Concept of Functionally Graded Materials for Advanced Thermal Barrier Coating Applications

Abstract

This feature article explores the concept of creating functionally graded metal‐ceramic composite microstructures for thermal barrier coatings used in gas‐turbine applications. From a thermomechanical perspective, this concept offers the possibility of significantly improving the life and reliability of thermal barrier coatings. However, prior research reveals that progress has been somewhat limited because of the oxidative instability exhibited by some metal‐ceramic composite microstructures. The present study addresses some of the materials criteria and research issues associated with preparing chemically stable, yet mechanically durable, graded metal‐ceramic microstructures for realistic application environments.

Problem of FGM TBC coated cylinder

“…These residual stresses may be significant relative to thermo-mechanical stresses applied subsequently. As regards FG layer processing, plasma spray TBC leads to lamellar microstructures, whereas columnar-lamellar microstructures are produced when using electron beam physical vapor deposition, see Lee et al [20], Schulz et al [16].…”

On The Stress Free Deformation Of Linear FGM Interface Under Constant Temperature

“…These residual stresses may be significant relative to thermo-mechanical stresses applied subsequently. As regards FG layer processing, Plasma Spray Thermal Barrier Coating leads to lamellar microstructures, whereas columnarlamellar microstructures are produced when using Electron Beam Physical Vapour Deposition, see Lee et al (1996), Schulz et al (2003).…”

Advanced Thermal Barrier Coating

“…The exact mechanics depend on the system under consideration, and Figure 3 provides a plausible picture of the progression of damage. Microcracks initially form in the TGO and often tend to propagate along the bond-coat/TGO interface [3,4,9,12]. Continued oxidation and opening of these cracks initiate bulges that manifest as surface irregularities on the YSZ outer surface.…”

“…Those will be amplified in a later section. Figure 5 illustrates results from a finite element method (FEM) analysis with a sinusoidal alumina/YSZ interface [12]. The YSZ layer is on the right, and the TGO is on the left side of the figure.…”

“…The mechanics of buckling induced YSZ spallation has also been probed [12]. In the absence of any interface crack, the critical stress for buckling of the YSZ is approximately 9 GPa, whereas the actual in-plane compressive stress in the YSZ is only about 150 MPa.…”