Nondestructive Determination of Thickness and Elastic Modulus of Plasma Spray Coatings Using Laser Ultrasonics
Plasma sprayed coatings are widely used to protect parts from aggressive environments. In applications such as land-based gas turbines, Thermal barrier Coatings (TBCs) are utilized to protect the turbine components from very high operating or firing temperatures . The TBCs are commonly applied by standard air plasma spray process, which is an open-loop operation with no feedback about the coating conditions during deposition. Unfortunately, on-line variations of the spray conditions, such as the continuous wearing of the torch hardware, can adversely affect the coating quality and create significant part-to-part variations. The standard method of evaluating coatings is destructive in nature; hence these tests cannot be performed on each produced part . As a result, coated parts may not have the consistent quality and durability needed for many applications .