Growth of TiN/AlN Superlattice by Pulsed Laser Deposition
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Growth of TiN/AlN Superlattice by Pulsed Laser Deposition H. Wang1, A. Gupta1, Ashutosh Tiwari1, X. Zhang2, and J. Narayan1 1 Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7916 2
Materials Science & Technology Division, Los Alamos National Laboratory,
Los Alamos, NM 87544 ABSTRACT TiN-AlN binary-components have attracted a lot of interests in coatings of high speed cutting tools, due to their higher oxidation resistance, higher hardness, lower internal stresses and better adhesion. Especially, nanometer-scale multilayer structures of AlN/TiN show superior structural and mechanical properties due to their tremendous interface area and become one of the promising candidates for superhard coatings. Here we present a novel method to grow highly aligned TiN/AlN superlattice by pulsed laser deposition. In this method TiN and AlN targets are arranged in a special configuration that they can be ablated in sequence, giving alternate layer by layer growth of TiN(1nm)/AlN(4nm). X-ray diffraction and transmission electron microscopy (TEM) analysis showed the structure to be cubic for both TiN and AlN in the nanoscale multilayers. Microstructure and uniformity for the superlattice structure were studied by TEM and Scanning transmission electron microscopy with Z-contrast (STEM). Nanoindentation results indicated a higher hardness for this new structure than pure AlN and rule-of-mixtures value. Four point probe electrical resistivity measurements showed overall insulating behavior.
INTRODUCTION Superhard thin films and coatings are needed for applications such as cutting tools that require improved surface resistance to wear, friction, oxidation and corrosion. Binary component coating materials exhibit interesting structural and mechanical properties which can fit in above requirements.1,2 For example, transition metal nitride thin films, especially titanium nitride (TiN), have served as the most practical and economical protective coatings, because TiN exhibits a metallic character with golden color and high hardness, high temperature stability, and abrasion resistance. However, TiN gets oxidized above 500oC to form a rutilestructure which limits its applications in high speed cutting tools.2,3 AlN thin layers have remarkable hardness, thermal and chemical stability and high electrical resistivity. TiN-AlN binary-component coatings can integrate their functionalities and show much higher oxidation resistance, lower internal stresses and better adhesion.4 TiN-AlN binary-components can be formed in two types of structures. One is uniform alloy which AlN concentration is lower than 60%.5,6 If AlN concentration is higher than 60%, phase separation results which may lead to precipitation hardening.7 The other type is mutilayer structure where there is no reaction between TiN and AlN. Especially, nanometer-scale multilayer structures attract a lot of interest due to their special interfacial structure which may leads to novel structural and mechanical properties.8, 9 In
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