Ceramic heat shields having surface infiltration for preventing corrosion and erosion attacks

Abstract

An improved ceramic heat shield for a gas turbine is provided. The ceramic heat shield has a porous ceramic body and according to the embodiments an infiltration coating that is provided in a surface layer of the porous ceramic body and contains an infiltration coating material designed to gas-tightly seal pores of the ceramic body.

Claims

1. A ceramic heat shield for a gas turbine, comprising: a porous ceramic body, including a surface, a surface layer and pores, wherein the porous ceramic body comprises mullite; and an infiltration coating which is infiltrated and penetrated into the surface layer of the porous ceramic body, which includes yttrium aluminum garnet that is configured for closing the pores of the surface layer of the porous ceramic body, and which has been fired in a firing procedure to establish a crystalline compound with the porous ceramic body and yttrium aluminum garnet and reactive phases, transition phases and dendrites between the porous ceramic body and the infiltration coating, wherein the infiltration coating does not extend past the surface of the porous ceramic body.

2. The ceramic heat shield of claim 1, wherein the porous ceramic body consists substantially of mullite.

3. The ceramic heat shield of claim 1, wherein the infiltration coating material consists substantially of yttrium aluminum garnet.

4. The ceramic heat shield as claimed in claim 1, wherein the infiltration coating is at least 10 μm thick and up to 600 μm thick.

5. The ceramic heat shield as claimed in claim 1, wherein the surface layer extends across an end face and across lateral faces of the porous ceramic body.

6. The ceramic heat shield as claimed in claim 1, wherein the infiltration coating comprises a thickness of 400 μm.

7. A gas turbine or a combustion chamber having a ceramic heat shield as claimed in claim 1.

8. A method for producing a ceramic heat shield for a gas turbine, comprising the following method steps: providing a porous ceramic body, wherein the porous ceramic body comprises mullite; generating an infiltration coating in a surface layer of the porous ceramic body, wherein the infiltration coating contains an infiltration coating material which is configured for closing pores of the porous ceramic body in a gas-tight manner, wherein the infiltration coating does not extend past the surface of the porous ceramic body, wherein the infiltration coating material comprises yttrium aluminum garnet, and wherein the generating of the infiltration coating includes immersing the porous ceramic body in a suspension containing the infiltration coating material and firing the porous ceramic body to establish a crystalline compound with the porous ceramic body and yttrium aluminum garnet and reactive phases, transition phases and dendrites between the porous ceramic body and the infiltration coating.

9. The method as claimed in claim 8, comprising a step of masking part of a surface of the porous ceramic body prior to immersing the porous ceramic body in the suspension.

10. The method as claimed in claim 8, wherein one or a plurality steps of preparing the suspension comprises/comprise a step of melting and stabilizing the melt of the infiltration coating material.

11. The method as claimed in claim 10, wherein the step of preparing the suspension comprises a step of grinding the infiltration material to at least one of the sub-micrometer range, a particle size ≤1 μm, and 500 nm to 100 nm.

12. The method as claimed in claim 8, wherein the infiltration is performed at a plurality of cycles.

13. The method as claimed in claim 8, wherein an overcoating of the infiltrated region is performed.

14. The method as claimed in claim 8, wherein the infiltration is performed at a positive pressure of up to 5 bar.

15. A refurbishment method comprising the following steps: removing at least one existing ceramic heat shield from a gas turbine; and installing a replacement ceramic heat shield in the gas turbine, the replacement ceramic heat shield comprising: a porous ceramic body, including a surface, a surface layer and pores, wherein the porous ceramic body comprises mullite; and an infiltration coating which is infiltrated and penetrated into the surface layer of the porous ceramic body, which includes yttrium aluminum garnet that is configured for closing the pores of the surface layer of the porous ceramic body, and which has been fired in a firing procedure to establish a crystalline compound with the porous ceramic body and yttrium aluminum garnet and reactive phases, transition phases and dendrites between the porous ceramic body and the infiltration coating, wherein the infiltration coating does not extend past the surface of the porous ceramic.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 shows an exemplary gas turbine 100 in a partial longitudinal section;

(3) FIG. 2 shows a combustion chamber 110 of a gas turbine;

(4) FIG. 3 shows an exemplary embodiment of a heat shield 155 according to embodiments of the invention; and

(5) FIG. 4 shows an exemplary embodiment of a manufacturing device 20 for use in the method according to embodiments of the invention.

DETAILED DESCRIPTION

(6) FIG. 1 in an exemplary manner shows a gas turbine 100 in a partial longitudinal section. The gas turbine 100 in the interior has a rotor 103 that is mounted so as to be rotatable about a rotation axis 102, said rotor 103 having a shaft 101 and also referred to as a turbine rotor.

(7) An intake housing 104, a compressor 105, a combustion chamber 110, in particular an annular combustion chamber, which is, for example, torus-like, having a plurality of coaxially disposed burners 107, a turbine 108, and the exhaust housing 109 are successively disposed along the rotor 103.

(8) The annular combustion chamber 110 communicates with a hot-gas duct 111 which is, for example, annular. For example, four turbine stages 112 disposed in series form the turbine 108 in said hot-gas duct 111.

(9) Each turbine stage 112 is formed from two blade rings, for example. Viewed in the flow direction of an operating medium 113, a guide vane row 115 in the hot-gas duct 111 is followed by a row 125 formed from rotor blades 120.

(10) The guide vanes 130 herein are fastened to an internal housing 138 of the stator 143, whereas the rotor blades 120 of a row 125 are attached to the rotor 103, for example by means of a turbine disk 133.

(11) A generator or a work machine (not illustrated) is coupled to the rotor 103.

(12) During the operation of the gas turbine 100, air 135 is suctioned through the intake housing 104 and compressed by the compressor 105. The compressed air provided at the turbine-side end of the compressor 105 is guided to the burners 107 and is mixed with a fuel there. The mixture, while forming the operating medium 113, is then combusted in the combustion chamber 110. The operating medium 113 from there flows along the hot-gas duct 111 and passed the guide vanes 130 and the rotor blades 120. The operating medium 113 relaxes on the rotor blades 120 so as to transfer an impulse such that the rotor blades 120 drive the rotor 103 and the latter drives the work machine coupled thereto.

(13) The components exposed to the hot operating medium 113 during the operation of the gas turbine 100 are subjected to thermal loadings. Besides the ceramic heat shields that clad the annular combustion chamber 110, the guide vanes 130 and rotor blades 120 of the first turbine stage 112, when viewed in the flow direction of the operating medium 113, are the most thermally stressed.

(14) To withstand the temperatures prevailing therein, said aforementioned components can be cooled by means of a coolant.

(15) Likewise, substrates of the components can have an oriented structure, that is to say they are monocrystalline (SX structure) or have only longitudinally oriented grains (DS structure).

(16) For example, super alloys based on iron, nickel, or cobalt are used as the material for the components, in particular for the turbine blades 120, 130 and components of the combustion chamber 110.

(17) Such super alloys are known, for example from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435, or WO 00/44949.

(18) The blades 120, 130 can have anti-corrosion or anti-oxidation coatings, for example MCrAlX (M is at least one element of the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and represents yttrium (Y) and/or silicon and/or at least one element of the rare earths, or hafnium (Hf), respectively). Such alloys are known from EP 0 486 489 B1, EP 0 T86 017 B1, EP 0 412 397 B1, or EP 1 306 454 A1.

(19) A protective aluminum oxide layer (TGO=thermal grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer).

(20) A heat insulation layer which is the outermost layer can also be provided on the MCrAlX, said heat insulation layer being composed, for example, of ZrO.sub.2, Y.sub.2O.sub.3—ZrO.sub.2, that is to say that said heat insulation layer is not, or partially, or completely stabilized by yttrium oxide and/or potassium oxide and/or magnesium oxide. The heat insulation layer covers the entire MCrAlX layer.

(21) FIG. 2 shows a combustion chamber 110 a gas turbine. The combustion chamber 110 is designed, for example, as a so-called annular combustion chamber in which a multiplicity of burners 107 that generate flames 156 and are disposed in the circumferential direction about a rotation axis 102 open into a common combustion chamber space 154. To this end, the combustion chamber 110 in the entirety thereof is designed as an annular structure which is positioned about the rotation axis 102.

(22) In order for a comparatively high degree of efficiency to be achieved, the combustion chamber 110 is conceived for a comparatively high temperature of the operating medium M of approximately 1000 degrees Celsius to 1600 degrees Celsius. In order for a comparatively long operating period to be enabled even in the case of these operating parameters which are unfavorable for the materials, the combustion chamber wall 153 on that side thereof that faces the operating medium M is provided with an internal cladding formed from ceramic heat shields 155.

(23) By virtue of the high temperatures in the interior of the combustion chamber 110, a cooling system can be provided for the heat shield elements 155, or for the holding elements thereof, respectively. The heat shield elements 155 in this instance are hollow, for example, and optionally also have cooling bores (not illustrated) which open into the combustion chamber space 154.

(24) FIG. 3 shows an exemplary embodiment of a ceramic heat shield 155 according to embodiments of the invention. The heat shield 155 is illustrated in a cross-sectional drawing and, only in an exemplary manner, on the lateral faces 13 thereof has a groove 14 and a tongue 15 by way of which a plurality of neighboring heat shields 155 can be connected so as to form an interior cladding. The heat shield 155 possesses a porous ceramic body 11 which according to embodiments of the invention in a surface layer 12 is equipped with an infiltration coating. The surface layer 12 in the example shown extends across the lateral faces 13 and an end face 16 of the ceramic heat shield 155, said end face 16 in the operation being exposed directly to the hot gas. The infiltration coating contains YAG and closes the pores of the ceramic body 11 such that hot gas cannot invade said pores. For example, a YAG-containing suspension can be directed across the surface of aluminum-oxide-containing ceramic body. The YAG configures the infiltration coating in the case of a subsequent firing procedure.

(25) FIG. 4 shows an exemplary embodiment of a manufacturing device 20 used in the method according to embodiments of the invention. The exemplary manufacturing device 20 possesses a process chamber 21 in which a porous ceramic body 11, or else a plurality of such ceramic bodies 11, is/are provided. The ceramic body 11 can be masked, for example, and/or be mounted on supports. The process chamber 21 is connected to a vacuum pump 24 which can be used for placing the process chamber 21 in a vacuum after said process chamber 21 has been closed. Suspension from a reservoir 22, which contains a supply of suspension, is directed through a supply line 25 into the process chamber 21 and thus across the ceramic body 11, such that the ceramic body 11 is immersed in the suspension. The suspension is discharged again from the process chamber 21 by way of a discharge line 26, such that an approximately consistent filling level of suspension is established in the process chamber for the duration of carrying out the immersion of the ceramic body in the suspension. The reservoir 22 herein can have a mixer 23 which ensures a uniform mixing of the suspension such that ideally no particles of the infiltration coating material within the reservoir 22 are discharged, which would cause a variable concentration of the infiltration coating material in the suspension. The supply line of the suspension is interrupted after a predetermined temporal duration has elapsed, and the quantity of suspension present in the process chamber 21 is directed back into the reservoir. The ceramic body 11 can still remain in the process chamber for a dwell time and thereby dry. However, it is also possible for said ceramic body 11 to be retrieved directly after the discharge of the suspension and to be mechanically relieved of any suspension adhering to the surface. In order for the degree of infiltration to be increased, as a further variant, the chamber after the evacuation using a vacuum can be subsequently impinged with a pressure of 1 bar, or in a further cycle being impinged with up to 5 bar, so as to achieve a complete infiltration of the bricks. The ceramic body 11 is subsequently fired so as to form a heat shield, wherein the infiltration coating material that has been drawn into the pores of the ceramic body 11 is fixedly connected to the ceramic body 11 and in this way configures the desired advantageous infiltration coating.

(26) Although the invention has been illustrated and described in greater detail with reference to the preferred exemplary embodiment, the invention is not limited to the examples disclosed, and further variations can be inferred by a person skilled in the art, without departing from the scope of protection of the invention.

(27) For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.