Growth and Structure of Tungsten Carbide-Transition Metal Superlattices
- PDF / 1,808,458 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 68 Downloads / 229 Views
GROWTH AND STRUCTURE OF TUNGSTEN CARBIDE-TRANSITION METAL SUPERLATTICES T.D. Moustakas*, J.Y. Koo and A. Ozekcin *Boston University College of Engineering, Boston, MA 02215 Exxon Research and Engineering Company Annandale, N.J. 08801
ABSTRACT
Superlattices between ceramic materials, such as tungsten carbide, and transition metals have been synthesized for the first time. The growth and structure of these superlattices were investigated by low angle X-ray diffraction and TEM lattice imaging and microdiffraction. The data show that the low temperature process of forming these two dimensional composites leads to unique crystal structures and morphology in the nanoscale range.
INTRODUCTION
Artificially layered strucrues made of pure metals, such as Au-Ni(1), Cu-Pd(1), CuNi(2), Ag-Pd(3), Cu-Au(3), Nb-Cu(4), Mo-Ni(5), Ni-V(6), etc. have been studied extensively the past few years. Some of these systems, for example, Cu-Ni, forrm solid solutions in their binary phase diagram and have matching lattice constants, while others, for example Nb-Cu, have a eutectic binary phase diagram (8) and do not have matching lattice constants. Growth and epitaxial phenomena in these systems were primarily investigated by X-ray diffraction studies (9,10) and by Transmission Electron Microscopy (11). The work has primarily been motivated by early reports that some of these systems exhibit enhanced elastic modulii (1-3,12) and other novel physical properties (9,13,14). In addition, such composition-modulated films are suitable systems for studying stability and critical phenomena in solid solutions (15). Superlattices between ceramic materials, such as refractory metal carbides, and metallic materials, such as transition metals, have been prepared only recently (16). The work has been motivated by the need to form two dimensional composites, which in analogy with the family of cemented carbides (17) should combine the high hardness and wear resistance of the carbide layers with the mechanical and thermal shock resistance of the metallic layers. In the present paper we report on phenomena related to crystal growth and structure of tungsten carbide and cobalt superlattices. More specifically, we examined how epitaxy and strain affect the structure and sharpness of the individual layer. These studies were carried out by using both low angle X-ray diffraction and modern analytical electron microscopy, including high resolution latice imaging and mnicrodiffraction.
EXPERIMENTAL METHODS
Tungsten carbide-cobalt superlattices were formed by RF sputtering from cobalt and hexagonal tungsten carbide (WC) targets, utilizing a diode system with a rotating substrate table. The system was pumped by a combination of a turbomolecular pump, roots pump and a mechanical pump to a total leak rate of 3 x 10- Torr-ll/ec, and sputtering was performed at 9mTorr of argon. The power in each target was adjusted for approximately the same deposition rate, namely 55A/min for the cobalt and 60A/min for the tungsten Mat. Res. Soc. Symp. Proc. Vol. 103.
s1988 Materia
Data Loading...
