Non-Destructive Optical Test to Detect Damage in Turbine Blades

Abstract

Researchers at the University of Central Florida and the German Aerospace Center (DLR) have invented a new, non-destructive optical test to identify whether thermal or environmental barrier coatings on components have been infiltrated with particulates, such as dust, sand and ash debris, which can lead to coating failure.  Besides detecting particulates, the test also measures the depth of infiltration, so that technicians can evaluate the anticipated lifetime of a coating and the level of damage sustained. The information can thus assist in determining whether a coated part requires a partial or full repair.

Thermal barrier coatings (TBC) help to extend the lifetime of components in high-pressure and high-temperature equipment (turbines, automotive parts, aircraft). Additionally, environmental barrier coatings (EBC) protect parts that are susceptible to water vapor-assisted damage. When equipment treated with such coatings operates under extreme temperatures, calcium, magnesium and aluminum-silicate (CMAS) particles from the equipment’s surroundings can melt and infiltrate the porous structure of the coatings. This can lead to cracking, spalling, and sub-surface delamination that is not easily identified prior to part failure. The ability to detect and locate these defects is crucial to reducing maintenance costs, minimizing downtime, and assuring system safety and reliability. Yet, current methods for analyzing CMAS infiltration and assessing the lifetime of a coated part destroy the component instead of leaving it intact. The invention resolves these issues by using 3D confocal Raman spectroscopy, which provides a non-destructive way to directly measure a CMAS infiltration within a coating, including the depth of infiltration.

Technical Details

The invention is a 3D confocal Raman spectroscopy sensing method that provides a non-destructive technique for characterizing CMAS infiltration and CMAS-assisted damage in TBCs and EBCs. In one example use of the invention, UCF researchers investigated the effects of CMAS infiltration within 7% yttria stabilized zirconia (7YSZ). The test determined the location, composition and concentration of the infiltration based on the phase change initiated by the CMAS within the material. Using 3D-visual output, the test also correlated the results to CMAS infiltration damage. With the ability to determine the composition and location of a CMAS infiltration by detecting a CMAS-induced phase change, the measurement technique could be linked with other existing test measurements to provide definitive correlations between stress and CMAS-affected areas. This measurement can be performed on parts that could then be repaired and replaced or tested within equipment assemblies with portable instrumentation.

Benefit

Market Application