On the role of imperfections in the failure of a thermal barrier coating made by electron beam deposition

Effect of Y Distribution on the Oxidation Kinetics of NiCoCrAlY Bond Coat Alloys

“…Close inspection of the location of the Y-rich oxide inclusions revealed that for both alloys almost all inclusions were formed above alloy grain or phase boundaries (Fig. 2), in agreement with previous reports [13,17,28,29]. In some samples, internal oxidation of Y in advance of the O/M interface was observed, but the total amount of internally oxidized Y was very small compared with the amount of Y oxides within the scale.…”

“…2b-d). The formation of these so-called protrusions (or pegs) at the O/M interface is a commonly observed phenomenon for the oxidation of MCrAlY alloys [17,28] and coatings [13][14][15][16]. Close inspection of the location of the Y-rich oxide inclusions revealed that for both alloys almost all inclusions were formed above alloy grain or phase boundaries (Fig.…”

“…The fact that the oxide scales on MCrAlY alloys are not pure a-Al 2 O 3 , but also contain Y-rich oxide inclusions [13][14][15][16][17][18] may explain this deviation from parabolic growth kinetics. When the reactive element Y from the MCrAlY alloy becomes incorporated as Y-rich oxide inclusions in the a-Al 2 O 3 scale, localized enhanced growth of the alumina around the Y inclusions occurs, resulting in the formation of protrusions (pegs) at the oxide/metal (O/M) interface.…”

Anisotropic TGO rumpling in EB-PVD thermal barrier coatings under in-phase thermomechanical loading

“…Degradation of TBCs and the underlying substrate can be caused by many factors. In most cases, partial delamination of the TBC is regarded as a critical failure and considerable research has been conducted in order to understand the delamination mechanisms [7][8][9][10][11]. It is now commonly accepted that delamination is strongly affected by thermally grown oxide (TGO) layer growth and rumpling (evolution of periodic undulations).…”

The effect of the thermal barrier coating on the displacement instability in thermal barrier systems

“…These cracks eventually coalesce and cause fai lure of the TBC by large·scale buckling [9,[11][12][13]. The incidence of cracking w ith in the TBC differentiates such fa ilures from those occurring between the TGO and the bond coat [4]. The experimental evi· dence for this instability is unambiguous [2,7,[9][10][11][12], as is its association with imperfections on the bond coat surface prior to deposition of the TBC [11,12,15].…”