Formation of Metastable Structures and Amorphous Phases in cu-w Alloys Using the Triode Sputtering Technique
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FORMATION OF METASTABLE STRUCTURES AND AMORPHOUS PHASES IN Cu-W ALLOYS USING THE TRIODE SPUTTERING TECHNIQUE H. F. Rizzo, L. E. Tanner, and M. A. Wall Lawrence Livermore National Laboratory, Livermore, T. B. Massalski Carnegie-Mellon University, Pittsburgh, PA 15213 E. D. McClanahan Pacific Northwest Laboratory, Richland, WA 99352
CA 94550
ABSTRACT The triode sputtering technique and a "split-target" arrangement were used to produce metastable crystalline and amorphous phases in the Cu-W Large metastable extensions system under essentially oxygen-free conditions. of solid solubility were observed both from the Cu (fcc) and W (bcc) sides of the phase diagram, and a wide range of metallic glass formation was observed, approximately between 30 and 65 at.% W. The thickness of the amorphous Cu-W phase (40-160 pm) that can be deposited without the formation of the metastable bcc phase appears to be dependent on the Cu-W alloy composition. On heating, the crystallization temperature of the The behavior of the lattice amorphous alloys was higher than 350°C. parameter and near-neighbor distance has been studied with x-ray diffraction, showing small positive deviations from an assumed Vegard's Law. Hardness measurements indicate that the metastable crystalline phases are relatively harder than the amorphous phase.
INTRODUCTION Although the phase diagram of the Cu-W binary system is not known, mutual solubility, and no compound there are indications that very little formation, occur between Cu and W under conditions of equilibrium [1,2]. This prediction is further supported by an estimate of the heat of formawhich was found to be large tion recently calculated by Nastasi et al. [11, and positive (A Hf - 16-24 kJ/gm-atom). Nevertheless, any possible alloying effects that can occur in this system under metastable conditions are of great interest, including the possible formation of amorphous and metastable phases. Such effects have been reported in several recent investigations of the Cu-W alloys utilizing co-evaporation of thin films on suitable substrates, (1,3,41 ion-beam irradiation (51, and laser heating [6]. In the present paper we report a study of Cu-W alloys obtained by triode sputtering, using a split target of Cu and W. This technique has been used successfully to prepare relatively thick deposits of gradually varying composition in several binary systems [7,8].
EXPERIMENTAL TECHNIQUES A description of the triode sputtering system and procedures is given in earlier papers [7,9]. Cu-W alloys were sputtered from split-target half discs of W and Cu, 76.2 mm in diameter, on water-cooled (15-18°C) Al circular substrates, 50.8 mm in diameter. The purity of the starting Deposition rates could be varied between materials was at least 99.99 wt%. 20 and 150 A/sec by increasing the target voltage between -200 V and -2000 V. The composition change obtained in the deposited coating across each sample varied according to the angular distribution of the sputtered Figure 1 Cu and W components and their respective sputtering yiel
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