EP3102360A1

EP3102360A1 - Method for producing a thermal barrier coating on a component

Info

Publication number: EP3102360A1
Application number: EP15741839.3A
Authority: EP
Inventors: Jens Dietrich; Jan Münzer
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2014-04-25
Filing date: 2015-03-26
Publication date: 2016-12-14
Also published as: WO2015161981A1; DE102014207789A1; US20170216969A1

Abstract

The invention relates to a method for producing a thermal barrier coating on a component, more particularly on a turbine component and preferably on a turbine blade, wherein the component is provided with the thermal barrier coating and structures are then created in the outer surface of the thermal barrier coating using a laser ablation process so as to segment the surface of the thermal barrier coating, the structures being created in the surface of the thermal barrier coating by an ultrashort pulse laser, more particularly a femtosecond laser.

Description

Process for producing a thermal barrier coating on a

component

The present invention relates to a method for the manufacture ^¬ development a thermal barrier coating on a component, in particular a turbine component, and preferably at a ^turbine blade, is provided in which the component with the thermal barrier coating and then into the outer surface of the thermal barrier coating by a laser removal process structures are introduced to segment the surface of the thermal barrier coating.

Turbomachines, in particular gas turbine plants, comprise a gas turbine in which a hot gas, which was previously compressed in a compressor and heated in a combustion chamber, is released for work recovery. For high mass flows of the hot gas and thus high power ranges gas turbines are designed in the Axialbauweise, wherein the gas turbine is formed by a plurality of successively in the flow direction blade rings. The blade rings have circumferentially disposed blades and vanes with the blades secured to a rotor and the vanes secured to the housing of the gas turbine.

It is known that the thermodynamic efficiency of turbine systems and in particular gas turbine systems increases with increasing inlet temperature of the hot gas into the gas turbine. However, the height of the inlet temperature are sets limits ^¬ ge by the thermal load of the turbine blades. Accordingly, an objective is to provide Turbi ^¬ nenschaufeln, which have sufficient for the operation of the guest Rubine mechanical strength even at high thermal loads.

Such turbine blades consist of a turbine blade body, which is made of a superalloy, in particular a nickel-based or cobalt-based superalloy. Such a superalloy is characterized by high Festig ^¬ ability and low tendency to fatigue and high mechanical strength even at high temperatures, especially at temperatures between 800 ° C and 1200 ° C. The structure of the superalloy may be microcrystalline, columnar in the form of a bundle of parallel crystallites or monocrystalline.

The superalloy is designed in view of its relevant mechanical properties, but not in terms of its behavior by the load with the hot gases to which the turbine blade is exposed during operation. Inso ^¬ away of the turbine blade body is provided with a thermal barrier coating system (termal barrier coating, TBC) is provided, which measures will be seen on the outer surface of the turbine blade body ^¬, to protect the turbine blade body to excessive thermal stress and corrosion and oxidation by constituents of flowing around the hot gas. Usually a sol ^¬ ches thermal barrier coating system comprises a coating applied to the turbine blade body metallic adhesion layer and provided thereon a ceramic thermal barrier coating. The adhesive layer consists of a resistant to corrosion and Oxi ^¬-oxidation at high temperature alloy, especially an alloy of the type MCrAlY. Herein M stands for one or more elements Fe, Ni or Co and Y for yttrium and / or one or more elements of the rare earths. Such an adhesive layer has the advantage that it continues to provide protection against corrosion and oxidation in case of failure of the ceramic thermal barrier coating.

The thermal barrier coating usually consists of a stabili ^¬ overbased or partially stabilized zirconium oxide, which by means of physical vapor deposition with electron beam (elec- tron beam physical vapor deposition, EB-PVD) is applied. Alternatively, the thermal barrier coating may be applied to the turbine blade body by atmo ^¬ spherical plasma spraying (air-plasma spraying, APS). To further increase the allowable turbine inlet temperature turbine blades are cooled during operation of the gas turbine. Here, film cooling is a very effective and reliable method for cooling highly stressed turbine blades. Cooling air is tapped from the compressor and fed into the turbine blades provided with internal coolant fluid channels. After convective cooling of the material from the inside of the turbine blades, the air is directed through the cooling fluid passages to the outer surface of the turbine blade. There it forms a film that flows along the outer surface of the turbine blade and cools it, while protecting it from the hot flow. The use of thermal barrier coating systems with a ceramic thermal barrier coating is subject to the problem that the ceramic material is brittle. Due to the brittleness, it can never be completely ruled out that cracks in the thermal barrier coating system and spalling of the ceramic occur during operation. Under certain circumstances, the metallic

Pad of the ceramic exposed and the hot gas flow out ^¬ sets. Although any existing metalli ^¬ specific adhesive layer provides some protection against oxidation and corrosion, particularly when the adhesive layer consists of an MCrAlY alloy or an aluminide. The elimination of the thermal insulation, however, the adhesive layer is exposed to extreme thermal stress, so that can be expected with a prompt failure of the adhesive layer.

In order to counter this problem it is known, for example from DE 602 08 274 T2, to produce a thermal barrier coating with a segmentation of the surface in order to improve the properties of the thermal barrier coating that are associated with the thermal shock resistance.

Specifically, structures are engraved in the outer surface of a thermal barrier coating by means of a YAG laser in order to To form cracks in the surface, which counteract undesirable cracking due to stresses in the thermal barrier coating. It is also known from US 4,377,371 A, in a by

Plasma spraying applied ceramic layer to deliberately create cracks. The outer surface of the ceramic layer is partially aufgeschmol ^¬ zen by means of a continuous wave C02 laser. As the molten regions cool and resolidify, a variety of benign microcracks of the ceramic layer are formed due to shrinkage during consolidation of the molten regions.

It has been shown that the introduction of engraving-like structures into the surface of a thermal barrier coating can extend their service life. The efforts are, however, to further increase the life of thermal barrier coatings. Object of the present invention is therefore to provide a method for producing a thermal barrier coating, which has an increased life.

This object is achieved in a method according to the present invention in that the structures are introduced into the surface of the thermal barrier coating by an ultrashort pulse laser, in particular a femtosecond laser.

According to the invention ultrashort pulse lasers are used to introduce the engraving-like structures in the surface of the thermal barrier coating. Ultrashort pulse lasers are laser beam sources which emit pulsed laser light with pulse ^duration in the range of picoseconds and femtoseconds. These include picosecond lasers and femtosecond lasers, which are usually mode-locked

Laser acts. Attosecond lasers (1000 attoseconds = 1 femtosecond) have already been developed in research. According to current usage, these also count if to the ultrashort pulse lasers. Ultrashort pulse lasers operate with lower pulse energy compared to conventional CO ₂ or YAG lasers, so that the thermal penetration depth is comparatively low. The pulse durations are below the relaxation time of the ceramic material of the thermal insulation ^¬ layer. As a result, the ceramic material is not melted in the production of engraving-like structures as in the use of CO ₂ - or YAG lasers, but there is a cold, melting-free removal takes place. It has been shown that as a result, a formation of stress in the surface of the thermal barrier coating can be avoided or at least reduced with the result that increases the life of the thermal barrier coating. The use of ultrashort pulse lasers has the further advantage that the removal per carry is only a few ^micrometers . Desired engraving depths can therefore be produced with high precision. Similarly, structures can be introduced in the surface of the thermal barrier coating at least partially a depth of at least 300 .mu.m, in particular ^¬ sondere least 500 ym, preferably over 1000 ym have ^¬.

According to one embodiment of the invention, it is provided that the ultrashort pulse laser has an optical system which includes a galvo or microscanner in order to deflect the laser beam generated in the desired direction. In this way, high feed rates in the range of a few millimeters / second to more than 1000 millimeters / second can be generated.

In an embodiment of the invention, it is provided that for producing a structure / structure line of predetermined width, the laser beam generated by the ultrashort pulse laser is guided several times along a structure line to be generated, with tracks staggered in the width direction of the structure being generated. In contrast to the prior art, in which the engraving geometry by widening the focus of the laser beam is achieved, in this embodiment, a track offset is used for the production of an engraving. An engraving is thus made by several, parallel staggered tracks. Another possibility for adjusting the track width and / or the track geometry is the method of the wobble, in which the feed movement of the laser beam is superimposed on a transverse thereto directed deflection movement. In a known manner, continuous or discontinuous struc ^¬ can ren / structure line are brought a ^¬ in the surface of the thermal barrier coating by the inventive method. In this case, the discontinuous structures may comprise blind-hole microbores, which are introduced into the surface of the heat ^¬ layer with a defined distance, diameter and depth. Also, the discontinuous ^¬ union structures V- or U-shaped structures can include.

By such discontinuous points of intersection engravings engravings and the associated undesirable increase in the engraving depth ver ^¬ can be avoided at maximum spatial coverage. In principle, however, it is also possible to introduce intersecting structures into the surface of the thermal barrier coating. The engraved tracks or engraving lines can be U-shaped in cross section. Alternatively, it is also possible to produce cross-sectionally V-shaped tracks. These can be produced with high precision and with a comparatively high depth by the low volume removal that takes place during processing by an ultrashort pulse laser.

In the drawing, embodiments of engraving-like structures are shown, which can be produced by the inventive method, ie by laser ablation using ultrashort pulse laser. It shows

Figure 1 shows a structure for segmentation of the surface

a thermal barrier coating with continuous structure or engraving lines,

2 shows an embodiment of a structure with continu ^¬ ous intersecting engraved lines, Figure 3 shows an embodiment of a structure for segmenting the surface of a thermal barrier coating having a plurality of discontinuous engraved lines, one embodiment of a structure with bag ^¬ holes for generating a Kunstporosität,

Figure 5 shows an embodiment of a structure for segmenting the surface of a thermal barrier coating, which is produced by wobble, and

FIG. 6 shows a schematic representation in which the scanning movement of a laser radiation for producing a wide engraving line is shown.

1 shows an example of a structure is presented to the surface of a thermal barrier coating to segmen ^¬ animals. The structure consists here of several kontinuierli chen structure or engraving lines 1, which extend parallel zuein other and straight. The engraving lines 1 can also be formed, for example, serpentine. It is essential that the engraving lines 1 do not intersect. In the embodiment of Figure 2 are in addition to the paral ^¬ lel each other running engraving lines 1 of the embodiment shown in Figure 1 oriented transversely thereto, mutually parallel engraving lines 2 are provided, wherein Forming of crossing points a grid-like engraving line structure is generated.

In the embodiment of Figure 3, a plurality of Z-like engraving lines 3 are provided, which are arranged distributed along the surface of a thermal barrier coating, without cutting. The Z-shaped engraving lines 3 are parallel to each other, but positioned offset in the longitudinal and transverse directions against each other. The arrangement is made such that the extension regions of adjacent Z-förmi ^¬ gene engraving lines 3 overlap.

In the exemplary embodiment illustrated in FIG. 4, structures in the form of blind-hole bores 5 for producing an artificial porosity are provided in the surface of a thermal barrier coating 4, wherein the blind bores have a defined depth T and a defined diameter D.

In the exemplary embodiment illustrated in FIG. 5, it is shown that engraving lines are used to produce a desired

Track width and geometry can be generated by Wobbein. Here ^¬ at the advance movement, which is indicated by an arrow f, is a transversely directed to deflection movement, which is indicated by a double arrow A superimposed. The deflection movement A, and possibly also the feed motion f is generated by a galvo or micro scanner wel ^¬ cher deflects the laser beam generated by an ultrashort pulse laser accordingly. Finally, FIG. 6 shows how, as an alternative to the wobble, an engraving line 7 with a large width can be produced. Here, a laser beam L is traversed a plurality of times along the engraving line to be generated, wherein in the width direction of the engraving line 7 staggered tracks are generated. For this purpose, the laser beam L is deflected by a suitable Galvo or microscanner accordingly, as indicated by an arrow S. Although the invention in detail by the preferred embodiment has been illustrated and described in detail, as not ^¬ limited by the disclosed examples is the invention, and other variations can be derived therefrom by the skilled artisan without departing from the scope of the invention.

Claims

claims

1. A method for producing a thermal barrier coating on a component,

in particular on a turbine component and preferably on a turbine blade,

in which the component is provided with the thermal barrier coating and subsequently structures are introduced into the outer surface of the thermal barrier coating by a laser ablation process in order to segment the surface of the thermal barrier coating,

characterized in that

the structures are introduced into the surface of the thermal barrier coating by an ultrashort pulse laser, in particular a femtosecond laser.

2. The method according to claim 1,

characterized in that

the ultrashort pulse laser has an optic which has a

Galvo or microscanner includes.

3. The method according to claim 1 or 2,

characterized in that

for the production of structures the method of the wobble is used, in which the advancing movement of the

Laser beam is superimposed on a transversely directed movement.

4. Method according to one of the preceding claims,

characterized in that

for producing a structure of predetermined width of the laser beam generated by the ultrashort pulse laser is performed several times along a structure line to be generated,

wherein tracks offset from one another in the width direction of the structure are generated.

5. Method according to one of the preceding claims,

characterized in that

several continuous structures are introduced into the surface of the thermal barrier coating.

6. The method according to any one of the preceding claims,

characterized in that

discontinuous structures are introduced into the surface of the heat insulating layer ^¬.

7. The method according to claim 6,

characterized in that

the discontinuous structures include blind hole microbores, which are introduced with a defined distance, diameter and depth in the surface of the thermal barrier coating.

8. The method according to claim 6,

characterized in that

the discontinuous structures comprise V- or U-shaped structures.

9. Method according to one of the preceding claims,

characterized in that

intersecting structures are introduced into the surface of the heat insulating layer ^¬.

10. The method according to any one of the preceding claims,

characterized in that

Structures in the surface of the thermal barrier coating ^¬ be introduced, which at least partially have a depth of at least 300 ym, in particular at least 500 ym and preferably ^¬ over 1000 ym.