Search for metallic glasses at eutectic compositions in the Ag-Cu-Ge, Ag-Cu-Sb and Ag-Cu-Sb-Ge systems
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tion is well defined. Similar "Hume-Rothery glasses", related to the binary Ag-Cu eutectic, and ranging in electron concentration between 1.6 and 1.9, have been discovered independently recently by Mizutani and Yazawa. 6 2. EXPERIMENTAL PROCEDURES Alloys were melted initially in quartz capsules under the atmosphere of pure argon. Ribbons of several alloys of composition close to the ternary eutectic were prepared by melt spinning, using an ejection pressure of 80 KPa and a nozzle diameter of 0.75 mm. The molten metal was ejected in vacuum on a 7.5 cm diam copper wheel rotating at 8000 rpm. Thin foils were obtained using ion beam milling. Diffraction experiments were done with an X-ray diffractometer or with the JEM-100 electron microscope. Phase transformations in ribbons were studied with the Perkin-Elmer DSC, at a heating rate of 20 ~ Slowly (furnace) cooled samples were studied by optical metallography after suitable etching (ammonium hydroxide/hydrogen peroxide followed by hydrochloric acid/ferric chloride), and the compositions of individual phases and eutectic regions were determined using an ARL electron microphobe. 3. RESULTS AND DISCUSSION The compositions of the relevant alloys, and some of the measured arrest temperatures, are listed in Table I. Based on the ternary phase diagram Ag-Cu-Ge proposed by Nowotny and Bachmayer 7 two eutectic depressions are expected in this system. However, slowly cooled alloys E~ and E2, prepared at these compositions indicated the presence of a proeutectic primary phase in each case (Fig. l(a) and (b)).
ISSN 0360-2133/81/0511-0773500.75/0 9 1981 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
VOLUME 12A, MAY 1981--773
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Nowotny and Bochmayet.[ 7 ] Proposed modJftcotlons Experlmentol points
&= a A g + L
o=Ge+L
\ a ~o~
L +a
.
Ag
o
20
40 6o at. % Cu "--~
80
Cu
Fig. 2--Liquidus projection surface in the ternary Cu-Ag-Ge system. Dotted lines show previous data7, and solid lines the presently proposed modifications.
Fig. l - - O p t i c a l m i c r o s t r u c t u r e s o f s l o w l y c o o l e d a l l o y s E l ( a ) , E2(b), a n d E(c), in the s y s t e m A g - C u - G e .
After several experiments, the composition of a single invariant eutectic point was determined to be Ag38.sCu33.4Ge28.1,* as indicated by the point E in Fig. *All c o m p o s i t i o n s g i v e n in a t o m i c p e r c e n t .
2. Figure l(c) shows that the microstructure of an alloy prepared at this composition consists of only the three-phase eutectic mixture. The large light-etching cyrstals visible in Fig. l(a) and (b) were determined by microprobe to be the OtAgsolid solution, indicating that both alloys E] and E2 lie within the same fcc OtAg primary crystallization field. Gray crystals visible in Fig. l(b) (also identifiable as a part constituent of the pseudobinary eutectic with OtAg)were determined to be the Cu3Ge 7t phase, while the gray crystals in Fig. l(a) have the hcp structure of the g" phase (CusGe). Even at a relatively high magnification only two
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