Phase Formation in a Wedged Au-Ag-Cu Multilayered Structure
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PHASE FORMATION IN A WEDGED Au-Ag-Cu MULTILAYERED STRUCTURE
1.GOLDFARB, E. ZOLOTOYABKO AND D. SHECHTMAN Department of Materials Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel. ABSTRACT
An advanced method for investigation of multicomponent systems is proposed. Thin wedged-shape films of pure components are subsequently deposited to form a multilayered structure with continuously-varying composition as a function of sample location, providing a large number of differently composed samples in one deposition run. Each sample is then subjected to various heat treatments, and phase content as well as the microstructure formed is under investigation. In this study an Au-Ag-Cu multilayered structure was sputtered at a room temperature onto 55 Formvar-coated Mo grids. The satellite-like X-Ray Diffraction (XRD) patterns of these samples revealed the formation of an artificial composition-modulated ternary superlattice, complete destruction of which was observed during heat treatments, where phase formation according to the ternary Au-Ag-Cu phase diagram took place. Several aspects of phase formation were analyzed using XRD, Electron Probe for MicroAnalysis (EPMA) in Scanning Electron Microscopy (SEM), and Scanning Transmission Electron Microscopy (STEM) combined with Selected Area Electron Diffraction (SAED), Digital X-Ray Mapping (DXM), Secondary Electron Mapping and EPMA methods. INTRODUCTION
The major interest in many areas of materials research is connected with the understanding of equilibria among phases in multi-component systems. Conventional methods, dealing usually with bulk samples, are based upon delineating the regions of alloy compositions according to the phases present, to obtain the boundaries between the phases. These methods suffer from several disadvantages, such as : - production of an excessive amount of samples with fixed concentrations - prolonged homogenization treatments required for bulk samples - prolonged heating periods required to attain the state of equilibrium The proposed method consists of multi-layered structure preparation, where each film is in the form of a wedge. This way compositional gradients are formed allowing a large number (N) of samples with continuous variation of the component concentrations within one deposition run. Dispersion of composition inside each sample is inversely proportional to N and can be made low enough because the N-value is practically unlimited. Periods required for homogenization and equilibrium attainment are very short (few hours) due to the small average film thickness (-50 A). Here we present the results for Au-Ag-Cu ternary system, which was chosen due to the following reasons: this system has been under investigation for a long time and a substantial amount of information obtained for bulk as well as for a flat Au-Cu bi-layered samples is available for comparison ; numerous ordering reactions occur at low temperatures leading to a variety of phases formed. Some facts connected, for example, with differentiation betwee
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