Nature of large Ti 4 Cu 2 O particles formed during annealing of Cu 55 Ti 45 metallic glass ribbons
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I.
INTRODUCTION
THE possible utilization of metallic glasses either in their glassy state or as starting materials for the production of refined or novel crystalline microstructures depends, to a large extent, on the ability to characterize these materials on a Very fine scale. ~Such characterization may be performed readily using analytical electron microscopy techniques. Among these techniques are convergent beam electron diffraction (CBED) and energy dispersive X-ray spectroscopy (EDXS), where, respectively, microstructural (point and space groups) 2'3 and microcompositional4'5'6 information can be obtained from very small volumes of sample. The Ti-Cu system has been the subject of a number of rapid quenching studies 7's where it has been reported that metallic glasses can be formed readily over a rather wide composition range. A summary of work on this alloy system has been published recently by Murray. 9 In addition, Shull et al.l~ examined the phase decomposition sequence of a Cu55Ti45 metallic glass using a combination of experimental techniques. Also, Marshall et al. ~l reported the formation of a metastable bcc phase in the early stage of crystallization of an amorphous Cu60Ti40 alloy. The purpose of the present paper is to describe the identification of Ti4Cu20 present in metallic glass ribbons after heating to 850 ~ for 20 hours. Convergent beam electron diffraction has been used to identify the structure of this compound while energy dispersive X-ray spectroscopy has been used for the compositional determination (of the metallic elements).
II.
EXPERIMENTAL PROCEDURE
Rapidly solidified ribbons* of Cu55Ti45 were prepared by *The melt spun ribbons were kindly provided by A. Maeland, Allied Corp., Morristown, NJ.
melt spinning prealloyed samples contained in yttria crucibles onto a Be-Cu wheel. Previously, the amorphous nature of these ribbons was indicated by the absence of any Bragg scattering peaks in either large angle X-ray or neutron diffraction spectra.i~ In addition, differential thermal analysis (DTA) data indicated the crystallization temperature (T,) for this material was 400 ~ lo The samples analyzed in the M. J. KAUFMAN and R. D. SHULL are Metallurgists in the Metallurgy Division at the National Bureau of Standards, Gaithersburg, MD 20899. Manuscript submitted February 19, 1985. METALLURGICAL TRANSACTIONS A
present study were taken from melt spun ribbons which had been sealed inside quartz tubes (previously evacuated to 1.3 • 10-4 Pa pressure) containing one atmosphere of He exchange gas and sequentially heat treated as follows: 300 ~ (9 hours), 350 ~ (1 hour), 403 ~ (1 hour), 475 ~ (2.25 hours), and 850 ~ (20 hours). ~oSamples suitable for transmission electron microscopy were prepared by standard twin-jet electropolishing procedures using a solution of 6 pct perchloric acid, 34 pct butanol, and 60 pct methanol (by volume). The CBED and EDXS analyses were performed using a Philips EM400T transmission electron microscope equipped with an EDAX energy dispersive X-ray spectrometer and a 91
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