Development of Advanced Thermal Barrier Coatings for Severe Environments

Nelson, Warren A.; Orenstein, Robert M.; DiMascio, P. S.; Johnson, Curtis A.

doi:10.1115/95-gt-270

Cited by 5 publications

(1 citation statement)

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“…Thermal-sprayed coatings exhibit a lamellar microstructure usually containing many defects (porosity and poor bonding between successively deposited layers), whereas chemical or physical vapor deposited coatings have a columnar-oriented structure. ], 2 Due to the particular microstructure, some physical properties of the coating may be quite different from those measured on the same bulk material. The knowledge of sprayed coating elastic properties is necessary to predict the structural behavior of a component in terms of strength and stiffness.…”

Section: Introductionmentioning

confidence: 98%

Measurement of coatings' elastic properties by mechanical methods: Part 2. Application to thermal barrier coatings

Beghini

Benamati

Bertini

et al. 2001

Experimental Mechanics

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ABSTRACT--Elastic properties of a thermal barrier ceramic coating composed of an NiCoCrAIY bond coat and a ZrO2(Y203) top coat were measured by a four-point bending rig in the temperature range 20~176 Different types of specimens (i.e., with bond coat only or with bond coat and top coat, on one side or on both sides) were employed. Test procedures were based on the theory discussed in Part 1 to enhance accuracy and to estimate confidence intervals. In particular, the method employed at high temperature was calibrated at room temperature by comparing the results with those obtained by methods with low sensitivity to layer thicknesses. For the bond coat, Young's modulus was found to be temperature independent up to about 500~ a decreasing trend was observed above this temperature. For the top coat, a slightly decreasing Young's modulus was observed over the whole temperature range examined. A possible explanation is given on the basis of phase transformation and the microstructure of the two layers. At room temperature, Poisson's ratio for the bond coat was found to be near 0.3, whereas a near zero value was measured for the top coat.KEY WORDS--Coatings, elastic modulus, Poisson's ratio, mechanical testing, temperature dependence Nomenclature B = specimen width H = total specimen thickness L = total specimen length S = specimen length subjected to constant bending a = spacing between the inner and outer loading pins in the four-point bending testEs, Ebc, Etc = Young's modulus of substrate, bond-coat and top-coat materials Vs, Vbe, Vtc = Poisson's ratio of substrate, bond-coat and top-coat materials hs, hbc, htc = thickness of the substrate, bond-coat and top-coat layers gs, gbc, gtc -----depth coordinate of the substrate, bond-coat and top-coat centroid, with reference to the geometric center of the specimen M. Beghini is a Professor,

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Section: Introductionmentioning

confidence: 98%

Measurement of coatings' elastic properties by mechanical methods: Part 2. Application to thermal barrier coatings

Beghini

Benamati

Bertini

et al. 2001

Experimental Mechanics

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Measurement of coatings' elastic properties by mechanical methods: Part 1. Consideration on experimental errors

Beghini

Bertini

Frendo

2001

Experimental Mechanics

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ABSTRACT--A critical analysis of some mechanical methods employed for measuring the elastic properties of coatings is presented. A rational basis for properly choosing test methods, transducers and layer thicknesses is provided. The analyzed methods, usually applied to relatively thick coatings, include four-point bending tests and the resonance technique. General relationships for the evaluation of coatings' elastic properties, derived from the multUayer beam and plate theories, are discussed. On the basis of the error propagation theory, for different combinations of materials and layer thicknesses, the influence of typical experimental errors, test setup parameters and material properties is analyzed, and sensitivity coefficients for relative errors are discussed. The critical experimental variables and their effect on measurement accuracy are highlighted, suggesting suitable conditions for selecting specimen geometry and testing conditions. A procedure for measurement at high temperature is outlined.KEY WORDS--Coatings, elastic modulus, sensitivity analysis, experimental errors Nomenclature X, Y, Z = Cartesian coordinate system ~X, E:y, ~Z = normal strains ~x, cry, cr z = normal stresses hk = thickness of the kth layer lk = z-coordinate of the kth layer's centroid Ik-1 = z-coordinate of the inferior surface of the kth layer lie = z-coordinate of the superior surface of the kth layer gk = depth coordinate of the kth layer centroid, with reference to the geometric center of the specimen B = specimen width H = total specimen thickness K}, = specimen bending stiffness in the Rx, Ry = radii of curvature of the specimen geometrical axis in the Z-X and Z-Y planes Cx, Cy = normal strains of the centroid fiber in the Z-X and Z-Y cross sections 8 = position, in the beam model, of the neutral axis related to the geometric centroid of the specimen L = total specimen length S = inner spacing between the loading pins in the FPB test a = spacing between the inner and outer loading pins in the FPB test P = half load, applied in the FPB test Es, Ec = elastic modulus of the substrate and coating materials hs, hc = thickness of the substrate and coating layers ~s, ec = measured longitudinal strain on the external coating surface and substrate surface w = midsection displacement, related to the fixed external loading pins k = distance of the measuring gage from the neutral axis of the specimen f = first bending resonance frequency of the specimen = 4.73004 m = mass of the specimen = ratio of the transverse to the longitudinal strain measured on the external specimen surface F = ratio of the longitudinal strains measured on the substrate and coating surfaces R = ratio of the substrate to the coating thickness cz = ratio of the coating to the substrate elastic modulus Pe,.c = slope of the experimental regression line correlating the measured load and strain on the substrate or coating surfaces Pw = slope of the experimental regression line correlating the measured load and midsection displacement = relationship giving the coating ...

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TBC experience in land- based gas turbines

Nelson¹,

Orenstein²

1997

J Therm Spray Tech

124

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This paper summarizes prior and on-going machine evaluations of TBC coatings for power generation applications.Rainbow testing of various TBCs on turbine nozzles, shrouds and buckets are described along with one test on combustor liners. GEPG has conducted over 15 machine tests with TBC coated turbine nozzles of various coatings. Rainbow test times generally range between 10,000 to 24,000 hours. TBC performance has been quite good and additional testing, including TBC's on shrouds and buckets, is continuing.The results show that TBCs have the capability of surviving in power generation machines for the times required. The earlier rainbow tests which evaluated various top coat compositions resulted in confu'mation of the superiority of YSZ and especially the 6-8 YSZ composition.On-going tests are more focused on TBC process and property variations. The prevalent failure modes seen thusfar in the various rainbow tests are erosion, foreign object damage and buildup of deposits. Additional post test analysis is required to investigate bond coat oxidation and other time/temperature dependent changes to the system.

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Development of Advanced Thermal Barrier Coatings for Severe Environments

Cited by 5 publications

References 0 publications

Measurement of coatings' elastic properties by mechanical methods: Part 2. Application to thermal barrier coatings

Measurement of coatings' elastic properties by mechanical methods: Part 2. Application to thermal barrier coatings

Measurement of coatings' elastic properties by mechanical methods: Part 1. Consideration on experimental errors

TBC experience in land- based gas turbines

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