The influence of platinum on the failure of EBPVD YSZ TBCs on NiCoCrAlY bond coats

The oxygen permeability of an undoped polycrystalline -Al 2 O 3 wafer that was exposed to oxygen potential gradients was evaluated at temperatures up to 1973 K. Oxygen preferentially permeated through the grain boundaries of -Al 2 O 3 . The main diffusion species, which were attributed to oxygen permeation, depended on oxygen partial pressures (P O2 ), forming oxygen potential gradients. Under oxygen potential gradients generated by P O2 below about 1 Pa, oxygen permeation occurred by oxygen diffusing from regions of higher P O2 to regions of lower P O2 . By contrast, under oxygen potential gradients generated by P O2 above about 1 Pa, oxygen permeation proceeded by aluminum diffusing from regions of lower P O2 to regions of higher P O2 . In other words, O 2 molecules were adsorbed onto a surface at higher P O2 and subsequently dissociated into oxygen ions (forming Al 2 O 3 ), while oxygen ions on the opposite surface at lower P O2 were desorbed by association into O 2 molecules (decomposition of Al 2 O 3 ). The grain-boundary diffusion coefficients of oxygen and aluminum as a function of P O2 were determined from the oxygen permeation constants.

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“…[3][4][5][6][7] Thus, suppressing masstransfer through the -Al 2 O 3 scale is anticipated to further improve the durability of TBCs.…”

Section: Introductionmentioning

confidence: 99%

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

2009

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“…The coating was obtained on the specimens by electroplating of Ni followed by Al-pack cementation. The high Al activity pack cementation was carried out in a vacuum of 10 -3 Pa at 800°C for 20 min by burying the Ni-plated specimens into a mixture of Al metal powder (15 wt%), NH 4 Cl (5 wt%) as an activator, and Al 2 O 3 powder as an anti-sintering agent. The compositions of the coating were determined to be (71-98) at.% Ni and *40at.%Ni-60at.%Al from the substrate, namely, the coating consisted of an internal Ni-rich layer and an external Ni 2 Al 3 layer [6].…”

Section: Methodsmentioning

confidence: 99%

“…Moreover, the inward diffusion of Al to the alloy substrate and outward diffusion of the alloying elements in the substrate could lead to decreases in the mechanical properties of the alloy substrate [3]. Due to acceleration of interdiffusion between the alloy substrate and the bond-coat, the precipitation of detrimental phases from the substrate occurs, and the rapid growth of a thermally grown oxide on the bond-coat results in enhancement of the top-coat spallation [4].…”

Section: Introductionmentioning

confidence: 99%

The Improvement of Oxidation Resistance of a Re-Based Diffusion Barrier/Ni–Al Coating on the Single-Crystal Ni-Based TMS-82+ Superalloy

Wang

Song

et al. 2011

Oxid Met

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Oxidation behavior of a Re-based diffusion barrier/Ni-Al coated singlecrystal (SC) Ni-based TMS-82? superalloy was studied to compare with those of the base and Ni-Al coated superalloys under cyclic air at 1150°C for 200 h. The base superalloy showed a negative mass gain due to extensive oxide spallation, and the Ni-Al coated superalloy without the diffusion barrier started to spall slightly after about 90 h. The oxidation resistance of the Ni-Al coated superalloy with the Re-based diffusion barrier was greatly improved due to the formation of a dense a-Al 2 O 3 layer in the scale. The Re-based alloy was an effective diffusion barrier layer against inward diffusion of Al and outward diffusion of alloying elements in the alloy substrate due to the reduced thickness of interdiffusion zone with small amount of detrimental precipitates and higher content of Al in the Ni-Al coating that supplied enough Al for formation of the a-Al 2 O 3 layer.

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“…One of these studies systematically varied the Co content of a 3rd generation (high Re) composition and found that a low 2 wt.% Co alloy provided the maximum TBC life compared to 8 or 12 wt.% Co [30]. Other studies employed NiCoCrAlY bond coats [32][33][34][35] (Kim, Nijdam, Schulz, and coworkers) or a Pt coating over NiCoCrAlY(Ta) bond coat [36][37][38] (Yanar, Vande Put, and coworkers).…”

Section: Overview Of Fct Studies Citedmentioning

confidence: 99%

Compiled furnace cyclic lives of EB-PVD thermal barrier coatings

Smialek

2015

Surface and Coatings Technology

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a b s t r a c t a r t i c l e i n f oFurnace cycling has been widely used to study the failure of EB-PVD thermal barrier coatings. This contribution compiles TBC furnace cyclic lives over a broad literature base to highlight optimum systems and generalized trends not always apparent in one study. Systems included typical bond coats (Pt-modified aluminides, diffused Pt-only γ/γ′, and NiCoCrAlY (± Pt, Hf) overlays) and superalloy substrates (1st, 2nd, 3rd generation single crystals, directionally solidified, or conventionally cast). Pretreatments included controlled low p(O 2 ) bond coat pre-oxidation and grit blasting (or none). The aggregate lives (~70) suggest a general trend with temperature,~10-fold decrease for every 100°C increase. Measured alumina scale thicknesses (~30) were, on average, 6.1 ± 1.8 μm at failure and independent of temperature for conventional systems. Most failures thus occurred in less time than that predicted to grow 7 μm of alumina scale (as estimated from separate TGA studies of a Ptmodified aluminide coated 2nd generation single crystal superalloy). A tentative activation energy indicated from the broad distribution of failure times was~280 kJ/mol, while that from homogeneous TGA testing was 380 kJ/mol, with regression coefficients of r 2 = 0.57 and 0.98, respectively. Published by Elsevier B.V.

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The influence of platinum on the failure of EBPVD YSZ TBCs on NiCoCrAlY bond coats

Cited by 78 publications

References 2 publications

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

The Improvement of Oxidation Resistance of a Re-Based Diffusion Barrier/Ni–Al Coating on the Single-Crystal Ni-Based TMS-82+ Superalloy

Compiled furnace cyclic lives of EB-PVD thermal barrier coatings

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