COATING METHOD AND COMPONENT

Abstract

A coating method for applying a cover layer to a base material is provided. A solder positioned on a surface of the base material is heated until it is molten, for joining the solder to the base material in a heat treatment. Oxygen is diffused in the molten lot for forming a diffusion layer in the cover layer. A component for a steam turbine is also provided.

Claims

1. A coating process for applying a covering layer onto a base material, comprising: heating a solder positioned on a surface of the base material in a heat treatment until the solder is molten to join the solder to the base material, wherein oxygen is diffused into the molten solder to form a diffusion layer in the covering layer.

2. The coating process as claimed in claim 1, wherein a titanium alloy is used as the base material.

3. The coating process as claimed in claim 2, wherein a titanium-based solder is used as the solder.

4. The coating process as claimed claim 1, wherein the solder is mixed with an additional base material which consists of the same material as the base material.

5. The coating process as claimed in claim 4, wherein the additional base material is present in a proportion by mass of from 30% to 70% in the solder.

6. The coating process as claimed in claim 1, wherein the solder is used in a pulverulent form.

7. The coating process as claimed in claim 6, wherein a ribbon in which the pulverulent solder has been applied to a support layer is used.

8. A component for a steam turbine, comprising: a base material; and a covering layer affixed to a surface of the base material, wherein the covering layer has a diffusion layer in which atomic oxygen is embedded in a metal lattice of the covering layer.

Description

BRIEF DESCRIPTION

[0021] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0022] FIG. 1 depicts an illustration of the coating process and the component according to an embodiment of the invention; and

[0023] FIG. 2 depicts a flowchart of the coating process according to an embodiment of the invention.

DETAILED DESCRIPTION

[0024] FIG. 1 shows an illustration of the coating process 10 according to embodiments of the invention. A base material 16 is depicted therein in various stages a), b), c) and d).

[0025] The base material 16 is, in particular, part of a low-pressure blade of a steam turbine.

[0026] In stage a), the base material 16 is in operation and is subjected to operational influences, for example droplet impact and abrasive wear. Water droplets 19 which impinge on the base material 16 are shown illustratively here. Mechanical notches can be formed here by rutting of the material.

[0027] In stage b), the base material 16 has been eroded as a result of the operational influences. Droplet impact erosion 20, which in the case of low-pressure blades of steam turbines represents a specific form of notch formation, is depicted by way of example. In the case of steam turbines, mist droplets are formed in the stream of steam and these are captured by guide blades, accumulate there and at the exit edges thereof break off as water droplets 19. As a result of high circumferential velocities and prevailing flows at the rotor blades, these water droplets 19 lead to surface rutting due to droplet impact erosion 20.

[0028] In stage c), the eroded base material 16 is provided with a covering layer 17. The eroded material is thereby filled. The filling of the material can, for example, have been carried out by means of deposition soldering. This method is known in the prior art.

[0029] Stage d) shows the base material 16 after a repair by means of the coating process 10 according to embodiments of the invention and an illustrative embodiment of the component 21 according to the invention.

[0030] The base material 16 has been coated with a covering layer 17. The covering layer fills the eroded regions. In addition, the covering layer 17 comprises a diffusion layer 18. In the diffusion layer 18, atomic oxygen is embedded in the metal lattice of the covering layer. The diffusion layer 18 forms the surface of the component 21. The base material 16 is, in particular, TiA16V4. The covering layer 17 is, for example, formed by Ti braze. The diffusion layer has, in particular, a layer thickness of more than 80 m, in particular in the range from 0.5 mm to 2 mm. The component 21 is a steam turbine part and in particular a low-pressure blade.

[0031] One possible way of producing the component 21 of embodiments of the invention is the coating process 10 of the invention. The coating process 10 is depicted in an illustrative variant in a flow diagram in FIG. 2 from a start 11 to an end 15.

[0032] The coating process 10 of embodiments of the invention represents a combination of a soldering process and an oxygen diffusion process. Here, the covering layer 17 is produced from a solder on a surface of the base material 16.

[0033] In particular, a titanium alloy such as TiA16V4, in particular, is used as base material 16 and a titanium-based solder, for example Ti braze, is used as solder. It is possible to mix the solder with a material which consists of the same material as the base material 16. The mixing ratio here is in the range from 30 percent by mass to 70 percent by mass.

[0034] The solder is, in particular, used in powder form. For this purpose, the solder powder can have been applied to a support layer. The support layer and the solder powder together form a ribbon. The ribbon is, in particular, adhesively bonded onto the surface of the base material 16.

[0035] The solder which has been positioned on the surface of the base material 16 is subjected to a heat treatment 12. The heat treatment takes place, for example, in a furnace. Firstly, the solder is heated to its melting point by a heating step 13. Oxygen is subsequently introduced into the molten solder by a diffusion step 14. The diffusion step 14 takes, in particular, 0.5 hours. During the diffusion step 14, an atmosphere, a temperature and a pressure which cause oxygen to diffuse into the solder are produced.

[0036] After a cooling process, the solder forms the covering layer 17 which is firmly bound to the base material 16. The region of the solder into which the oxygen has diffused forms the diffusion layer 17.

[0037] Although the invention has been illustrated and described in detail by the preferred working example, the invention is not restricted to the examples disclosed and other variations can be derived therefrom by a person skilled in the art, without going outside the scope of protection of the invention.