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At least 793 records · Page 44

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NASA NTRS1979

Development of RF sputtered chromium oxide coating for wear application

The radio frequency sputtering technique was used to deposite a hard refractory, chromium oxide coating on an Inconel X-750 foil 0.1 mm thick. Optimized sputtering parameters for a smooth and adherent coating were found to be as follows: target-to-substrate spacing, 41.3 mm; argon pressure, 5-10 mTorr; total power to the sputtering module, 400 W (voltage at the target, 1600 V), and a water-cooled substrate. The coating on the annealed foil was more adherent than that on the heat-treated foil. Substrate biasing during the sputter deposition of Cr2O3 adversely affected adherence by removing naturally occurring interfacial oxide layers. The deposited coatings were amorphous and oxygen deficient. Since amorphous materials are extremely hard, the structure was considered to be desirable.

Bhushan, B.↗

NASA NTRS1980

Similarity tests of turbine vanes - Effects of ceramic thermal barrier coatings

The role of material thermal conductivity was analyzed for its effect on the thermal performance of air-cooled gas turbine components coated with a ceramic thermal barrier material when tested at reduced temperatures and pressures. This study shows that the thermal performance can be evaluated reliably at reduced gas and coolant conditions. However, thermal conductivity corrections are required for the data at reduced conditions. These corrections for a ceramic thermal barrier coated vane are significantly different than the corrections for an uncoated vane. Comparison of uncorrected test data, therefore, would show erroneously that the thermal barrier coating was ineffective. When thermal conductivity corrections are applied to the test data these data are then shown to be representative of engine data and also show that the thermal barrier coating increases the vane cooling effectiveness by 12.5 precent.

Gladden, H. J.↗

NASA NTRS1981

Evaluation of several corrosion protective coating systems on aluminum

A study of several protective coating systems for use on aluminum in seawater/seacoast environments was conducted to review the developments made on protective coatings since early in the Space Shuttle program and to perform comparative studies on these coatings to determine their effectiveness for providing corrosion protection during exposure to seawater/seacoast environments. Panels of 2219-T87 aluminum were coated with 21 different systems and exposed to a 5 percent salt spray for 4000 hr. Application properties, adhesion measurements, heat resistance and corrosion protection were evaluated. For comparative studies, the presently specified Bostik epoxy system used on the SRB structures was included. Results of these tests indicate four systems with outstanding performance and four additional systems with protection almost as good. These systems are based on a chromated pretreatment, a chromate epoxy primer, and a polyurethane topcoat. Consideration for one of these systems should be included for those applications where superior corrosion protection for aluminum surfaces is required.

Higgins, R. H.↗

NASA NTRS1981

Sputtered protective coatings for die casting dies

This investigation determined whether selected ion beam sputtered coatings on H-13 die steel would have the potential of improving the thermal fatigue behavior of the steel used as a die in aluminum die casting. The coatings were selected to test candidate insulators and metals capable of providing protection of the die surface. The studies indicate that 1 micrometer thick W and Pt coatings reduced the thermal fatigue more than any other coating tested and are candidates to be used on a die surface to increase die life.

Mirtich, M. J.↗

NASA NTRS1981

Solar energy absorption characteristics and the effects of heat on the optical properties of several coatings

The solar energy absorption characteristics of several high temperature coatings were determined and effects of heat on these coatings were evaluated. Included in the investigation were an electroplated alloy of black chrome and vanadium, electroplated black chrome, and chemically colored 316 stainless steel. Each of the coatings possessed good selective solar energy absorption properties at laboratory ambient temperature. Measured at a temperature of 700 K (800 F), the emittances of black chrome, black chrome vanadium, and colored stainless steel were 0.11, 0.61, and 0.15, respectively. Black chrome and black chrome vanadium did not degrade optically in the presence of high heat (811 K (1000 F)). Chemically colored stainless steel showed slight optical degradation when exposed to moderately high heat (616 K (650 F)0, but showed more severe degradation at exposure temperatures beyond this level. Each of the coatings showed good corrosion resistance to a salt spray environment.

Lowery, J. R.↗

NASA NTRS1980

Anti-reflection coatings applied by acid leaching process

The Magicote C process developed by S.M. Thompsen was evaluated for use in applying an antireflective coating to the cover plates of solar panels. The process uses a fluosilicic acid solution supersaturated with silica at elevated temperature to selectively attack the surface of soda-lime glass cover plates and alter the physical and chemical composition of a thin layer of glass. The altered glass layer constitutes an antireflective coating. The process produces coatings of excellent optical quality which possess outstanding resistance to soiling and staining. The coatings produced are not resistant to mechanical abrasion and are attacked to some extent by glass cleansers. Control of the filming process was found to be difficult.

Pastirik, E.↗

NASA NTRS1981

Corrosion resistant thermal barrier coating

A thermal barrier coating system for protecting metal surfaces at high temperature in normally corrosive environments is described. The thermal barrier coating system includes a metal alloy bond coating, the alloy containing nickel, cobalt, iron, or a combination of these metals. The system further includes a corrosion resistant thermal barrier oxide coating containing at least one alkaline earth silicate. The preferred oxides are calcium silicate, barium silicate, magnesium silicate, or combinations of these silicates.

Levine, S. R.↗

NASA NTRS1981

Burner Rig Evaluation of Thermal Barrier Coating Systems for Nickel-Base Alloys

Eight plasma sprayed bond coatings were evaluated for their potential use with ZrO2-Y2O3 thermal barrier coatings (TECs) which are being developed for coal derived fuel fired gas turbines. Longer TBC lives in cyclic burner rig oxidation to 1050 C were achieved with the more oxidation resistant bond coatings. These were Ni-14.1Cr-13.4A1-0.10Ar, Ni-14.1C4-14.4Al-0.16Y, and Ni-15.8Cr-12.8Al-0.36Y on Rene 41. The TBC systems performed best when 0.015-cm thick bond coatings were employed that were sprayed at 20 kW using argon 3.5v/o hydrogen. Cycling had a more life limiting influence on the TBC than accumulated time at 1050 C.

Gedwill, M. A.↗

NASA NTRS1980

Titanium dioxide antireflection coating for silicon solar cells by spray deposition

A high-speed production process is described for depositing a single-layer, quarter-wavelength thick antireflection coating of titanium dioxide on metal-patterned single-crystal silicon solar cells for terrestrial applications. Controlled atomization spraying of an organotitanium solution was selected as the most cost-effective method of film deposition using commercial automated equipment. The optimal composition consists of titanium isopropoxide as the titanium source, n-butyl acetate as the diluent solvent, sec-butanol as the leveling agent, and 2-ethyl-1-hexanol to render the material uniformly depositable. Application of the process to the coating of circular, large-diameter solar cells with either screen-printed silver metallization or with vacuum-evaporated Ti/Pd/Ag metallization showed increases of over 40% in the electrical conversion efficiency. Optical characteristics, corrosion resistance, and several other important properties of the spray-deposited film are reported. Experimental evidence indicates a wide tolerance in the coating thickness upon the overall efficiency of the cell. Considerations pertaining to the optimization of AR coatings in general are discussed, and a comprehensive critical survey of the literature is presented.

Kern, W.↗

NASA NTRS1981

Thermal and stress analysis of thermal barrier coatings

An analysis has been performed that predicts the thermomechanical behavior of thermal barrier coated specimens. The analysis predicts the behavior during both plasma spray coating application and burner rig testing conditions simulating engine operation. The analysis was accomplished through utilization of one-dimensional through thickness and two-dimensional finite element calculations. The results of these calculations showed that specimens with a substrate control temperature between 300 F and 600 F would be optimum. Controlling substrate temperature was found to have a more dominant effect on the mechanical strains than the ceramic or substrate thicknesses. The predicted stresses and mechanical strains at the bond-coating interface are large enough to cause cracks in this region where post-test observations have determined coating failures originate.

Cassenti, B. N.↗

NASA NTRS1981

Assessment of variations in thermal cycle life data of thermal barrier coated rods

The reported study had the purpose to examine variations in cyclic life and in adhesive/cohesive coating strength. Possible effects of heating rate, stress reversal, temperature level, and ceramic deposition methods on coating life were also investigated. Life cycle data for 22 thermal barrier coated rods were examined and found to be statistically modeled by normal or log-normal distributions. The sample mean was 1330 cycles with a standard deviation of 520 cycles. Adhesive/cohesive pulloff strength data for 20 thermal barrier coated flat head piston specimens were taken. The average pulloff stress was 9 MPa with a standard deviation of 4.2 MPa. It was found that variations in heating rate can produce significant variations in the life cycle data.

Hendricks, R. C.↗

NASA NTRS1980

Thermal barrier coatings for superalloys

The current status of ceramic thermal barrier coatings for protection of turbine airfoil components is reviewed. Test results for an early duplex coating system ZrO2-12% Y2O3/Ni-16% Cr-6% Al-0.6% Y, improved system ZrO2-8% Y2O3/Ni-17% Cr-5% Al-0.35% Y, and air/fuel impurity tolerant systems based on ZrO2-8% Y2O3, 2CaO-SiO2, and a MgO-NiCrAlY cermet are discussed. Preliminary test results at 800 C for a graded ZrO2-8% Y2O3/Ni-20% Cr-11% Al-0.4% Y coating system show that the coating can survive at least 500 hr in the presence of 50 ppm V plus other fuel contaminants and additives.

Miller, R. A.↗

NASA NTRS1982

Sputtered silicon nitride coatings for wear protection

Silicon nitride films were deposited by RF sputtering on 304 stainless steel substrates in a planar RF sputtering apparatus. The sputtering was performed from a Si3N4 target in a sputtering atmosphere of argon and nitrogen. The rate of deposition, the composition of the coatings, the surface microhardness and the adhesion of the coatings to the substrates were investigated as a function of the process parameters, such as: substrate target distance, fraction nitrogen in the sputtering atmosphere and sputtering pressure. Silicon rich coating was obtained for fraction nitrogen below 0.2. The rate of deposition decreases continuously with increasing fraction nitrogen and decreasing sputtering pressure. It was found that the adherence of the coatings improves with decreasing sputtering pressure, almost independently of their composition.

Grill, A.↗

NASA NTRS1982

Spray coating apparatus having a rotatable workpiece holder

A spray coating apparatus is provided for rotating a workpiece relative to a spray station to obtain a uniform coating of the workpiece. In a typical example, the workpiece comprises a ceramic tile which is to be coated with a ceramic coating and the tile is to be used as a reusable component of the thermal protection system for a space shuttle. The apparatus for rotating the workpiece includes a base support having a first rotatable stage for rotation in the horizontal plane and a second rotatable stage for rotation in a second plane inclined at an angle, such as 45 degrees, to the horizontal plane and the workpiece is supported on this second stage. Thus the workpiece is rotatable in both of two planes of rotation.

Smith, M.↗

NASA NTRS1982

Evaluation of waveguide coating materials

Waveguide coating materials were tested at 8470 MHz for insertion loss. Samples of these coatings on waveguide pieces without flanges were tested in an environmental chamber to simulate the effects of high power microwave heating. Test results indicated that three types of coating materials are acceptable with regard to insertion loss. However, simulated microwave heating caused debonding of Metcot 7 and BD-991 coatings, resulting in peelings in the waveguide. The higher cost Chemglaze R104 does not exhibit this problem.

Chen, W. C. J.↗

NASA NTRS1981

Development of CdO-graphite-Ag coatings for gas bearings to 427 C

Graphite is one of the most commonly known lubricants. Its effectiveness in a range between room temperature (RT) and 540 C is reportedly improved by adding cadmium oxide. CdO-graphite powder in a gas carrier has been used in numerous applications that rely on dry lubrication. A coating of this composition was developed and successfully tested in foil air bearings for long periods up to a temperature of 427 C and at a normal contacting load (during starting and stopping) of 14 kPa based on bearing projected area. The addition of ultra-fine silver to the CdO-graphite has improved the coating endurance. At 427 C, the CdO-graphite-Ag coating performed better than CdO-graphite without silver, both for extended periods at 14 kPa loading and for limited periods at 35 kPa. At 288 C, the coating was tested for an extended period up to 28 kPa and has also successfully completed high-speed shock tests to an acceleration level of 100g.

Bhushan, B.↗

NASA NTRS1982

Infrared emission spectrophotometric study of the changes produced by TiN coating of metal surfaces in an operating EHD contact

Infrared emission spectra and related measurements were obtained from an operating ball/plate elastohydrodynamic (EHD) sliding contact under a variety of operating conditions. In order to be able to compare the effect of the ball surface, some of the balls were coated with a thin layer of titanium nitride (TiN) by vapor deposition. Polyphenyl ether (5P4E) was used as lubricant and 1 percent of 1,1,2-trichloroethane (TCE) as a surface-probing additive. TiN is chemically inert and its thermal conductivity is lower than that of steel. Therefore, the overall temperatures with TiN coated balls were higher. Nevertheless, no scuffing was observed with the coated balls under conditions giving rise to scuffing with the uncoated balls. Tractions were lower with the TiN coated balls and always when TCE was added to the 5P4E. These findings were found to be inversely related to the degree of polarization of the spectral emission bands. The intensity and the dichrosim of these bands were related to shear rates and inlet conditions of the EHD contact.

Keller, L. E.↗

NASA NTRS1982

Space stable thermal control coatings

A specification quality zinc orthotitanate coating was developed. This silicate-bonded Zn2TiO4 coating is discussed. The effects of precursor chemistry, precursor mixing procedures, stoichiometry variations, and of different heat treatments on the physical and optical properties of Zn2TiO4 are investigated. Inorganic silicates are compared to organic silicone binder systems. The effects of pigment to binder ratio, water content, and of different curing procedures on the optical and physical properties of Zn2TiO4 potassium silicate coatings are also studied. Environmental tests were conducted to determine the UV vacuum stability of coatings for durations up to 5000 equivalent Sun hours.

Harada, Y.↗