ICMCTF2016 Session A2-2: Thermal and Environmental Barrier Coatings

Tuesday, April 26, 2016 8:00 AM in Room Royal Palm 4-6
Tuesday Morning

Time Period TuM Sessions | Abstract Timeline | Topic A Sessions | Time Periods | Topics | ICMCTF2016 Schedule

Start Invited? Item
8:00 AM A2-2-1 Silver Coated Fabrics to Prevent Thermal Detection
Jie Ding (DST Group, Australia); Tong Lin (Deakin University, Australia)

A thermal detector (camera) can detect a temperature difference between a person and his/her surroundings. However, a thermal detector does not capture the temperature of the person; it detects the thermal radiation from an object. The intensity of the radiation depends on the temperature and natural emissivity of the material's surface. Avoiding heat transfer between the body and the garment or coating low emissivity materials onto the fabric surface are two effective ways to provide a person with thermal camouflage.

Coating silver on textiles using various coating processes for antibacterial effects has been intensively investigated [1-3]. Here we develop an effective route to apply silver nanoparticles on a fabric surface using chemical deposition. An effective layer-by-layer (LBL) silver plating process for applying silver nanoparticles on fabric surface has been investigated. The LBL coating based on a spraying process produces a smooth and dense silver coating layer with small amounts of silver nanoparticles. The treated fabric has a reasonably low emissivity property and good bonding strength. Two catalysts, SnCl2 and L-Cystine, were used to improve the silver loading on fabrics. Chitosan/DMDHEU was proven to be the best resin for overlay protection of the silver coating. It has a very small influence on the emissivity properties of the fabric, but gives excellent washing fastness for the silver coating film.

This technique can also be used to develop other silver related products. Silver is a wide spectrum and high efficiency antibacterial agent, and the controlled release of the silver atom/ion to the fabric surface can provide a long-lasting antibacterial function.

Reference

1. Klueh, U., Wagner, V., Kelly, S., Johnson, & A, Bryers, JD. Efficacy of silver-coated fabric to prevent bacterial colonization and subsequent device-based biofilm formation. J Biomed Mater Res. 53, 621-31(2000).

2. Chen, Y.H., Hsu, C. C.,& He, J. L. Antibacterial silver coating on poly(ethylene terephthalate) fabric by using high power impulse magnetron sputtering. 232, 868-875 (2013).

3. El-Rafie, M.H., Mohamed, A.A., Th.I. Shaheen., & A. Hebeish, A. Antimicrobial effect of silver nanoparticles produced by fungal process on cotton fabrics. Carbohydrate Polymers. 80, 779–782 (2010).

8:20 AM A2-2-2 Behavior of Chromium Barrier Interconnector Coatings for Steam Electrolysis under Pressure Exposed to Water Vapor and Pure Oxygen
Vladislav Kolarik, MariadelMar Juez Lorenzo, Veronica Kuchenreuther-Hummel (Fraunhofer ICT, Germany); Martin Pötschke, Danilo Schimanke (sunfire GmbH, Germany)

The conversion of electric power from renewable energy sources into liquid fuels (power-to-liquid) is currently an upcoming issue of special interest. For achieving a high efficiency, the steam electrolysis used to split water to hydrogen and oxygen is run under pressure up to 30 bar at temperatures around 850°C. The impact of such severe conditions on the behavior of the interconnector coatings designed to retain evaporating chromium is a crucial issue and needs detailed understanding to ensure a reliable operation.

Two coatings, one based on Mn-Co-Fe oxide (MCF) and the other on La-Sr-Mn oxide (LSM) were deposited on the interconnector material Crofer 22 APU by thermal spraying and by roll coating for cost savings. 100% water vapor and pure dry oxygen, both representing the opposite extremes of the possible process atmospheres, were selected for the study. Laboratory test autoclaves from Alloy 602 were prepared to conduct the experiments under pressure. The samples were exposed at 850°C and 30 bar to 100% water vapor for up to 1000 h and to pure oxygen for up to 3000 h.

In water vapor the MCF coating decomposes after 300 h to metallic Co and manganese oxide. The higher redox potential of Co compared to that of Mn is considered as an explanation of the selective reduction of Co by hydrogen from the water vapor. No Cr was detected in the coating after exposure to pure water vapor indicating that the evaporated gaseous Cr species does not react with no component of the coating. The LSM coating shows in water vapor a grain coarsening after 1000 h as well as a separation of grains with higher La content towards the surface and grains containing Mn towards the interface. Cr is detected very weakly in the areas with high La contents.

In pure oxygen the MCF coating forms a two-layer structure with large pores between them. The outer layer consists of dense large grains and the inner layer exhibits a highly porous structure. Cr is detected homogeneously distributed in the MCF coating. X-ray diffraction revealed that Cr is bound in the coating by forming Cochromite (CoCr2O4/CoO∙Cr2O3), which is an electrically insulating spinel. The LSM coating exhibits after exposure to pure oxygen a homogeneous morphology with higher porosity in the case of the roll coating. Cr stemming from evaporation was found in the whole LSM coating when deposited by rolling and concentrated on the coating surface when thermal spray was applied. The phases binding the Cr were identified by X-ray diffraction. After 1000 h the semi-conducting LaCrO4 and SrCrO4 are formed and after 3000 h CrMn2O4, which exhibits an electrical conductivity an order of magnitude higher than that of Cr2O3.
8:40 AM A2-2-3 Influence of Embedded MoSi2 Particles on Microstructure and Heat transfer in Dense Yttria-stabilised Zirconia
Justyna Kulczyk-Malecka, Xun Zhang, James Carr (The University of Manchester, UK); Alexandra Carabat, Willem G. Sloof, Sybrand van der Zwaag (Delft University of Technology, Netherlands); Federico Cernuschi (RSE SpA – Ricerca sul Sistema Energetico, Italy); Franck Nozahic, Daniel Monceau, Claude Estournès (Université de Toulouse, Institut Carnot CIRIMAT, France); Philip Withers, Ping Xiao (The University of Manchester, UK)

Yttria-stabilised zirconia (YSZ) is a good thermal insulator that provides thermal protection of working components in high temperature applications, such as gas turbines and hot sections of aircraft engine turbine blades. However, the thermal mismatch in the thermal barrier coating (TBC), leads to generation of cracks, delamination of the coating and, ultimately, to failure of the TBC system.

To prolong the lifetime of TBCs a new method of crack healing has been developed, which relies on embedding molybdenum disilicide (MoSi2) healing particles within the TBC matrix. Upon high temperature oxidation, MoSi2 decomposes and amorphous silica (SiO2) is formed as a reaction product. SiO2 fills and seals the cracks created during thermal cycling thus providing a self-repairing mechanism to prolong the lifetime of the TBC.

MoSi2 has relatively high thermal conductivity (30 W/mK at 1400 oC). Therefore, embedding a good thermal conductor into a thermally insulating matrix (thermal conductivity of dense YSZ is about 2.3 W/mK at 1000 oC) could have an unfavourable impact on thermal conductivity of the TBCs.

In this work the thermal conductivity of YSZ embedded with various volumetric percentages of MoSi2 healing particles prepared by spark plasma sintering (SPS) was investigated using the laser flash method. Measurements were performed on free- standing composite material at the temperature range 100-1000 oC. The measurements were compared with results from microstructure-based finite element (FE) models and analytic models (asymmetric Bruggeman model) to address how the addition of MoSi2 particles has affected the apparent thermal conductivity. Microstructural analysis was carried out by SEM combined with image analysis to determine the size, distribution and area fraction of healing particles. X-ray diffraction (XRD) analysis was carried out to evaluate the chemical structure and composition of the composite materials. The results presented here show an increase in the thermal conductivity of the composite material with the ratio of MoSi 2 particles.
9:00 AM A2-2-4 Silica Depletion of Yttrium Silicates in High-Temperature High-Velocity Water Vapor
Robert Golden, Elizabeth Opila (University of Virginia, USA)

High-temperature high-velocity water vapor exposures of Y2Si2O7 and Y2SiO5 were conducted to determine the potential of these oxides as Environmental Barrier Coatings (EBCs) and/or matrix constituents for SiC-based composites. Liquid water was pumped at a controlled rate into a fused quartz capillary held inside a tube furnace at temperatures between 1200°C and 1400°C. The vaporization of water within the capillary resulted in a large volume expansion and acceleration of the steam out of the capillary, simulating the high-temperature high-velocity steam conditions of a turbine engine. The high-velocity steam impinged on the specimen under study leading to surface silica depletion via the formation of volatile silicon hydroxide species. Specimens were characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, Electron Backscatter Diffraction and X-ray Diffraction before and after exposure. The effects of sample density, exposure time and temperature on silica depletion were explored. Steam-jet exposures of Y2Si2O7 resulted in the formation of porous Y2SiO5. SiO2 depletion from Y2Si2O7 increased with decreasing density due to additional paths for ingress of steam to the specimen interior. SiO2 depletion rates from dense Y2Si2O7 slowed with time due to increasing path lengths for steam ingress through the growing porous layer of Y2SiO5. Surprisingly, SiO2 depletion from dense Y2Si2O7 decreased with increasing temperature due to sintering of the porous conversion layer. Y2Si2O7 has four polymorphs, however, no effects of phase on SiO2 depletion were observed. Surface faceting was found to correspond to the disilicate crystallographic orientation. No SiO2 depletion from Y2SiO5 was observed for steam-jet exposures at 1200 – 1300°C, exposure times of 250 – 500 hours, and steam velocities of 150 – 200 m/s.

9:20 AM Invited A2-2-5 Synthesis and Related Properties of Low K TBCs with Hollow Alumina Particles
Fernando Pedraza, Germain Boissonnet, Beatriz Fernandez (University of La Rochelle, France); Baptiste Bouchaud (GE Aviation Czech, Czech Republic); Renaud Podor (CEA Marcoule, France)

Thermal barrier coatings (TBCs) for aeronautical applications are mostly based on yttria stabilized zirconia (YSZ) deposited by either thermal spray or electron-beam physical vapour deposition (EB-PVD) in the combustion chamber and the high pressure turbine components. The increase of the turbine inlet temperatures demands greater oxidation and thermal insulation to the turbine parts that are not currently TBcoated. This work explores the mechanisms involved in the synthesis of full TBC systems in a single step process from slurries containing Al microspheres. The microspheres simultaneously deform and oxidise allowing Al to be supplied to the Ni-based superalloy substrate. The combustion synthesis mechanisms allow then fast aluminisation of the superalloy. Once Al is consumed by diffusion to the substrate, a bisque of hollow alumina microspheres is left on top that provides very low thermal conductivity (k) as measured by a laser flash method. The thermal conductivity values with respect other conventional –industrial- TBCs will be established. While the erosion resistance is to be improved, this coating system appears to provide resistance to both molten salt in Na2SO4-V2O5 and to oxidation in wet and dry air.

10:00 AM A2-2-7 Progress In Making Higher Temperature Thermal Barrier Coatings Using The Solution Plasma Spray Process
Maurice Gell, Eric Jordan, Jeffrey Roth, Rishi Kumar (University of Connecticut, USA); Balky Nair, Chen Jiang (Solution Spray Technologies LLC, USA)
Based on laboratory tests, we have previously shown that yttrium aluminum garnet (YAG) thermal barrier coatings (TBCs) fabricated by the Solution Precursor Plasma Spray (SPPS) process have the potential to be used at temperature 300oC higher than air plasma spray (APS) YSZ TBCs. This conclusion was based on phase stability, sinter resistance, and CMAS testing. In addition, the elevated temperature thermal conductivity was shown to be less than that of APS YSZ. Despite higher thermal expansion mismatch strains, these SPPS YAG TBCs exhibit favorable durability compared to APS YSZ because of the strain tolerant microstructure provided by through-thickness vertical cracks. This presentation will cover the recent research to further lower the thermal conductivity, improve the deposition rate and efficiency, and promote commercialization of SPPS YAG TBCs.
10:20 AM A2-2-8 Microstructure Design for Blended Feedstock and its Thermal Durability in Lanthanum Zirconate Based Thermal Barrier Coatings
Dowon Song, Ungyu Paik (Hanyang University, Republic of Korea); Jing Zhang (Indian University-Purdue University, USA); Zhe Lu, Je-Hyun Lee, Yeon-Gil Jung (Changwon National University, Republic of Korea)
Lanthanum zirconate (La2Zr2O7) can be used as a new advanced thermal barrier coating (TBC), because it has lower thermal conductivity, greater sintering resistance, and higher phase stability than yttria-stabilized zirconia (YSZ). However, La2Zr2O7 has a low thermal durability, resulting in poor lifetime performance, which is caused by its lower coefficient of thermal expansion than typical bond coat material. To improve the thermal durability of La2Zr2O7 based TBCs and to give both thermal and mechanical properties to TBCs, microstructure was designed with blended feedstock powders which were consisted of La2Zr2O7 and YSZ with different volume ratios (50:50 and 25:75). Layered microstructure with a buffer layer was deposited by air plasma spray method, and then thermal durability of each TBC was evaluated through the thermal shock (TS) and jet engine thermal shock (JETS) tests. The TBC with the buffer layer showed improved thermal durability than single layered TBC in the both TS and JETS tests. The effects of microstructure design on the failure mechanism and thermal durability are extensively discussed based on the obtained thermomechanical properties.
10:40 AM A2-2-9 Effects of Powder Mixture Condition on the Microstructure and Phase Forming Behavior of Zirconate
Yoon-Suk Oh (Korea Institute of Ceramic Engineering & Technology, Republic of Korea); Suna Choi, Jungmin Chae, Yoonsoo Han, Seongwon Kim, Sungmin Lee, Hyung-Tae Kim (Korea Institute of Ceramic Engineering & Technology, Korea); Jongkee Ahn, Taehyung Kim (Hanwha Techwin, Korea); Donghoon Kim (Agency for Defense Development, Korea)
TBC (Thermal barrier coating) is inevitable technology in turbine system of aero engine. Among the fabrication methods of TBC, Electron beam (EB) evaporation method is being studied as one of the substitutions due to its higher structural stability than conventional plasma spray method. During the EB process, usually the source materials are exposed to high power electron beam with focused area. Therefore the material source for EB evaporation process is needed to form as ingot with appropriate density and microstructure to sustain their shape and stable melt status during EB irradiation. In this study we tried to find the optimum condition of fabrication process for the ingot of 8 wt%(4 mol%) yttria stabilized zirconia(8YSZ) and Lanthanide added zirconates to obtain uniform and thick film by EB evaporation. It seems that the ingot fabricated by bi-modal type mixture of initial particles, which are composed of several tens of micrometer and nanometer size particles, was shown better performance than that of which fabricated using simple nanometer scale mono-scale particles when exposed to high power EB irradiation. Furthermore, it also found that the stability of ingot is depend on the contents of monoclinic phase of initial powder.
Time Period TuM Sessions | Abstract Timeline | Topic A Sessions | Time Periods | Topics | ICMCTF2016 Schedule