Real-Time Thickness Measurement Technology for Process Control of Coating Manufacturing

Highly engineered ceramic coatings, called thermal barrier coatings (TBCs), have been used for many years in the gas turbine industry, and more recently, in internal combustion engines for automotive, truck, and construction vehicle applications. These coatings increase the performance and durability of the engines. The gas turbine industry has shown that coating thickness variations are major sources of variation in coating and component service lives. To define and control service life, there is a strong need to be able to measure coating thickness during processing, especially on components with a small radius of curvature. The goal of the proposed program is to demonstrate a laser-induced ultrasonic coating thickness measurement system capable of measuring relatively thin (25-350 μm) ceramic coatings, with a spot size less than 1 mm. Applications include both postcoating part inspection and real-time measurement during thermal spray. The SST proposed measurement system will consist of a pulsed laser to excite ultrasonic waves in the coating, and a continuous probe laser to monitor the resulting surface oscillations. The propagation time of the wave through the coating is directly related to its thickness.