EP2069080B1

EP2069080B1 - Method for making heat barrier coatings

Info

Publication number: EP2069080B1
Application number: EP07820675A
Authority: EP
Inventors: Nelso Antolotti; Andrea Scrivani; Gabriele Rizzi
Original assignee: Turbocoating SpA
Current assignee: Turbocoating SpA
Priority date: 2006-10-05
Filing date: 2007-09-28
Publication date: 2010-11-03
Anticipated expiration: 2027-09-28
Also published as: ATE486975T1; PL2069080T3; DE602007010327D1; EP2069080A1; ES2355859T3; ITPR20060087A1; WO2008040678A1

Abstract

A method for making a thermal barrier coating (11), such as for gas turbine components (5) and mainly heat shields, combustion chambers or turbine wall covering panels, said thermal barrier coating (11 ) resulting from successive deposition of various numbers of layers (13, 15) which join together to form the coating (11 ), which coating (11 ) is obtained by any Thermal Spray process, including the steps of laying at least three coating layers (13), each of said layers being deposited at a different angle (t, ß, a) of the spray torch (33); said angles (t, ß, a) being defined relative to the surface to be sprayed and covering a range from 30° to 150° with respect to the tangent to the surface (3) of the component (5) to be coated. Protection also extends to the component so coated and the covering structure.

Description

The present invention relates to the development of a thick TBC coating, for application on gas turbine components, mainly on heat shields, combustion chambers and turbine wall covering panels, and the method for making it.
Nevertheless, protection is not only requested hereby for such application, but for any TBC deposition application, such as in the automotive industry (combustion engines).
The present invention relates to coatings, typically of ceramic material, deposited on a previously deposited layer used as a bond coat, said layers being obtained by Thermal Spray processes, such as:

➢ Air Plasma Spray,
➢ Vacuum Plasma Spray
➢ High Velocity Oxygen Fuel

By decreasing the operating temperature of the components coated thereby, these coatings improve corrosion and heat-oxidation resistance of components, such as gas turbines and aeronautical engines.
US 5 897 921 discloses a method for making thick thermal barrier coatings according to the preamble of claim 1.
The above mentioned deposits may be, for instance, of a metal material obtained from a M-CrAlY alloy (where M means Ni,Co,Fe or a combination thereof) followed by yttria partially stabilized zirconia (YPSZ) coatings.
The process or method of deposition of thermal barrier coatings (TBC) divides ceramic coatings according to their thickness: thin TBCs are defined as coatings of a thickness from 200 to 800 µm, whereas thick TBCs are ceramic coatings of a thickness greater than 1 mm, generally in a range from 1,2 to 3 mm.
Particularly, the present invention relates to the particular method for depositing thick coatings, i.e. the particular handling/pivoting of the torch relative to the surface on which the coating has to be deposited, to obtain an improved coating microstructure as compared with currently available ones.
The present invention applies to both thick and thin coatings.
Furthermore, the structure so obtained improves resistance of the coating to thermal cycling fatigue (TFC), and thereby increases the performances of the components coated thereby (reduced operating temperatures and extended life of the component).
The principle of thermal spray technologies consists in supplying energy to the material to be deposited until it melts, and transfer it to the substrate to be coated. Energy may be supplied to the material to be deposited from various sources: energy deriving from combustion between oxygen and a fuel, either in gas form (propane, acetylene, hydrogen) or in liquid form (kerosene) or deriving from recombination of ions in a plasma.
Thermal spray technologies include:

Combustion Flame Spray,
Arc Flame Spray,
Plasma Spray,
HVOF (High Velocity Oxygen Fuel).

The coating results from successive deposition of various numbers of layers which join together to form the coating (passes).
An important variable influencing the structure of the coating so obtained and consequently its performances is the tilt of the spray torch relative to the surface to be coated.
This invention provides a combination of successive tilts for the various passes that leads to an ideal coating structure: fine porosity with small pores evenly diffused over the coating structure.
The above objects and advantages are achieved by the method for making thermal barrier coatings according to this invention, which is characterized as set out in the annexed claims.
These and other features will be more apparent from the following description of a few embodiments, which are shown by way of example and without limitation in the accompanying drawings, in which:

Figure 1 shows a component to be coated according to the present method, namely a part of combustion chamber
Figure 2 shows the structure of a thermal barrier
Figure 3 is an exemplary micrograph of the thermal barrier obtained by the present method, showing that porosity is variable
Figure 4 is a schematic view of the system for thermal spray deposition of the coating, showing the changing angle of incidence of the torch relative to the surface to be coated.

Particularly referring to Figure 1, numeral 5 designates a component to be coated by TBC as described above; the component 5 may be part of a gas or aeronautical turbine.
In this case, the surface 3 is the one to be coated with the thick TBC.
Particularly referring to Figure 2, a thermal barrier coating system 11 according to the inventive specifications is shown, which barrier 11 is laid over the surface 3 of the component 5.
The thermal barrier coating system (TBC) 11 has a substrate 15 acting as a binder and/or a plurality of other layers designed for other possible purposes, such as: corrosion resistance, adhesion, diffusion barrier.
The substrate 15 is preferably deposited on the surface 3 of the component 5 using a conventional well-known process.
Then, the coating 15 is deposited on said substrate 15 to act as a thermal battier, using the method as described below.
Particularly referring to Figure 3, a possible microstructure of the thick TBC 13 is shown, as obtained by the coating method of the invention.
This microstructure has pores 23 of varying sizes according to the deposition technologies and the parameters being used.
Such porosities are characterized by a highly homogeneous arrangement, as ensured by the inventive deposition system.
The dispersion of the pores 21 and 23 is shown, whose number changes depending on the energy supplied during deposition. Therefore, the structure exhibits a variable porosity with fine pores evenly dispersed in the body of the coating obtained by the method of the present invention.
High ceramic cohesion areas 21 are also visible.
Referring to Figure 4, a schematic view of one of the combinations of the method for depositing the coating 13 is shown, which is carried out through successive passes at different angles of incidence of the torch 33.
During the tests, a cylindrical component to be coated was pivoted about its own axis and the torch was displaced over a rectilinear path along a straight line parallel to the axis of rotation of the component to be coated. The torch tilt relative to an ideal surface tangent to the one to be coated may be described as follows: the torch 33 carries out a first deposition step at a certain angle α relative to the surface 3 to be coated; then, the torch 33 is pivoted to such a position as to form a second angle of incidence β, other than α, to carry out another deposition step on the coating that has just been laid at a tilt angle α; finally, the torch 33 is positioned/pivoted to form a third angle of incidence τ and a further deposition step is carried out.
The tests used the following angles τ, β and α

first pass at 45° ± 15°, [τ]
second pass at 90° ± 15°, [β]
third pass at 135° ± 15°, [α]

This 3-pass cycle with 3 tilts can be repeated a number of times until reaching the desired thickness.
While the example relates to a 3-pass cycle with 3 tilts, a different cycle may be provided.
A constant tilt pass may be repeated n times, which means that the cycle may include:

n passes at tilt angle α
n passes at tilt angle β
n passes at tilt angle τ

Cycles like these have been tested.
The above cycle may be repeated a desired number of times.
The succession of the various passes at different tilts provides a coating microstructure composed of fine pores evenly dispersed in the coating structure.
The number of pores increases with the energy used during the deposition.
The scope of the present invention encompasses both the mechanical component 1 (such as the gas or aeronautical turbine) having thick TBC coatings (typically of thicknesses from 0.8 to 3 mm) of ceramic material, such as yttrium oxide stabilized zirconia, obtained by a Thermal Spray process, deposited on the bond coat surface of the component, and the method for making it, in which the thermal coating 13 is obtained with three or more different tilts of the deposition torch 22, at different and well-defined angles relative to the surface to be sprayed.
These angles τ, β and α are preferably as follows:

in a first pass 45° ± 15°, [τ]
in a second pass 90° ± 15°, [β]
in a third pass 135° ± 15°, [α]

Nevertheless, the order in which the torch 33 is tilted to form the various incidence angles τ, β and α for deposition of the coating within each cycle can change and different combinations from the above may be provided.
While reference has been specially made herein to three precise angles of incidence, the present method allows the head 33 to operate at angles in a range from 30° to 150° relative to the tangent to the surface 3 to be coated.
In the above coating cycle; the torch 33 is tilted at least at three different angles, by carrying out a deposition step for each of them, a required number of passes being performed for each angle.
The scope of the present invention obviously encompasses all the coatings obtained with the above method, for any substrate and component (not necessarily a part of a gas turbine or an aeronautical engine) coated with the TBC.
The coating 13 may be composed of zirconia, possibly stabilized with other materials (e.g. ceria, dysprosia, ytterbia, Ca or Mg oxide) or other ceramic materials (alumina, titania, spinels, perovskite, etc.).
The scope of the invention further encompasses the coating itself, obtained using the method described herein.
The invention as described herein provides an essential contribution to the thermal cycling fatigue resistance of TBC coatings, particularly thanks to the structure of the coating.
In ordinary industrial practice, the higher the porosity, the higher the thermal cycling fatigue resistance. Thanks to the present invention, thermal cycling fatigue resistance is obtained regardless of the porosity (from 11% to 28% in the tests).
By the present invention, four different porosity levels were obtained using the same structure with fine pores evenly dispersed over the coating body.
These structures are also within the scope of the invention, as they are obtained by the same method.
It shall be finally noted that the above deposition method applies to deposition of thermal barriers and of ceramic materials in general, regardless of the parameters being used to supply enough energy to the powder for such powder to be melted.

Claims

A method for making thick thermal barrier coatings (11), for use on gas turbine components (5) and mainly heat shields, combustion chambers or turbine wall covering panels, said thermal barrier coating (11) resulting from successive deposition of various numbers of layers (13, 15) which join together to form the coating (11), which coating (11) is obtained by any Thermal Spray process, characterized in that it includes the steps of laying at least three coating layers (13), each of said layers being deposited at a different angle (τ, β, α) of a spray torch (33); said angles (τ, β, α) being defined relative to the surface to be sprayed and covering a range from 30° to 150° with respect to the tangent to the surface (3) of the component (5) to be coated; the structure of said coating layers (13) exhibits a variable porosity with fine pores evenly dispersed in the body of the coating obtained.
A method as claimed in claim 1, characterized in that said angles (τ, β and α) are preferably 45° ± 15°, 90° ± 15° and 135° ± 15°; the order in which the torch (33) is tilted to form said angles (τ, β and α) of incidence can change to any combination whatever.
A method as claimed in claim 1, characterized in that the torch (33) performs one or more coating passes for each of said at least three angles.
A method as claimed in claim 1, characterized in that it can be repeated an arbitrary number of times.