DE102014018693A1 - Method for producing a thermal barrier coating and thermal barrier coating produced by this method - Google Patents

Abstract

The present invention relates to a method for producing a thermal barrier coating (39, 130) on a component (10, 110), characterized by the following features: a) grinding a glass material into a first solid in the form of a powder; b) mixing the powder with at least one liquefier to form a suspension; c) processing the suspension (10, 110) by means of a high-speed flame spraying process, wherein c1) the liquid phase of the suspension (10, 110) is evaporated in the flame; c2) the glass material is melted or melted and then deposited on the component. The present invention further relates to such a thermal barrier coating (30, 130) and a piston provided with such a thermal barrier coating.

Description

The present invention relates to a method for producing a thermal barrier coating and to a thermal barrier coating produced by means of this method.

A generic thermal barrier coating, inter alia for gas turbines, is from the German patent DE 198 52 285 C1 known. This known thermal barrier coating consists of 10% by mass to 90% by mass of glass and moreover of a ceramic and / or a metal and / or a metal alloy.

The EP 1 580 296 A2 describes a porous thermal barrier coating made of a ceramic material.

The object of the present invention is to provide a method for producing a thermal barrier coating and such a thermal barrier coating, which is suitable for components for internal combustion engines, in particular pistons for internal combustion engines.

The solution consists of a process having the following features: a) grinding a glass material into a first solid in the form of a powder; b) mixing the powder with at least one liquid to form a suspension; c) processing the suspension by means of a high-speed flame spraying process, wherein c1) the liquid phase of the suspension is evaporated in the flame; c2) the glass material is melted or melted and then deposited on the component.

The present invention furthermore relates to a heat-insulating layer produced by means of the method according to the invention and to a piston having a piston bottom which is provided wholly or partly with such a thermal barrier coating.

High Velocity Oxy Flame Spraying (HVOF) or High Velocity Suspension Flame Spraying (HVSFS) in the context of the present invention is understood to mean a thermal spraying process in which continuous combustion is gaseous or liquid Fuels under oxygen supply at high pressure within a combustion chamber takes place. In general, a fuel gas-oxygen mixture or a fuel-oxygen mixture is used, wherein as the fuel gas or fuel, for example. Propane, ethene, propene, butane, acetylene, Methylacetylenpropadien, hydrogen, natural gas or diesel, N-paraffins, Purified petroleum and kerosene can be used. The pressure of the burning fuel-oxygen mixture produced in the combustion chamber and the (usually downstream) expansion nozzle produce the necessary high speed of the gas jet resulting from the combustion process. The spray material present in powder form or as a suspension is generally supplied axially in the combustion chamber or radially in the region of the expansion nozzle, so that it is accelerated to the speed required in order to achieve the desired coating.

The method according to the invention is characterized in that a solid in the form of a powder of a ground glass material is mixed with the aid of at least one liquid to form a suspension. This is processed by means of a high speed suspension flame spraying (HVSFS) process. In this case, the liquid is evaporated, and in the resulting thermal barrier coating closed pores are formed. Since the glass material itself has a low coefficient of thermal conductivity and the pores additionally have a heat-insulating effect, according to the invention a highly effective thermal barrier coating is obtained compared with the prior art.

Advantageous developments emerge from the subclaims.

The solid in the form of the pulverized powdery glass material preferably has an average particle size of 1 .mu.m to 10 .mu.m. The D10 value is in the range of 0.2 μm to 3.0 μm. The D90 value is preferably in the range of 3 μm to 20 μm. Preference is given to a D50 value of 1 μm (variant A) and a D50 value of 5 μm (variant B) in order to achieve a particularly uniform size distribution within the thermal barrier coating produced according to the invention.

Preferably, a glass material having the following composition is used (all data in% by weight): 10-50 B ₂ O ₃ , 1-10 SiO ₂ , 1-10 TiO ₂ , 10-50 ZnO, 1-10 ZrC ₂ , 1 -10 Nb ₂ O ₅ , 10-50 La ₂ O ₃ and 1-10 WO ₃ . This glass material is characterized by a particularly low coefficient of thermal conductivity. Furthermore, other borosilicate glasses and aluminosilicate glasses are suitable. For example, a glass material of the following composition may be used: (all in wt .-%): 1-10 B ₂ O ₃ , 1-10 MgO, 10-50 Al ₂ O ₃ , at least 50 SiO ₂ , 10-50 CaO, 0.1-1 Sb ₂ O ₃ , 1-10 BaO.

In particular, water or at least one organic solvent or a mixture thereof is suitable as liquid for the preparation of the suspension. Particularly suitable organic solvents are alcohols, such as, for example, ethanol and isopropanol, preferably a mixture of 60% by weight. Water and 40 wt .-% isopropanol can be used.

A further development of the method according to the invention consists in adding at least one second solid in the form of at least one pore former in step b), which in step c) is thermally decomposed to at least one gaseous product which causes pore formation. The at least one pore-forming agent is preferably selected from the following group of substances: sodium oxalate, sodium bicarbonate, sodium carbonate, azodicarboxamide. Optionally, a second pore-forming agent in the form of activated carbon or carbon black may be added.

The thermal barrier coating according to the invention preferably has a pore content of from 30% by volume to 35% by volume. This represents a particularly preferred compromise between effective thermal insulation and the mechanical stability of the thermal barrier coating according to the invention required in engine operation.

As the third solid, at least one catalyst can be admixed to the suspension, which can in particular be selected from the substance group comprising iron (III) hydroxide and silicon carbide.

The suspension particularly preferably comprises 85% by weight of plasticizer and 15% by weight of solid, in particular the solids content of at least 5% by weight (based on the total solids) of at least one pore-forming agent and at least 5% by weight. may consist of at least one catalyst.

Preferably, a coating tool is used, which performs a meandering movement with respect to a stationary component under feed. The resulting thermal barrier coating according to the invention has, in a particularly advantageous manner, a particularly uniform layer thickness. Of course, it is also possible, for example, to arrange a stationary or a linear movement-executing coating tool over a rotating component.

Preferably, a cover layer is applied to the thermal barrier coating according to the invention in order to close off any pores that may open in the thermal barrier coating and to produce a smooth surface. Such a cover layer can, for example, consist of a stabilized or partially stabilized zirconium oxide, in particular of an yttrium-stabilized zirconium oxide (YSZ).

The component to be coated may be wholly or partly provided with the thermal barrier coating applied according to the invention, wherein preferably a mask is used to cover the areas of the component that are not to be coated. The component to be coated is in particular a piston, in the piston head a combustion bowl is introduced, which has a trough bottom and a circumferential trough wall. Preferably, the trough bottom is provided with the thermal barrier coating according to the invention, wherein a mask is used, which covers the circumferential trough wall in whole or in part.

Embodiments of the present invention will be described below with reference to the accompanying drawings. In a schematic, not to scale representation:

1 a first embodiment of a provided with a thermal barrier coating according to the invention piston;

2 a further embodiment of a piston provided with a thermal barrier coating according to the invention;

3 an enlarged partial view of a thermal barrier coating according to 2 ;

4 an enlarged partial view of a piston according to 2 with an embodiment of a mask according to the invention used for the preparation of the thermal barrier coating;

5 a schematic representation of the manufacturing process for a thermal barrier coating according to the invention using the mask according to 4 ,

1 shows an example of a coated component according to the invention 10 in the form of a one-piece cooling channel piston. The component to be coated can be chosen arbitrarily, provided that it has a surface suitable for a high-speed flame spraying process (HVSFS).

The piston according to 1 has a piston head 11 with a piston bottom 12 into, into a combustion chamber 13 is introduced. The combustion bowl 13 has a well bottom in a conventional manner 14 and a circumferential trough wall 15 on which into the piston bottom 12 passes. The piston head 11 also has a lancet 16 as well as a ring lot 17 with annular grooves for receiving piston rings (not shown). The piston is at the level of the ring section 17 with a circulating cooling channel 18 Mistake. The piston also has a piston shaft in a manner known per se 21 with piston hubs 22 on, which with hub bores 23 for receiving a piston pin (not shown) are provided. The piston hubs 22 are in known manner on treads 24 connected with each other.

In the embodiment, the piston crown 12 as well as the trough bottom 14 and the hollow wall 15 the combustion bowl 13 with a thermal barrier coating according to the invention 30 Mistake. The thermal barrier coating 30 In the exemplary embodiment has a uniform thickness in the range of 150 .mu.m to 200 .mu.m. The thermal barrier coating 30 can be optional with a topcoat 31 be provided, which preferably has a layer thickness of 10 microns to 50 microns. The thermal barrier coating 30 or the cover layer 31 are applied by means of a high speed flame spraying method ('HVSFS').

The 2 to 4 show a further embodiment of a coated with a thermal barrier coating component according to the invention 110 , here a piston. The piston according to the 2 to 4 corresponds to the in 1 represented piston, so that identical structural features are provided with the same reference numerals and to the description 1 is referenced. Unlike the in 1 illustrated embodiment, only the trough bottom 14 the combustion bowl 13 with a thermal barrier coating 130 Mistake. The thermal barrier coating 130 In the exemplary embodiment has a uniform thickness in the range of 150 .mu.m to 200 .mu.m. Like from the 3 and 4 shows, the thermal barrier coating 130 in the transition area between trough bottom 14 and hollow wall 15 an outlet zone 132 on, which extends in the embodiment about 1 mm. In the area of the outlet zone 132 reduces the thickness of the thermal barrier coating 130 evenly, starting from a starting point S in the direction of the trough wall 15 to an end point E with the layer thickness zero.

From the 4 and 5 also shows that for applying the thermal barrier coating 130 a mask 140 is used. The mask 140 covers the piston crown 12 completely except for the trough bottom 14 the combustion bowl. The mask 140 is in the embodiment with a circumferential aperture 141 provided, which the trough wall 15 completely or partially covers. It has been found that with complete coverage of the trough wall 15 , In the exemplary embodiment with an aperture about 10 mm long 141 , the thermal barrier coating 130 has a particularly uniform thickness.

In 5 schematically shows that to carry out the high-speed flame spraying method, a burner 60 is used. The burner 60 is movably arranged while the component 10 . 110 opposite the burner 60 is arranged fixed. The burner 60 becomes meandering over the component 10 . 110 or the mask 140 moved, with a thermal barrier coating 30 . 130 produced with a particularly uniform thickness. This method has the further advantage that the mask 140 can have any shape, so that the non-coated area of the component 110 can be covered in a particularly simple manner.

An exemplary embodiment of a production method for a thermal barrier coating according to the invention is described below. First, an emulsion of 85% by weight of a mixture of 60 parts by weight of water and 40 parts by weight of isopropanol and 15% by weight of solid is prepared. Alternatively, pure water or pure isopropanol can be used to prepare the emulsion.

The solid may consist exclusively of a glass material with a low coefficient of thermal conductivity in the form of a finely ground powder. A particularly suitable glass material has, for example, the following composition (all data in% by weight):
10-50 B ₂ O ₃
1-10 SiO ₂
1-10 TiO ₂
10-50 ZnO
1-10 ZrC ₂
1-10 Nb ₂ O ₅
10-50 La ₂ O ₃
1-10 WO ₃

The average particle size of the powder after the Gaussian distribution is preferably 1 μm to 10 μm.

Preferably, at least one additional solid is used for the preparation of the suspension. Particular preference is given to adding at least one pore former, in particular selected from the group comprising sodium oxalate, sodium bicarbonate, sodium carbonate and azodicarboximide. Optionally, an additional pore-forming agent in the form of activated carbon or carbon black may be added. Further, if necessary, a catalyst, for example. Iron (III) hydroxide or silicon carbide may be added.

The proportions of the additives are preferably (all data in% by weight based on the total solids present in the finished suspension):
From 5% to 10% by weight of sodium oxalate;
From 10% to 50% by weight of sodium carbonate;
5% by weight azodicarboxamide;
From 5% to 10% by weight of activated carbon;
10% by weight of iron (III) hydroxide;
10 wt .-% to 15 wt .-% silicon carbide.

The surface of the component to be coated 10 . 110 is first roughened, preferably irradiated with corundum particles and then cleaned. The surface to be coated should have a roughness Ra of 0.6 μm to 5.0 μm.

The suspension is then applied to the component by means of a high-speed suspension flame spraying (HVSFS) process 10 . 110 plotted. In this case, propane or ethene is preferably used as fuel gas. The fuel gas amount is preferably in the range of 35 liters to 130 liters per minute. The amount of oxygen is chosen in the range of 180 to 400 liters per minute. The coating unit used is a TopGun burner. The suspension is injected into the flame. This can be done both inside the burner and externally. The distance between the burner and the component to be coated is in the range of 40 to 250 mm

The thermal conductivity of the thermal barrier coating according to the invention 30 . 130 was measured at 0.30 and 0.70 W / mK whereas prior art thermal barrier coatings have values of at least 1.0 to 1.6 W / mK.

The total porosity of the thermal barrier coating according to the invention 30 . 130 is 30 vol .-% to 35 vol .-% based on the total volume of the thermal barrier coating 30 . 130 , The maximum open porosity of the thermal barrier coating according to the invention should not exceed 10% to 15%, based on the total pore content. The mean pore size after the Gaussian distribution should be 2 μm to 10 μm. In the exemplary embodiment, these values were determined in a manner known per se by means of a gray scale analysis on light microscopic polished transverse sections.

The thermal barrier coating according to the invention 30 can with a topcoat 31 , in particular from yttrium-stabilized zirconia are provided in order to obtain a smooth surface.

Typical process parameters when using a TopGun SS HVSFS burner (GTV Verschleißschutz GmbH, Luckenbach, Germany) are, for example:
Fuel gas: ethene Nl / min: 100-130)
Oxygen Nl / min: 250-350
Spray distance [mm]: 120.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19852285 C1 [0002]
• EP 1580296 A2 [0003]

Claims (23)

Method for producing a thermal barrier coating ( 30 . 130 ) on a component ( 10 . 110 ), characterized by the following features: a) grinding a glass material into a first solid in the form of a powder; b) mixing the powder with at least one liquid to form a suspension; c) processing the suspension ( 10 . 110 ) by means of a high-speed flame spraying process, wherein c1) the liquid phase of the suspension ( 10 . 110 ) is evaporated in the flame; c2) the glass material is melted or melted and then deposited on the component. A method according to claim 1, characterized in that in step a) an average particle size of the powder of 1 .mu.m to 10 .mu.m is obtained. A method according to claim 1, characterized in that in step a) a glass material in the form of an aluminosilicate glass and / or a borosilicate glass is used A method according to claim 1, characterized in that in step a) a glass material having the following composition is used (all data in wt .-%): 10-50 B ₂ O ₃ 1-10 SiO ₂ 1-10 TiO ₂ 10-50 ZnO 1-10 ZrC ₂ 1-10 Nb ₂ O ₅ 10-50 La ₂ O ₃ 1-10 WO ₃ A method according to claim 1, characterized in that in step a) a glass material having the following composition is used (all data in wt .-%): 1-10 B ₂ O ₃ 1-10 MgO 10-50 Al ₂ O ₃ min. 50 SiO ₂ 10-50 CaO 0.1-1 Sb ₂ O ₃ 1-10 BaO A method according to claim 1, characterized in that in step b) is used as the condenser water or at least one organic solvent or a mixture of water and / or at least one organic solvent. A method according to claim 6, characterized in that as at least one organic solvent, an alcohol is used. A method according to claim 7, characterized in that a mixture of 60 wt .-% water and 40 wt .-% isopropanol is used. A method according to claim 1, characterized in that in step b) of the suspension at least a second solid in the form of at least one pore-forming agent is added, which is thermally decomposed in step c) to at least one gaseous product. A method according to claim 9, characterized in that in step b) the at least one pore-forming agent is selected from the following group of substances: sodium oxalate; sodium hydrogencarbonate; Sodium; Azodicarboxamide. A method according to claim 9, characterized in that in step b) an additional pore-forming agent in the form of activated carbon or carbon black is added. A method according to claim 1, characterized in that in step b) as a third solid at least one catalyst is added. A method according to claim 12, characterized in that the at least one catalyst is selected from the following group of substances: iron (III) hydroxide, silicon carbide. A method according to claim 1, characterized in that in step b) a suspension of 85 wt .-% liquefier and 15 wt .-% solid is prepared. A method according to claim 9, characterized in that in step b) a solid mixture of a powder of crushed glass material with a proportion of at least 5 wt .-% of at least one pore former and a proportion of at least 5 wt .-% of at least one catalyst is used. A method according to claim 1, characterized in that in step c) the component ( 110 ) only partially coated and a mask ( 140 ) to cover the non-coating area of the component ( 110 ) is used. A method according to claim 16, characterized in that as a component ( 10 . 110 ) a piston with a in the piston head ( 112 ) introduced combustion body ( 113 ) with a trough bottom ( 114 ) and a circumferential trough wall ( 115 ) used and that a mask ( 140 ) is used, which the trough wall ( 115 ) at least partially covers. Method according to claim 1, characterized in that a coating tool ( 60 ), which is opposite a stationary component ( 10 . 110 ) performs a meandering movement under feed. A method according to claim 1, characterized in that on the thermal barrier coating ( 30 ) a cover layer ( 31 ) is applied. A method according to claim 19, characterized in that as material for the cover layer ( 31 ) a stabilized or partially stabilized zirconium oxide is used. A method according to claim 20, characterized in that an yttrium-stabilized zirconium oxide is used. Thermal barrier coating ( 30 . 130 ), producible by means of a method according to one of the claims 1 to 21. Piston for an internal combustion engine with a piston head ( 12 . 112 ), characterized in that the piston head ( 12 . 112 ) in whole or in part with a thermal barrier coating ( 30 . 130 ) is provided according to claim 22.

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