EP1743053B1 - Method for production of a coating - Google Patents

Description

The invention relates to a method for producing a corrosion-resistant and / or oxidation-resistant coating according to the preamble of patent claim 1,

When operating components, in particular components of gas turbines, at high temperatures, their free surfaces are exposed to highly corrosive and oxidizing conditions. For example, when used in gas turbines, such components may consist of a nickel base or cobalt base superalloy. To protect against corrosion, oxidation or erosion, the components are provided with coatings. Preference is given to PtA1 coatings, with which a particularly good corrosion protection and / or oxidation protection can be realized.

The EP 0 784 104 Bl discloses a PtA1 coating for gas turbine components and a method of making such a coating. According to the method described there, a PtA1 coating is produced on a substrate by depositing a platinum layer on a substrate surface, wherein after the deposition of the platinum layer, diffusion of platinum from the platinum layer into the substrate surface is carried out. After deposition of the platinum layer and the diffusion of the platinum, the thus coated substrate is a-lit, ie coated with aluminum, wherein the aluminum is preferably diffused into the substrate surface.

From the documents US 5,415,761A and WO 03/088316 A are known processes for the electrodeposition of metallic coatings on substrate surfaces, which proceed in terms of process technology in two or more temporally successive stages. The process stages preferably differ by a different current intensity or current density and thus a different deposition behavior.

The deposition of platinum on the substrate surface before Alitieren the substrate is preferably carried out by electroplating. The present invention relates to details of a method of making a corrosion resistant and / or oxidation resistant coating on a substrate, which involves electrodepositing a platinum group metal, particularly platinum and / or palladium, or an alloy based on at least one platinum group metal. So it is essential for the quality of the corrosion-resistant and / or oxidation-resistant coating that a uniformly defined Deposition of particular platinum is realized by galvanic way, so as to realize a uniform thickness of the platinum coating. For example, a minimum value of the coating thickness of approximately 1 μm may not be undershot, since this would result in insufficient hot gas resistance and locally rapid failure of the coating. On the other hand, layer thicknesses of 8 to 15 .mu.m may not be exceeded, since this would waste precious valuable metal on the one hand and on the other hand would impair the properties of the coating. Another problem with the galvanic deposition of particular platinum on a substrate is when the platinum is to be deposited, for example, on components with a complex three-dimensional shape. Such substrates with a complex three-dimensional contour are, for example, gas turbine blades, because they are on the one hand highly asymmetrical, and on the other hand have edge-, corner- and tip-like surfaces as well as cavities and undercuts. With the methods known from the prior art for the galvanic deposition of platinum, a uniformly defined deposition of platinum on substrates with a complex three-dimensional contour can be realized only insufficiently.

On this basis, the present invention is based on the problem to provide a novel method for producing a corrosion-resistant and / or oxidation-resistant coating, which is a platinum group metal-A1 coating.

This problem is solved by a method for producing a corrosion-resistant and / or oxidation-resistant coating in the sense of claim 1. According to the invention, the galvanic deposition of the or each platinum group metal or alloy is carried out in a two-stage deposition process, wherein in a first stage of the deposition process in a coating time T1, a current applied for electroplating is increased continuously or stepwise from a start value to a maximum value , and in a second stage of the deposition process in a coating time T2, the current applied for plating is kept constant at the maximum value.

Preferred embodiments of the invention will become apparent from the dependent claims and the description below.

The process according to the invention for producing a corrosion-resistant and / or oxidation-resistant coating, preferably a PtAl coating, will be described in greater detail below.

The present invention relates in particular to those details which relate to the electrodeposition of at least one platinum group metal, in particular platinum and / or palladium, or an alloy based on at least one platinum group metal on a substrate to be examined. At this point it should be noted that after the galvanic deposition of platinum and / or palladium or a related alloy on the substrate and before Alitieren the so galvanically coated substrate diffusing the platinum and / or palladium or the corresponding alloy into the substrate can.

Before the actual galvanic deposition of the or each metal of the platinum group or the corresponding alloy, a surface pretreatment of the substrate takes place. The surface pretreatment of the substrate comprises at least the following three steps: In a first step of the surface pretreatment, the surface of the substrate to be coated is blasted. The blasting takes place with Al ₂ O ₃ particles which have a particle diameter of 100 to 200 μm and are directed at a pressure of 1.5 to 3.5 bar onto the substrate surface to be irradiated. When blasting, a coverage of 200 to 1500% is used, which means that each surface section is blasted between two and fifteen times or detected by a corresponding number of particle beams. After blasting, there is a metallically bright and oxide-free substrate surface. Following blasting, the blasted surface is electrochemically cleaned or degreased, in a NaOH-containing solution. Following degreasing or cleaning of the substrate surface, the same is activated in a 40 to 60% strength by volume HCl solution.

In connection with the surface pretreatment of the substrate, the galvanic deposition of the or each metal of the platinum group or of the corresponding alloy takes place by means of a deposition process. According to a first aspect of the present invention, the electrodeposition takes place in a two-stage deposition process, wherein in a first stage of the deposition process, a current applied for electroplating is increased continuously or stepwise from a initial value to a maximum value, and wherein in a second stage of the deposition process the current applied for electroplating is kept constant at the maximum value.

In this case, the electrodeposition is carried out over a total coating time T, wherein the first stage of the cutting process, in which the current applied for plating is continuously or stepwise increased to the maximum value from the initial value, takes place in a coating time T ₁ , and wherein the second stage the deposition process, in which the current applied to the plating is kept constant at the maximum value, in a coating time T _{2 is} performed. The coating time T _{1 of} the first stage of the deposition process amounts to approximately 50% of the total coating time, the coating time T _{2 of} the second stage of the deposition process is also approximately 50% of the total coating time T. Accordingly, the total coating time T then applies: T = T ₁ + T ₂ .

According to a first preferred development of this first aspect of the present invention, the current intensity I is continuously increased to the maximum value starting from an initial value which corresponds approximately to 10% of the maximum value I _MAX of the current applied for electroplating within the coating time T ₁ . Alternatively, the current intensity I in the coating time T ₁ can be increased stepwise from the initial value to the maximum value I _MAX . In any case, after reaching this maximum value I _MAX , during the second stage of the deposition process, the current applied to the plating current I is maintained at this maximum value I _MAX .

$$I=\{\begin{array}{c}0,1*I_{\mathit{MAX}}\mathit{für}0\le t<0,1*T\\ 0,4*I_{\mathit{MAX}}\mathit{für}0,1\le t<0,3*T\\ 0,7*I_{\mathit{MAX}}\mathit{für}0,3\le t<0,5*T\\ I_{\mathit{MAX}}\mathit{für}0,5*T\le t<T\end{array}$$

In particularly preferred embodiments, in which the coating time T _{1 of} the first stage and the coating time T _{2 of} the second stage are each 50% of the total coating time T, and in which the initial value of the current I in the first stage of the deposition process 10% of the maximum current I _MAX , the current applied to the electrodeposition electrode I preferably has one of the following conditions, wherein the condition (1) corresponds to the continuous increase of the current I in the first phase of the deposition process, and the condition (2) of the stepwise increase of the current I corresponds during the first phase of the deposition process. $$I=\{\begin{array}{c}0.1*I_{\mathit{MAX}}+\frac{0.9*I_{\mathit{MAX}}}{0.5*T}*t\mathit{For}0\le t\le 0.5*T\\ I_{\mathit{MAX}}\mathit{For}0.5*T\le t\le T\end{array}$$

$$I=\{\begin{array}{c}0.1*I_{\mathit{MAX}}\mathit{For}0\le t<0.1*T\\ 0.4*I_{\mathit{MAX}}\mathit{For}0.1\le t<0.3*T\\ 0.7*I_{\mathit{MAX}}\mathit{For}0.3\le t<0.5*T\\ I_{\mathit{MAX}}\mathit{For}0.5*T\le t<T\end{array}$$

It should be noted at this point that the maximum current I _MAX applied for the galvanic deposition corresponds, depending on the type of galvanic bath used, to a magnitude of 0.2 to 3.5 A / dm ² , preferably with maximum currents of 1.5 A. / dm ² or 2 A / dm ² worked. Although in the above embodiment, an initial value of the current I is used, which is about 10% of the maximum current I _MAX , it is also possible to work with an initial value of the current I which is approximately 15% or even 20% of the maximum current I _MAX is.

For the purposes of the present invention, the substrate to be coated during the entire Abscheideprczesses, ie during the entire first stage and the entire second stage of the deposition process, connected cathodically and thus negatively. For the purposes of the present invention, the substrate to be coated can be anodically or positively treated prior to the actual deposition process and thus introduced into the galvanic bath. Alternatively, it is also possible to switch the substrate to be coated directly cathodically.

For the purposes of the present invention, preferably several substrates are coated simultaneously in a galvanic bath with the or each metal of the platinum group or a corresponding alloy. By egg is a rational production of relatively large quantities in batch mode possible. With the method according to the invention, moreover, a uniform deposition of platinum and / or palladium or a corresponding alloy on substrates having a complex, three-dimensional geometry is possible.

Claims (8)

1. Method for producing a corrosion-resistant and/or oxidation-resistant coating, wherein at least one metal of the platinum group, in particular platinum and/or palladium or an alloy based on at least one metal of the platinum group, is deposited by means of galvanization onto a surface of a substrate, and wherein subsequently aluminization of the thus galvanically coated substrate is carried out, characterised in that
   the galvanic deposition of the or each metal of the platinum group or of the corresponding alloy is carried out in a two-stage deposition process, wherein in a first stage of the deposition process in a coating time T1 a current intensity that is applied for galvanization is increased continuously or stepwise starting from an initial value to a maximum value of the order of magnitude of 0.2 to 3.5 A/dm², and wherein in a second stage of the deposition process in a coating time T2 the current intensity applied for galvanization is kept constantly at the maximum value, and
   the deposition process is carried out over a total coating time T, wherein the coating time T₁ of the first stage amounts to approximately 50% of the total coating time T, and the coating time T₂ of the second stage amounts to approximately 50% of the total coating time T, and wherein T = T₁ + T₂.
2. Method according to claim 1,
   characterised in that
   the initial value of the current intensity applied in the first stage corresponds to approximately 10 to 20% of the maximum value.
3. Method according to claim 1 or 2,
   characterised in that
   starting from the initial value of the current intensity the current intensity is increased continuously to the maximum value in the coating time T₁ of the first stage.
4. Method according to claim 1 or 2,
   characterised in that
   starting from the initial value of the current intensity the current intensity is increased stepwise to the maximum value in the coating time T₁ of the first stage.
5. Method according to one of claims 1 to 4,
   characterised in that
   the substrate that is to be coated is connected cathodically or negatively throughout the deposition process.
6. Method according to one of claims 1 to 5, characterised in that
   before the deposition process the substrate that is to be coated is connected anodically or positively and is thus introduced into a galvanic bath.
7. Method according to one of claims 1 to 6,
   characterised in that
   before the deposition process and, if applicable, before the anodic or positive connection of the same the substrate that is to be coated is subjected to surface pretreatment, wherein

   a) the surface of the substrate that is to be coated is jet-blasted;

   b) subsequently the jet-blasted surface is electrochemically cleaned or degreased;

   c) subsequently the cleaned or degreased surface is activated.
8. Method according to claim 7,
   characterised in that
   during the surface pretreatment

   a) the surface of the substrate that is to be coated is jet-blasted with Al₂O₃ particles, which have a particle diameter of 100 to 200 µm, at a pressure of 1.5 to 3.5 bar;

   b) subsequently the jet-blasted surface is electrochemically cleaned or degreased in a NaOH solution;

   c) subsequently the cleaned or degreased surface is activated preferably in a 40 to 60 viol % HCl solution.