Method for the electroplating of TiAl alloys

Abstract

The present invention relates to a method for the coating of a surface of a TiAl alloy, in which at least one layer is electroplated on the surface of the TiAl alloy, wherein the surface of the TiAl alloy is subjected to an at least two-step surface treatment for the formation of a roughened surface, this treatment comprising at least one electrochemical processing and at least one electroless chemical processing.

Claims

1. A method for coating a surface of a TiAl alloy, comprising the steps of: providing a TiAl alloy having a surface; roughening the surface of the TiAl alloy in a two-step surface treatment, including: applying an electrochemical process to the surface; and treating the surface with an electroless chemical process after the electrochemical process; wherein the surface of the TiAl alloy is sufficiently roughened after the electrochemical process and electroless chemical process without mechanical roughening of the surface of the TiAl alloy; chemically activating the surface of the TiAl alloy after roughening the surface of the TiAl alloy in the two-step surface treatment; and electroplating at least one layer on the surface of the TiAl alloy after the step of chemically activating the surface of the TiAl alloy, wherein the electrochemical processing is conducted by anodic etching in an acetic acid-hydrofluoric acid solution, wherein concentrations by weight of 800 to 900 g/L of acetic acid and 100 to 200 g/L of hydrofluoric acid are selected for the composition of the acetic acid-hydrofluoric acid solution.

2. The method according to claim 1, wherein the step of electroless chemical processing is etching the surface of the TiAl alloy with a fluoroboric acid-sodium tetrafluoroborate solution.

3. The method according to claim 1, further comprising the steps of: between the electrochemical processing step and the electroless chemical processing step cleaning the surface of the TiAl alloy with compressed air and/or a water jet; and drying the surface of the TiAl alloy after cleaning the surface.

4. The method according to claim 1, further comprising the step of: prior to the two-step surface treatment, chemically etching of the surface of the TiAl alloy with a nitric acid solution containing ammonium bifluoride, wherein, weight concentrations of 300 to 400 g/L of nitric acid and 50 to 80 g/L of ammonium bifluoride are selected for the nitric acid solution.

5. The method according to claim 4, further comprising the step of: prior to the step of chemical etching of the surface of the TiAl alloy with the nitric acid solution containing ammonium bifluoride, chemically cleaning the surface with an alkaline cleaning solution.

6. The method according to claim 1, wherein the step of chemically activating the surface of the TiAl alloy is chemically activating of the surface with a sulfuric acid solution.

7. The method according to claim 1, further comprising the step of: rinsing of the surface with demineralized water between and/or after each of the individual processing steps.

8. The method according to claim 1, wherein a nickel or cobalt layer is deposited as the electroplated layer.

9. The method according to claim 1, further comprising the step of: depositing at least one second layer on the electroplated layer.

10. The method according to claim 9, wherein the at least one second layer is deposited by a method that is selected from the group consisting of electroplating, physical vapor deposition, chemical vapor deposition, thermal spraying, welding, and soldering.

11. The method according to claim 1, wherein the TiAl alloy further comprises niobium and/or molybdenum as additional components, wherein the niobium content is in the range of 0 to 5 at. % and/or the molybdenum content lies in the range of 0 to 3 at. % and the Al content lies in the range of 40 to 45 at. %, with the remainder being Ti and other additional alloy components.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) The appended figures are shown, in which:

(2) FIG. 1 is a scanning electron micrograph of a cross section through an electroplated coating on a TNM alloy;

(3) FIG. 2 is a scanning electron micrograph of the surface of the TNM alloy prior to the electroplating; and in

(4) FIG. 3 is the surface of FIG. 2, which was taken in a larger magnification and with the secondary electron detector of the scanning electron microscope.

DESCRIPTION OF THE INVENTION

(5) Further advantages, characteristics and features of the present invention will be made clear in the following detailed description of an example of embodiment, the invention not being limited to this embodiment example.

(6) In the exemplary embodiment, a component made of a TNM alloy is subjected to a coating, which contains 43 to 45 at. % aluminum, 0.5 to 3 at. % molybdenum, 0 to 4.0 at. % niobium, a sum total of 0 to 5 at. % vanadium, chromium, manganese and iron, a sum total of 0 to 0.5 at. % hafnium and zirconium, 0.1 to 1 at. % carbon, and 0.05 to 0.2 at. % boron, as well as 0 to 1 at. % silicon. The component that is formed completely from the TiAl material in the present case, but which can also only have a surface region made of the TiAl material, is first subjected to a chemical cleaning with an alkaline cleaning solution of the name TURCO 5948 DPM (protected tradename of the Henkel Co.).

(7) After the chemical cleaning, a chemical etching is carried out in a nitric acid containing ammonium bifluoride, with 350 g/L of nitric acid and 60 g/L of ammonium bifluoride. After the etching with the nitric acid solution containing ammonium bifluoride, the TiAl-containing surface is sprayed with compressed air or a water jet from an air/water gun for the removal of the etching slurry, and subsequently dried.

(8) After this, an anodic etching is carried out in concentrated acetic acid/hydrofluoric acid solution with a composition of 850 g/L of acetic acid and 150 g/L of hydrofluoric acid. Also after the anodic etching, the surface is cleaned by spraying with compressed air and/or a water jet from an air/water gun.

(9) Subsequently, the chemically active etching is conducted with a fluoroboric acid-sodium tetrafluoroborate solution.

(10) After this processing step, the surface is rinsed with demineralized water. The rinsing with demineralized water can be provided in addition to the other cleaning steps described, both after the chemical cleaning as well as after the chemical etching and the anodic etching.

(11) To conclude the pretreatment of the TiAl-containing surface for the subsequent electroplating, a chemical activation of the surface is carried out in a sulfuric acid solution.

(12) After rinsing with demineralized water, the thus-pretreated TiAl component can be subjected to electroplating with a layer of nickel and/or cobalt, which has a layer thickness of at least 5 m.

(13) Subsequently, the most diverse coatings, such as thermal insulation layers, oxidation protection layers, erosion protection layers, layers for protection against wear, layers for weight correction, can be deposited by the most varied methods.

(14) The individual method steps need not be carried out directly one after the other, but after a cleaning step and a drying step, the method can be interrupted and then continued again later after a pause by the next processing step.

(15) FIG. 1 shows a metallographic cross section in a scanning electron micrograph, wherein the TNM base material can be seen in the lower region of the image (dark gray), and the electroplated coating can be seen in the upper part (light gray). It can be clearly recognized that the interface has a rough structure that makes possible the electroplating and brings about a good adhesive strength of the deposited layer.

(16) FIGS. 2 and 3 show scanning electron micrographs of the surface of the TNM component prior to the deposition of the electroplated layer. Here also it can be recognized that the surface has a pronounced structuring that makes possible the subsequent electroplating of the layer and improves the adhesive strength of the electroplated layer.

(17) Although the present invention has been described clearly on the basis of the example of embodiment, it is obvious to a person skilled in the art that the invention is not limited to this example of embodiment, but rather that many deviations are possible in the sense that individual features can be omitted or other combinations of features can be realized. The present disclosure includes all combinations of the individual features presented.