Potassium sodium niobate (KNN)‐based lead‐free piezoelectric ceramic coatings on steel structure by thermal spray method

Abstract For the first time, potassium sodium niobate ( KNN )‐based lead‐free piezoelectric ceramic coating with strong piezoelectric response was fabricated on stainless steel substrates by thermal spray process, after introducing NiCrAlY and yttria‐stabilized zirconia ( YSZ ) intermediate layers. A large effective piezoelectric coefficient (d 33 ) of 125 pm/V was obtained with the thermal‐sprayed KNN ‐based ceramic coating on the steel substrates. The mechanisms of improving the structure and enhancing the properties of the KNN ‐based piezoelectric ceramic coatings by introducing the intermediate layers were analyzed. Ultrasonic transducers were designed and fabricated from the KNN ‐based coatings directly formed on a steel plate structure, and the feasibility for generation and detection of ultrasonic waves for structural health monitoring using the thermal‐sprayed lead‐free piezoelectric ceramic coating was demonstrated.