RAMAN STUDIES ON EB-PVD 7%YTTRIA- STABILIZED ZIRCONIA COATINGS WITH CMAS DEPOSITS

Abstract

Thermal barrier coatings (TBCs) benefit the performance of turbine blades under operational conditions by successfully maintaining their integrity. However, reduced effectiveness of TBCs is experienced when foreign materials deposit on their surface, specifically those leading to infiltration of siliceous debris and calcium-magnesium-alumina silicate (CMAS) deposits. In this paper, the microstructural properties of Electron Beam Physical Vapor Deposition (EB-PVD) 7%YSZ coatings exposed to CMAS deposits were investigated. Raman spectroscopy was used to track the phase transformation of Zirconia from its tetragonal (t) to its monoclinic phase (m). Our results show that the behavior of the TBCs is location and temperature-dependent. For coatings heated at 1250° C for 10 hours, the YSZ top coat was partially dissolved in the CMAS, resulting in a decreasing monoclinic phase volume faction further into the coating and away from the CMAS infiltrated region. These results suggest that the band corresponding to the monoclinic phase of the material can be used to detect the CMAS within the TBC.