formed in A1-Ge alloys, depending upon quenching rate.I4] Reliable data of solid solubility o f Ge in A1, which are indispensable to analyze the above phenomena, have not yet been obtained, although the solubility o f Ge in A1 has been already investigated by St~hr et al.~5~ and Caywood. i6j In the present work, the solid solubility and residual resistivity f o r Ge in A1 were investigated by resistivity measurement at 77 K, giving special attention in the sample preparation, thermal treatment, and measurement methods. Furthermore, the resistivity o f A1-1.32 at. pct Ge alloys aged for different times at 573 and 623 K was measured at 77 K. The result was used to obtain the time variation o f the average concentration o f Ge atoms in the matrix, w h i c h is attendant to the coarsening process o f the Ge precipitates. The data were analyzed to obtain the value o f the solute concentration ce in the matrix in equilibrium with the Ge particle o f infinite size using the analysis method f7,81 on the Ostwald ripening o f precipitates. The values were compared with the solid solubility o f Ge in A1 determined in the present work. SHIN-ITIROH FUJIKAWA, Lecturer, is with the Department of Materials Science, Faculty of Engineering, T o h o k u University, Sendai 9 8 0 , Japan. YOH-ICHIROH IZEKI, formerly Graduate Student, Department of Materials Science, Tohoku University, is Chief Engineer, Industrial Research Institute of Nii-gata Prefecture, Abumi-nishi, Niigata, Japan. Manuscript submitted February 2 7 , 1992.
METALLURGICAL TRANSACTIONS A
II.
EXPERIMENTAL PROCEDURES
A . Preparation o f Al-Ge Alloys An AI-Ge m a s t e r alloy containing about 54 mass pct Ge was prepared by melting 99.999 mass pet A1 and 99.999 mass pct Ge in a high-purity graphite crucible using a high-frequency induction furnace. The A1-Ge alloys o f desired composition were prepared by alloying the m a s t e r alloy or 99.999 mass pct Ge with 99.999 mass pct AI using the induction furnace o r the zone-leveling method with induction heating. The zoneleveling was repeated six times at the rate o f about 4 x 10 -5 m s -t to distribute Ge atoms uniformly. Each ingot was homogenized at the temperature 30 K l o w e r than the corresponding solidus line and formed into wires 0.6 mm in diameter by cold swaging and drawing. The Ge concentration in A1-Ge alloys was determined using an induction-coupled plasmas (ICP) method, t91 Figure 1 shows the flow chart o f the chemical analysis method. Table I shows the results for the Ge concentrat
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