Thermal sprayed lead-free piezoelectric ceramic coatings for ultrasonic structural health monitoring.

Structural health monitoring (SHM) is growing rapidly with strong demand from industrial automation, digital twins, and Internet of Things (IoT). In contrast to the manual installation of discrete devices, piezoelectric transducers by directly coating and patterning the piezoelectric materials on the engineering structures show the potential for achieving SHM function with improved benefits over cost. Until the recent years, high performance lead-free piezoelectric ceramic coatings, including potassium-sodium niobate (KNN) and bismuth sodium titanate (BNT)-based coatings, are produced by thermal spray method. This paper reviews the background and progresses of using thermal spray method for fabricating piezoelectric ceramic coatings and their values for SHM applications. The review shows the combination of environmentally friendly lead-free compositions and the scalable thermal spray processing method opens substantial application opportunities. Ultrasonic SHM technology enabled by thermal sprayed piezoelectric ceramic coatings is an important area where the lead-free piezoelectric ceramic materials can play with their technical competitiveness and commercial values over the lead-based compositions.