Papers by Author: Morito Akiyama

Abstract: Aluminum nitride (AlN) thin films formed on the heat-resistant alloy substrates were heated to 1100K. Cracking was observed in the AlN film formed on the stainless steel substrate (SUS430), while no crack was seen in that on the nickel-base superalloy substrate (IN750X). The electrical impedance measurements, X-ray diffraction analysis and finite element method calculation have been conducted to discuss the relationship between the cracking and the stress introduced into the AlN films. The AlN film cracking would be significantly affected by grain refinement of AlN.

Abstract: Aluminum nitride (AlN) is a promising Acoustic Emission (AE) sensor element for high-temperature environments such as gas turbines and other plants because AlN maintains its piezoelectricity up to 1200°C. Highly c-axis-oriented AlN thin-film sensor elements were prepared on silicon single crystals by rf magnetron sputtering. Both ordinary-temperature AE sensors and high-temperature AE sensors have been developed using these elements. In this paper, to study effects of d33 and thickness of AlN elements on sensor sensitivity, AlN elements with d33 from 2 to 7 pm/V and thickness from 3 to 9 /m were prepared. It is confirmed that the AE sensor sensitivity increased with d33 and thickness of AlN elements. The sensitivity of the high-temperature AE sensor was also improved by a design of the sensor structure. The sensor characteristics were evaluated at elevated temperatures from 200 to 600°C. It was confirmed that the AE sensor works well at 600°C and does not deteriorate.