Effect of Microstructure on the Electrical Properties of Nano-Structured TiN Coatings Deposited by Vacuum Cold Spray
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.-Y. Wang, Y. Liu, G.-J. Yang, J.-J. Feng, and K. Kusumoto (Submitted March 9, 2010; in revised form July 8, 2010) TiN coatings on Al2O3 substrates were fabricated by vacuum cold spray (VCS) process using ultrafine starting ceramic powders of 20 nm in size at room temperature (RT). Microstructure analysis of the samples was carried out by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Sheet resistance of the VCS TiN coatings was measured with a four-point probe. The effects of microstructure on the electrical properties of the coatings were investigated. It was found that the sheet resistance and electrical resistivity of TiN coatings were significantly associating with the spray distance, nozzle traversal speed, and deposition chamber pressure. A minimum sheet resistance of 127 X was achieved. The microstructural changes can be correlated to the electrical resistivity of TiN coatings.
Keywords
electrical resistivity, microstructure, TiN coating, vacuum cold spray
1. Introduction Vacuum cold spray (VCS) is a novel and promising spray technology developed at the turn of this century. In this process, ultrafine sub-micro-sized ceramic particles are accelerated up to a very high velocity by a carrier gas through a micro-orifice nozzle and subsequently impact and form a coating onto a substrate in a vacuum chamber at room temperature (RT). As the solid ceramic powder is mixed with carrier gas to form an aerosol flow, the technique is also called aerosol deposition (AD) method (Ref 1, 2). Attractive advantages the deposition technology are as follows: (1) during the whole deposition, ceramics in solid state can be deposited onto a ceramic, metallic, or polymer substrate at RT. Consequently, the microstructure of the ceramic powder can be retained without any crystal grain growth or structural changes. This is especially very important for nano-sized or nanostructured ceramic powders. (2) Deposition rate of the VCS process when ceramic powder is used as feedstock This article is an invited paper selected from presentations at the 4th Asian Thermal Spray Conference (ATSC 2009) and has been expanded from the original presentation. ATSC 2009 was held at Nanyang Hotel, XiÕan Jiaotong University, XiÕan, China, October 22-24, 2009, and was chaired by Chang-Jiu Li. Y.-Y. Wang, Y. Liu, G.-J. Yang, and J.-J. Feng, State Key Laboratory for Mechanical Behavior of Materials, XiÕan Jiaotong University, Shaanxi 710049, China; and K. Kusumoto, Department of Mechanical Systems Engineering, Engineering Faculty of Gunma University, Gunma 376-0052, Japan. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
can reach up to several microns to dozens of microns per minute, which is much faster than other deposition techniques for ceramic films such as sol-gel, sputtering, metalorganic chemical vapor deposition (MO-CVD), and ionbeam deposition. Therefore, VCS technology has many advantages compared with conventional ceramic film and coating deposition methods or thermal spray
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