AlN thin film transducers for high temperature non-destructive testing applications

Abstract

AlN thin film ultrasonic transducers are being developed for non-destructive testing (NDT) applications in detection and monitoring in a high temperature environment. The ultrasonic transducers were fabricated by RF sputter deposition of c-axis oriented AlN films on aluminum alloy and carbon steel substrates. High temperature performance and durability of the transducers were investigated using pulse-echo experiments at elevated temperatures, and the transducer failure mode was characterized. Results showed that the sputtered AlN films maintained a stable crystalline structure and orientation at elevated temperatures up to 600 °C. The high temperature performance of the ultrasonic transducers, however, was limited by the deterioration of substrate properties. The high temperature limit for the films on aluminum alloy was found to be the melting temperature of the substrate. The AlN films deposited on the carbon steel substrate operated up to 500 °C, but if the temperature was increased further, rapid surface oxidation of the carbon steel caused the transducer to fail.