Study on Structure and Ultrasonic Performance of ZnO Piezoelectric Coatings on Smart Bolts After 300 ∘C Annealing

The accurate measurement of the preload on bolt has been extensively investigated ecent years using longitudinal ultrasonic waves. For ultrasonic measurement of bolt preload ZnO coatings have exhibited excellent piezoelectric properties and stable structure. In this paper, ZnO piezoelectric coatings were prepared onto Si(100) substrates by radio frequency (RF) magnetron sputtering, and the effect of annealing on the structure and ultrasonic performance of the coatings was investigated. The morphology, structure and ultrasonic signal characteristics were characterized by SEM, AFM, XRD and ultrasonic measurement instruments. The experimental results show that ZnO coatings have good stability at 300 ∘C for 200 h. There are not obvious effects of annealing on the surface morphology and crystalline orientation of the coating. The ultrasonic echo signals of the coatings deposited on the bolts demonstrate good stability after longtime heat treatment.