The AI-Ali 8 Mo 3 section of the binary system aluminum-molybdenum
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I.
INTRODUCTION
E A R L Y reports on the phase diagram of the Al-rich end of the binary A1-Mot~,2] were corroborated and extended to higher Mo contents by Sperner, f3] who proposed a diagram temperatu~ (T) vs composition (x) featuring the eutectic liquid ~ A1 + Al12Mob a cascade of peritectic isotherms (liquid + A15Mo ~ AI~2Mo, liquid + A13Mo ~ A15Mo, liquid + A13Mo J~o A12Mo), and a congruent melting point (>1900 ~ for the phase A12Mo. P6tzschke and Schubert [4] confirmed the occurrence of intermediate phases at or near the compositions indicated by Sperner and advanced the knowledge of their crystal structures (Table I) but indicated also the existence of additional phases as well as stability ranges incompatible with the simple diagram of Sperner. P6tzschke and Schubert did not, however, rationalize their findings in the form of a revised phase diagram. In this situation, several authors E5,6'71came to strikingly different conclusions when attempting to assess the constitution of the system based on P6tzschke and Schubert's report plus other isolated bits of information available then. ts,9,1~ Others [11"12] adopted diagrams essentially unchanged with respect to the diagram by Speruer and thus ignored P6tzschke and Schubert's data. Hence, a complete reinvestigation of this section of the AI-AlsMo3 partial system seemed necessary. II.
EXPERIMENTAL PROCEDURES
Fifteen binary A1-Mo alloys ranging in composition from 12 to 28 at. pct Mo were prepared from powders of aluminum (purity: 2N8, from Alpha Division, Ventron Corporation, USA) and molybdenum (purity: 3N, from Metallwerk Plansee, Austria) by pressing powder blends into tablets and arc melting them under Ti-gettered argon. Portions of each of these master alloys were heat-treated in evacuated and sealed quartz tubes at temperatures ranging from 600 ~ (for 240 hours) to 1220 ~ (for 3 hours). These alloys were water quenched and ana-
JULIUS C. SCHUSTER, Institut fiir Physikalische Chemie, and HERBERT IPSER, Institut fiir Anorganische Chemie, are with the Universit~it Wien, A-1090 Wien, Austria. Manuscript submitted August 1, 1990. METALLURGICAL TRANSACTIONS A
lyzed by X-ray powder diffraction using Huber Guinier cameras (Cu Ks, radiation, Ge standard). Intensity data were collected with an Officina Elettrotecnico di Tenno KD/530 film densitometer. The X-ray diffraction data obtained were processed using the interactive computer program package STRUKTUR t~31 running on IBM* or *IBM is a trademark of International Business Machines Corporation, Armonk, NY.
compatible personal computers. Differential thermal analysis (DTA) runs were performed on well-annealed alloys (600 ~ 240 hours) of about 1 g in AI203 containers using a Netzsch DTA-404S/3 thermal analyzer. The heating rate was 5 K/min. The reproducibility of the temperatures was -+2 K. The melting point of AlsMo3, which is outside the range of our DTA, was determined using the Pirani technique. About 10 g of pure AlsMo3 powder were prepared and sintered into bars of approximately 4 • 5 • 40 mm. These bars
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