Materials Science and Chemistry

Biography

Biography: Maryam Ali Bash

Abstract

Yttria partially stabilized zirconia (YPSZ) systems which are worldwide acceptable TBC for many advanced turbine engines, since developed before more than 30 years till now are widely investigated for high temperature corrosion resistance and for laser sealing. New system based on ceria-yttria stabilized zirconia ceramic thermal barrier coating sprayed above Ni24.5Cr6Al0.4Y bond coat deposited using semiautomatic air plasma spray on Inconel 738 LC superalloy substrate was investigated. The upper surfaces of thermal barrier coating system were sealed using high power Yb⁺³-YAG laser. The as-sprayed and as-sealed coatings were tested for hot corrosion resistance at different temperatures and exposure times in a mixture of eutectic V₂O₅-Na₂SO₄. The upper surface plan views and transverse sections of the exposed samples were analysis using SEM, EDS, EPMA, XRD, FT-IR, atomic force microscopy and Raman spectroscopy. The laser sealed samples showed higher hot corrosion resistance under all tested conditions compared with its counterpart plasma sprayed coating. The presence of ceria in the thermal barrier coating reduced considerably the corrosion rate of as-sprayed and as-sealed thermal barrier coatings. The most dominant phase formed was YVO₄ rather than CeVO₄. The most detrimental defects accelerate the hot corrosion rate were porosity and voids. The presence of depression in the sealed coatings encouraged the reaction between the harmful species and the constituent of the zirconia based coating. The formation of harmful products of YVO₄ and CeVO₄ encourage the transformation of non-transformable tetragonal phase to monoclinic phase.

Sever attacks of salts at depressions of laser sealed plasma sprayed coating at 900 ^oC for 8 hr showing the harmful nature of depressions.