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Title:
DVC-COATING WITH FULLY AND PARTIALLY STABILIZED ZIRCONIA
Document Type and Number:
WIPO Patent Application WO/2016/202495
Kind Code:
A1
Abstract:
A dense vertical cracked microstructure in a ceramic layer system made of an underline partially stabilized zirconia layer and an above laying fully stabilized zirconia layer show good erosion resistance and long life time.

Inventors:
FLORES RENTERIA ARTURO (DE)
HITCHMAN NEIL (US)
STAMM WERNER (DE)
ZOIS DIMITRIOS (DE)
Application Number:
EP2016/059828
Publication Date:
December 22, 2016
Filing Date:
May 03, 2016
Export Citation:
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Assignee:
SIEMENS AG (DE)
International Classes:
C23C28/00; F01D5/28
Foreign References:
US20050170200A12005-08-04
EP1674663A22006-06-28
Other References:
None
Download PDF:
Claims:
Patent claims

1. Ceramic layer system,

at least comprising:

a substrate ( 4 ) ,

especially a metallic substrate (4),

very especially made of a nickel or cobalt based super al¬ loy,

optionally a metallic bond coat (7) on the substrate (4), which is especially metallic and

very especially made of a NiCoCrAlY-based alloy,

an inner partially stabilized zirconia layer (10) and on it (10) a fully stabilized zirconia layer (13),

wherein vertical cracks (16, 19, 21) are present.

2. Ceramic layer system according to claim 1,

wherein the fully stabilized zirconia layer (13) is re- placed partially or fully by a layer comprising or consist¬ ing of a pyrochlore material,

especially by gadolinium zirconate.

3. Ceramic layer system according to claim 1 or 2,

wherein the cracks (19) are only present in the fully sta¬ bilized zirconia layer (13) or the outer layer with the pyrochlore material.

4. Ceramic layer system according to any of the claims 1, 2 or 3 ,

wherein the cracks (21) are present in both ceramic layers (10, 13) . Ceramic layer according to any of the preceding claims, wherein the porosity of the fully stabilized zirconia laye (13) or the layer with the pyrochlore material is lower than 5%,

especially lower than 3%.

Ceramic layer system according to any of the preceding claims ,

wherein the thickness of the partially stabilized zirconia layer (10) is between 75ym - 800ym.

7. Ceramic layer system according to any of the preceding claims ,

wherein the thickness of the fully stabilized zirconia layer (13) or the layer with the pyrochlore material is be tween 50ym - 800ym.

Ceramic layer system according to any of the preceding claims ,

wherein the zirconia or the zirconia layers (10, 13) are stabilized by yttria,

especially only by yttria.

Ceramic layer system according to any of the preceding claims ,

wherein the porosity of the partially stabilized zirconia layer is lower than 5%,

especially lower than 3%.

10. Ceramic layer system according to any of the preceding claims ,

wherein the partially stabilized zirconia is stabilized by yttria,

especially is 8YPSZ .

Description:
DVC-Coating with fully and partially stabilized zirconia

The invention relates to a ceramic layer-system with par- tially and fully stabilized zirconia which has also a dense vertical cracked microstructure (DVC) .

Field feedback has shown that the current Thermal Barrier Coatings (TBC) of turbines suffer from issues related to:

1) Erosion: turbine blades with high porosity coatings con ¬ taining a large number of unmolten or semimolten particles show low erosion resistance.

The development during the last years has pushed thermal spray coatings porosity upwards. However, that has caused the shrinkage of the spray ability window that allows coatings to receive high porosity and good cohesion. As a result, erosion has started manifesting itself as a major issue for coatings in specific parts and engines.

2) Drilling damage: High porosity coatings contain less inti ¬ mate contacts between splats or splat and substrate and thus the required energy for a crack to propagate is relatively low .

This problem has been addressed by drilling before the coat ¬ ing deposition and reopening of the holes after coating deposition. This approach minimizes the interaction between coating and laser and that reduces significantly the coating de- lamination around the drilled holes. However, since each part has to be processed twice, this solution is associated with longer drilling times that are reflected as increased cost.

3) Coating life: Thermal Spray porous coatings do not demon ¬ strate at the same level the high strain tolerance along the coating thickness which can be seen in other coating types such as EB-PVD.

The thermal barrier coatings porosity has been increased to improve strain tolerance. However as mentioned above, that can reduce the spray ability process window and influence negatively the cohesion and erosion resistance of the coat ¬ ings . 4) YSZ for TBC chemistries are currently limited to 1528K maximum temperature due to phase transformation issues.

New chemistries have been adopted that present phase stabil ¬ ity in higher temperatures. However they show significantly lower fracture toughness compared to the partially stabilized zirconia and it is certain that their erosion resistance will be even less.

The task of the invention is therefore to solve the problems given above .

The problem is solved by a ceramic layer system according to claim 1.

In the subclaims further advantages are given which can be abitrality combined with each other to yield additional ad ¬ vantages .

The figure and the description show only examples of the in ¬ vention .

The problems named under point 1 are addressed by adopting Dense Vertical Cracked (DVC) coatings.

1) Erosion. DVC thermal barrier coatings have shown signifi- cantly lower rates compared to their porous counterparts.

That means for the same chemistry a porous coating will show more than 3x the erosion rate compared to the DVC one.

2) DVC coatings have increased cohesion and adhesion compared to the typical porous coatings. The reason is that a very high ratio of fully molten particles deposit on hot substrate or hot previously deposited splats which promotes a good in ¬ timate bonding to develop between them. Improved adhesion re- quires high energy for a horizontal crack to propagate so that guarantees a lower delamination .

3) Coating life. Due to the intimate contact between splats, the DVC coatings show high fracture toughness along the par ¬ allel to the substrate plane. That, combined with their abil ¬ ity to accommodate thermal strain along the coating thickness due to their columnar microstructure ensures a high TBC life. 4) DVC microstructures can be adopted on the new coating chemistries. That will create a bilayer DVC with partially stabilized zirconia as a lower layer and fully stabilized zirconia as the upper layer. The lower layer will accommodate CTE mismatch with the bond coat and the TGO while the upper layer will provide the higher temperature capability.

The system consists of partially stabilized zirconia, espe ¬ cially 8YSZ as the high fracture toughness lower layer to ac ¬ commodate the CTE mismatch with bond coat and TGO and a lower toughness upper layer of fully stabilized zirconia, espe ¬ cially 48YSZ to provide the high temperature capability.

Unlike other possible bilayer coating approaches, the similar chemistry between the two coatings enhances their bonding. Appropriate preheating of the DVC PSZ will prepare its sur ¬ face to receive the fully molten particles of FSZ and due to the high local temperatures during spraying allow diffusion between the two similar materials. Ideally a number of the vertical cracks will progress from one coating to the other demonstrating the continuity between the two coatings. In this manner the interface which has shown to be the weakest link in other bi-layer systems will be reinforced.

The advantages that arise are: 1) The low fracture toughness of the FSZ with the adoption of a DVC microstructure will significantly increase. That will improve the erosion resistance of the coating. 2) A good bonding between the two layers and as well with the bond coat will increase the drilling damage tolerance. Less delamination will be observed compared to other bilayer coating systems which have suffered in the past from drilling. 3) The columnar microstructure along the bilayer coating thickness will allow improved strain tolerance, thus in ¬ creased coating life.

4) Higher temperature capability compared to single layer DVC coatings.

The figure shows a layer system 1.

The layer system 1 comprises a substrate 4 which is prefera- bly metallic and very preferably made of a nickel or cobalt based super alloy.

On the substrate 4 a bond coat especially a metallic bond coat 7 and very especially a NiCoCrAlY-based bond coat 7 is applied on.

On this bond coat 7 there is a thermally grown oxide (TGO, not shown) layer which is formed during further application of the ceramic layers or by an additional oxidation step or at least during use of the layer system 1.

On the bond coat 7 there is applied a first zirconia layer 10 made of a partially stabilized zirconia.

The thickness of the partially stabilized zirconia layer 10 is preferable between 75ym - 800ym.

The porosity of the partially stabilized zirconia 10 is pref ¬ erably lower than 5% and very preferably lower than 3%. As an outer ceramic layer there is applied a fully stabilized zirconia layer 13, which is especially the outer most layer of the layer system 1. This outer layer can also be made of a pyrochlore ceramic, such as gadolinium zirconate (GZO) , which partially or fully replaces the fully stabilized zirconia (FSZ) .

The porosity of the fully stabilized zirconia 13 is lower than 5% and preferably lower than 3%.

The thickness of the fully stabilized zirconia 13 is prefera ¬ ble between 50ym - 800ym.

The same parameters for thickness and porosity are also valid for the pyrochlore layer or pyrochlore/FSZ layer.

The stabilization in this zirconia based system can be reached by yttria or by any other rare earth element as known by the state of the art or by a combination of that. Preferably yttrium is used for stabilization.

In this layers 10, 13 there are cracks 16 present, which 19 are mostly present in the outer most layer 13 and preferably some of them 21 are present in both layers 10, 13.