Effects of EB-PVD Process TGO Formation and Growth within Thermal Barrier Coatings

Abstract

It has been found that under oxygen partial pressure of ~2×10-6 kPa, the high-temperature oxidation of thermal barrier coatings (TBCs) occurred during an electron beam physical vapor deposition (EB-PVD) process for producing the TBCs top ceramic coating. In the present investigation, two modified bond coats (BCs) of NiCrAlY with Si addition, and NiCrAlY with Co and Hf additions, were developed by Arc Ion-plating technique to study the effects of the EB-PVD process on thermally grown oxide (TGO) formation and growth. The isothermal and cyclic oxidation tests were conducted and the cross-sectional morphologies of the specimens were examined to compare the high-temperature oxidation behaviors of the two TBCs. It was found that a mixed oxide layer have been developed in the as-deposited TBCs with a NiCrAlYSi BC. The mixed oxide layer mainly included Cr2O3, NiO, Al2O3 and their spinel. With the mixed oxide layer, TBCs with the NiCrAlYSi BC showed a superior high-temperature resistance on later high-temperature exposure to TBCs with NiCoCrAlYHf BC, where no mixed oxide layer was observed. The pre-formed mixed oxide layer apparently shortened the time to fully develop a protective α-Al2O3 layer and therefore restrained the TGO growth in TBCs.

Effect of diffusion barrier on the high-temperature oxidation behavior of thermal barrier coatings

“…Table 5 The relative elemental concentrations of areas "A" and "B" in the SEM image (at.%) as shown in Fig. 11a coat, and the existence of mixed-oxides is also regarded as a crucial factor to cause the failure of TBCs [3,17,18].…”

“…␤-NiAl, (Ni,Pt)Al, et al) or overlay (MCrAlYX, M = Ni or/and Co, X = Hf, Ta, Re or Si, et al) metallic bond coat, and a Ni-based superalloy substrate. Currently, TBCs are usually produced by either EB-PVD or atmospheric plasma spraying [3].…”

Thermal cycling behavior of La2Zr2O7 coating with the addition of Y2O3 by EB-PVD

“…7f and h). The higher is the content of pure Al 2 O 3 in the TGO layer, the longer is the thermal cycling life of TBCs [32].…”

Double-ceramic-layer thermal barrier coatings of La2Zr2O7/YSZ deposited by electron beam-physical vapor deposition

“…To meet these requirements, thermal barrier coatings (TBCs) have been applied in aircraft propulsion and land-based power generation systems to increase turbine inlet temperature and the thermal efficiency. The state-of-the-art and conventional TBCs system usually consist of a ceramic topcoat of yttria stabilized zirconia (YSZ), a metallic bond coat (BC, MCrAlYX, M = Ni/Co, X = Hf, Ta, Re, Si) and a Ni-based superalloy substrate [4]. Currently, TBCs are usually produced by either electron beam-physical vapor deposition (EB-PVD) or atmospheric plasma spraying (APS).…”