Nature of Large Ti4Ou20 Particles Formed during Annealing of Cu55Ti45 Metallic Glass Ribbons M.J. KAUFMAN and R. D. SHULL Large particles observed in annealed Cu55Ti45 metallic glass ribbons have been identified using convergent beam electron diffraction and energy dispersive X-ray spectroscopy as Ti4Cu20 (diamond cubic, space group Fd3m), consistent with the structure derived earlier by Mueller and Knott (Trans. AIME, 1963, vol. 227, p. 674) using different experimental techniques. In addition, evidence is presented which suggests that these particles form prior to and independent of either of the two binary equilibrium phases, TiCu and Ti3Cu4, which also form during the crystallization annealing treatment. 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 dif- fraction (CBED) and energy dispersive X-ray spectroscopy (EDXS), where, respectively, microstructural (point and space groups) 2'3 and microcompositional 4'5'6 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 identi- fication 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 metal- lic 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 cru- cibles onto a Be-Cu wheel. Previously, the amorphous na- ture 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 analy- sis (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. 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). ~o Samples 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 per- formed using a Philips EM400T transmission electron mi- croscope equipped with an EDAX energy dispersive X-ray spectrometer and a 9160 data analysis system.* *Certain trade names and company products are mentioned in the text to specify adequately the equipment used. In no case does such identification imply a recommendation or endorsement by the National Bureau of Stan- dards, nor does it imply the products are necessarily the best available for the purpose. III. RESULTS AND DISCUSSION The microstructure typically observed in the ribbon foils following the 850 ~ heat treatment consisted of large, usu- ally circular, particles in a faulted matrix (Figure 1). Selec- ted area diffraction patterns (SADPs) obtained from the matrix surrounding these particles were consistent with the stable TiCu and Ti3Cu4 structures. 9 However, SADPs from the large circular particles could not be indexed on the basis of any of the binary Ti-Cu phases reported in Reference 9 or the metastable bcc phase reported by Marshall et al. H As a result, convergent beam diffraction patterns (CBPs) were obtained from these large particles; the patterns necessary for the structure analysis are included in Figure 2. For the [001] CBP** in Figure 2(a), the projection diffraction and **Although the zone axes of the CBPs and the corresponding indices of the reflections in Figure 2 were determined following the space group analysis, they are included here for reference purposes. whole pattern symmetries*** are both 4mm (a four-fold ***The terms projection diffraction and whole pattern symmetries have the same meaning as in Reference 2. rotation axis parallel to two independent mirror planes). From Table 2 in Buxton et al.,2 it is possible to determine the possible diffraction groups for this zone axis as 4ram and 4mml~. When the [011] CBP is considered (Figure 2(b)), the projection diffraction and whole pattern symmetries are both 2mm and the corresponding diffraction group is either METALLURGICAL TRANSACTIONS A U.S. GOVERNMENT WORK VOLUME 17A, APRIL 1986--575 NOT PROTECTED BY U.S. COPYRIGHT