Patent Application
20120064255
The present invention relates generally to vibration damping coatings and, more particularly, to vibration damping coatings for high temperatures such as those experienced in a turbine engine.
Vibration-induced high cycle fatigue (HCF) failures of static and rotating components exist in turbine engines and are a concern for the operation and life of the engine. These HCF failures are generally due to high vibratory stresses due to the response of components at resonant frequencies. The vibratory response at resonant frequencies of a structure is limited by the damping in the system. Engine rotating components include one-piece integrally bladed rotors (IBRs), which are increasingly used in military engine compression system components. In general, IBRs are lighter weight and offer performance benefits over conventional bladed disk assemblies. However, the one-piece nature of the IBR results in low inherent structural damping and an increased susceptibility to HCF failures. Other engine static components include variable and non-variable compressor vanes which also experience HCF failures. In addition to military turbine engine components, HCF can occur in commercial aircraft turbine engines, ground-based power turbines, automotive turbochargers and many other types of structures operating in an environment that can induce high vibratory resonant stresses at elevated temperatures.
High velocity oxygen fuel (HVOF) thermal spray coatings have been tried as coatings to reduce the HCF failures, but have been unsuccessful, in particular at elevated temperatures similar to those experienced in turbine engines. The HVOF thermal spray process is basically the same as the combustion powder spray process (LVOF) except that this process has been developed to produce extremely high spray velocity. HVOF thermal spray coatings are produced by first mixing a fuel gas and oxygen within a chamber. The resulting mixture exits the chamber through the nozzle and ignites. The powder feedstock is then fed via carrier gas, axially, into the ignited gases and is propelled uniformly to the work piece. In using both kinetic and thermal energy, the molten particles impact the substrate producing a coating with characteristics fundamentally different than a coating from a Plasma Spray Coating Method. The HVOF process creates extremely dense coatings having a very predictable and homogeneous chemistry with bond strengths in excess of 10,000 PSI with very low surface roughness, which make the HVOF coatings less suitable for damping at the high temperatures experienced in turbine engines.
Disclosed are high temperature damping coatings for reducing the resonant vibration of turbine engine components or other high temperature structures that experience resonant frequencies at temperatures of at least about 700° F. The coatings are examples of a class of coatings which include plasma sprayed “hard” materials such as ceramic, metallic or cermet with small quantities of embedded glass, or porcelain enamel, material. In one embodiment, the glass or porcelain enamel is present as less than about 15% by weight, more preferably less than about 10% by weight. The plasma sprayed coatings consist of dense microstructures of the hard material which exhibit a complex structure with microvoids and microcracks having the glass or porcelain enamels distributed to interact with the microvoids and microcracks. In particular, in the elevated temperature range, the glass or porcelain enamel starts to soften and exhibits viscoelastic behavior which dissipates mechanical strain energy in the form of thermal energy resulting in damping of the resonant vibration of the coated structure.
For a given thickness of a damping coating, which in one embodiment may comprise a relatively thin bond coat with a relatively thicker top coat, the one measure of damping merit is Young's loss modulus. Factors that effect the Young's loss modulus include the glass or porcelain enamel used, the percent by weight of glass or porcelain enamel in the coating, the temperature, and the frequency of vibration.
In one aspect, a method of applying a vibration damping surface structure to an article is disclosed herein that includes: a) providing a coating material comprising a ceramic, metallic or cermet and a viscoelastic glass frit, and b) plasma spraying the coating material onto the article, wherein the coating material forms a plurality of ceramic, metallic or cermet microstructures with the viscoelastic glass frit distributed to interact with the microstructures to provide vibration damping to the coated article. The viscoelastic glass frit provides the vibration damping by converting vibrational energy in the article to thermal energy. In one embodiment, the microstructures are generally pancake-like lamellae and include voids such as microcracks, pores, regions of incomplete bonding, and combinations thereof. The method may also include the step of applying a bondcoat to the article. In one embodiment, the bondcoat is applied as a plasma spray coating.
In one embodiment, the coating material is a mixture of the ceramic, metallic or cermet and the viscoelastic glass frit, wherein each is provided as a powder. The mixture may include about 15% by weight or less of the viscoelastic glass frit. In one embodiment, the mixture includes about 10% by weight or less of the viscoelastic glass frit and, in another embodiment, includes about 5% by weight or less of the viscoelastic glass frit. The viscoelastic glass frit may have an initial softening point of at least about 700° F. In another embodiment, the viscoelastic glass frit may have an initial softening point of 900° F.
In one embodiment, the ceramic, metallic, or cermet includes zirconia such as a yttria-stabilized zirconia. The yttria-stabilized zirconia may be about a 3% to about 10% yttria-stabilized zirconia. In one embodiment, the zirconia is about a 5% to about 8% yttria-stabilized zirconia.
In one embodiment, the plasma sprayed coating material has a Young's loss modulus at 1000 Hertz of greater than 200 ksi between 800° F. and 1500° F. In another embodiment, the plasma sprayed coating material has a Young's loss modulus at 1000 Hertz of greater than 600 ksi or greater than 700 ksi or even greater than 1000 ksi between 800° F. and 1500° F.
In other embodiments, the glass frit is present in the coating as 10% by weight and the plasma spray coating material had a Young's loss modulus at 1000 Hertz of greater than 600 ksi between 950° F. and 1080° F., or greater than 700 ksi between 980° F. and 1280° F., or greater than 1000 ksi between 1110° F. and 1320° F. In one embodiment, where the Young's loss modulus is greater than 600 ksi between 950° F. and 1080° F., the viscoelastic glass frit includes 20-30% by weight Al, 50-60% by weight B, and 20-30% by weight Na or comprises 90-95% by weight Al, 1-5% by weight Ba, and 1-5% by weight Sb. In one embodiment, where the Young's loss modulus is greater than 1000 ksi between 1110° F. and 1320° F., the viscoelastic glass frit includes 22-27% by weight Al, 10-20% by weight Ba, 45-50% by weight B, 10-20% by weight F, and 15-20% by weight Na.
In another aspect, plasma spray coatings are disclosed for damping vibrations. The plasma spray coating includes a ceramic-glass frit composite coating capable of reducing resonant vibrations in a substrate at temperatures between 800° F. to 1500° F. The ceramic and glass frit components of the composite may be similar to those described above and the plasma spray coating may have any of the Young's loss moduli described herein. In one embodiment, the plasma spray coating is coating a surface of a substrate and may include a bondcoat between the substrate and the layer comprising the ceramic-glass frit composite.
The following detailed description will illustrate the general principles of the invention, examples of which are additionally illustrated in the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.
Surface structures for turbine components are disclosed which provide vibration damping at elevated temperatures by absorbing vibration of the components and/or altering resonance frequencies of the components. The vibration damping increases fatigue lives of the components, for example, gas turbine components such as airfoils or rotor blades, compared to undamped components. Such surface structures may similarly be utilized to provide other benefits such as erosion resistance and thermal protection.
Referring to
Referring now to
As shown in
The microstructures deposited by the thermal spray techniques typically include a multitude of pancake-like lamellae called ‘splats’, formed by flattening of the liquid or melted droplets of a feedstock material. The feedstock powders may have sizes from micrometers to above 100 micrometers, thus the lamellae likely have a thickness in the micrometer range and lateral dimension from several to hundreds of micrometers. Between these lamellae, there are small voids, such as pores, cracks and regions of incomplete bonding. As a result of this unique structure, the deposits can have properties significantly different from bulk materials. These are generally mechanical properties, such as lower strength and modulus, higher strain tolerance, and lower thermal and electrical conductivity. Also, due to the rapid solidification, metastable phases can be present in the deposits. A SEM 25 μm scale top view image of a plasma spray coating layer 116 having zirconia microstructures and 10% of a viscoelastic glass frit material distributed therein is shown in
Referring to
The coating layer 116 is believed to reduce the vibration amplitude and modifies the vibration resonant response of the substrate by providing damping. In particular, Applicant believes that the viscoelastic glass frit material 126 dissipates mechanical strain energy in the form of thermal energy resulting in damping of the resonant vibrations and thereby prevents failures due to high cycle fatigue (HCF). Other factors that may affect the couplings 128, 130 and the overall damping of the substrate 114 may include, but are not limited to: the viscoelastic properties of the glass frit material 126; the density of the coating layer 116, the concentration of glass frit material 126 present in the coating layer 116; the material selected as the hard material that forms the microstructures 122; and the size of the microstructures 122 and/or glass frit material 126 present in the coating layer 116.
The coating layer 116 may be plasma sprayed onto the substrate 114 at a thickness of about 0.005 to about 0.01 inches thick. In one embodiment, the coating layer 116 is about 0.01 inches thick. In another embodiment, the coating layer 116 is about 0.0058 inches thick.
As mentioned above, the hard material may be a ceramic, metallic, or cermet material, but is not limited thereto. The hard material may be provided as a powder. The powder may have an average particle size of about 5 μm to about 120 μm, preferably about 10 μm to about 50 μm.
The ceramic may be, but is not limited to, an alumina, an alumina-titania blend, a chromia-alumina blend, a zirconia, a zirconia-silicate, a yttria stabilized zirconia, or combinations thereof. In one embodiment, the ceramic is a yttria-stabilized zirconia. The yttria-stabilized zirconia may contain about 3% to about 10% yttria, more preferably about 5% to about 8% yttria. In one embodiment, the yttria-stabilized zirconia is a 7% yttria-stabilized zirconia. In another embodiment, the yttria-stabilized zirconia is an 8% yttria-stabilized zirconia. When the coating layer 116 includes zirconia, the coating layer 116, in addition to providing damping characteristics to the article, can provide the article with a thermal barrier.
The hard material may be a metallic material, i.e., any metal or metal alloy powder. The metallic material may be, but is not limited to, an aluminum based powder, a cobalt based powder, a copper based powder, an iron based powder, a molybdenum based powder, and a nickel based powder. Various metal and metal alloy powders are available from Praxair Surface Technologies, Inc. Indianapolis, Ind.
The hard material may be a cermet. “Cermet” means a material comprising a metal or a metal alloy and a ceramic powder or a mixture of ceramic powders. Cermet is fabricated from the ceramic powder selected from a group of compounds represented and exemplified by the titanium-aluminum oxide system. Other systems, such as and including zirconium, hafnium, beryllium, vanadium oxides, nitrates, silicates or borides, etc., in combination with a metal, such as titanium, aluminum, magnesium, nickel, lithium, calcium, or their alloys are equally suitable for fabrication of cermets of the invention. In addition to these named systems, any other suitable alloy system meeting the general conditions for processing of the cermets may also be advantageously used to fabricate these cermets using the molten-metal-infiltration method and process and are intended to be within the scope of the invention. In one embodiment, the cermet may be a mixture of a ceramic, such as for example, aluminum oxide, zirconium oxide, hafnium oxide, beryllium oxide, vanadium oxide, boron carbide, aluminum nitride, zirconium nitride, hafnium nitride, vanadium nitride, aluminum boride, zirconium boride, hafnium boride, vanadium boride, aluminum silicate, zirconium silicate, hafnium silicate, vanadium silicate powders or their mixtures, in combination with a metal such as titanium, aluminum, magnesium, nickel, lithium, calcium, or other suitable metals, or their alloys, etc.
As used herein, the term “viscoelastic glass frit” refers to glass or porcelain enamel that starts to soften and exhibits viscoelastic behavior in a particular temperature range. In one embodiment, the temperature range of interest is about 700° F. to about 1500° F. In another embodiment, the temperature range of interest is about 900° F. to about 1100° F. In another embodiment, the temperature range of interest is about 1100° F. to about 1300° F.
To provide damping at temperatures between about 700° F. to about 1500° F., the glass frit should have a glass transition temperature (Tg) of at least about 700° F. or at least 900° F. In one embodiment, the glass transition temperature is between about 900° F. to about 1200° F. In one embodiment, the glass frit has an initial softening point of at least 700° F. or of at least 900° F. In another embodiment, the glass frit has an initial softening point of about 900° F. to about 1000° F. These softening points may be determined by placing the glass frit in an air furnace for 1 hour, removing the glass frit for visual examination for evidence of melting or softening, and replacing the glass frit in the air furnace, increasing the temperature of air furnace by 25 degrees and repeating the process until evidence of melting or softening is observed.
The glass frits may include, but is not limited to aluminum, silicon, barium, boron, fluorine, sodium, antimony, cobalt, lead, cadmium, lithium, vanadium, titanium, phosphorus, and combinations thereof. In one embodiment, the glass frit includes aluminum, silicon, barium, boron, fluorine, sodium, or combinations thereof. In another embodiment, the glass frit includes aluminum, barium, boron, fluorine, sodium. In yet another embodiment, the glass frit includes silicon, barium, boron, fluorine, sodium, and trace amounts of lithium, vanadium, titanium, phosphorus, or combinations thereof. In one embodiment, the glass frit includes about 20-30% by weight aluminum or about 90-95% by weight aluminum. The glass frit may also include one or both of about 45-60% by weight boron and about 1-20% by weight barium. Glass fits are commercially available, for example, from Pemco International. The glass frit is preferably a powder. The powder may have particles having an average particle size of about 5 μm to about 50 μm.
The hard material powder and the glass frit powder may be mixed together to create a powder mixture that is plasma sprayed onto substrate 114. The mixture may be blended by mechanical blending, sintering, or a combination thereof. In one embodiment, the mixture was blended by mechanical blending to provide a powder feedstock for the plasma spray apparatus. The glass frit, in particular the viscoelastic glass frit powder, may be about 15% or less by weight of the mixture. In one embodiment, the glass frit is about 10% or less by weight of the mixture. In another embodiment, the glass frit is about 5% or less by weight of the mixture.
The optional bondcoat 118 may be a metal or metal alloy layer applied to the substrate 114 to improve adhesion of the coating layer 116 to the substrate 114. Accordingly, the bondcoat is applied before depositing the coating layer 116. The metal or metal alloy may be a powder for thermal spray applications such that the bondcoat may be provided as a plasma spray coating. The bondcoat 118 may be applied at a thickness of about 0.002 to about 0.004 inches. In one embodiment, the bondcoat 118 is about 0.003 inches thick. The metal or metal alloy may be a powder, for example, but not limited to, an aluminum, cobalt, copper, iron, molybdenum, nickel metal or metal alloys. Such powders are available from Praxair Surface Technologies, Indianapolis, Ind. In one embodiment, the bondcoat is a NiCrAlY alloy.
The Young's loss modulus was used to measure the effectiveness of the coating layer 116 at providing damping to the substrate 114. The damping from a coating is proportional to the Young's loss modulus multiplied by the thickness of the coating.
In the following examples, beams coated with surface structure 112 were tested to ascertain the influence strain amplitude has on its material properties. The testing of the surface structure 112, which included a layer having the plasma sprayed damping coating 116 with a dispersed viscoelastic glass-fit material therein and a bondcoat 118 coating both sides of a rectangular beam substrate of Hastelloy® X (composition: Ni 47%, Cr 22%, Fe 18%, Mo 9%, Co 1.5%, and less than 1% C, Mn, W, B, and Si). The rectangular beam was 0.0625 in thick, 0.75 inches wide and included a free section 8.5 inches long. The rectangular beam was then mounted on a large shaker with the free section inserted sufficiently far into a heating chamber as to assure a nearly uniform temperature distribution while isolating sensitive shaker components, Thereafter, the rectangular beam was excited as a cantilevered beam to measure the frequency response functions of the system and extract therefrom the system's resonant frequency and loss factors.
The surface structure 112 included a plasma spray bondcoat 118 of NiCrAlY adjacent to the outer surface of the substrate and as a plasma spray damping coating 116 adjacent to the bondcoat. The bondcoat 118 was present as a 3 mil layer and the damping coating 116 was present as a 10 mil layer for the examples, unless stated otherwise in the examples below.
Testing was conducted by obtaining frequency functions through excitation of the above test piece with an Unholtz-Dickie model SA15-560 shaker (rated at 600 pounds). The shaker was controlled using Vibration View or Unholtz-Dickie software and a feedback control system through an accelerometer located on the fixture near the root of the test piece. The test piece was clamped as a cantilevered beam using a support fixture mounted to the top of the shaker. The support fixture was made from a solid piece of Inconel® material and uses 1.5″ thick steel blocks to clamp the specimen in place.
A Polytec® single point laser vibrometer was used to take velocity measurements on the specimen with nominal influence on the response of the specimen. Measurement of velocities up to 10 m/s were possible. A reflective sticker of negligible mass and stiffness was attached to the specimen at the measurement point, chosen at a point well-removed from any node of the mode of interest, as determined from the displacement mode shapes of the cantilever beam.
Using the above equipment and test method, three test pieces each having a 3 mil bondcoat of NiCrAlY and a 10 mil damping coating were prepared. Test piece one had an 8% yttria-stabilized zirconia damping coating with no viscoelastic glass frit present. Test piece two had a damping coating containing an 8% yttria-stabilized zirconia with 5% by weight of a viscoelastic glass frit dispersed therein. Test piece three had a damping coating containing an 8% yttria-stabilized zirconia with 10% by weight of a viscoelastic glass frit dispersed therein. The viscoelastic glass frit (“Frit 4”) included 22-27% by weight Al, 10-20% by weight Ba, 45-50% by weight B, 10-20% by weight F, and 15-20% sodium.
From the frequency responses of the coated specimens and data on the coating thickness and densities at 1000 Hz over the temperature range of 800° F. to 1500° F. the Young's loss modulus was calculated for each test piece. The results are presented graphically in
Using the above equipment and test method, three test pieces were prepared for testing for comparative analysis. The test piece of interest is the “Frit 4 in Zirconia” containing a 3 mil bondcoat of NiCrAlY and a 10 mil damping coating containing an 8% yttria-stabilized zirconia with 10% by weight of a viscoelastic glass frit dispersed therein. This test piece was compared to a “Lord LD-400” test piece (a room temperature damping material commonly used as a free layer coating) and an “APS 600 in Titania” test piece (a VEM infiltrated damping coating optimized for 200-300° F.).
From the frequency responses of the coated specimens and data on the coating thickness and densities at 1000 Hz over the temperature range of about 0° F. to 1600° F., the Young's loss modulus was calculated for each test piece. The results are illustrated in
Using the above equipment and test method, four test pieces each having a 3 mil bondcoat of NiCrAlY and a 10 mil damping coating were prepared. Test piece one is the baseline having only an 8% yttria-stabilized zirconia damping coating. Test piece A had a damping coating containing an 8% yttria-stabilized zirconia with 10% by weight of Frit 4 dispersed therein. Test piece B had a damping coating containing an 8% yttria-stabilized zirconia with 10% by weight of a viscoelastic glass frit of 20-30% by weight Al, 50-60% by weight B, and 20-30% by weight Na dispersed therein. Test Piece C had a damping coating containing an 8% yttria-stabilized zirconia with 10% by weight of a viscoelastic glass frit of 90-95% by weight Al, 1-5% by weight Ba, and 1-5% by weight Sb dispersed therein.
From the frequency responses of the coated specimens and data on the coating thickness and densities at 1000 Hz over the temperature range of 800° F. to 1500° F. the Young's loss modulus was calculated for each test piece. The results are presented graphically in
Accordingly, an article having a plasma sprayed coating material containing a plurality of ceramic, metallic, or cermet microstructures with a viscoelastic glass frit distributed therein to interact with the microstructures has a Young's loss modulus at 100 Hz greater than about 200 ksi between about 800° F. to about 1500° F., more preferably between about 900° F. to about 1300° F. In another embodiment, the article having such a plasma spray coating has a Young's loss modulus at 100 Hz greater than about 200 ksi between about 1000° F. to about 1500° F. In another embodiment, the article has a Young's loss modulus at 1000 Hz greater than about 600 ksi between about 800° F. to about 1500° F., more preferably between about 950° F. to about 1080° F. In another embodiment, the article has a Young's loss modulus at 1000 Hz greater than about 700 ksi between about 980° F. to about 1280° F. In another embodiment, the article has a Young's loss modulus at 1000 Hz greater than about 1000 ksi between about 1110° F. to about 1320° F.
The durability of the plasma spray coatings disclosed herein were tested using a micro jet turbine engine 200, available from Aviation Micro Turbines USA, and shown in
After the test, the rotor 202 was removed and was inspected. A photograph of the rotor 202 is provided as
The embodiments of this invention shown in the drawing and described above are exemplary of numerous embodiments that may be made within the scope of the appended claims. It is contemplated that numerous other configurations of the vibration damping coating may be created taking advantage of the disclosed approach. In short, it is the applicant's intention that the scope of the patent issuing herefrom will be limited only by the scope of the appended claims.
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract No. W911W6-07-C-0043 awarded by Aviation Applied Technology Directorate, US Army Research, Development and Engineering Command.
