Synthesis and Mechanical Properties of TiN-AIN Thin Film Heterostructures
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Synthesis and Mechanical Properties of TiN-AlN Thin Film Heterostructures C. Waters, D. Kumar, S. Yarmolenko, Z. Xu and J. Sankar, North Carolina Agricultural and Technical State University, Greensboro, NC 27411, USA ABSTRACT TiN and AlN are promising thin film materials. There is continuing interest in their mechanical, electronic and optoelectronic properties. Our studies have shown that mechanical properties can be changed by forming thin film heterostructures of the two materials. We report on our pulsed laser deposition assisted synthesis, microstructural characterizations and mechanical properties of TiN/AlN multi-layer structures. The TiN/AlN superlattice structures are fabricated on (100) silicon substrates at different temperatures (400-800oC) and different nitrogen ambient pressures. The nano-mechanical hardness properties of the multi-layered structures were examined as a function of thickness of individual layers keeping the overall thickness of heterostructures constant. Thickness variations of the films are measured with a optical phase-shift interferometer. The mechanical properties of the TiN-AlN heterostructures have been found to be associated with interfacial interaction between layers. The interfacial interaction, in turn, depends on processing parameters the most important among which is substrate temperature. INTRODUCTION Aluminum Nitride, one of the Series III nitrides, is useful for its electrical resistivity, certain mechanical and chemical properties and its ability to be used in hostile environments [1]. Limitations arise from the fact that it is covalent and not easily bonded to metallic substrates. Titanium Nitride on the other hand, has high electrical conductivity, excellent corrosion and tribological properties, a high sublimation temperature, and a high hardness compared with AlN [2]. Oxidation can pose a problem however for TiN, therefore AlN is useful as an exterior coat. TiN is known as a wear-resistant coatings for cutting tools, and metal forming tools and is found to increase tool life by many hundred percent [2]. However, TiN/AlN multilayered thin film composite coatings have been proven to achieve the same performance as monolayer TiN films many times the thickness [3]. The strength and toughness of many hard coatings may be enhanced by combining the attractive properties of different material layers in a single protective layer [4, 5]. Multilayer thin films can behave as completely new, engineered materials unknown in bulk form. The advantage of this multilayer is a new composite coating system with reduced thin film thickness and improved performance by increasing adherence to the substrate, and reduced internal stresses. In addition, adjusting the material composition and microstructure can optimize the strength and toughness in hard coatings [4] for specific applications. Expanded temperature studies of the AlN/TiN multilayer thin film composites are appropriate. The measurement of mechanical properties is important for understanding how the microstructure of the
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