Article Having A Heat-Insulating Coating System and Method For the Production Thereof

Abstract

A system comprising a substrate and a ceramic thermal barrier layer formed of columns which is applied to the substrate, characterized in that the columns are spatially separated from each other at the substrate or at least hardly contact each other is disclosed. A method for producing the system by laser welding is also disclosed. The disclosed material makes it possible to produce durable, heat-resistant components that can be used, for example, in turbines or in metal-supported fuel cells.

Claims

1. A system comprising a substrate and a ceramic thermal barrier layer formed of columns which is applied to the substrate, wherein the columns are spatially separated from each other at the substrate or at least hardly contact each other.

2. The system according to claim 1, wherein a ceramic material of the ceramic thermal barrier layer is dense at the substrate.

3. The system according to claim 1, wherein the columns have a cavity spaced from the substrate, and a material of the columns below the cavity is dense.

4. The system according to claim 1, wherein a diameter of the columns is larger than 0.1 mm and/or the diameter of the columns is smaller than 0.9 mm.

5. The system according to claim 1, wherein the columns have a widening.

6. The system according to claim 5, wherein the columns are connected to each other in a layer-like manner by widenings above the substrate or that a layer is applied to the columns.

7. The system according to claim 1, wherein the ceramic thermal barrier layer is formed by first and second columns and the second columns are applied to the first columns and the second columns are arranged offset with respect to the first columns.

8. The system according to claim 1, wherein an upper side of the substrate is formed by an adhesion promoter layer or by a ceramic layer on an adhesion promoter layer.

9. The system according to claim 8, wherein the adhesion promoter layer is applied to a component consisting of a metal.

10. The system according to claim 1, wherein the ceramic thermal barrier layer consists of yttrium-stabilized zirconium oxide.

11. The system according to claim 1, wherein the columns are producible by laser welding.

12. The system according to claim 1, wherein the columns are arranged according to a uniform pattern.

13. A method for producing a system that includes a substrate and a ceramic thermal barrier layer, wherein a ceramic column of the ceramic thermal barrier layer is produced from a powder that is welded by light of a laser.

14. The method according to claim 13, wherein the laser and/or an optics focusing the light of the laser are moved away from a surface of the substrate during a welding process, namely perpendicularly or at least substantially perpendicularly.

15. The method according to claim 14, wherein the moving away of the laser and/or the optics is slowed down and after slowing down the laser is switched off.

16. The method according claim 15, wherein the powder is welded using a plurality of laser pulses wherein a time between two laser pulses is 1 to 5 seconds.

17. The method according to claim 16, wherein during the time between two pulses the laser and/or an optics focusing the light of the laser is moved away from the surface of the substrate, namely perpendicularly or at least substantially perpendicularly.

18. The method according to claim 16, wherein the powder is changed in the time between two laser pulses.

19. The method according to claim 17, wherein a duration of a laser pulse is 0.1 to 0.5 seconds long.

20. The system according to claim 1, wherein a diameter of the columns is larger than 0.3 mm and/or the diameter of the columns is smaller than 0.7 mm.

Description

[0062] The invention is illustrated in more detail below with the aid of figures. They show

[0063] FIG. 1: schematic representation of the process;

[0064] FIG. 2: Top view of a sample with thermal barrier layer;

[0065] FIG. 3: Top view of the sample of FIG. 2 after thermocycling tests;

[0066] FIG. 4: Photo of a cross-section polish of the sample in FIG. 3;

[0067] FIG. 5: Photo of a cross-section polish of another sample;

[0068] FIG. 6: Photo of a cross-section polish of a sample not according to the invention, produced by EB-PVD (electron beam physical vapor deposition);

[0069] FIG. 7: Photo of a cross-section polish of a sample not according to the invention, produced by PS-PVD (plasma spray-physical vapor deposition);

[0070] FIG. 8: Photo of a cross-section polish of a sample not according to the invention, produced by SPS (suspension plasma spraying);

[0071] FIG. 9: Schematic representation of a system with first and second columns in different planes;

[0072] FIG. 10: Schematic representation of a system with a top layer above columns;

[0073] FIG. 11: Schematic representation of a system with widenings of columns in a central area;

[0074] FIG. 12: Schematic representation of a system with widenings of columns to the outside of thermal barrier layer;

[0075] FIG. 13: Schematic top view on columns of a system;

[0076] FIG. 14: Schematic top view on columns of a system with varying diameters;

[0077] FIG. 15: Schematic top view on columns of a system with hardly contacting columns

[0078] FIG. 16: Photo of a homogeneously produced column.

[0079] FIG. 1 shows a substrate 1 in section. The substrate 1 comprises a metallic base body 2 and an adhesion promoter layer 3 on the upper side of the base body 2. Columns 4 are produced on the adhesion promoter layer 3. FIG. 1 already shows four completed columns 4. The production of a fifth column 4A is shown. For the production of the fifth column 4A, ceramic powder 5 is fed via nozzles 6 with the aid of air to the point where a fifth column 4A is produced. The flow direction of the powder 5 includes an acute angle with the V.sub.z direction, as illustrated by FIG. 1. The V.sub.z direction is the direction perpendicular to the surface of the substrate 1. The flow of the powder 5 is focused on the location where the fifth column 4A is produced. During production, the powder 5 flows uniformly and continuously to this location. Two individual streams of the powder 5 may be directed to the location or site where the fifth column 4A is formed. More than two individual streams of the powder 5 may be directed to the location or site where the fifth column 4A is formed, for example three or four streams. The stream of powder 5 may form a funnel, the bottom of which is then located at the location where the fifth column 4A is made. However, only one stream of powder 5 may suffice to produce a fifth column 4A, but this is less convenient.

[0080] The light 7 of a laser 8 travels along the V.sub.z direction. Thus, the light 7 of the laser 8 runs orthogonal or perpendicular to the surface of the substrate 1. The light 7 of the laser 8 is directed to the location where the column 4A is formed. The diameter of the light 7 is much smaller than the diameter of the column 4A to be produced. For example, at the growth point, the diameter of the light in one case was only about 17 ?m compared to the column of about 450 ?m. In order to be able to suitably adjust the diameter of the light 7, an optics focusing the light 7 is provided, such as a convex optical lens 9. The light 7 is then passed through the optics 9 and thereby focused. It is thus possible to provide a suitably powerful light cone such that the powder 5 can be melted at a suitable location at and on the surface of the column 4A to be manufactured. The focus 10 of the light 7 can advantageously be adjusted such that it is located above the surface of the column 4A to be manufactured, as shown in FIG. 1. The position of the focus 10 of the light 7 is advantageously such that the focus 10 is located within flowing powder, as shown in FIG. 1. Heat is thus supplied to the powder 5 in the maximum possible manner just before the powder 5 impinges on the surface of the column 4A to be produced. The powder is first further heated after impact and thereby finally suitably melted.

[0081] During production, the optics 9 is moved upward away from the surface of the substrate 1 in the V.sub.Z direction. However, the laser 8 can also be moved upward away from the surface of the substrate 1 in the V.sub.Z direction together with the focusing optics 9. The speed of movement corresponds to the growth speed of the column 4A. This allows the previously melted powder 5 to re-solidify, thus producing the column 4A. Alternatively, the substrate could be moved.

[0082] Movements principally include acceleration and deceleration (slow-down) processes. For example, an acceleration process allows for pre-treatment (melting of the substrate).

[0083] In one case, a column almost exactly 6 mm high was obtained with a programmed 6 mm movement. Thus, the growth rate on average corresponded to the rate of movement of the optics.

[0084] Once column 4A has been completed, the laser 8 is switched off. The laser 8 is moved together with the optics 9 and the nozzles 6 in V.sub.XY direction, i.e. parallel to the substrate surface, until the position is reached where a next column can be produced at a desired location. The associated optics 9 or the laser 8 with the optics 9 are moved again in V.sub.Z direction towards the substrate 1 until a new starting position is reached from which a production of a next column can be started.

[0085] The laser can be switched on already in the approach process with deviating laser parameters in order to carry out a pretreatment of the substrate on the base surface of the column to be manufactured.

[0086] Moving the nozzles in the V.sub.Z direction is not necessary to suitably produce a column. This applies at least if the height of the column is not to be excessive. In principle, however, it is also possible to move the nozzles 8 together with the optics 9 and/or the laser 8 also in V.sub.Z direction.

[0087] It may be useful to first apply a thin ceramic layer with the aid of the powder in order to improve the adhesion between the adhesion promoter layer 3 and the ceramic material. The thin ceramic layer may be porous.

[0088] The described process results in columns 4 that are not porous. If a cavity is to be incorporated into a column 4, the first step is to slow down the movement of the optics 9 and, if necessary, the laser 10. Then the laser 10 is switched off.

[0089] To avoid oxidation of the material, the process is expediently carried out in a vacuum or in a shielding gas atmosphere.

[0090] Columns have been produced according to the previously described process. A coating unit included nozzles 6, laser 8 and optics 9. The laser used was an Nd-YAG laser with a light wavelength of 1064 nm, namely the TruFiber400 laser of TRUMPF GmbH+Co. KG of Ditzingen, Germany. The laser was used in a TruCell3008 laser unit from TRUMPF GmbH+Co. KG. The divergence of the laser light was 5?. The diameter of the laser focus was 17 ?m. The focus of the laser was in the focus of the supplied powder. The diameter of the focus of the powder was approximately 200 ?m. The laser was operated both continuously at a power of 15 W and in a pulsed manner at a power of 40 W with a pulse frequency of 1000 Hz and a pulse length of 0.1 ms. The laser was operated both continuously with a power of 15 W (for column production) and for pre-treatment with deviating parameters. Pre-treatment was used in the case of direct column coating of an adhesion promoter layer. For this, the laser was activated 3 mm vertically above the starting point of the coating. The laser was then moved at (programmed) maximum speed to the starting point of column growth. During this fast procedure, the laser was operated in a pulsed manner with a power of 40 W on average, more precisely with a pulse frequency of 1000 Hz and a pulse length of 0.1 ms at 400 W. The powder used was spherical zirconia partially stabilized with yttrium d50=34 ?m of Metco 233B, Oerlicon Metco Pf?ffikon, Switzerland. A continuous argon flow was used for powder delivery and for the protective atmosphere. The argon stream was 20 L/min for powder delivery of about 2.5 g/min.

[0091] The coating unit was moved to a starting point of coating. The substrate surface was then briefly melted to achieve good adhesion. The coating unit was then moved perpendicular to the substrate surface by a certain height with the laser switched-on. During this process, the applied powder was fed coaxially. In one case, the moving speed averaged 300 mm/min in the V, direction upward away from substrate 1. This speed corresponded to the growth rate of the produced columns. Thus, the welding direction was perpendicular to the substrate 1 as previously described. Welding was performed under shielding gas to avoid oxidation of the materials used. Towards the end of the production of a column, first the moving speed was slowed down and then the laser was switched off. Homogeneous dense columns with almost exactly the height of the programmed moving path in V.sub.Z direction were produced.

[0092] The substrate surface was a porous YSZ layer produced by thermal spraying on an Inconel 738 component with a thermally sprayed MCrAlY adhesion promoter layer, FIGS. 2-4, or a vacuum plasma sprayed MCrAlY adhesion promoter layer on structural steel, FIG. 5.

[0093] Thus, thermal barrier layers of different dimensions were produced on different substrates. Both the case where the substrate comprised an adhesion promoter layer with a thin ceramic layer on top and the case where columns were prepared directly on the adhesion promoter layer were investigated.

[0094] FIG. 2 shows a photographic image of columns 4 produced as previously described on a substrate from above. The columns 4 form a thermal barrier layer for the substrate below. A comparison substrate of basically the same structure was produced, but in which the thermal barrier layer was applied in a conventional manner by a gas deposition process. This reference sample had a conventionally produced thermal barrier layer with a thickness corresponding to the total thickness of the thermal barrier layers of the sample produced as intended.

[0095] Two systems produced in this way, as shown in FIG. 2, were tested in thermocycling experiments. The ceramic front side, i.e. the thermal barrier layer, of the respective sample was heated with a gas burner, while the back side was cooled with compressed air. For thermocycling, the gas burner was removed from the front side at regular intervals. The temperature of the front side was measured with a pyrometer. The temperature of the back side of the sample was determined using a thermocouple in the sample. The two tested thermal barrier layers according to the invention failed after 2264 and 1725 cycles of 5 min heating and 2 min cooling, respectively, at 1300? C. front side temperature for the first sample and 1400? C. front side temperature for the second sample. The mean temperature of the adhesion promoter layer during the heating phase was 1077? C. and 1082? C., respectively, while the back side of the substrate was cooled to 1050? C. on average in each case. FIG. 3 shows such a sample after 2264 cycles exposed to a temperature of 1300? C. It can be seen that the thermal barrier layer 4 is partially no longer present.

[0096] The thermal insulation, as can be seen from the temperature difference between the front and rear sides, corresponded to the thermal insulation of the similarly constructed reference sample not according to the invention. However, a longer service life was achieved, since only up to 1200 cycles were possible in the case of the comparison sample.

[0097] The layer thicknesses of the samples according to the invention were determined after thermocycling on the basis of cross-section polishes. One such cross-section polish is shown in FIG. 4. FIG. 4 illustrates the presence of a cavity 11 at each outer end of the columns 4. The extension of the cavities ranged from about 50 ?m to 150 ?m, as illustrated by FIG. 4. The columns 4 had a height and diameter of about 400 ?m to 450 ?m, as shown by FIG. 4. FIG. 4 also shows that there was spacing between the columns 4. Examination of the sample shown in FIGS. 3 and 4 revealed that the system failed at the interface of non-columnar ceramic coating 12 and adhesion promoter layer 3. The bond between the ceramic coating 12 and the columns 4 was maintained.

[0098] The photographic image shown in FIG. 4 with the added scale shows that the ceramic coating 12 was approximately 150 ?m thick and the adhesion promoter layer 3 was approximately 300 ?m thick. The distance between two columns was always at least 10 ?m.

[0099] Direct coating of an adhesion promoter layer 3 with columns 4 is also possible. This is shown by the photograph of a cross-section polish through another prepared sample in FIG. 5. The surface of the substrate, i.e. the surface of the adhesion promoter layer 3, was first pretreated with a pulsed laser beam to melt the surface. Thus, a good adhesion of the columns 4 to the adhesion promoter layer 3 could be achieved. The adhesion promoter layer was approximately 300 ?m thick. Columns four were approximately 600 ?m high and up to 550 ?m wide. The material of the columns 4 showed isolated small pores. However, the vast majority of the material was dense. Without exception, there were clear distances of at least 50 ?m between the columns 4.

[0100] FIG. 6 shows a comparative example, not according to the invention, of a columnar YSZ thermal barrier layer produced by EB-PVD on a substrate. The comparative example illustrates that it is not possible to produce columns in a comparably controlled and uniform manner by EB-PVD. The shapes of the columns are very irregular. The columns can branch irregularly above the substrate. The upward gradients (V.sub.z direction) are very irregular and point in different directions. In particular, at the underside of the thermal barrier layer, there are very few gaps between two adjacent columns. The columns therefore contact each other at least predominantly, particularly at the substrate. A regular arrangement of the columns according to a pattern is not present. The material is cracked and porous. The bonding of the spring-like structures in the lower region of the thermal barrier layer is less stable than any of the columns produced according to the invention.

[0101] FIG. 7 shows a comparative example, not according to the invention, of a columnar YSZ thermal barrier layer produced by PS-PVD on a substrate. The result is similar to that shown in FIG. 6. By PS-PVD it is also not possible to produce columns in a controlled manner comparable to the invention. Especially at the underside of the thermal barrier layer, the columns produced by PS-PVD inevitably contact each other extensively. A regular arrangement of the columns according to a pattern is not present. The material is riddled with cracks. Comparable to the EB-PVD layers, a poorer bonding is present in the lower thermal barrier layer region.

[0102] FIG. 8 shows a comparative example, not according to the invention, of a columnar thermal barrier layer produced by SPS. In particular, at the underside of the thermal barrier layer, the columns produced by PS-PVD contact each other completely. Also, gaps between columns above the substrate are small. The width of a column can be more than twice the width of an adjacent column without this being selectively controllable. With the gaps, cracks inevitably occur, which can lead into the columns and thus limit the cohesion of the columns. Cracks comparable to this are not present in the columns according to the invention. The material has a closed-pore appearance, i.e. it is porous.

[0103] FIG. 9 schematically shows a system in which the thermal barrier layer is formed by first and second columns 4, 13. The second columns 13 have been applied to the first columns 4 by laser welding. The second columns 13 are offset from the first columns 4. This creates air chambers between the first columns 4, which are at least partially closed off from the outside of the thermal barrier layer by the second columns 13. The heat insulating properties can thus be improved.

[0104] FIG. 10 schematically shows a system in which the columns 4 on the outside of the thermal barrier layer are shielded from the outside by a cover layer 14. This improves thermal insulation and protects the interior of the thermal barrier layer from contamination. The cover layer 14 may be completely closed.

[0105] FIG. 11 schematically shows a system in which the columns have been widened close to the outside of the thermal barrier layer. The widening 15 creates a kind of layer that protects against contamination and improves thermal insulation. The layer may be completely closed. However, it may also be a layer that is predominantly closed.

[0106] FIG. 12 schematically shows a system in which the columns have been produced in a cone-like widened manner towards the outside of the thermal barrier layer. In this way, a kind of closed or at least partially closed layer can be formed on the outside of the thermal barrier layer, which protects against contamination and improves thermal insulation.

[0107] The schematic view according to FIG. 13 shows that the columns 4 can be arranged uniformly according to a pattern. This is not possible with conventional manufacturing processes. Thus, a first row of columns 4 can be manufactured with the columns being substantially equally spaced from one another. A second row of such columns 4 may be arranged adjacent thereto. As shown, the second row may be arranged offset with respect to the first row in order to achieve the highest possible packing density and to be able to provide uniform protection from heat. The columns of the samples shown in FIGS. 2 to 4 have been produced according to this arrangement.

[0108] The schematic top view according to FIG. 14 shows that the columns 4 can be arranged uniformly according to a pattern and can have different diameters in order to be able to selectively adjust the width of air cushions. Rows of columns with small and large columns alternate. Such patterns are not possible with conventional manufacturing processes.

[0109] FIG. 15 is a schematic top view of a system and shows the case where the columns 4 hardly contact each other. The columns 4 are arranged uniformly according to a pattern. For the most part, the surfaces of the columns 4 at the substrate 1 do not contact each other. Also, the columns 4 always contact each other in approximately the same way, i.e., also in the manner of a pattern. The idealized columns 4 shown are circular and have the same diameters. A column 4 therefore has a total of up to six contact points 16 to adjacent columns 4. Each contact point 16, viewed along the circumference, is several times smaller than the circumference of the respective column, as illustrated by FIG. 15. Even if all contact points 15 seen along the circumference are added up, then the result of the sum is clearly smaller than half the circumference of the respective column 4.

[0110] FIG. 16 shows a photograph of a very homogeneous column which has been produced step by step with the aid of a pulsed laser. The duration of a laser pulse is preferably between 0.1 and 0.5 seconds. In the case of the column shown in FIG. 16, the duration of the laser pulses was 0.2 seconds. The time between two pulses was one or two seconds. However, a pause between two laser pulses could also be longer and be, for example, four or five seconds long. Gradually, the focus of the laser and the powder feed in position were adjusted during these pauses between two laser pulses. A pause of 1 to 2 seconds between two pulses is sufficient to change the powder material. Thus, through the invention, a very homogeneous column can be produced which can be formed from different materials.