FIELD OF THE INVENTION

[0002] The invention relates to a method for the surface treatment of a component having a curved component surface, in which material is removed from the component surface by means of a particle jet which is generated from a particle source. The invention also relates to a device for the surface treatment of a component having a curved component surface.

BACKGROUND OF THE INVENTION

[0003] The book “Plasma Spraying of Metallic and Ceramic Materials” by D. Matejka and B. Benko, John Wiley & Sons, Chichester, U.K., 1989, has disclosed the method of plasma spraying together with applications, for example on components of an internal combustion engine of a motor vehicle. The section 6.1 “Preliminary preparation of surface prior to spraying” describes various methods which are used to prepare a component which is to be coated. This section describes a method for cleaning the surface of the product by means of a jet of abrasive particles prior to the actual coating operation. The abrasive particles are entrained in a compressed-air stream and preferably impinge on the surface to be treated at right angles. The blasting treatment with the abrasive particles can be carried out in a chamber or using a suction device, so that substantially the entire quantity of abrasive particles is recovered and is available for a further blasting treatment. Abrasive particles can in this case be produced from cast iron, steel from synthetic corundum (aluminum oxide Al ₂ O ₃ ), silicon carbide or silicate sand (quartz sand). The abrasive particles may have a diameter of between 350 μm and 1400 μm. The blasting is preferably carried out by means of what is referred to as grit blasting, in which the abrasive particles are corundum particles with a diameter of between 200 μm and 800 μm. These particles are used to prepare a surface having a coating with a layer thickness of up to 200 μm, which coating is applied to the prepared surface in a coating process. Particle diameters of up to 1400 μm are used for coatings with a greater layer thickness. The compressed air in which the abrasive particles are entrained is preferably at a pressure of up to 0.35 MPa when using corundum.

[0004] U.S. Pat. No. 4,321,310 has described a method for producing a coating on a gas turbine component which is a turbine blade or vane. The turbine blade or vane has a base body made from a base material. The base material used is a cobalt-base or nickel-base alloy, such as for example IN 100, MAR M200, MAR M509 or WI 52. A bonding layer of the type MCrAlY is applied to this base material. In this context, M denotes, for example, a combination of the metals nickel and cobalt. Cr represents chromium, Al represents aluminum and Y represents yttrium. A ceramic layer of zirconium oxide, which is grown on in columnar form, the columns being oriented substantially perpendicular to the surface of the base body, is applied to this bonding layer. Prior to the application of the zirconium oxide layer used as thermal barrier coating to the bonding layer, the bonding layer is polished until a surface roughness of approximately 1 μm is established.

[0005] U.S. Pat. No. 5,683,825 likewise reveals a method for applying a thermal barrier coating to a component of a gas turbine. An NiCrAlY bonding layer is applied to a base body by low-pressure plasma spraying. The surface of the bonding layer is polished, so that it has a surface roughness of approximately 2 μm. A ceramic thermal barrier coating comprising yttrium-stabilized zirconia is applied to the bonding layer which has been polished in this way by means of a physical vapor deposition (PVD) method. The thermal barrier coating is in this case preferably applied using the electron beam PVD method. The thermal barrier coating may also be applied by means of plasma spraying. U.S. Pat. No. 5,498,484 likewise describes the application of a thermal barrier coating to a bonding layer of a component of a gas turbine. The mean surface roughness of the bonding layer is given as being at least over 10 μm.

[0006] U.S. Pat. No. 5,645,893 relates to a coated component having a base body made from a superalloy and having a bonding layer and a thermal barrier coating. The bonding layer includes a platinum aluminide and an adjoining thin oxide layer. The thin oxide layer includes aluminum oxide. This oxide layer is adjoined by the thermal barrier coating, which is applied by means of the electron beam PVD method. In this case, yttrium-stabilized zirconia is applied to the bonding layer. Prior to the application of the bonding layer, the surface of the base body is cleaned by means of a grit blasting method. Alumina grit is used for the material-removing preparation of the base body.

[0007] WO 97/047781 A1 has disclosed a gas turbine component, for example a gas turbine blade or vane or a heat shield element of a combustion chamber. The base material of the gas turbine component is a nickel-base or cobalt-base superalloy. A bond coat comprising a nitride is applied to the base material. The bond coat is adjoined by a ceramic thermal barrier coating. The surface of the bond coat has a mean surface roughness of over 6 μm, in particular between 9 μm and 14 μm.

[0008] WO 99/23272 has described a method for producing a protective coating on a base body which is designed to be exposed to hot gases in order to protect against oxidation and/or corrosion. The protective layer is compressed by a hot isostatic pressing method, during which it remains unsealed. In the process, the protective layer remains chemically substantially unchanged. During the hot isostatic pressing, a pressure exerted by a compressed gas is used to compress the porous protective layer for a time of between approimately 0.1 and 3 hours at temperatures of from approximately 800° C. to 1200° C. Unlike the documents mentioned above, the hot isostatic pressing is a surface treatment which does not involve removal of material.

SUMMARY OF THE INVENTION

[0009] It is an object of the invention to describe a method for the surface treatment of a component. It is a further object of the invention to provide a device for the surface treatment of a component.

[0010] According to the invention, the object relating to a method is achieved by a method for the surface treatment of a component (having a curved component surface, in which material is removed from the component surface along a contour line on the component surface by means of a particle jet which is generated from a particle source and is characterized by the jet parameters blasting distance, blasting intensity, blasting angle and blasting time, in which method at least one of the jet parameters is deliberately matched to the contour line in such a way that a homogeneous surface roughness is established along the contour line.

[0011] The invention is based on the consideration that irregularities in the component surface and uneven removal of material during the material-removing preparation of component surfaces have an adverse effect on the quality of the component surface and therefore on its usability. In methods for the surface treatment of components which have been disclosed hitherto, in particular in the case of material-removing preparation, uniform surface preparation of the component is not ensured over the entire component surface or over relatively large adjoining regions of the component surface. Particularly in the case of components with a complex component geometry, in particular with a curved component surface, the curvature leads to a local variation in the jet parameters. By way of example, a complex component geometry leads to a variation in the jet distance, i.e. the distance from the particle source to the component surface which is to be treated, which leads, for example, to different surface roughnesses in different areas of the component surface. This is true in particular of those areas of the component surface which have a different curvature. Furthermore, those areas of the component surface which have a curvature which varies greatly on a local basis and those areas which are difficult for the particle jet to gain access to using conventional methods are subject to irregularities (inhomogeneity) in the surface structure. Furthermore, only limited reproducibility can be ensured in the surface treatment of a multiplicity of components.

[0012] The method has for the first time taken account of characteristic jet parameters of the particle jet in relation to the local component geometry. In this context, the term blasting distance refers to the distance from the particle source to the point of impingement of the particle jet on the component surface. The blasting angle is defined in a local, component-related system of coordinates. In this reference system, the blasting angle is the angle between the blasting direction of the particle jet and the local normal to the component surface at the point of impingement of the particle jet on the component surface. The blasting intensity is understood as meaning the number of particles emitted from the particle force per second and solid angle, i.e. the blasting intensity is given as a particle flow rate. The number of particles which impinge each second on a local surface region on the component surface therefore results in a simple way from the blasting distance, the size of the surface region and the blasting angle. The blasting time is understood as meaning the residence time of the particle jet on a selected section of the contour line. The residence of the particle jet and therefore the number of particles which locally impinge on the component surface can be varied by means of the speed at which the particle jet is guided along the contour line. The method allows the amount of material removed from the component surface to be deliberately matched to the geometry of the component. In this way, it is possible to produce a predeterminable homogeneous surface roughness along the contour line. As a result of a plurality of cohesive contour lines being tracked in succession, it is possible for large areas of the component surface to be treated and homogenized in terms of their roughness. In particular, the entire component surface can be subjected to a surface treatment of this type.

[0013] For an efficient application of the method, the method will preferably be operated continuously. For this purpose, the particle jet is guided along the contour line as a continuous function of time. As an alternative, the removal of material from the component surface along the contour line could also be carried out discontinuously, with the method being temporarily interrupted. With the method, it is possible to deliberately set the surface roughness characteristic variables, for example maximum profile height, maximum profile depth, roughness average. The roughness average, that is to say the arithmetic mean of the absolute values of the profile deviations within a reference distance (e.g. a partial section of a contour line) is in this case preferably used to compare surfaces of identical or similar character.

[0014] It is also possible for various partial regions of the component surface, which may, for example, be differently curved or oriented, to be deliberately produced with different predeterminable surface roughnesses. Each partial region in this case has a homogeneous surface roughness. Where appropriate and intended, it would also be possible for the surface roughness to be set according to a predeterminable, optionally non-constant function along a contour line.

[0015] By means of the blasting matched to the contour line using the particle jet, the component surface is smoothed in order to set a predetermined surface roughness in a predetermined region of the component surface. Furthermore, the blasting with the particle jet can be used for surface cleaning of the component surface, leading to activation of the component surface. In this way, the component surface is prepared for other methods—for example methods—which follow the surface treatment.

[0016] It is preferable for the jet parameters to be adapted automatically. This ensures good reproducibility. Furthermore, manual interventions in the method are no longer required.

[0017] It is preferable for the particle source and the component to be moved relative to one another. This involves relative translational movements, relative rotational movements and or combinations of translational movements and rotational movements. This relative movement of particle source and component makes it possible to guide the particle jet to a desired location and along a contour line on the component surface. The speed at which the relative movements are carried out allows the blasting time to be varied. Particularly in the case of components with a complex component geometry, for example with a curved component surface, the relative movements are used to influence jet parameters, such as for example blasting angle and blasting distance. A wide range of operating modes with regard to the relative movements of component and particle source are possible. A few preferred configurations in the method are described below:

[0018] In a preferred configuration of the method, the particle source is moved relative to the component in such a way that the blasting distance is constant. As a result, given a constant blasting intensity of the particle source, the number of particles which impinge each second on a surface element of the component surface which is arranged at right angles at a constant blasting distance, is a constant value. Furthermore, it is preferable for the particle source to be moved relative to the component in such a way that the blasting angle is constant. If an operating mode in which both the blasting distance and the blasting angle are constant is selected, removal of material which is particularly is well matched to the geometry of the component is ensured, and in particular homogeneous surface treatment of the component is possible as a result.

[0019] The relative movements are carried out in such a way that, in a preferred method configuration, the particle source is moved in a plurality of axes with respect to the component which is simultaneously stationary. In this context, the term in a plurality of axes means that the particle source is moved along at least two Cartesian coordinate axes. The combination of movements in a first axis and in a second axis which is perpendicular thereto also allows the particle source to rotate about a rotation axis, for example about an axis which runs through the component (cf. Figure axis). Furthermore, it is preferable for the particle source to be moved in a plurality of axes with respect to the component which is simultaneously rotating. Furthermore, it is preferable for the particle source to be moved in a plurality of axes with respect to the component which is simultaneously being moved in a plurality of axes.

[0020] Preferably, the component is moved in a plurality of axes with respect to the particle source which is simultaneously stationary. The wide range of different method configurations with regard to the relative movements provides a high level of flexibility. The combination of the various movement modes allows very complex component geometries to be subjected to a surface treatment in the method.

[0021] The component preferably has a base body with a base material, the base body having the component surface which, for a first coating to be applied to the base body, is treated with a first coating material. The blasting with a stream of particles leads to surface cleaning of the base body. This surface cleaning results in activation of the surface. As a result, particularly good bonding of a first coating to the base body is possible in a coating method. The method can therefore be used as a subprocess of a method for producing a layer on a component. The method allows high-quality preparation of the component surface prior to a coating operation. This has a very advantageous effect on the coating which is to be applied to the base body, primarily its adhesion and layer quality. The base body is produced, for example, from a metallic material. In this case, in the case of high-temperature applications, alloys which are able to withstand high temperatures, for example nickel, cobalt or chromium superalloys, are used as material for the base body.

[0022] In this case, it is preferable for an alloy or an intermetallic compound to be used as the first coating material in the coating process. The first coating material used is preferably an alloy which forms a bonding layer, such as for example an alloy of the type MCrAlX. In this context, M represents a metal, in particular one or more elements selected from the group consisting of nickel, cobalt and iron. Cr represents chromium and Al represents aluminum. X represents one or more elements selected from the group consisting of yttrium, rhenium and the rare earths, such as for example hafnium. Alloys of this type are provided in particular in high-temperature applications.

[0023] The first coating preferably also has the component surface which, for a second coating to be applied to the component, is treated with a second layer material.

[0024] In a preferred configuration, the component has a base body with a base material, a first coating comprising a first coating material being applied to the base body, and the coated component, for a second coating to be applied to the component, being treated with a second coating material. The method is advantageously suitable not only for treating the surface of a base body, but also for the treatment and preparation of a layer which has been applied to the base body prior to the application of a further layer to the first layer. The method can therefore be integrated in a process for producing a layer system on a component. This allows very high-quality layer systems, which in particular have sufficient long-term stability and have a complex geometry of the base body, to be produced significantly more successfully.

[0025] In the coating process, it is preferable for a ceramic to be used as the second coating material. Examples of suitable ceramic materials are those which include zirconium oxide (ZrO ₂ ), which has been partially or completely stabilized by yttrium oxide, cerium oxide or another oxide. A second coating of this type, which includes a ceramic, is, for example, a thermal barrier coating and as such has a layer thickness of approximately >50 μm, in particular approximately >200 μm. A thermal barrier coating may also include other metal-ceramic oxides, in particular including metal-ceramic mixed oxide systems, for example perovskites (e.g. lanthanum aluminate), pyrochlores (e.g. lanthanum hafnate) or spinels such as for example the classic magnesium aluminate spinel MgAl ₂ O ₄ .

[0026] A layer system on a metallic base body which has a bonding layer as the first coating and a thermal barrier coating, which adjoins the bonding layer, as second coating, is used in particular for high-temperature applications. In a preferred configuration of the method, the component is designed for a hot gas to flow around it. Furthermore, it is preferable for the component used to be a turbine rotor blade, a turbine guide vane or a heat shield element of a combustion chamber. Components of thermal machines, such as for example a gas turbine, an internal combustion engine, a furnace or the like, have to be designed to be exposed to a hot aggressive medium, in particular a hot gas. The temperatures to which a component is exposed during normal use may in this case be well over 1000° C.

[0027] The particle jet preferably includes abrasive particles which are entrained in a pressurized carrier medium, in particular compressed air. The abrasive particles preferably impinge on the component surface at a blasting angle of approximately 20° to 90° C., in particular of approximately 50° to 90°. The diameter of the abrasive particles, the blasting angle and the pressure of the pressurized carrier medium depend on the material of the abrasive particles, the material of the component surface on which they impinge, and on the effect which is to be achieved, in particular with regard to surface cleaning or removal of material in order to establish a desired surface roughness. If a large amount of material is to be removed, the angle at which the abrasive particles impinge on the surface is approximately between 50° and 90°, in particular approximately 60°. For cleaning and activation of the component surface, the angle is in a range between 20° and 60°. The abrasive particles which are entrained in the carrier medium may be provided in the form of a powder or, if relatively large particles are present (globular particles), can be broken up by a milling process, in order to produce sharp-edged abrasive particles which then have an increased abrasive action on the component surface.

[0028] According to the invention, the object relating to a device for the surface treatment of a component is achieved by a blasting installation for the automated surface treatment of a component having a curved component surface, which installation has a particle source for generating a particle jet and a component holder for holding the component, the particle source and the component being movable relative to one another in such a way that, to produce a homogeneous component surface in a blasting process using the particle jet, the blasting distance and/or the blasting angle adopts a predetermined, in particular constant value along a contour line on the component surface.