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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Overlay coating degradation by simultaneous oxidation and coating/substrate interdiffusion

Degradation of NiCrAlZr overlay coatings on various NiCrAl substrates was examined after cyclic oxidation. Concentration/distance profiles were measured in the coating and substrate after various oxidation exposures at 1150 C. For each stubstrate, the Al content in the coating decreased rapidly. The concentration/distance profiles, and particularly that for Al, reflected the oxide spalling resistance of each coated substrate. A numerical model was developed to simulate diffusion associated with overlay-coating degradation by oxidation and coating/substrate interdiffusion. Input to the numerical model consisted of the Cr and Al content of the coating and substrate, ternary diffusivities, and various oxide spalling parameters. The model predicts the Cr and Al concentrations in the coating and substrate after any number of oxidation/thermal cycles. The numerical model also predicts coating failure based on the ability of the coating to supply sufficient Al to the oxide scale. The validity of the model was confirmed by comparison of the predicted and measured concentration/distance profiles. The model was subsequently used to identify the most critical system parameters affecting coating life.

Nesbitt, J. A.↗
NASA NTRS1972

Apollo 9 thermal-control-coating degradation

Analytical studies, ground-test data, and flight data before 1967 indicated that degradation of Apollo thermal-control coatings could be expected, possibly to an extent requiring spacecraft design changes to accomplish the worst-case lunar-landing mission. On the Apollo 9 mission, specimens of Apollo thermal-control coatings were retrieved by the astronauts during the extravehicular activity. These specimens were the first to be returned to earth from space unaffected by entry conditions. Subsequent measurements of the thermophysical properties (solar absorptance and hemispherical emittance) of the thermal-control-sample coatings revealed degradation levels well within the design capability of the Apollo spacecraft.

Smith, J. A.↗
NASA NTRS1967

Coatings degradation, section VIII

Vacuum chambers for particle irradiation of thermal control coatings, and testing of paint samples of alkali silicates and methyl silicones

SILICONE↗
NASA NTRS1985

Mechanisms of thermal barrier coating degradation and failure

The objectives and initial results of a Thermal Barrier Coating (TBC) Life Prediction Model Development Program are described. The goals of this program are to: identify and understand TBC failure modes; generate quantitative TBC life data; and develop and verify a TBC life prediction model. The coating being studied is a two layer thermal barrier system incorporating a nominal ten mil outer layer of seven percent yttria partially stabilized zirconia plasma deposited over an inner layer of highly oxidation resistant low pressure plasma sprayed NiCrAlY bond coating. This coating currently is in flight service on turbine vane platforms in the JT-9D and PW2037 engines and is bill-of- material on turbine vane airfoils in the advanced PW4000 and IAE V2500 engines. Effort currently is in progress on the first task, which involves the identification and understanding of TBC failures. Five modes of coating damage were considered: thermomechanical ceramic failure; oxidative bond coat failure; hot corrosion; foreign object damage (FOD); and erosion.

Demasi, J. T.↗
NASA NTRS1984

Modeling degradation and failure of Ni-Cr-Al overlay coatings

Degradation of a Ni-16Cr-25Al-0.06Zr overlay coating on a Ni-22Cr substrate was examined after oxidation accompanied by thermal cycling. Concentration/distance profiles were measured in the coating and substrate after various one-hour cycles at 1150 C. A numerical model was developed to simulate coating degradation by simultaneous oxidation and coating/substrate interdiffusion. The validity of the model was confirmed by comparison of predicted and measured concentration/distance profiles. The ability of the model to identify critical system parameters was demonstrated for the case of initial Al and Cr content of the coating and substrate.

Nesbitt, J. A.↗
NASA NTRS1984

Modeling degradation and failure of Ni-Cr-Al overlay coatings

Degradation of a Ni-16Cr-25Al-0.06Zr overlay coating on a Ni-22Cr substrate was examined after oxidation accompanied by thermal cycling. Concentration/distance profiles were measured in the coating and substrate after various one-hour cycles at 1150 C. A numerical model was developed to simulate coating degradation by simultaneous oxidation and coating/substrate interdiffusion. The validity of the model was confirmed by comparison of predicted and measured concentration/distance profiles. The ability of the model to identify critical system parameters was demonstrated for the case of the initial Al and Cr content of the coating and substrate.

Nesbitt, J. A.↗
NASA NTRS1986

Evaluation of active thermal control options for Space Station

An analysis of various Space Station (MSS) active thermal control systems options under consideration because of their potential low weight, efficiency and reliability is reported. The study addressed ordinary and diode-action body mounted radiators, thermal storage, the area and pumping power requirements for single-phase cooling of cold plates, and single-phase and two-phase active cooling loops. The base configuration considered was a core MSS formed by four habitable modules on which are mounted heat pipe radiators articulated to be always edge-on to the sun. A simulation was performed which accounted for the available heat sinks, several thermal loads and the heat rejection capability. No benefits were found with diode-action radiators if the solar absorption is 0.1 or less, although diode-action heat pipes will maintain a higher level of performance in the presence of coating degradation. Thermal storage becomes important only with radiator coating degradation. Water can be up to three times as efficient as Freon as a heat transfer medium. Finally, single-phase cooling offers a lower system mass than two-phase cooling if varying temperature heat loads can be accommodated.

Schuster, J. R.↗
NASA NTRS1982

Ceramic thermal barrier coatings for gas turbine engines

The results of studies concerning the high temperature corrosion resistance of ZrO2-Y2O3, ZrO2-MgO, and Ca2SiO4 plasma-sprayed coatings, which may be used as gas turbine engine thermal barriers, are reported. The coatings were evaluated in atmospheric burner rig and pressurized passage tests, using GT No. 2 fuel in pure form and with sodium, sulfur and vanadium corrosive impurities doping. It is found that, while the coatings performed well in both pressurized passage and burner rig tests with pure fuel chemical reactions between the ceramic coatings and combustion gases/condensates resulted in coating degradation with impure fuels. Chemical reactions between the ceramic coatings and vanadium compounds played a critical role in coating degradation.

Bratton, R. J.↗
NASA NTRS2004

Development and Fatigue Testing of Ceramic Thermal Barrier Coatings

Ceramic thermal barrier coatings will play an increasingly important role in future gas turbine engines because of their ability to effectively protect the engine components and further raise engine temperatures. Durability of the coating systems remains a critical issue with the ever-increasing temperature requirements. Thermal conductivity increase and coating degradation due to sintering and phase changes are known to be detrimental to coating performance. There is a need to characterize the coating thermal fatigue behavior and temperature limit, in order to potentially take full advantage of the current coating capability. In this study, thermal conductivity and cyclic fatigue behaviors of plasma-sprayed ZrO2-8wt%Y2O3 thermal barrier coatings were evaluated under high temperature, large thermal gradient and thermal cycling conditions. The coating degradation and failure processes were assessed by real-time monitoring of the coating thermal conductivity under the test conditions. The ceramic coating crack initiation and propagation driving forces and failure modes under the cyclic thermal loads will be discussed in light of the high temperature mechanical fatigue and fracture testing results.

Zhu, Dong-Ming↗
NASA NTRS2004

Development and Testing of Ceramic Thermal Barrier Coatings

Ceramic thermal barrier coatings will play an increasingly important role in future gas turbine engines because of their ability to effectively protect the engine components and further raise engine temperatures. Durability of the coating systems remains a critical issue with the ever-increasing temperature requirements. Thermal conductivity increase and coating degradation due to sintering and phase changes are known to be detrimental to coating performance. There is a need to characterize the coating behavior and temperature limits, in order to potentially take full advantage of the current coating capability, and also accurately assess the benefit gained from advanced coating development. In this study, thermal conductivity behavior and cyclic durability of plasma-sprayed ZrO2-8wt%Y2O3 thermal barrier coatings were evaluated under laser heat-flux simulated high temperature, large thermal gradient and thermal cycling conditions. The coating degradation and failure processes were assessed by real-time monitoring of the coating thermal conductivity under the test conditions. The ceramic coating crack propagation driving forces and resulting failure modes will be discussed in light of high temperature mechanical fatigue and fracture testing results.

Zhu, Dongming↗
NASA NTRS2015

Process Development for Removal of Siloxanes from ISS Atmosphere

Dimethylsilanediol (DMSD) has been identified as a problematic organic contaminant aboard the ISS. This contaminant was initially identified in humidity condensate and in the Water Processor Assembly (WPA) product water in 2010 when routine water quality monitoring an increasing total organic carbon (TOC) trend in the WPA product water. Although DMSD is not a crew health hazard at the levels observed in the product water, it can degrade the WPA catalytic reactor's effectiveness and cause early replacement of Multifiltration Beds. DMSD may also degrade the performance of the Oxygen Generation System (OGS) which uses the WPA product water for electrolysis. An investigation into the source of DMSD has determined that polydimethylsiloxane (PDMS) compounds are likely hydrolyzing in the Condensing Heat Exchangers (CHX) to form DMSD. PDMS compounds are prevalent aboard ISS from a variety of sources, including crew hygiene products, adhesives, caulks, lubricants, and various nonmetallic materials. PDMS compounds are also known to contribute to CHX hydrophilic coating degradation by rendering it hydrophobic and therefore adversely affecting its ability to effectively transmit water to the condensate bus. Eventually this loss in performance results in water droplets in the air flow exiting the CHX, which may lead to microbial growth in the air ducts and may impact the performance of downstream systems. Several options have been evaluated to address these concerns. Modifications to the Water Processor Multifiltration Beds and Catalytic Reactor for removal of DMSD were not considered viable, and did not address the issue with PDMS compound degradation of the CHX coating. Design concepts are now in development for removing PDMS compounds from the air stream before they can reach the CHX coating, thus preventing coating degradation and hydrolysis of the PDMS compounds to DMSD. This paper summarizes the current status of the effort to treat these contaminants on ISS.

Carter, Layne↗