Abstract
Thin film thermocouples are widely used for local temperature determinations of surfaces. However, depending on the environment in which they are used, thin film thermocouples need to be covered by a wear or oxidation resistant top layer. With regard to the utilization in wide-slit nozzles for plastic extrusion, Ni/Ni-20Cr thin film thermocouples were manufactured using direct-current (DC) magnetron sputtering combined with Aluminiumnitride (AlN) and Boron-Carbonitride (BCN) thin films. On the one hand, the deposition parameters of the nitride layers were varied to affect the chemical composition and morphology of the AlN and BCN thin films. On the other hand, the position of the nitride layers (below the thermocouple, above the thermocouple, around the thermocouple) was changed. Both factors were investigated concerning the influence on the Seebeck coefficient and the reaction behaviour of the thermocouples. Therefore, the impact of the nitride thin films on the morphology, physical structure, crystallite size, electrical resistance and hardness of the Ni and Ni-20Cr thin films is analysed. The investigations reveal that the Seebeck coefficient is not affected by the different architectures of the thermocouples. Nevertheless, the reaction time of the thermocouples can be significantly improved by adding a thermal conductive top coat over the thin films, whereas the top coat should have a coarse structure and low nitrogen content.
Highlights
In the future, surface integrated sensor systems will become increasingly significant for smart products
Different multilayer architectures were investigated regarding the impact on the reaction time of Ni/Ni-20Cr thin film thermocouples
Ni and Ni-20Cr thin films was analysed. Both coatings were deposited on thermally sprayed Al2 O3, as well as on a BCN and three different AlN thin films
Summary
Surface integrated sensor systems will become increasingly significant for smart products. For tribological contacts, a sufficient knowledge concerning the temperature or pressure is of special interest. In order to measure the temperature in combustion engines [1] or in plastic injection moulds [2] a fast response of the thermocouples is necessary. Temperature measurement and control are very important in polymer extrusion, especially to ensure the process stability and quality of the products [3]. For this reason, thin film thermocouples and thin film pressure sensors are ideal for a variety of applications. Thin film thermocouples have a lower mass compared to wire thermocouples and, respond faster [4]
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