Non-Destructive Evaluation of Thermal Barrier Coating Damage and Molten Sand Deposits on Gas Turbine Engine Components via Scanning Acoustic Microscopy

摘要

Emerging challenges in gas turbine engine (GTE) and thermal barrier coating (TBC) technology require the maturation of non-destructive evaluation (NDE) techniques to streamline and bring down costs of materials and component level research and development. In this paper, Scanning Acoustic Microscopy (SAM) is demonstrated to be an effective way for evaluating molten sand accumulation, due to melting of ingested sand and environmental particulates, on the surface and internal channels of nozzle vanes of GTE components evaluated in a full scale engine test. The use of transducers with a wide range of frequencies makes this a versatile technique for assessing both macroscalc damage such as cracking and delamination, as well as mesoscale characteristics such as the porosity of sand deposits. In this paper, SAM studies are conducted using both a 15 MHz transducer for evaluation of the entire nozzle doublet, and a 100 MHz transducer to characterize sand accumulation and porosity with higher resolution. SAM enables determination of surface cooling hole blockage, internal channel sand accumulation, and characterization of the molten sand scales on the surface. In addition, utilizing simpler geometries (i.e., button cells), it is possible to assess damage on TBCs exposed to sand laden combustion environments. Comparative analysis of an as-deposited air plasma sprayed (APS) TBC and an APS TBC exposed to sand laden combustion environments is conducted to assess the effectiveness of NDE TBC damage detection via SAM.