Thermal barrier coating life prediction model development

This report describes work performed to determine the predominat modes of degradation of a plasma sprayed thermal barrier coating system and to develop and verify life prediction models accounting for these degradation modes. The primary TBC system consisted of a low pressure plasma sprayed NiCrAlY bond coat, an air plasma sprayed ZrO2-Y2O3 top coat, and a Rene' 80 substrate. The work was divided into 3 technical tasks. The primary failure mode to be addressed was loss of the zirconia layer through spalling. Experiments showed that oxidation of the bond coat is a significant contributor to coating failure. It was evident from the test results that the species of oxide scale initially formed on the bond coat plays a role in coating degradation and failure. It was also shown that elevated temperature creep of the bond coat plays a role in coating failure. An empirical model was developed for predicting the test life of specimens with selected coating, specimen, and test condition variations. In the second task, a coating life prediction model was developed based on the data from Task 1 experiments, results from thermomechanical experiments performed as part of Task 2, and finite element analyses of the TBC system during thermal cycles. The third and final task attempted to verify the validity of the model developed in Task 2. This was done by using the model to predict the test lives of several coating variations and specimen geometries, then comparing these predicted lives to experimentally determined test lives. It was found that the model correctly predicts trends, but that additional refinement is needed to accurately predict coating life

Thermal Barrier Ceramic Coatings — A Review

Thermal barrier coatings (TBCs) provide effective thermal barrier to the components of gas turbine engines by allowing higher operating temperatures and reduced cooling requirements. Plasma spraying, electron-beam physical vapor deposition, and solution precursor plasma spray techniques are generally used to apply the TBCs on the metallic substrates. The present article addresses the TBCs formed by different processing techniques, as well as the possibility of new ceramic, glass-ceramic, and composite materials as TBCs. Promising bond coat materials for a TBC system have been also stated

Hot corrosion behaviour of new candidates for thermal barrier coatings application in turbine simulated environments

Thermal barrier coatings (TBCs) are used gas turbine engines. The current material of choice (YSZ) degrades when it contacts with impurities arise from low quality fuels such vanadium and sulfur. YSZ cannot be used in temperature higher than 900˚C. Higher efficiency and performance of gas turbine engines will require a new generation of thermal barrier coatings (TBCs). In current work, hot corrosion behavior of new candidates including Gd2Zr2O7, ZrO2 stabilized with Ta2O5, zirconia stabilized with both Ta2O5 and Y2O3 and zirconia stabilized with CeO2 and TiO2 is investigated. For YSZ case, the reaction between NaVO3 and Y2O3 produces YVO4 and leads to the transformation of tetragonal ZrO2 to monoclinic ZrO2. Comparing to YSZ, under a temperature of 1050 °C, Gd2Zr2O7 is found to be more stable, both thermally and chemically, than YSZ, and exhibits a better hot corrosion resistance. To examine the effect of stabilizing zirconia with tantalum oxide, different compositions of ZrO2-Ta2O5 samples in the presence of molten mixture of Na2SO4 + V2O5 at 1100˚C were tested. Hot corrosion results show that orthorhombic zirconium-tantalum oxide is more stable, both thermally and chemically in Na2SO4+V2O5 media at 1100˚C, and shows a better hot corrosion resistance than the tetragonal phase. When zirconia stabilized with yttria and tantalum oxide (TaYSZ sample), minor amounts of NaTaO3, TaVO5 and Ta9VO25 are formed as the hot corrosion products with only traceable amounts of YVO4. Due to the synergic effect of doping of zirconia with both Y2O3 and Ta2O5, the TaYSZ sample has a much better hot corrosion resistance than YSZ. In zirconia stabilized with CeO2 coating, the formation of CeVO4 crystals possibly postponed the formation of YVO4 and transformation of tetragonal zirconia to monoclinic. On surface of zirconia stabilized with TiO2 coating, TiVO4 crystals are significantly smaller (about 5µm in length) than the large plate shaped YVO4 and CeVO4 found on the YSZ and CSZ samples. TiSZ coating was found to have a better hot corrosion resistance at a temperature of 1050˚C than both YSZ and CSZ coatings

Termal bariyer kaplamalarda bağ tabakasının farklı yöntemlerle üretilmesi ve özelliklere etkisi

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Bu çalışmada, CoNiCrAlY bağ ve YSZ (ZrO2+Y2O3) üst kaplama içeriğine sahip termal bariyer kaplama (TBC) sistemleri incelenmiştir. Inconel 718 süper alaşım altlık malzeme üzerine bağ kaplamaların üretiminde; atmosferik plazma sprey (APS), yüksek hız oksi asetilen yakıt (HVOF) ve soğuk gaz dinamik sprey (CGDS) teknikleri kullanılmıştır. Üst kaplamaların üretiminde ise APS tekniği kullanılarak TBC sistemlerinin üretimi sağlanmıştır. Farklı bağ kaplama teknikleriyle üretilen TBC’lerde oksidasyon ve termal çevrim/şok koşulları altında termal olarak büyüyen oksit (TGO) yapısı oluşumu ve büyüme davranışları incelenerek, farklılıklar literatürdeki çalışmalar dikkate alınarak ortaya konulmuştur. Farklı tekniklerle üretimleri gerçekleştirilen TBC’lerin mikro yapısal ve mekanik özellikleri; optik mikroskop, SEM, EDX-elementel haritalama, stereo mikroskop, porozite, XRD, yapışma mukavemeti, mikrosertlik, nanoindentasyon analiz ve ölçümleriyle özellikleri belirlenmiş ve birbirleriyle karşılaştırmaları yapılmıştır. 1000 °C, 1100 °C ve 1200 °C sıcaklıklarda 8, 24, 50 ve 100 saatlik süreçlerde yapılan izotermal oksidasyon testleri ve oksidasyon testlerine paralel olarak gerçekleştirilen termal çevrim/şok testleri sonrasında, oluşan TGO yapısı ve büyüme davranışları incelenerek, açıklamalar getirilmiştir.In this study, thermal barrier coating (TBC) systems with CoNiCrAlY bond and YSZ (ZrO2+Y2O3) top coating were investigated. In the production of bond coatings on Inconel 718 superalloy substrate material, atmospheric plasma spray (APS), high velocity oxy fuel (HVOF) and cold gas dynamic spray (CGDS) techniques were used, while in the production of top coatings APS technique was used, and TBC systems were produced. The formation and growing behaviors of oxide (TGO) structure thermally growing in TBCs produced by different bond coating techniques under the oxidation and thermal cycle/shock conditions were investigated, and the differences were shown considering the studies in literature. The microstructural and mechanical properties of the TBCs produced by different techniques were determined by optical microscope, SEM, EDX-Maping, stereo microscope, XRD, porosity, adhesion strength, hardness and nanoindentation analysis and measurements were compared with each other. The structure and growth behavior of the TGO, that formed after the isothermal oxidation tests performed at temperatures of 1000 ºC, 1100 ºC and 1200 ºC at periods of 8, 24, 50 and 100 hours and thermal cycle/shock tests carried out in parallel with the oxidation tests, were investigated and explained

Computer model to predict electron beam-physical vapour deposition (EB-PVD) and thermal barrier coating (TBC) deposition on substrates with complex geometry

For many decades gas turbine engineers have investigated methods to improve engine efficiency further. These methods include advances in the composition and processing of materials, intricate cooling techniques, and the use of protective coatings. Thermal barrier coatings (TBCs) are the most promising development in superalloy coatings research in recent years with the potential to reduce metal surface temperature, or increase turbine entry temperature, by 70-200°C. In order for TBCs to be exploited to their full potential, they need to be applied to the most demanding of stationary and rotating components, such as first stage blades and vanes. Comprehensive reviews of coating processes indicate that this can only be achieved on rotating components by depositing a strain-tolerant layer applied by the electron beam-physical vapour deposition (EB-PVD) coating process. A computer program has been developed in Visual c++ based on the Knudsen cosine law and aimed at calculating the coating thickness distribution around any component, but typically turbine blades. This should permit the controlled deposition to tailor the TBC performance and durability. Various evaporation characteristics have been accommodated by developing a generalised point source evaporation model that involves real and virtual sources. Substrates with complex geometry can be modelled by generating an STL file from a CAD package with the geometric information of the component, which may include shadow-masks. Visualisation of the coated thickness distributions around components was achieved using OpenGL library functions within the computer model. This study then proceeded to verify the computer model by first measuring the coating thickness for experimental trial runs and then comparing the calculated coating thickness to that measured using a laboratory coater. Predicted thickness distributions are in good agreement even for the simplified evaporation model, but can be improved further by increasing the complexity of the source model

Bibliography of Lewis Research Center technical publications announced in 1992

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1992. All the publications were announced in the 1992 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses