Two-layer ceramic layer system, ceramic powder and a layer

Abstract

The invention relates to a layer system (1) at least comprising (in wt.%) a metallic substrate (4), optionally a metallic adhesion promoter layer (7) on the substrate (4), and a ceramic base layer (10) made of partially stabilized, tetragonal zirconia, comprising Yttrium oxide, Ytterbium oxide, and Gadolinium oxide as stabilizers as well as a ceramic top layer (13) made of fully stabilized cubic zirconia on the ceramic base layer (10), wherein the proportion of stabilizers is between 17.5% and 25.5%.

Description

Description Two-layer ceramic layer system, ceramic powder and a layer The invention relates to a two-layer ceramic layer system, a ceramic powder and a layer. Ceramics generally have high temperature stability and are therefore often used as ceramic coatings on high-temperature components, such as turbines, especially gas turbines.Important in this type of application is the use of the ceramic as a coating on a substrate, which often represents a metallic substrate.Metallic adhesive layers (bond coat) on the substrate, such as based on NiCoCrAlY, but also ceramic bonding layers or TGO are known. Often a two-layer layer system of two different ceramic layers is used. Fully stabilized ceramic Zirconium oxide (Zirconia) layers with 20YSZ are state of the art, but need to be improved in terms of bonding to a ceramic sublayer. Therefore, it is desired to improve the thermal insulation properties and lifespan of the ceramic layer systems with fully stabilized Zirconia layers. Therefore, it is the task of the invention to solve the above-mentioned problem. The task is solved by a two-layer system according to claim 1, a ceramic powder according to claim 11, and a layer according to claim 12. The subclaims list further advantageous measures that can be combined with each other arbitrarily to achieve further advantages. Ceramic layers based on zirconium oxide with stabilizers are known, wherein fully stabilized zirconium oxide is often used due to its better thermal stability. The aim of the idea is to use fully stabilized zirconium oxide with improved thermal stability and good adhesion to a ceramic sublayer. The figure schematically shows an embodiment of the invention. The figure and the description only represent embodiments of the invention. In a layer system 1, a ceramic layer 10 is applied to metal, with preferably nickel- or cobalt-based superalloys being used as substrate 4, a metallic adhesive layer 7 is present, which forms aluminum oxide (TGO, not shown). The metallic adhesive layer 7 is preferably an aluminide, platinum aluminide, or represents a NiCoCrAlY alloy as a base, optionally with x = Ta, Re, Fe and / or Si. A ceramic top layer 13 can be applied by plasma spraying (APS, …), HVOF, EB-PVD, … and preferably has a columnar structure or a segmented structure.The porosity of the ceramic top layer 13 is preferably below 12%, especially below 10%. The ceramic top layer 13 preferably has a layer thickness of 300µm to 2000µm, preferably between 300µm to 1200µm.  Similarly, there is a ceramic sublayer 10, whose layer thickness, however, is at least 20% thinner than that of the ceramic top layer 13. Ceramic sublayer 10 and ceramic top layer 13 form the ceramic layer system 15. All following data are in wt.%. The ceramic sublayer 10 comprises tetragonal zirconium oxide with stabilizers of yttrium oxide, ytterbium oxide, and gadolinium oxide.The following proportions are used:2.5% to 4.5% yttrium oxide,3.5% to 6.5% ytterbium oxide, and3.0% to 5.0% gadolinium oxide,preferably3.0% to 4.0% yttrium oxide,4.0% to 6.0% ytterbium oxide, and3.5% to 4.5% gadolinium oxide,most preferably3.5% yttrium oxide,4.5% ytterbium oxide, and4.0% gadolinium oxide.Also preferably, only yttrium oxide, ytterbium oxide, and gadolinium oxide are used as stabilizers.Other oxides (Hf, Al, Fe, Ti, Si) as impurities may be present, but should be minimized, even if they each reach proportions up to 1%. Accordingly, a ceramic powder for a layer of the ceramic sublayer 10 is used,comprisingzirconium oxide,with yttrium oxide, ytterbium oxide, and gadolinium oxide as stabilizers,preferably only yttrium oxide, ytterbium oxide, and gadolinium oxide as stabilizers.The amounts are2.5% to 4.5% yttrium oxide,3.5% to 6.5% ytterbium oxide, and3.0% to 5.0% gadolinium oxide,preferably3.0% to 4.0% yttrium oxide,4.0% to 6.0% ytterbium oxide, and3.5% to 4.5% gadolinium oxide,most preferably3.5% yttrium oxide,4.5% ytterbium oxide, and4.0% gadolinium oxide. The powder can contain polymers for forming pores during coating, binders for spraying, slip-casting or binder-jet printing, or abrasive particles (no zirconium oxides, especially BN, ZrC..). A ceramic top layer 13 with a cubic structure of zirconium oxide (FSZ) is applied to the ceramic sublayer 10. The cubic zirconium oxide preferably contains a yttrium oxide stabilized zirconium oxide (YSZ), with the proportion of yttrium oxide being 18.0 wt% to 22.0 wt%, in particular 20.0 weight percent.Preferably only Yttrium oxide is used as stabilizer. It is also possible to use cubic zirconium oxide with stabilizers of yttrium oxide, ytterbium oxide, and gadolinium oxide. Yttrium oxide represents the largest proportion in comparison to the other two stabilizers.Only these stabilizers are preferably used.The following proportions are preferably used:9.0% to 11.0% yttrium oxide,4.5% to 6.5% ytterbium oxide, and4.0% to 6.0% gadolinium oxide.Particularly preferably,9.5% to 10.0% yttrium oxide,5.2% to 6.0% ytterbium oxide, and4.8% to 5.6% gadolinium oxide are used.Also preferably, only yttrium oxide, ytterbium oxide, and gadolinium oxide are used as stabilizers. Also preferably, the ceramic top layer (13) is composed of cubic zirconium oxide:The fully stabilized zirconium oxide (FSZ) is stabilized with 14.0% to 16.0% ytterbium oxide, especially with 14.5% to 15.5% ytterbium oxide (Yb2O3)and with4.0% to 6.0% yttrium oxide (Y2O3)and optionally hafnium oxide and / or aluminum oxide.The ceramic material preferably contains 14.0% to 16.0% ytterbium oxide (Yb2O3), preferably 4.5% to 5.5% yttrium oxide (Y2O3).The ceramic material optionally contains: aluminum oxide, up to a maximum of 1.0% and / or hafnium oxide (HfO2) with 0.2% to 4.0%,especially 0.5% to 2.5% hafnium oxide (HfO2). Example for a composition of a sublayer 10:3.4%Y2O3 / 4.7% Yb2O3 / 3.9% Gd2O3 - ZrO2;examples for a composition of a top layer 13:20%Y2O3 - ZrO2or15.0% Y2O3 / 4.9% Yb2O3 - ZrO2or10.0% Y2O3 / 5.5% Yb2O3 / 5.3% Gd2O3 - ZrO2result in improved properties. 

Claims

 1. Layer system (1)at least comprising (in wt.%): a metallic substrate (4),optionally a metallic adhesion promoter layer (7) on the substrate (4), anda ceramic sublayer (10) of partially stabilized, tetragonal zirconia,comprisingyttrium oxide, ytterbium oxide, and gadolinium oxide as stabilizers,preferably only yttrium oxide, ytterbium oxide, and gadolinium oxide as stabilizers,wherein 2.5% to 4.5% yttrium oxide,3.5% to 6.5% ytterbium oxide, and3.0% to 5.0% gadolinium oxide,preferably 3.0% to 4.0% yttrium oxide,4.0% to 6.0% ytterbium oxide, and3.5% to 4.5% gadolinium oxide, are used as well as a ceramic top layer (13)of fully stabilized cubic zirconia on the ceramic underlayer (10),wherein the proportion of the stabilizers is between 17.5% and 25.5%.  2. Layer system according to claim 1,wherein the ceramic sublayer (10) comprises yttrium oxide, ytterbium oxide, and gadolinium oxide stabilized zirconia,wherein preferably 3.5% yttrium oxide, 4.5% ytterbium oxide, and 4.0% gadolinium oxide are used,in particular, only these three stabilizers yttrium oxide, ytterbium oxide, and gadolinium oxide are used.  3. Layer system according to claim 1 or 2,wherein the ceramic top layer (13) comprises zirconia,wherein stabilizers of yttrium oxide, ytterbium oxide, and gadolinium oxide are present,wherein the following proportions are preferably given:9.0% - 11.0% yttrium oxide,4.5% - 6.5% ytterbium oxide, and4.0% - 6.0% gadolinium oxide,especially preferred9.75% - 10.0% yttrium oxide,5.2% - 6.0% ytterbium oxide, and4.8% - 5.6% gadolinium oxide,in particular only these three stabilizers yttrium oxide, ytterbium oxide, and gadolinium oxide are used.  4. Layer system according to claim 1 or 2,wherein the ceramic top layer (13) comprises zirconia,wherein stabilizers (in wt.%) of yttrium oxide and ytterbium oxide are present,wherein the following proportions are preferably given:zirconia with 14.0% to 16.0%,in particular with 14.5% to 15.5% yttrium oxide (Y2O3)as well as with 4.0% to 6.0% ytterbium oxide (Yb2O3) andoptionallyhafnium oxide and / or aluminum oxide with a maximum total of 5.0%.  5. Layer system according to claim 4,wherein the ceramic top layer (13) comprises (in wt.%) zirconia, wherein stabilizers of yttrium oxide and ytterbium oxide are present,wherein the following proportions are given:15% ytterbium oxide (Yb2O3),4.5% to 5.5% yttrium oxide (Y2O3),optionallyhafnium oxide (HfO2) with 0.2% to 4.0%,in particular 0.5% to 2.5% hafnium oxide (HfO2).  6. Layer system according to one or both of the claims 1 or 2,wherein the ceramic top layer (13) has yttrium oxide stabilized zirconia,wherein the proportion of yttrium oxide is 18.0 wt.% to 22.0 wt.%,especially 20.0 wt.%,in particular only yttrium oxide is used.  7. Layer system according to one or more of the claims 1, 2, 3, 4, 5 or 6,comprisinga metallic adhesive layer (7) between the ceramic sublayer (10) and the metallic substrate (4),especially directly on the substrate (4),wherein the adhesive layer (7) comprises an alloy of the type NiCoCrAlY—X, X is optionally = Ta, Re and / or Si,especially NiCoCrAlY or NiCoCrAlY-Ta.  8. Layer system according to one or more of the claims 1, 2, 3, 4, 5, 6 or 7,wherein the ceramic sublayer (10) under the ceramic layer (13) is at least 20% thinner.  9. Layer system according to one or more of the preceding claims,wherein the porosity of the ceramic top layer (13) is below 12%, especially below 10%.  10. Layer system according to one or more of the preceding claims wherein the ceramic top layer (13) has a layer thickness of 300µm to 2000µm, preferably between 300µm to 1200µm.   11. Ceramic powder,comprisingzirconia,with yttrium oxide, ytterbium oxide, and gadolinium oxide as stabilizers,preferably only yttrium oxide, ytterbium oxide, and gadolinium oxide as stabilizers,preferably3.0% to 4.0% yttrium oxide,4.0% to 6.0% ytterbium oxide, and3.5% to 4.5% gadolinium oxide,very preferably3.5% yttrium oxide,4.5% ytterbium oxide, and4.0% gadolinium oxideis used.  12. Layer comprising a composition according to claim 11 or made from a powder according to claim 11.

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