Fabrication of thin film ultrasonic transducers for high temperature industrial applications

摘要

This paper presents some of the exploration work on developing AlN thin film ultrasonic transducers for high temperature defect detection and monitoring of industrial plants and components. Highly c-axis oriented AlN films were grown on carbon steel substrates by RF sputtering deposition. High temperature performance and durability of the transducer were examined by pulse-echo experiments after heating to different temperatures. XRD and SEM were employed for film characterisation and investigation of transducer failure mode. It can be shown that sputtered AlN films could still maintain good performances at temperatures up to 500 °C. The high temperature performance of the transducer, however, was limited by the heat-induced surface oxidation of the carbon steel substrate at the elevated temperatures, which led to the decoupling of the film from the substrate due to the formation of scales or rust at the interface.