Microstructure and Mechanical Properties of Combinatorially Prepared Thin Film Aluminum-Silicon Nanocomposites
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Microstructure and Mechanical Properties of Combinatorially Prepared Thin Film Aluminum-Silicon Nanocomposites Charles Olk1, Michael Lukitsch2, and Daad B Haddad3 1 Materials and Processes Lab, General Motors Research and Development, MC 480-106-224, 30500 Mound Rd, Warren, MI, 48090-9055 2 Materials and Processes Lab, General Motors Research and Developmen, MC 480-106-224, 30500 Mound Rd, Warren, MI, 48090-9055 3 School of Materials Engineering, Purdue University, West Lafayette, IN, 47907
ABSTRACT We have undertaken the exploration of the AlxSi1-x systems to discover new alloys with enhanced properties. We describe the mechanical properties of thin film AlxSi1-x alloys determined through indentation experiments. Combinatorial methods were used to systematically control thin film microstructure through variations in composition and growth temperature. Discrete libraries of compositionally graded films have been sputter deposited onto silicon substrates to produce two structural phase regions: amorphous Al-Si and amorphous Si plus crystalline Al. The mechanical properties of the thin films were determined by analyzing the load-displacement traces based on the Oliver-Pharr method. X-ray diffraction was used to investigate the microstructures and determine the crystallite sizes.
INTRODUCTION Due to their high strength-to-weight ratio and good mechanical properties, Al-Si alloys are favorable candidates for replacement materials in many critical automotive components. Exceptional physical properties such as low wear, low coefficient of thermal expansion, high corrosion resistance and high thermal conductivity make this materials system a model for investigation. Most of the enhancements in these properties have been attributed to particular features in the microstructure including the size, growth orientation, and the distribution of the Al crystallites within the Si matrix. Reports have shown that finer grain structure and engineered surfaces can lead to significant mechanical property improvements [1-3]. We have employed combinatorial methods to systematically control thin film microstructure through variations in composition and growth temperature. This has allowed us to produced arrays of discrete films (libraries) containing phase and composition differences using magnetron sputtering, a shadow mask, and spatial control of the deposition rates. A variety of microstructures and nanophase directly result from adjusting the deposition rate of the Si and Al and controlling substrate temperature (i.e., nucleation and diffusion kinetics). Details of the composition, microstructure, and phase content have been determined using electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Indentation experiments were performed and analysis of the load-displacement traces, based on the Oliver-Pharr [4] method, allowed us to correlate the mechanical property enhancements with the composition, phase and microstructure. EXPERIMENT Our alloy combinatorial libraries were deposited in an ultra-high vacuum cha
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