Ceramic coatings containing layered porosity

These Invention relates to the field of ceramic, thermal barrier coatings and abradable ceramics for use in gas turbine seal applications. More particularly, this invention relates to ceramic thermal barrier coatings and abradable seals which have a plurality of layers, wherein which at least one of the layers is porous.

Gas turbine engines are widely used as sources of motive power and for other Purposes such as for electric generation and fluid pump can be used. Gas turbine manufacturers face a constant demand of Customers for better performance, increased efficiency and improved Life over. A possibility, the power efficiency and performance is to improve the operating temperatures to increase. An Increase of operating temperatures usually reduces the Machine life and is only within the limits of the Machine materials used effectively.

current Gas turbine engines are mainly constructed from metallic materials, superalloys Nickel base widely used in high-temperature areas of the machine will. Such superalloys are currently used in machines with gas temperatures very close to their melting point of superalloys are. Increases in engine operating temperature are not possible without simultaneous steps to protect superalloys against directly Gas temperatures to be exposed, in which melting occurs. Such steps include the supply of cooling air (what the engine efficiency reduced) and the use of insulating coatings.

Insulating Ceramic materials, in particular in the form of coatings or thermal barrier coatings, are the main subject of this invention. Such coatings are most common ceramic and are usually by plasma spraying applied or by electron beam vapor deposition. These Invention focuses on coatings by electron beam vapor deposition be applied. The electron beam vapor deposition method is in the U.S. Patents 4,405,659; 4,676,994 and 5,087,477 described. Typical Patents, the thermal barrier coatings describe the current state of technology, are as follows: 4 405,660, 5,262,245 and 5,514,482.

The most frequently Thermal barrier coating used covers for use in rotating components in turbine engines a bonding layer material (bond coat material), whose composition is described in US Patent 4,419,416, a thin layer of aluminum oxide annealed to the bonding layer and an aluminum oxide layer on the Ceramic coating with columnar grains, such as described in US Patent 4,405,659. This coating was carried the applicant has developed and is currently estimated at more than 100,000 gas turbine components applied per year. Despite the success of this coating and its widespread acceptance there is a desire for advanced thermal barrier coatings, the principle desired Improvement improved specific thermal insulation properties (Corrected by the density of thermal insulation) are.

If a coating with improved density corrected insulation properties could be developed, could such a coating either with the same thickness as that are currently being used commercially, is used to heat flow to reduce (resulting in a reduction in cooling air and thereby to a Increase machine efficiency allows), or it could be a reduced thickness are used for the same degree of insulation and heat flux to care, but with reduced coating weight. Such weight reductions are essential, especially in rotating components, since the Weight of the thermal barrier coating to centrifugal forces while machine operation of up to 2000 pounds (about 9000 N) to a single turbine blade resulting in a large aircraft engine. On Reducing Laufschaufelzentrifugalkräften has positive effects in the design requirements for equipment components related with the blade, in particular the retaining disc.

The Gas turbine efficiency can be improved by reducing gas leakage will. In particular, the gap between the tips must the rotating blade and the surrounding casing structure be minimized. This is typically achieved by providing an abradable seal material to the housing. In operation the blade tips cut a channel in the abradable material and thus reducing gas leakage.

EP-A-0 605 196 discloses a thermal barrier coating with a dense and a porous ceramic layer, which is applied by an air plasma spray process. US-A-5350 599 describes a thermal barrier coating, deposited by physical vapor deposition. rotation of the substrate during deposition interrupted to porous layers with a columnar preferably to produce microstructure and denser layers without porosity. EP-A-0 <?page 3?>366 924 describes bond coats for layered ceramic materials.

Out View of a first aspect the present invention provides a porous ceramic material prior to having a plurality of ceramic layers by the physical Vapor deposition have been deposited, at least one of the layers is a first layer comprising more than 20 vol .-% porosity and another layer is at least a second layer, the less than 5 vol .-% porosity and wherein the material has more than three first layers and wherein said first layers from each other by at least one arranged between them second layer are separated.

In a preferred embodiment, , the present invention provides a coated substrate, comprising a a substrate. b. a bonding layer; c. stratified Ceramic coating of the ceramic material of the present invention on the binding layer.

In accordance with a further preferred embodiment, the present Invention a coated substrate before, in which the binding layer on the substrate of MCrAlY or aluminide coatings, or combinations of these.

The present invention comprises a layered ceramic material, which is preferably applied as a coating. Different layers in the structure have different microstructures, with at least one of the layers is relatively dense and another of the layers is less dense and defect-prone. The structure of the less dense, defect-affected layer can be modified by heat treatment, order for porosity to care. porosity yields reduced thermal conductivity and increased abradability.

The Layers are preferably deposited by electron beam physical vapor deposition. Sputtering is an alternative application technique for the invention process, However, as it is currently running, a slow and generally uneconomic Process.

Mostly have the layers have different chemical compositions, although under certain circumstances for the Layers is possible, that they have a common chemical composition. The layers be applied under conditions that the differences aforementioned in density and porosity generate between alternating layers.

The relatively dense layers by electron beam vapor deposition applied under conditions which lead to the deposition of the one to lead, what those with the technique of physical vapor deposition are familiar, described as Zone II or Zone III structures. Herein following the term zone-II / III is used, to designate structures that a either a Zone II or Zone III type structure or a combination of Zone II and Zone III structures have. The less dense layers (ie, layers which are porous) be applied under conditions which result in microstructures those familiar with the art of physical vapor deposition are referred to as Zone I structures. As used herein is, the term Zone I a layer having either a Zone I structure, as it was deposited or a Zone I structure as was deposited and heat-treated was to the porosity to increase.

The resultant structure is heat-treated, the porosity to increase by sintering, which the pore size increases and the ceramic portions which surround the pores compacted.

The Invention coating finds particular application in the field of Gas turbine components. Such components include turbine airfoils blades (running and vanes) and abradable seals with blade tips intended to cooperate, or knife edge seals to prevent unwanted gas flow to to reduce.

According to a second aspect, the present invention provides a method for Applying before a layered ceramic coating, in which at least some of the layers of porous are, to a substrate, comprising the steps of: depositing a plurality of ceramic layers by physical vapor deposition on the substrate under conditions to at least one first Layer having a Zone I microstructure and at least a second Layer having a Zone II microstructure or zone III microstructure or a mixture of them lead, wherein the material is more than three of said first layers having a Zone I microstructure Has; and heat treating the coated substrate with the plurality of layers to porosity in the three or generate more Zone I microstructure layers such that more than 20 vol .-% porosity have, wherein the at least one Zone II and / or III microstructure layer less than 5 vol .-%, said first layers each other, separated by at least one second layer disposed therebetween are.

It are now certain preferred embodiments of the present Invention example only and with reference to the accom<?page 4?>border described drawings, wherein:

<figref idrefs="S22">1</figref> the Structure of EBPVD deposited coatings as a function the substrate surface temperature shows;

<figref idrefs="S23">2</figref> the Microstructure of an exemplary coating as deposited was shown;

<figref idrefs="S24">3</figref> the Microstructure of the coating after heat treatment shows; and

<figref idrefs="S25">4</figref> the thermal conductivity a preferred coating and stabilized with 7% yttria Zirconia.

Physical Vapor deposition of ceramics, including electron beam and Sputtering techniques have been studied extensively. A BA Movchan and AB Demchishin published Article entitled "Study of the Structure and Properties of Thick Vacuum Condensates of Nickel, Titanium, Tungsten, Aluminum oxide, and zirconium oxide "in 1969, the Journal Physics of Metallurgy and Metallography (USSR), Volume 28, page 83, analyzes the vapor deposition of materials under different Conditions. These authors were the first to the structure of the by electron beam over physical vapor deposited coatings as a Function of substrate surface temperature have characterized. <figref idrefs="S22">1</figref> from Article herein was as <figref idrefs="S22">1</figref> reproduced. Published in 1974 Thornton a similar Article related to sputter deposition, J. Vac. Sci, Technol. 11: 666.70, (1974), with similar Results.

<figref idrefs="S22">1</figref> shows the three zones in physical vapor deposition coatings deposited occur as a function of substrate surface temperature while deposition. Zone I is a coating with low density an extremely large Defect content (micropores, microvoids, dislocations, vacancies and the same). Zone II is a denser structure columnar grains wherein each column a single grain, and Zone III is an even more dense coating (Substantially completely tight), having the equiaxed recrystallized grains. It is believed, that the change in the separation character (effective increasing the density by Increasing the substrate temperature) from the increased mobility of the gas phase deposited atoms after they have impinged on the substrate surface, results.

For ceramics have Movchan et al. found that the boundary between Zone 1 and zone II typically occurs at a homologous temperature (Homologous temperature refers to the proportion of the absolute Melting temperature of the material) of 0.22 to 0.26, and the boundary between Zone II and Zone III typically occurs a homologous temperature of between about 0.45 and 0.5.

It can be seen that a single ceramic composition so deposited can be that it has three different structures by the Temperature of the substrate surface, on which the coating is deposited is controlled. There the deposited coating microstructure is a function of the substrate temperature is can also be seen that different ceramic materials having different melting points and therefore different homologous Temperatures on a substrate at constant surface temperature can be deposited and have different zone structures.

The Substrate surface temperature refers to the temperature at the surface to which the coating is deposited, this temperature often the temperature of the Substrate bulk (English: bulk) differs and radiated Energy flow and the surface by the coating material, which occurs on the surface, inputted energy is affected. Higher substrate surface temperatures permit lateral diffusion of deposited atoms, leading to deposits higher Density results.

The Essence of the present invention is the deposition of at least a first layer having a zone I structure and at least one the second layer having a Zone II or Zone III structure, where the operation is repeated at least three first layers form (followed by appropriate heat treatment; a directive suitable heat treatment temperature would be a Temperature above about 0.5 to 0.8 of the homologous temperature the layer composition in which form the porosity). Preferably the Zone I layer between adjacent layers of Zone II / III structures arranged. The Zone I structure, being less dense, inhibits heat flow , thereby ensuring thermal insulation, the less dense structure will also abradable be for Sealing applications. The relatively denser Zone II / II structure layer ensures Mechanic solidity. The layer thickness varies between 0.05 and 5000 microns and preferably between 0.1 and 1000 microns. The total coating thickness may be between about 10 microns and about 1 mm for Thermal barrier coatings and up to 5 mm for abradable coatings are. The practical applications of the invention have many alternating layers of materials to more than 10 layers and most preferably more than 100 Layers.

Practical Applications of the invention set&lt;?page 5?&gt;preferably zen and heat treatments after deposition of the coating layer in order to sinter of the Zone I structure and the formation of large pores or accumulated effect of porosity. Such pore agglomeration improves the mechanical properties of the coating by densifying the ceramic in regions between the pores. The average Pore ​​size is greater than 0.01 and preferably than 0.1 microns. The resultant pores have a rounded shape that characterized is that for a pore average diameter "D" (measured several diameters) of the smallest radius of the pore wall is greater than 0.1 D and preferably greater than 0.3D is.

These relatively smooth rounded geometry distinguishes the pores in coating of the invention be found, from the flaws in plasma sprayed Coatings are found. Plasma sprayed coatings are the impact or the spraying (splattering) or melted softened powder particles formed. The resultant coating has irregular pores with sharp corners between the solidified splashes. It will no plasma sprayed porosity found in layers separated by layers which substantially free of porosity are.

After heat treatment the porous Zone I layer substantially greater than about 20% porosity by volume and more preferably more than about 35% porosity have per volume. The Zone II / Zone III layers are less than about 5% by volume and preferably less than about 2% porosity by volume exhibit. Substantially free from porosity means less than about 5% by volume and preferably less than about 2% by volume.

In its broadest definition, the invention comprises at least three or more Zone I layers (heat treated, the porosity increase) and at least one Zone II / Zone III layer. are Preferably it contains at least 10 layers with at least three, the zone I and at least three, the Zone II and / or Zone III type. Preferably, there are more than 100 layers in the coating, wherein at least 10 layers Zone I type and at least 10 from the Zone II or Zone III structure are.

A Bond layer is usually between the substrate and the coating of the invention stratified porosity positioned. Preferred bond coats include those layers, known as MCrAlY coatings and aluminide coatings are. Both types of coatings form dense, adherent alumina layers reasonable purity and it is this alumina layer to the coating according to the invention liable.

The Concept of this invention, by consideration of the following Example, which meant merely illustrative and not restrictive is be better understood.

example

On Single crystal superalloy substrate having a nominal composition of 5% Cr, 10% Co, 1.9% Mo, 5.9% W, 3% R, 8.7% Ta, 5.65% Al, 0.1% Hf and balance Ni was provided. The surface of the Substrate was cleaned by grit blasting and then a thin bonding layer (Nominally 0.005 inch (0.127 mm) thick) MCrAlY type having a nominal composition of 22% C, 17% Cr, 12.5 Al, 0.25% Hf, 0.4% Si, 0.6% Y and the balance Ni applied. The bonding layer was prepared by conventional Plasma spray deposited. The bond coat surface was then glass bead blasted to increase their density. On Heat treatment step was then carried out, a thermally grown oxide (mainly alumina) to form. The treatment was at 1500 ° F (816 ° C) for 15 minutes at an oxygen flow of 70 standard cm³/ Min (sccm) at a Pressure of about 10^-4 Torr (13.1 MPa). minimal Experimentation is required to obtain the desired oxide thickness of from 0.01 to 2.0 microns and preferably 0.1 to 0.7 microns to develop.

A layered coating consisting of alternating layers of cerium oxide, the wt .-% of yttria stabilized zirconia and contains 12 with 7 wt .-% of yttria was then applied on the binding layer surface. Coating thicknesses were about 0.5 microns for the stabilized zirconia and about 0.5 microns for the Yttria-ceria. About 300 pairs of coating layers were for a Total coating thickness of about 300 microns is applied.

These Coating layers by means of an electron beam vaporize individual top ceramic materials applied. The electron beam was diverted to alternate the different ceramic components vaporize. The individual sources by an electron beam evaporated, the at about 10 kV and a current of about 0.4 A for an evaporation power worked from about 4 kW. The dwell time of the electron beam on the yttria-ceria was about 4 seconds and on the yttria-zirconia about 6 sec. The spacing distance from the substrate to the ceramic vapor source was about 3 inches (76 mm). The substrate was coated with about 28 U / min ro&lt;?page 6?&gt;Animal T, and the bulk substrate temperature was about 1400 ° F (760 ° C). The coatings were at a reduced pressure of about 4 × 10^-6 Torr (532 × 10^-6 Pa) applied, and oxygen was introduced into the chamber at a rate of about 70 standard cm³/ Min flowed, the Beschichtungsstöchiometrie to ensure. The total time to apply this coating was about 60 min.

During the Coating deposition the coating source heated the substrate surface during the Yttria-zirconia deposition to a greater extent than during the yttria-ceria deposition. This process resulted in that the yttria-zirconia layers had a dense Zone II structure, whereas the yttria-ceria a highly defective zone I structure with micro voids and microporosity trained. The estimated porosity the yttria-zirconia was less than about 5%. Thermal radiation from the evaporating target material was the primary source of the substrate surface heating (above the bulk substrate temperature) during the coating process of physical evaporation by electron beam.

The increased warming the substrate surface while the deposition of the yttria-zirconia layers resulted from the high temperature of the yttria-zirconia target material while evaporation. While the coating process was significantly more heat from the yttria-zirconia during generates the evaporation, because this material has a relatively low Vapor pressure, so that the yttria-zirconia material has to be heated at a high temperature and melted material with a reasonable vaporize rate. The yttria-ceria composition has a much higher Vapor pressure and evaporates at a much lower temperature, apparently by sublimation, and thus does not form a hot molten Reservoir as that during real evaporation is formed. The yttria-ceria target material is at a lower temperature and no molten reservoir while evaporation forms such as yttria-zirconia, heats the substrate less effective.

summary was the substrate surface, has been coated, at a relatively high temperature during the Deposition of yttria-zirconia due to the effective heating by the yttria-zirconia target source and the resultant Vapor cloud, and the yttria-zirconia vapor condensed as a structure of the Zone II type. While However, the deposition of yttria-ceria was the substrate surface a relatively low temperature due to limited heating by the yttria-ceria target source and the ceria vapor cloud, which produced a structure from Zone I type.

The Microstructure of the coating is deposited in such as <figref idrefs="S23">2</figref> shown. The dark bands in of the coating are the defective yttria-ceria layers, and the bright bands the stabilized zirconia layers. After deposition the coating at 2200 ° F (1204 ° C) for a period 48 h heat-treated, and the microstructure of the heat treated Coating is in <figref idrefs="S24">3</figref> shown. You can see that a high degree of porosity present. porosity is in the layers that were originally Yttria-ceria were (Structural Zone I type). There is none visible porosity in the yttria-stabilized zirconia layers.

<figref idrefs="S25">4</figref> is a representation of the thermal conductivity a preferred embodiment, as described in this example and the conventional Yttria-stabilized zirconia coating described in US Patent described 4,405,659. It can be seen that the thermal conductivity of the preferred coating over a wide temperature range is significantly less than that the conventional Coating. about the biggest part shows the temperature range the coating of the preferred embodiment a thermal conductivity, is about 80% lower than that of the conventional coating. This is a substantial improvement in the insulation ability.

The previous example, the invention by a combination illustrated ceramic material. Of course there are many combinations of Ceramic materials which may be deposited.

Some Variations and alternate details are described below.

I. substrate

At the common substrate may comprise any high temperature material, such as ceramics, carbon, carbon compounds and like, and superalloys. For turbine blades Super alloys are most suitable. Superalloys are metallic Materials based on iron, nickel or cobalt with a yield strength of more than 50 ksi (345 MPa), and more typically greater than 100 ksi (690 MPa) at 1000 ° F (538 ° C).

As discussed below, bond coats are often desired to form a coating liability at. the substrate to ensure under certain conditions, for some superalloys ever&lt;?page 7?&gt;but no need for a bonding layer composed. Superalloys coated can be without the necessity of a bond coat are those which form naturally a layer of high purity aluminum on their outer surfaces, when exposed to oxidizing conditions at elevated temperatures will. Typical superalloys which do not require a bond coat are, described in US Patent 5,262,245.

If the coating of the invention a ceramic material, such as aluminum oxide, is to be applied, there is usually no need for a bond coat.

II. Binding layer

In rule is a binding layer portion of the coating system according to the invention be. The need for a bonding layer depends of the substrate from and to the conditions governing the function the thermal barrier coating, the operating temperature, the desired Life and other environmental factors including thermal Cycles and the ambient gas composition. There are a variety by binding layers used with the present invention can be. These include overlay coatings and aluminide. Typical overlay coatings are described in US Patents 3,928,026 and 4,419,416 and are Variations on nickel and cobalt-based superalloys were optimized to adhesion-resistant, high-purity alumina layers to develop if they oxidation conditions at elevated temperatures get abandoned.

Overlay coatings be on the surface applied the substrate and are embodied in the coatings MCrAlY type, which have the following general composition: <tables><table><tgroup cols="2"><colspec colnum="1" colname="1" colwidth="1*" /><colspec colnum="2" colname="2" colwidth="1*" /><tbody><row><entry colname="1">M = Fe, Ni, Co and (Ni + Co)</entry><entry colname="2">= rest</entry></row><row><entry colname="1">Cr =</entry><entry colname="2">= 10-30%</entry></row><row><entry colname="1">Al =</entry><entry colname="2">= 5-15%</entry></row><row><entry colname="1">Y = (Y + Hf + La + Ce + Sc)</entry><entry colname="2">= 0.01-1%</entry></row><row><entry colname="1">(Si + Ta + Pt + Pd + Re + Rh + Os)</entry><entry colname="2">= 0-5%</entry></row></tbody></tgroup></table></tables>

Overlay coatings can Plasma spraying, be applied by EBPVD and by electroplating. aluminide are produced by diffusing aluminum into the substrate and are in <patcit><text>US 5514482</text></patcit> described. As used herein, the term aluminide coating includes Aluminide coatings which, by the addition of Pt, Rh, Os, Pd, Ta Re, Hf, Si, Cr and mixtures of them are modified.

It is also known combinations of overlay and aluminide coatings apply, for example, an aluminide have also applied overlay coating and vice versa.

The important common features of a useful bond coat are required, are that it adheres to the substrate, that it thermally and diffusion moderately stable is that it form a stable alumina layer which at the liable in the operating environment to be deposited ceramic layer.

IV. Ceramic compositions

Nearly each Kermikzusammensetzung obtained by physical vapor deposition can be applied, can be used in the present invention will. Offensicherlicherweise the ceramic is of the person skilled in in reasonable selected way leaving them with the bonding layer and / or the substrate, the other present in the coating compositions and the ceramic is operating environment compatible. The ceramic coating can be a single ceramic composition or different ceramic compositions which are applied in alternating layers, exhibit. The critical feature is that the coating is treated to alternating Zone I / Zone II or Zone III layer structures forms. According to the work of Movchan et al. and Thornton, any ceramic evidently with Zone I, Zone II or Zone III structures are applied when the appropriate substrate surface temperatures be maintained. Preferably, the ceramics used those that at first glance slight thermal bulk thermal conductivity exhibit. These include stabilized zirconia, ceria rare-earth additives and oxide pyrochlore compositions.

We prefer to use a sublimating ceramic to form the Zone I layers, and a ceramic from evaporating type to form the Zone II / III layers. That was illustrated in the example.

The Arrangement of the ceramic coating can be varied widely. The most thorough description is that the coating consists of multiple layers, wherein more than three layers so be deposited so as to have a structure of the Zone I type. The Zone I structure is subsequently heat treated to porosity &lt;?page 8?&gt;form. The layers of the structure of the Zone I type from each other by at least one interposed Zone II and / or Zone III structure separated, in order for mechanical support and to ensure maintenance.

We believe that fine porosity is most effective heat flux to reduce. This must be weighed against the idea that small Pores are less stable since they tend to be at high temperatures to shrink and close up or heal. A pore closure will not be a significant problem if the use temperature is less than the pore shrinkage temperature.

Preferably has the the binding layer or layer adjacent to the substrate a structure of the Zone II / Zone III type. Preferably, the outermost layer also a structure of the Zone II Zone III type.

Among certain circumstances can other layers are built without the benefits of thermal compromising isolation of the invention. For example, an outer layer to get voted, order for special properties that Special applications desirable are to provide, such as thermal emissivity, hardness, abrasion resistance, resistance against environmental influences (Oxidation, sulfidation, nitridation etc.) and / or resistance to diffusion of adverse environmental agents such as oxygen; of the underlying coating layer and / or the connection layer and / or would affect the substrate adversely. For example, alumina as an outer layer he wishes be because it is relatively hard and resistant to diffusion of oxygen is.

For sealing applications meet many of the same considerations. The total coating thickness will generally be greater, up to about 100 mils (2.54 mm), preferably 50 mils (1.27 mm). The individual layer thickness and pore volume and pore size optimized for the to provide mechanical properties for abradability are needed.

V. Aluminiumdioxidschicht

A Aluminiumdioxidschicht is an important feature of the invention, no matter whether formed directly on the substrate or on a bond coat. In general, the aluminum oxide layer is thermally grown, but it is also known to use sputtering to this layer to form. The general thickness of the aluminum layer is 0.01 to 2 microns, preferably 0.1 to 0.7 microns.