CERAMIC MATERIAL FOR HIGH TEMPERATURE SERVICE
A high purity yttria or ytterbia stabilized zirconia powder wherein a purity of the zirconia is at least 99.5 weight percent purity and with a maximum amount of specified oxide impurities.
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The present application is a continuation of parent U.S. application Ser. No. 15/836,369 filed Dec. 8, 2017, which is a continuation of U.S. application Ser. No. 13/913,101 filed Jun. 7, 2013 (now U.S. Pat. No. 9,975,812 issued May 22, 2018), which is a continuation of U.S. application Ser. No. 11/790,430 filed Apr. 25, 2007 (now U.S. Pat. No. 8,603,930 issued Dec. 10, 2013), which is a continuation-in-part of U.S. patent application Ser. No. 11/520,043 filed Sep. 13, 2006 (now U.S. Pat. No. 7,723,249 issued May 25, 2010), which claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/724,268 filed Oct. 7, 2005, the disclosures of which are expressly incorporated by reference herein in their entireties.
STATEMENT REGARDING SPONSORED RESEARCH OR DEVELOPMENTNot Applicable.
REFERENCE TO SEQUENCE LISTINGNot Applicable.
BACKGROUND OF THE INVENTION Field of the InventionThe invention relates to ceramic materials for thermal barriers and abradable coating systems in high temperature and high temperature cycling applications, and more particularly to ultra-pure zirconia materials for use in thermal barrier and abradable coating applications.
Description of Related ArtSuperior high-temperature properties are required to improve the performance of heat resistant and corrosion resistant members. These members include, for example gas turbine blades, combustor cans, ducting and nozzle guide vanes in combustion turbines and combined cycle power plants. Turbine blades are driven by hot gasses, and the efficiency of the gas turbine increases with the rise in operational temperature. The demand for continued improvement in efficiency has driven the system designers to specify increasingly higher turbine operating temperatures. Thus, there is a continuing need for materials that can achieve higher operational temperatures.
Thermal barrier coatings are used to insulate components, such as those in a gas turbine, operating at elevated temperatures. Thermal barriers allow increased operating temperature of gas turbines by protecting the coated part (or substrate) from direct exposure to the operating environment. An important consideration in the design of a thermal barrier is that the coating be a ceramic material having a crystalline structure containing beneficial cracks and voids, imparting strain tolerance. If there were no cracks in the coating, the thermal barrier would not function, because the differences in thermal expansion between the metal substrate system and the coating will cause interfacial stresses upon thermal cycling that are greater than the bond strength between them. By the creation of a crack network into the coating, a stress relief mechanism is introduced that allows the coating to survive numerous thermal cycles. Repeating crack networks are typically imparted into the coating on varying space scales by manipulating the thermodynamic and kinetic conditions of the manufacturing method, and different structures known to perform the coating task have been optimized likewise. In addition to this, cracks are also formed during service, so the structure formed upon coating manufacture changes with time, depending on the starting material phases in the manufactured coating and thermal conditions during service.
Another design factor determining coating lifetime is the sintering rate of the coating. When the coating is cycled above half of its absolute melting temperature, the coating begins to sinter causing volume shrinkage. As the coating shrinks, the stress difference between the coating and substrate increases. At a certain amount of shrinkage (which varies depending on the type of structure and thermal conditions during service), the stress difference exceeds the bonding strength of the coating and it becomes detached. Decreasing the sintering rate of the thermal barrier increases the amount of time before the catastrophic shrinkage is experienced, so it can become a major design consideration. For high purity zirconia alloys, the onset of sintering commences at temperatures above 1000° C.
Historically, high temperature thermal barrier coatings have been based on alloys of zirconia. Hafnia may also be employed due to its chemical similarity to zirconia, but is generally cost-prohibitive. Hafnia also is typically present in most zirconia materials in more than trace amounts due to difficulty in separating the two oxides. Zirconia and/or hafnia have the following combination of desirable properties that other known ceramic systems do not possesses for the application. First, zirconia alloys have some of the highest melting points of all ceramics, and this means theoretically some of the highest temperatures for which the onset of sintering occurs. Second, zirconia alloys have one of the lowest thermal conductivities of all ceramics. Third, zirconia has one of the highest coefficients of thermal expansion of all ceramics, so it is most compatible with transition metal alloys during thermal cycling.
Zirconia alone cannot fulfill the coating requirements because it undergoes a phase transformation from tetragonal to monoclinic during thermal cycling. This transformation is presumed to cause a detrimental volume change resulting in large strain differences between the coating and the substrate. When the resulting stresses exceed the bond strength of the coating to the substrate, the coating will detach. For this reason a phase stabilizer is added to the zirconia and/or hafnia, such as yttria, which suppresses the tetragonal to monoclinic phase transformation.
Thermal spray abradable coatings are commonly used in gas turbine applications. Abradable coatings are designed to preferentially abrade when contact is made with a mating part. These coatings have low structural integrity so they are readily abraded when they come into contact with a moving surface with higher structural integrity (such as the blade of a turbine). The coatings are designed so as not to damage the mating surface. In many applications abradable coatings are subject to the same thermal cycling conditions as the thermal barriers described above. Thus, there is a continuing need for materials suitable for abradable coatings that can achieve higher operational temperatures.
Some previous efforts to improve coating life have focused on the coating material and microstructure upon entry into service. However, the heat cycle of in service parts also causes cracks throughout the service life of the part. Thus, the microstructure formed upon coating manufacture changes with time, depending on the starting material phases in the manufactured coating and thermal conditions during service. Because a consistent optimal crack network is not typically maintainable throughout the service life of the part, coating lifetime is ultimately determined by the material selection and its manufacturing process. There remains a need in the art for a coating material, coating material manufacturing method, and coating manufacturing method that address the changes in the coating microstructure during its service lifetime.
SUMMARYAccordingly, the invention is directed to a ceramic material for use in thermal barriers for high temperature cycling applications and high temperature abradable coatings. The material is an alloy formed predominantly from ultra-pure stabilized zirconia (ZrO2) and/or hafnia (HfO2) alloys that have uncharacteristically high sintering resistance to achieve a high service lifetime. The invention provides a desired coating material so that the changes in the coating microstructure over the in-service lifetime are retarded.
The limits for impurities discovered to decrease sintering rate and therefore increase service lifetime compared with current impurity concentrations when used as a coating and partially stabilized with a rare earth oxide, for example, yttria (Y2O3) and/or ytterbia (Yb2O5), are disclosed herein. Oxide impurities are defined as materials which, when combined with each other or with zirconia and/or hafnia, form phases with melting points much lower than that of pure zirconia and/or hafnia.
In one aspect, the invention provides a ceramic material for use in high-temperature thermal barriers or abradable seal coatings. The said material has about 4 to 20 weight percent of a stabilizer of one or more rare earth oxides; and a balance of at least one of zirconia (ZrO2), hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and/or hafnia (HfO2) is partially stabilized by the stabilizer, and wherein the total amount of impurities is less than or equal to 0.15 weight percent.
In another aspect of the invention a blended ceramic material of one or more ceramic materials is provided. Each of the ceramic materials is for use in high-temperature thermal barriers or abradable seal coatings and is supplied in the form of one of a powder or a slurry of partially stabilized powder. Each of the ceramic materials has about 4 to 20 weight percent of a stabilizer of one or more rare earth oxides and a balance of at least one of zirconia (ZrO2), hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and/or hafnia (HfO2) is partially stabilized by the stabilizer, and wherein the total amount of impurities of the blended ceramic material is less than or equal to 0.15 weight percent. Additional ceramic materials or placeholder materials may also be included in the blended material.
Conventional approaches to improving coating life-cycles have focused on adding stabilizers to the base ceramic material. The approach of the present invention provides previously unexpected results in sintering data by identifying low-impurity materials. When looking at the sintering data, changing the amount of impurities slightly has a much greater effect on performance compared with changing the amount and types of stabilizers.
In embodiments, there is provided a high purity yttria or ytterbia stabilized zirconia powder wherein a purity of the zirconia is at least 99.5 weight percent purity and a maximum amount of oxide impurities is as follows: less than 0.005 weight percent SiO2; less than 0.015 weight percent Al2O3; less than 0.002 weight percent TiO2; less than 0.04 weight percent Fe2O3; less than 0.02 weight percent CaO; less than 0.002 weight percent MgO. The impurities may include less than 0.001 weight percent Cr2O3 and less than 0.002 weight percent Na2O.
In embodiments, the powder is a thermal sprayable powder.
In embodiments, the zirconia is partially stabilized by the yttria.
In embodiments, the powder has a particle size of from about 5 to 150 microns.
In embodiments, there is provided a method of applying a thermal barrier coating on a substrate, the method comprising thermally spraying the powder of claim 1 onto the substrate so as to form the thermal barrier coating having from about 5 to 250 vertical macro cracks per 25.4 mm length measured along a coating surface and being oriented perpendicular to a surface of the substrate containing said coating.
In embodiments, there is provided a high purity yttria or ytterbia stabilized hafnia powder wherein a purity of the hafnia is at least 99.5 weight percent purity and a maximum amount of oxide impurities is as follows: less than 0.002 weight percent Na2O; less than 0.005 weight percent SiO2; less than 0.015 weight percent Al2O3; less than 0.002 weight percent TiO2; less than 0.04 weight percent Fe2O3; less than 0.02 weight percent CaO; less than 0.002 weight percent MgO; and less than 0.001 weight percent Cr2O3.
In embodiments, the powder is a thermal sprayable powder.
In embodiments, the hafnia is partially stabilized by the yttria.
In embodiments, the powder has a particle size of from about 5 to 150 microns.
In embodiments, there is provided a method of applying a thermal barrier coating on a substrate, the method comprising thermally spraying the powder of claim 6 onto the substrate so as to form the thermal barrier coating having from about 5 to 250 vertical macro cracks per 25.4 mm length measured along a coating surface and being oriented perpendicular to a surface of the substrate containing said coating.
In embodiments, there is provided a high purity yttria stabilized zirconia powder comprising a purity of the zirconia being at least 99.5 weight percent purity, less than about 0.005 weight percent silicon dioxide (silica), less than about 0.015 weight percent aluminum oxide (alumina), less than about 0.02 weight percent calcium oxide, less than about 0.04 weight percent ferric oxide, less than about 0.002 weight percent magnesium oxide, and less than about 0.002 weight percent titanium dioxide.
In embodiments, the powder is a thermal sprayable powder.
In embodiments, the zirconia is partially stabilized by the yttria.
In embodiments, the powder has a particle size of from about 5 to 150 microns.
In embodiments, there is provided a method of applying a thermal barrier coating on a substrate, the method comprising thermally spraying the powder of claim 11 onto the substrate so as to form the thermal barrier coating having from about 5 to 250 vertical macro cracks per 25.4 mm length measured along a coating surface and being oriented perpendicular to a surface of the substrate containing said coating.
In embodiments, there is provided a method of coating a substrate with a thermal barrier coating (TBC) on a substrate via thermal spray, the method comprising spraying a powder coating material comprising a yttria stabilized material comprising zirconia and hafnia, wherein a purity of each of said zirconia and said hafnia being at least 99.5 weight percent and total impurities of said zirconia and said hafnia comprises less than or equal to: about 0.005 weight percent silica, about 0.002 weight percent titania, and about 0.002 weight percent magnesia and forming a TBC coating by depositing the coating material in the form of a collection of frozen droplets or splats, wherein the TBC coating comprises vertical cracks arranged at repeating intervals and extending in a thickness direction of said thermal barrier coating.
Embodiments are directed to a ceramic powder that includes a primary stabilizer oxide comprising 4-20 weight percent and oxide impurities up to a maximum of 0.15 weight percent and a first material comprising a balance of the ceramic powder. The first material is partially stabilized by the primary stabilizer oxide into a first partially stabilized material. The oxide impurities, when combined with each other or with the first partially stabilized material, form phases with melting temperatures at least 100° C. lower than the melting temperature of the first material.
According to embodiments, the first material can include at least one of zirconia or hafnia; and the primary stabilizer oxide can include at least one of a yttria or a ytterbia stabilizer. The oxide impurities may include less than 0.005 weight percent SiO2; less than 0.015 weight percent Al2O3; less than 0.002 weight percent TiO2; and less than 0.002 weight percent MgO. The oxide impurities may further include less than 0.04 weight percent Fe2O3; less than 0.02 weight percent CaO; less than 0.001 weight percent Cr2O3; and less than 0.002 weight percent Na2O.
In embodiments, the powder can be a thermal sprayable powder.
In accordance with other embodiments, powder may have a high purity of at least 99.5 weight percent purity.
According to still other embodiments, the powder may have a particle size of from about 5 to 150 microns.
Embodiments are directed to a blended ceramic powder that includes a first material composition having: a first primary stabilizer oxide comprising 4-16 weight percent and first oxide impurities up to a maximum of 0.15 weight percent and a first material comprising a balance of the first material composition, wherein the first material is partially stabilized by the first primary stabilizer oxide into a first partially stabilized material. The first oxide impurities, when combined with each other or with the first partially stabilized material, form phases with melting temperatures at least 100° C. lower than the melting temperature of the first material. The blended ceramic powder also includes a second material composition having: a second primary stabilizer oxide comprising 4-20 weight percent and second oxide impurities up to a maximum of 0.15 weight percent and a second material comprising a balance of the second material composition, wherein the second material is partially stabilized by the second primary stabilizer oxide into a second partially stabilized material. The second oxide impurities, when combined with each other or with the second partially stabilized material, form phases with melting temperatures at least 100° C. lower than the melting temperature of the second material.
In accordance with embodiments, the first material may include at least one of zirconia or hafnia, the first primary stabilizer oxide may include 4-12 weight percent of a yttria stabilizer, and a fraction of the first material in the blended powder may be 5-50 weight percent, and the second material may include at least one of zirconia or hafnia, the second primary stabilizer oxide may include 4-16 weight percent of a ytterbia stabilizer, and a fraction of the second material in the blended powder may be 50-95 weight percent.
According to further embodiments, the blended ceramic powder may further include a third material composition having a third primary stabilizer oxide comprising 4-20 weight percent and second oxide impurities up to a maximum of 0.15 weight percent and a third material including a balance of the third material composition, wherein the third material is partially stabilized by the third primary stabilizer oxide into a second partially stabilized material. The third first oxide impurities, when combined with each other or with the third partially stabilized material, may form phases with melting temperatures at least 100° C. lower than the melting temperature of the third material. Moreover, the third material composition can include at least one of zirconia or hafnia and the third primary stabilizer oxide can include at least one of 4-16 weight percent of a neodymium stabilizer or 4-20 weight percent Europa stabilizer. The fraction of the first material in the blended powder can be 10-90 weight percent, the fraction of the second material in the blended powder can be 5-45 weight percent and the fraction of the third material in the blended powder can be 5-45 weight percent.
In other embodiments, the first material can include at least one of zirconia or hafnia, the first primary stabilizer oxide can include 4-16 weight percent of a ytterbia stabilizer, and the first material fraction of the blended powder can be 5-50 weight percent, and the second material can include at least one of zirconia or hafnia, the second primary stabilizer oxide can include at least one of 4-16 weight percent of a neodymium stabilizer or 4-20 weight percent Europa stabilizer, and the second material fraction of the blended powder can be 50-95 weight percent.
According to other embodiments, the first material may include at least one of zirconia or hafnia, the first primary stabilizer oxide may include 4-12 weight percent of a yttria stabilizer, and the first material fraction of the blended powder may be 50-95 weight percent, and the second material may include at least one of zirconia or hafnia, the second primary stabilizer oxide may include at least one of 4-16 weight percent of a neodymium stabilizer or 4-20 weight percent Europa stabilizer, and the second material fraction of the blended powder may be 5-50 weight percent.
In accordance with still other embodiments, at least one of the first, second and third oxide impurities can include less than 0.005 weight percent SiO2; less than 0.015 weight percent Al2O3; less than 0.002 weight percent TiO2; and less than 0.002 weight percent MgO. Moreover, the at least one of the first, second or third oxide impurities can further include less than 0.04 weight percent Fe2O3; less than 0.02 weight percent CaO; less than 0.001 weight percent Cr2O3; and less than 0.002 weight percent Na2O.
In embodiments, the blended ceramic powder may be a thermal sprayable powder.
In other embodiments, the blended ceramic powder can have a particle size of from about 5 to 150 microns.
In accordance with still yet other embodiments, the blended ceramic powder may have a high purity of at least 99.5 weight percent purity.
Additional aspects, embodiments and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
The accompanying drawings are included to provide further understanding of the invention and are incorporated in and constitute a part of this specification. The accompanying drawings illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the figures:
Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.
In an exemplary use of a material of the invention,
When applied, the coating 110 contains a crack network that allows it to survive the stress of numerous thermal cycles. As described in the above background section, the crack network is altered to a less desirable state by sintering and temperature cycling during service. Thus the structure formed upon coating manufacture changes with time, the rate depending on the starting material phases. Decreasing the sintering rate increases the amount of time before the closing of microcracks and creation of massive cracks, increasing coating lifetime.
A dominant factor affecting sintering is the presence of specific impurity phases within the structure made up of oxides which when combined with each other or the zirconia alloy result in melting points hundreds of degrees lower than that of the zirconia alloy itself. These impurity oxides increase the sintering rate.
In one embodiment of the present invention, the material contains zirconia (ZrO2) and/or hafnia (HfO2) partially stabilized by a total of 4 to 20 weight percent of one or more rare earth oxides having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. For purposes of the invention, rare earth oxides can be defined as any oxide from group IIIB (column 3) of the periodic table of elements, which includes scandia (Sc2O3), yttria (Y2O3), lanthanide oxides and actinide oxides.
The material of the present invention contains zirconia (ZrO2) and/or hafnia (HfO2) partially stabilized by a total of 4 to 20 weight percent of a primary stabilizing oxide such as ytterbia and/or yttria, (and optionally additional stabilizers of one or more rare earth oxides) having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. For purposes of the present invention, oxide impurities can be defined as materials which when combined with each other or with zirconia form phases with melting points much lower than that of pure zirconia, especially—but not limited to—soda (Na2O), silica (SiO2), and alumina (Al2O3). Other specific concentration ranges of stabilizers are provided herein and in co-pending and commonly assigned U.S. patent application Ser. No. 11/520,041, entitled “HIGH PURITY CERAMIC ABRADABLE COATINGS,” U.S. patent application Ser. No. 11/520,044, entitled “OPTIMIZED HIGH TEMPERATURE THERMAL BARRIER,” and U.S. application Ser. No. 11/520,042, entitled “OPTIMIZED HIGH PURITY COATING FOR HIGH TEMPERATURE THERMAL CYCLING APPLICATIONS” each filed on Sep. 13, 2006 and each incorporated herein by reference.
In accordance with embodiments of the invention, the limits for known impurities in order to achieve a desirable sintering rate and therefore increase service lifetime when used as a coating are about:
In a preferred embodiment, the limits for known impurities are about:
The impurity limits in the embodiments above are not indicative that any or all of the impurities listed will be included in the material in any amount. The embodiment of the invention may include zero weight percent of one or more of the above-listed impurities.
In accordance with embodiments of the invention, in order to overcome the volume change caused by the undesired phase transformation described above, one or more elements are added to the zirconia to modify the amount of phase transformation that occurs. The stabilizing elements, which are suitable for changing the amount and rate of phase transformation that occurs in the oxide coating, may include the following: scandium, yttrium and the rare earths, particularly the lanthanides, since they have solubility in zirconia. Scandium is not typically used due to its rarity and resulting prohibitive cost. Use of rare earths metals from the actinide group such as uranium and thorium may be limited due to their radioactivity. Thus, yttrium is a preferred stabilizing element.
Phase transformation in partially stabilized zirconia may possibly cause localized stresses that lead to the formation of micron-sized micro-cracks in the coating upon thermal cycling that cancel out some of the massive stress caused by coating volume shrinkage. Thus, these two phenomena of the coating structure—shrinking and cracking—work against each other and finding a balance between them will maximize coating lifetime. This mechanism implies then that the structure of the crack network of the coating is changing with time as the phase of the ceramic material changes. This mechanism is required for a thermal barrier or high temperature abradable coatings to survive thermal cycling.
The addition of a stabilizing element affects two main properties of the zirconia coating system in a positive manner. First, the addition of a stabilizer as illustrated in
Rising fuel cost and other factors continue to drive the need for improved operational efficiency, and thus higher operating temperatures, of gas turbines. While yttria stabilized zirconia is the material of choice for stabilization, greater operational temperatures can be achieved using ytterbia (
A blend of two or more partially stabilized high-purity material compositions may also be used. For example, in another embodiment, a blended ceramic material for use in high-temperature thermal barriers is provided. The blended materials include a first material with a yttria (Y2O3) stabilizer, and a balance of at least one of zirconia (ZrO2) and hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and/or hafnia (HfO2) is partially stabilized by the yttria stabilizer, and having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. The range of Y2O3 stabilizer is about 4-12 weight percent, and preferably 6-9 weight percent. The second material of the blended material may contain a ytterbia (Yb2O5) stabilizer and a balance of at least one of zirconia (ZrO2) and hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and/or hafnia (HfO2) is partially stabilized by the ytterbia stabilizer, and having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. The range of Yb2O5 stabilizer is about 4-16 weight percent, and preferably 10-16 weight percent. In the blended material, the ytterbia (Yb2O5) stabilized zirconia (ZrO2) and/or hafnia (HfO2) fraction may include about 5-50 weight percent of the total and preferably about 15-30 weight percent of the total. The yttria stabilized zirconia (ZrO2) and/or hafnia (HfO2) fraction may include about 50-95 weight percent of the total and preferably about 70-85 weight percent of the total blend.
In another embodiment the blended material includes a first material with a ytterbia (Yb2O5) stabilizer, and a balance of at least one of zirconia (ZrO2) and hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and/or hafnia (HfO2) is partially stabilized by the ytterbia stabilizer, and having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. The range of Yb2O5 stabilizer is about 4-16 weight percent, and preferably 10-16 weight percent. The second material of the blended material may contain a stabilizer of at least one of neodymium (Nd2O3), europia (Eu2O5), and combinations thereof and a balance of at least one of zirconia (ZrO2) and hafnia (HfO2) and combinations thereof, wherein the balance is partially stabilized by the stabilizer, and having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. The range of Nd2O3 stabilizer is about 4-20 weight percent, and preferably 8-16 weight percent. The range of Eu2O3 stabilizer is about 4-16 weight percent, and preferably 10-16 weight percent. The range of the combined Nd2O3 and Nd2O3 stabilizer is about 4-16 weight percent. In the blended material, the ytterbia (Y2O3) stabilized zirconia (ZrO2) and/or hafnia (HfO2) fraction may include about 5-50 weight percent of the total and preferably about 15-30 weight percent of the total. The yttria stabilized zirconia (ZrO2) and/or hafnia (HfO2) fraction may include about 50-95 weight percent of the total and preferably about 70-85 weight percent of the total blend.
In another embodiment of the invention the blended material includes a first material with a yttria (Y2O3) stabilizer, and a balance of at least one of zirconia (ZrO2) and hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and/or hafnia (HfO2) is partially stabilized by the yttria stabilizer, and having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. The range of Y2O3 stabilizer is about 4-12 weight percent, and preferably 6-9 weight percent. The second material of the blended material may contain a stabilizer of at least one of neodymium (Nd2O3), europia (Eu2O5), and combinations thereof and a balance of at least one of zirconia (ZrO2) and hafnia (HfO2) and combinations thereof, wherein the balance is partially stabilized by the stabilizer, and having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. The range of Nd2O3 stabilizer is about 4-20 weight percent, and preferably 8-16 weight percent. The range of Eu2O3 stabilizer is about 4-16 weight percent, and preferably 10-16 weight percent. The range of the combined Nd2O3 and Eu2O3 stabilizer is about 4-16 weight percent. In the blended material, the neodymium (Nd2O3) and/or europia (Eu2O5) stabilized zirconia (ZrO2) and/or hafnia (HfO2) fraction may include about 5-50 weight percent of the total and preferably about 15-30 weight percent of the total. The yttria stabilized zirconia (ZrO2) and/or hafnia (HfO2) fraction may include about 50-95 weight percent of the total and preferably about 70-85 weight percent of the total blend.
In a further embodiment of the invention the blended material includes a blend of at least three materials. The first material may contain a yttria (Y2O3) stabilizer, and a balance of at least one of zirconia (ZrO2) and hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and/or hafnia (HfO2) is partially stabilized by the yttria stabilizer, and having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. The range of Y2O3 stabilizer is about 4-12 weight percent, and preferably 6-9 weight percent. The second material of the blend may contain a ytterbia (Yb2O5) stabilizer, and a balance of at least one of zirconia (ZrO2) and hafnia (HfO2) and combinations thereof, wherein the zirconia (ZrO2) and/or hafnia (HfO2) is partially stabilized by the ytterbia stabilizer, and having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. The range of Yb2O5 stabilizer is about 4-16 weight percent, and preferably 10-16 weight percent. The third material of the blend may contain a stabilizer of at least one of neodymium (Nd2O3), europia (Eu2O5), and combinations thereof and a balance of at least one of zirconia (ZrO2) and hafnia (HfO2) and combinations thereof, wherein the balance is partially stabilized by the stabilizer, and having total impurities less than or equal to 0.15 weight percent, and preferably less than or equal to 0.1 weight percent. The range of Nd2O3 stabilizer is about 4-20 weight percent, and preferably 8-16 weight percent. The range of Eu2O3 stabilizer is about 4-16 weight percent, and preferably 10-16 weight percent. The range of the combined Nd2O3 and Eu2O3 stabilizer is about 4-16 weight percent. In the blended material, the ytterbia (Y2O3) stabilized zirconia (ZrO2) and/or hafnia (HfO2) fraction may include about 5-45 weight percent of the total, and preferably about 15-30 weight percent of the total. The neodymium (Nd2O3) and/or europia (Eu2O5) stabilized zirconia (ZrO2) and/or hafnia (HfO2) fraction may also include about 5-45 weight percent of the total and preferably about 15-30 weight percent of the total. The yttria stabilized zirconia (ZrO2) and/or hafnia (HfO2) fraction may include about 10-90 weight percent of the total, and preferably about 30-60 weight percent of the total blend.
Material of embodiments of the present invention can be provided in a variety of forms for use in thermal spray applications. For example, the material is supplied in the form of a powder, a slurry of powder, or a chemical solution of the constituents. If in powder form, the powder may be in the form of a spray dried powder of the individual constituents and organic binder, spray dried powder of the combined individual constituents and organic binder, fused and crushed powder, agglomerated and sintered powder, plasma densified material or powder from chemical solution routes. Typical particle sizes for the powders may vary but typically range between about 5-150 microns when deposited by various thermal spray equipment, preferably ranging between about 15-125 microns for air plasma spray and ranging between about 5-30 microns for low pressure plasma spray.
Typically for thermal spray applications, a polymer or organic material in powder form can be added to the material blend. Powder may be in the form of a spray dried powder of the individual constituents and an organic binder, spray dried powder of the combined individual constituents and an organic binder, fused and crushed powder, agglomerated and sintered powder, plasma densified material or powder from chemical solution routes. The organic binder may be used to at least partially bond together the placeholder material and the ceramic material. For high temperature abradable coatings, the benefit of adding a fugitive phase is that a higher porosity than is achievable with conventional deposition methods. The increased porosity aids abradability by introducing more surfaces to the crack network of the coating, decreasing the coating elastic modulus and thus promoting controlled material removal. Thus, according to an embodiment of the invention, a coating material may have about 70 to 99 weight percent of an ultra-pure ceramic material as previously described and about 1-30 weight percent (and preferably 2-15 weight percent) of a placeholder material. The placeholder material may be an organic powder material or an inorganic powder material that can be burned out subsequent to deposition of the coating material.
Porosities and cracks provide strain tolerance to TBCs and help to reduce thermal conductivities. Using thermal spray process, such as air plasma spray, flame spray or low pressure plasma spray, a high purity coating structure 120 (shown in
In order to enhance the strain tolerance of the aforementioned high purity TBCs, macro cracks that runs normal to the top coat and substrate interface can be introduced into the coating. As a result, another high purity coating structure that comprise a ceramic matrix, porosity, macro cracks and micro cracks (
When coatings are produced using a vapor deposition process, such as electron beam assisted physical vapor deposition process (EB-PVD) or low pressure (lower than ambient) plasma spraying, the resulting coating has a unique columnar structure. The gaps between columns impart excellent strain tolerance to the coating. Accordingly, TBCs produce using vapor deposition process, such as EB-PVD or low pressure (lower than ambient) plasma spraying, usually have a higher durability than TBCs produced using thermal spray processes. As illustrated in
In low pressure (lower than ambient) plasma spraying process, if molten droplets are also generated during the vaporization of the invention high purity materials, then the entrapment and incorporation of these droplets into the coating results in the formation of another high purity coating structure. As illustrated in
While exemplary embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous insubstantial variations, changes, and substitutions will now be apparent to those skilled in the art without departing from the scope of the invention disclosed herein by the Applicants. Accordingly, it is intended that the invention be limited only by the spirit and scope of the claims, as they will be allowed.
Claims
1. A ceramic powder comprising:
- a primary stabilizer oxide comprising 4-20 weight percent and oxide impurities up to a maximum of 0.15 weight percent; and
- a first material comprising a balance of the ceramic powder, wherein the first material is partially stabilized by the primary stabilizer oxide into a first partially stabilized material;
- wherein the oxide impurities, when combined with each other or with the first partially stabilized material, form phases with melting temperatures at least 100° C. lower than the melting temperature of the first material.
2. The ceramic powder according to claim 1, wherein the first material comprises at least one of zirconia or hafnia; and
- the primary stabilizer oxide comprises at least one of a yttria or a ytterbia stabilizer.
3. The ceramic power according to claim 2, wherein the oxide impurities comprise:
- less than 0.005 weight percent SiO2;
- less than 0.015 weight percent Al2O3;
- less than 0.002 weight percent TiO2; and
- less than 0.002 weight percent MgO.
4. The powder of claim 3, wherein the oxide impurities further comprise:
- less than 0.04 weight percent Fe2O3;
- less than 0.02 weight percent CaO;
- less than 0.001 weight percent Cr2O3; and
- less than 0.002 weight percent Na2O.
5. The powder of claim 1, wherein the powder is a thermal sprayable powder.
6. The powder of claim 1 has a high purity of at least 99.5 weight percent purity.
7. The powder of claim 1, wherein said powder has a particle size of from about 5 to 150 microns.
8. A blended ceramic powder comprising:
- a first material composition comprising: a first primary stabilizer oxide comprising 4-16 weight percent and first oxide impurities up to a maximum of 0.15 weight percent; and a first material comprising a balance of the first material composition, wherein the first material is partially stabilized by the first primary stabilizer oxide into a first partially stabilized material; wherein the first oxide impurities, when combined with each other or with the first partially stabilized material, form phases with melting temperatures at least 100° C. lower than the melting temperature of the first material; and
- a second material composition comprising: a second primary stabilizer oxide comprising 4-20 weight percent and second oxide impurities up to a maximum of 0.15 weight percent; and a second material comprising a balance of the second material composition, wherein the second material is partially stabilized by the second primary stabilizer oxide into a second partially stabilized material; wherein the second oxide impurities, when combined with each other or with the second partially stabilized material, form phases with melting temperatures at least 100° C. lower than the melting temperature of the second material.
9. The blended ceramic powder according to claim 8, wherein the first material comprises at least one of zirconia or hafnia, the first primary stabilizer oxide comprises 4-12 weight percent of a yttria stabilizer, and a fraction of the first material in the blended powder is 5-50 weight percent, and
- wherein the second material comprises at least one of zirconia or hafnia, the second primary stabilizer oxide comprises 4-16 weight percent of a ytterbia stabilizer, and a fraction of the second material in the blended powder is 50-95 weight percent.
10. The blended ceramic powder according to claim 9, further comprising a third material composition comprising:
- a third primary stabilizer oxide comprising 4-20 weight percent and second oxide impurities up to a maximum of 0.15 weight percent,
- a third material comprising a balance of the third material composition, wherein the third material is partially stabilized by the third primary stabilizer oxide into a second partially stabilized material,
- wherein the third first oxide impurities, when combined with each other or with the third partially stabilized material, form phases with melting temperatures at least 100° C. lower than the melting temperature of the third material.
11. The blended ceramic powder according to claim 10, wherein the third material composition comprises at least one of zirconia or hafnia, the third primary stabilizer oxide comprises at least one of 4-16 weight percent of a neodymium stabilizer or 4-20 weight percent Europa stabilizer,
- wherein the fraction of the first material in the blended powder is 10-90 weight percent,
- wherein the fraction of the second material in the blended powder is 5-45 weight percent and
- wherein the fraction of the third material in the blended powder is 5-45 weight percent.
12. The blended ceramic powder according to claim 8, wherein the first material comprises at least one of zirconia or hafnia, the first primary stabilizer oxide comprises 4-16 weight percent of a ytterbia stabilizer, and the first material fraction of the blended powder is 5-50 weight percent, and
- wherein the second material comprises at least one of zirconia or hafnia, the second primary stabilizer oxide comprises at least one of 4-16 weight percent of a neodymium stabilizer or 4-20 weight percent Europa stabilizer, and the second material fraction of the blended powder is 50-95 weight percent.
13. The blended ceramic powder according to claim 8, wherein the first material comprises at least one of zirconia or hafnia, the first primary stabilizer oxide comprises 4-12 weight percent of a yttria stabilizer, and the first material fraction of the blended powder is 50-95 weight percent, and
- wherein the second material comprises at least one of zirconia or hafnia, the second primary stabilizer oxide comprises at least one of 4-16 weight percent of a neodymium stabilizer or 4-20 weight percent Europa stabilizer, and the second material fraction of the blended powder is 5-50 weight percent.
14. The blended ceramic powder according to claim 8, wherein at least one of the first, second and third oxide impurities comprise:
- less than 0.005 weight percent SiO2;
- less than 0.015 weight percent Al2O3;
- less than 0.002 weight percent TiO2; and
- less than 0.002 weight percent MgO.
15. The blended ceramic powder of claim 14, wherein the at least one of the first, second or third oxide impurities further comprises:
- less than 0.04 weight percent Fe2O3;
- less than 0.02 weight percent CaO;
- less than 0.001 weight percent Cr2O3; and
- less than 0.002 weight percent Na2O.
16. The blended ceramic powder of claim 8 is a thermal sprayable powder.
17. The blended ceramic powder of claim 8 has a particle size of from about 5 to 150 microns.
18. The blended ceramic powder of claim 8 has a high purity of at least 99.5 weight percent purity.
Type: Application
Filed: May 12, 2021
Publication Date: Aug 26, 2021
Applicant: OERLIKON METCO (US) INC. (Westbury, NY)
Inventors: Jacobus C. DOESBURG (Westbury, NY), Mitchell R. DORFMAN (Westbury, NY), Matthew GOLD (Westbury, NY), Liangde XIE (Mason, OH)
Application Number: 17/318,631