Moisture-induced delamination video of an oxidized thermal barrier coating

2008

MSF

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Abstract. Alumina scale adhesion on high temperature alloys is known to be affected primarily by sulfur segregation and reactive element additions. However adherent scales can become partially compromised by excessive strain energy and cyclic cracking. With time, exposure of such scales to moisture can lead to spontaneous interfacial decohesion, occurring while the samples are maintained at ambient conditions. Examples of this Moisture-Induced Delayed Spallation (MIDS) are presented for NiCrAl and single crystal superalloys, becoming more severe with sulfur level and cyclic exposure conditions. Similarly, delayed failure or Desk Top Spallation (DTS) results are reviewed for TBC's, culminating in the water drop failure test. Both phenomena are discussed in terms of moisture effects on bulk alumina and bulk aluminides. A mechanism is proposed based on hydrogen embrittlement and is supported by a cathodic hydrogen charging experiment. Hydroxylization of aluminum from the alloy interface appears to be the relevant basic reaction.

Section: High Temperature Corrosion and Protection Of Materialsmentioning

confidence: 79%

Enigmatic Moisture Effects on Al2O3 Scale and TBC Adhesion

2008

MSF

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“…A similar coating was tested on tests discs and survived 280 1-hr cycles at 1150 C before failing by water drop testing after 300 cycles [7]. Other similar coatings failed between 220 and 440 hr.…”

Section: Discussionmentioning

confidence: 99%

“…Studies of oxidized APS TBCs on no-bond coat superalloys were found to completely detach unexpectedly, well after cool down, but especially upon water immersion in 1100 and 1150 C tests [5,6]. Video recordings were later used to demonstrate water drop induced spallation of a PVD TBC from a Pt-aluminide bond coat after 300 hr cyclic oxidation at 1150 C [7] . The water drop video test, combined with acoustic emission, revealed the cracking history and PVD TBC delamination from a VPS NiCoCrAlY bond coat that was oxidized isothermally for 310 hr at 1050 C [8,9].…”

Section: Introductionmentioning

confidence: 99%

Moisture-Induced TBC Spallation on Turbine Blade Samples

Surface and Coatings Technology

2011

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Delayed failure of TBCs is a widely observed laboratory phenomenon, although many of the early observations went unreported. "The weekend effect" or "DeskTop Spallation" (DTS) is characterized by initial survival of a TBC after accelerated laboratory thermal cycling, then failure by exposure to ambient humidity or water. Once initiated, failure can occur quite dramatically in less than a second. To this end, the water drop test and digital video recordings have become useful techniques in studies at NASA (Smialek, Zhu, Cuy), DECHMA (Rudolphi, Renusch, Schütze), and CNRS Toulouse/SNECMA (Déneux, Cadoret, Hervier, Monceau). In the present study the results for a commercial turbine blade, with a standard EB-PVD 7YSZ TBC top coat and Pt-aluminide diffusion bond monitored by weight change and visual appearance. Failures were distributed widely over a 5-100 hr time range, depending on temperature. At some opportune times, failure was captured by video recording, documenting the appearance and speed of the moisture-induced spallation process. Failure interfaces exhibited alumina scale grains, decorated with Ta-rich oxide particles, and alumina inclusions as islands and streamers.The phenomenon is thus rooted in moisture-induced delayed spallation (MIDS) of the alumina scale formed on the bond coat. In that regard, many studies show the susceptibility of alumina scales to moisture, as long as high strain energy and a partially exposed interface exist. The latter conditions result from severe cyclic oxidation conditions, which produce a highly stressed and partially damaged scale. In one model, it has been proposed that moisture reacts with aluminum in the bond coat to release hydrogen atoms that 'embrittle' the interface. A negative synergistic effect with interfacial sulfur is also invoked.https://ntrs.nasa.gov/search.jsp?R=20110014519 2018-05-10T11:54:09+00:00Z Moisture-Induced TBC Spallation on Turbine Blade SamplesJames L. Smialek NASA Glenn Research CenterDelayed failure of TBCs is a widely observed laboratory phenomenon, although many of the early observations went unreported. "The weekend effect" or "DeskTop Spallation" (DTS) is characterized by initial survival of a TBC after accelerated laboratory thermal cycling, then failure by exposure to ambient humidity or water. Once initiated, failure can occur quite dramatically in less than a second. To this end, the water drop test and digital video recordings have become useful techniques in studies at NASA (Smialek, Zhu, Cuy), DECHMA (Rudolphi, Renusch, Schütze), and CNRS Toulouse/SNECMA (Déneux, Cadoret, Hervier, Monceau). In the present study the results for a commercial turbine blade, with a standard EB-PVD 7YSZ TBC top coat and Pt-aluminide diffusion bond coat are reported. Cut sections were intermittently oxidized at 1100 , 1150 , and 1200 C and monitored by weight change and visual appearance.Failures were distributed widely over a 5-100 hr time range, depending on temperature. At some opportune times, failure was captured by video recording, documen...

“…No distinction has been made regarding cooling temperature, which is very important, although most attain 30-80°C each cycle. It is well known that lower cooling temperatures, even near room temperature, and exposure to moisture, including ambient humidity, can accelerate scale spallation and TBC failure [14][15][16][17][18][19][20][21]. Typically a similar 2.54 cm dia.…”

Section: Experimental Factorsmentioning

confidence: 99%

“…Some studies also used modified (Y,Yb,Gd) SZ top coats [17,26] (Zhu, Smialek et al). One study pre-oxidized the bond coat prior to YSZ top coating, and reported a broad distribution band of failure times [27] (Tolpygo and Clarke).…”

Section: Overview Of Fct Studies Citedmentioning

confidence: 99%

Compiled furnace cyclic lives of EB-PVD thermal barrier coatings

Surface and Coatings Technology

2015

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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.