Energy Materials 2017: Materials for Gas Turbines: Coatings
Sponsored by: Chinese Society for Metals
Program Organizers: Jeffrey Fergus, Auburn University; Ji Zhang, China Iron and Steel Research Institute Group

Monday 8:30 AM
February 27, 2017
Room: 13
Location: San Diego Convention Ctr

Session Chair: Sanjay Sampath, Stony Brook University; Daniel Mumm, University of California, Irvine

8:30 AM  Keynote
Multilayered, Multifunctional Thermal Barrier Coatings for Gas Turbine Engines: Sanjay Sampath1; Vaishak Vishwanathan1; Gopal Dwivedi1; 1Stony Brook University
    Thermal barrier coatings (TBCs) are increasingly playing a vital role in enhancing efficiency and performance of gas turbine engines. As engine operating temperatures rise, yttria-stabilized zirconia (YSZ), the currentTBC, has reached its operational limits. Gadolinium Zirconate (GDZ)-based pyrochlores are now emerging contenders, as they offer low conductivity and resist attack by silicate deposits. However, GDZ cannot be directly substituted for YSZ due to its incompatibility with the thermally grown alumina layer, requiring multilayer strategies. In this study several multilayer architectures, based on both YSZ and the YSZ–GDZ system,have been developed and tested for durability under furnace thermal cycling conditions. Coating designs considered optimization of microstructure and properties of individual layers based on their location within the top-coat thickness to address competing interests of thermal conductivity, compliance, and resistance to silicates. The results point to new strategies in the design and manufacturing of optimal multilayer coatings.

9:10 AM  Invited
Thermal Barrier Coatings for More Efficient Gas-Turbine Engines: Nitin Padture1; 1Brown University
    Gas-turbine engines are to generate ~20% of world’s electricity, to propel aircraft. Ceramic thermal barrier coatings (TBCs) are used to insulate and protect hot-section metallic components in these gas-turbine engines. However, the higher temperatures and extreme conditions in high-efficiency engines are making TBCs prone to deposition of undesirable calcium-magnesium-alumino-silicates (CMASs) ingested by the engines, engendering new materials issues that are becoming critical for the development of more efficient engines. The undesirable CMAS can be in the form of fly ash in the case of syngas-fired engines used for electricity generation, and sand and volcanic ash in the case of aircraft engines. The understanding of mechanisms by which molten CMAS deposits damage conventional yttria-stabilized zirconia TBCs is presented. Demonstration and understanding of approaches to mitigate this type of CMAS-induced damage in new TBCs are also presented, together with a discussion of guidelines for the development of new TBCs.

9:40 AM  
Evolution of the Thermal Conductivity of Sm2Zr2O7 under CMAS Attack: Ahmet Bakal1; Kai Roebbecke1; Honglong Wang1; Wenzhuo Deng1; Xingxing Zhang1; Jeffrey Fergus1; 1Auburn University
    One impact of the reaction of thermal barrier coatings (TBCs) in gas turbine engines with volcanic ash or other debris (CMAS) is a change in the thermal conductivity. In this study, the effective thermal conductivity of the potential TBC material Sm2Zr2O7 was determined after CMAS reaction below and above the melting temperature of the CMAS. The conductivities of Sm2Zr2O7, CMAS, and the reaction layer were determined separately. The phase content and microstructure were characterized with scanning electron microscopy and x-ray diffraction. The change in microstructure and formation of Ca2Sm8(SiO4)6O2 led to an increase in the effective conductivity, which would reduce the effectiveness of the TBC.

10:00 AM Break

10:20 AM  Invited
The Effect of Superalloy and Coating Composition and Specimen Geometry on TBC Lifetime: Bruce Pint1; 1Oak Ridge National Laboratory
    Several factors are being investigated that affect the performance of thermal barrier coatings (TBC) for use in land-based gas turbines where coatings are mainly thermally sprayed. This study examined high velocity oxygen fuel (HVOF) and vacuum plasma sprayed (VPS) MCrAlYHfSi bond coatings with air-plasma sprayed YSZ top coatings at 1100C. For superalloy X4, 1483 and 247 substrates, no significant change in average lifetime (i.e. time to coating failure) was observed in 1-h or 100-h cycles in air+10%H2O when the HVOF bond coatings was sufficiently thick (>150m). For VPS coatings tested in 1-h cycles, removing 0.6%Si or adding 0.07%B had no effect on average lifetime, but adding 0.3%Ti had a negative effect. Without more compliant YSZ layers, initial results indicate that 12mm diameter rod specimens have much shorter 100-h cycle lifetimes than disk specimens. Research sponsored by the U. S. Department of Energy, Office of Fossil Energy, Coal and Power R&D.

10:50 AM  Cancelled
Thermal Gradient Mechanical Fatigue Testing and Life Modeling of Thermal Barrier Coating Systems: Zhongjiao Zhou1; Changpeng Li2; Guofeng Chen2; Xu Hua2; 1Tsinghua University; 2Corporate Technology, Siemens
    Detailed damage analyses of a Y2O3 stabilized ZrO2–MCrAlY–superalloy thermal barrier coating (TBC) system during thermal gradient mechanical fatigue (TGMF) tests had been performed to simulate the real working conditions for the investigation of empirical working life of TBC systems. The multiple influence factors, including strain ranges, preoxidation time and phase angles, for the TBCs lifetime were systematically investigated. Cracks were initiated in the valley region of the TGO/BC interface and propagated partly within the TGO and partly in the BC, forming the delamination cracks. When the delamination cracks connected with the segmentation cracks in top coat, the TBCs got spalled. Additionally, the stress distributions of TBCs were determined in finite element analyses taking into account BC roughness, TGO growth, top coat sintering and creep effects in both BC and top coat. Finally, a TGMF lifetime prediction model was established combining the experimental and modeling results.

11:10 AM  
Porous Yttria-stabilized Zirconia Microspheres for Advanced Reflective Thermal Barrier Coatings: Ricardo Castro1; Pieter Stroeve1; Roland Faller1; Maria Perez-Page1; Dereck Muche1; 1University of California, Davis
    Yttria-stabilized-zirconia (YSZ) microspheres are considered building blocks for high temperature photonics, with targeted application in advanced reflective thermal barrier coatings (TBCs). However, the synthesis of these microspheres typically relies on a complex wet-chemistry process with limited yield. In this work, YSZ microspheres were successfully synthesized by ultrasonic spray pyrolysis from aqueous solutions. During the process, liquid droplets containing the cationic precursors were dried and crystallized into the oxide phase in a continuous air flow mode with potential for scaling up. The obtained microspheres were analyzed in terms of sphere size, crystallinity, composition, and porosity. Rare earth doping is presented as a solution to control sizes and increase the thermal stability of the microspheres.

11:30 AM  Invited
Electrodeposited MCrAlY Coatings for Gas Turbine Engine Applications: Ying Zhang1; 1Tennessee Technological University
    Electrolytic codeposition is a promising alternative process for fabricating MCrAlY coatings. The coating process involves two steps, i.e., codeposition of CrAlY-based particles and a metal matrix of Ni, Co, or (Ni,Co), followed by a diffusion heat treatment to convert the composite coating to the desired MCrAlY microstructure. Despite the advantages such as low cost and non-line-of-sight, this coating process is less known compared to electron beam-physical vapor deposition and thermal spray processes for manufacturing high-temperature coatings. This presentation provides an overview of the electrodeposited MCrAlY coatings for gas turbine applications, highlighting the unique features of this coating process and some important findings in the past 30 years. Recent research efforts at Tennessee Tech University on the development of electrodeposited NiCoCrAlY coatings and modified NiCoCrAlY coatings with elements of Pt, Ta, Si, and/or Hf are also presented.