SE525925C2 - Ceramic thermal barrier coating for blades of gas turbine engine, has inner thermal barrier coating layer with different microstructure than outer thermal barrier coating layer - Google Patents

Abstract

A thermal barrier coating (TBC) layer (1) is deposited directly or through an intermediate bond coating (3), with respect to a metallic substrate (2). The TBC layer has an inner TBC layer (4) with a different microstructure than the outer TBC layer (5), attached directly to the substrate or to the intermediate bond coating. Independent claims are also included for the following: (1) coated metallic substrate; and (2) ceramic thermal barrier coating applying method.

Description

H 20 25 30 35 The TBC coating should have as low a thermal conductivity as possible while exhibiting sufficient thermomechanical properties, such as heat shock resistance and cycling strength, and also be thin to save weight and space.

OBJECT OF THE INVENTION An object of the present invention is to provide a method for applying such a coating which results in a coating which combines the properties of low thermal conductivity, sufficiently mechanical. strength and low weight.

The method of application or deposition of such a coating must be uncomplicated, easy to repeat and promote efficient production of coated substrates on an industrial scale (not only on a laboratory scale).

The resulting heat barrier coating should be suitable as a temperature insulating material on metallic structural elements operating in demanding heat conditions, typically a metal structural element in gas turbine engines, such as a turbine blade or a combustion chamber.

BRIEF DESCRIPTION OF THE INVENTION The object of the invention is achieved by means of the initially defined process, characterized in that the powder particles used for the production of the first TBC layer have a lower porosity than the powder particles used for the subsequent production of the the second TBC layer on the coated substrate, and that the first TBC layer has a different microstructure than the second, outer TBC layer. According to a preferred embodiment of the invention, the powder particles used for the application of the first TBC layer have a densely sintered structure. In order to achieve such a structure, the process according to the invention preferably comprises a step which comprises sintering agglomerates of powder grains in order to form said powder particles.

Preferably, the powder particles used for the application of the second TBC layer have a porous structure.

It has been found advantageous if each powder particle comprises an agglomerate of powder grains surrounded by a shell or a coating of molten powder material. Such a microstructure can be achieved by the method including a step involving HOSP treatment of powder grain agglomerate in order to form said powder particles.

The agglomerates of powder grains which are either sintered or HOSP-treated are normally prepared by a process in which a batch of powder, with a grain size of, for example, 0.5-5 micrometers, preferably 1-2 micrometers, is introduced into a liquid mixture containing a binder, to then be allowed to dry under such conditions that agglomerates with a typical diameter of 10-150 micrometers are formed when the liquid is eliminated.

According to a preferred embodiment, the different microstructure includes a different proportion, distribution or orientation of pores in the first layer compared to the second layer. Most preferably, the first layer has less porosity, i.e. a smaller proportion of pores, than the second layer. The second layer has a lower thermal conductivity than the first layer, the lower thermal conductivity being due to the difference in microstructure, while the first layer has a higher strength than the second layer, the higher strength being due to the difference in micro - structure. The task of the first layer is to give the ceramic TBC coating sufficient mechanical strength »and adhesion to the underlying material. Due to its increased porosity, the second layer itself does not make a sufficient contribution to the mechanical strength of the TBC coating. On the other hand, thanks to its increased porosity, the second layer guarantees a very low heat conduction. Preferably, the second TBC layer defines an outer layer that is directly exposed to the environment.

According to a preferred embodiment of the invention, the first and second layers have the same chemical composition.

By "same composition" is meant essentially the same main components or elements, e.g. zirconia or dysprosium oxide. The exact proportions of the elements in the TBC layers may differ between the first and second layers, but preferably the proportions are also the same for the two layers.

Preferably, the TBC coating comprises stabilized zirconia, present as ZrO 2, normally tetragonal or cubic stabilized zirconia. The stabilization of zirconia can be achieved by any stabilizer well known in the art, such as any metal oxide selected from the group consisting of erbium oxide, neodymium oxide, gadolinium oxide, yttria, calcium oxide, magnesium oxide, indium oxide, scandium oxide and mixtures. of these.

The TBC composition may also comprise any metal oxide containing a quadrivalent metal ion selected from the group consisting of hafnium dioxide, cerium dioxide, uranium dioxide and mixtures thereof.

The TBC composition may also comprise any metal oxide selected from the group consisting of nickel oxide, cobalt oxide or chromium oxide.

Preferably, however, the zirconia is stabilized by dysprosium oxide, DyO2. Typically, the proportion of -dysprosium oxide is between 2 and 30% by weight, preferably between 10 and 20% by weight. 10 15 20 25 30 35 r 'n .ff (1 fw w' v ._ k) f i .. k) 5 The thickness of the second layer should be greater than that of the first layer. The thickness of the first layer should be 10-100 micrometers, preferably 40-75 micrometers.

It will be appreciated that a bonding coating may be located between the metal substrate and the TBC coating. Such a bonding coating may comprise a metal oxide layer, preferably alumina, on the metal substrate. The binder coating may also comprise an aluminide, a platinum aluminide, an MCrAlY alloy or any other aluminum-containing alloy coating on the metal substrate, and optionally a metal oxide layer, preferably alumina, deposited thereon.

Typically, the metal substrate is a nickel superalloy or a cobalt superalloy.

Further features and advantages of the present invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the drawings, in which: Fig. 1 is a schematic cross-section, on an enlarged scale, of a mechanical article of a superalloy, which comprises a ceramic heat barrier coating formed in accordance with the invention, and Fig.; 2 is a schematic cross-section of a device for depositing a coating in accordance with the invention, which device operates in accordance with the invention according to the method.

DETAILED DESCRIPTION OF THE INVENTION The mechanical article shown in Fig. 1 comprises a ceramic heat barrier coating (TBC) 1 which is deposited in a single layer (e.g. in) (\ {\ f \ 4 * _ \ Similar to the method of the invention on a metal substrate 2 made of a superalloy. The substrate 2 is also covered with an intermediate, metallic underlayer or a bonding coating 3, which is deposited on the substrate 2 by means of a process known in the art (PVD, CVD, thermal spraying, etc.).

The binder coating 3 can be an oxide-corrosion-resistant alumina-forming alloy of the type MCrAlY (M = Ni and / or Co and / or Fe) or a nickel or cobalt taluminide, optionally modified by the addition of chromium and / or one or more precious metals selected from platinum, palladium, ruthenium, iridium, osmium and rhodium.

The ceramic TBC coating consists of a zirconia base and a dysprosium oxide for stabilizing the zirconia and reducing the thermal conductivity of the ceramic. To further reduce the thermal conductivity, the ceramic may also contain an additional metal oxide comprising a quadrivalent metal ion having an atomic mass greater than the atomic mass of zirconium ions. The quadrivalent metal ion can be cerium, hafnium or uranium.

The ceramic TBC coating is divided into two individual layers of essentially the same chemical composition. A first layer 4, which is attached to the bonding coating 3, and a second, outer layer 5, which is attached to the first layer. The first layer is relatively dense, in order to thereby adhere well to the bonding coating, and has a higher mechanical strength than the second layer 5.

The second layer 5 has a more open, porous structure than the first layer Å. Due to its porous structure, the second layer has an even lower thermal conductivity than would otherwise be the case. However, the price of the improved thermal conductivity properties is a reduced thermal conductivity. mechock strength or cycling strength, which is considerably lower than that of the first layer 4. As a result of their different microstructure, the first and second layers complement each other with their individual contributions to the mechanical strength or the low thermal conductivity.

The ceramic TBC coating has been deposited by plasma spraying. A plasma spray device 6 is shown schematically in Fig. 2. The device 6 comprises an anode 7 surrounding a cathode 8 and forming a nozzle for gases, this type of device being well known in the art and not requiring any further detail for - clearance. An arc and a plasma beam 9 are generated by means of the anode 7, the cathode 8 and gases flowing through the nozzle. The device further comprises a means 10 for introducing a stream of powder particles 12 into the plasma jet 9. The jet 9 is directed towards a substrate 13 and will transport the powder particles 12 towards the substrate 13 at the same time as it at least partially melts said particles 12.

According to the invention, the first TBC layer 4 is formed on the substrate 2, or more particularly on a bonding coating 3 covering the substrate 2, by introducing relatively dense, pre-sintered powder particles 12 into the jet 9. The powder particles 12 used for preparation of the first layer 4 has been formed by a process as described earlier in this text, i.e. through an agglomeration and sintering procedure.

The particles 12, or at least a substantial, preferably a predominant part thereof for the production of the first layer 4 are completely or almost completely melted when it hits the substrate 2 / the bonding coating 3, and will form a dense, pore-free layer 4. With dense here means less than 5% porosity by optical microscopy below 200X.

Thereafter, a second layer 5 is formed by introducing after the introduction of the first powder particles powder particles 12 having a different microstructure than before.

N U 20 25 30 35 f "fï F '4": fä F' v -_ .. '~ J v s-w / 8 The powder particles for producing the second layer have a more open, porous structure than the first powder particles. Preferably, they have been prepared in the manner previously described in the text, through an agglomeration / HOSP process, where by the HOSP process is meant a process of the type Homogeneous Oven Spherical Powder, which is a well-known process in the prior art. .

The powder particles 12 for producing the second layer 5 will only be partially melted when they hit the first layer 4 or any underlying material, whatever that may be. Preferably, substantially, or only, a previously formed shell or coating surrounding the agglomerating powder particle is melted by the jet 9. As a result, a porous second layer 5 is formed. The porosity is substantially laminar, wherein the pores are flattened in a plane which is substantially parallel to the plane of the underlying material 2, 3, 4.

The porosity is above 5% in contrast to the first layer with its porosity below 5%.

In order to perform the above-mentioned steps, various spray parameters must be adjusted correctly. Such parameters include current (voltage), gas flow, powder feed rate, powder temperature, powder rate, powder size, powder introduction site (relative to the beam and distance to the substrate), and substrate temperature.

The above parameters will affect coating properties such as microstructure, hardness, strength, stresses, etc., which in turn will affect the performance and service life of the ceramic TBC coating and the coated metal substrate or article 2.

It will be appreciated that the above presentation of the invention has been made for illustrative purposes only, and that alternative embodiments will be apparent to one skilled in the art. However, the scope of protection claimed in the claims is defined in the claims, which are supported by the description and the accompanying drawings.

Claims (11)

25 30 35 PATENT REQUIREMENTS A method of applying a ceramic heat barrier coating (1), TBC, to a substrate (2), the TBC coating being applied by thermal spraying of a powder of the TBC material onto the substrate (2) or an intermediate bonding coating. (3) between the substrate (2) and the TBC coating, wherein at least two layers (4, 5) of ceramic TBC coating are applied to the substrate (2) or the bond coating (3), and the powder particles used to produce a first TBC layer (4), which is adjacent to the substrate (2) or the bonding coating (3). UP- shows a microstructure other than the powder particles used for the subsequent production of a second TBC layer (5) on the coated substrate (2), characterized in that the powder particles used for the production of the first TBC layer (4) has a lower porosity than the powder particles used for the subsequent production of the second TBC layer (5) on the coated substrate (2), and that the first, inner TBC layer (4) has a different microstructure than the second, outer The TBC layer (5). Method according to claim 1, characterized in that the powder particles to be used for application of the first TBC layer (4) have a dense, sintered structure. A method according to claim 1 or 2, characterized in that it comprises a step comprising sintering agglomerates of powder grains into said powder particles. Method according to one of Claims 1 to 3, characterized in that the powder particles to be used for applying the second TBC layer (5) have a porous structure. A method according to claim 4, characterized in that each powder particle comprises an agglomerate of powder grains surrounded by a shell of molten powder material. 20 rfwr fi fé ~ g vr .-- '/-._LJ H A method according to claim 4 or 5, characterized in that it comprises a HOSP treatment of agglomerates of powder granules for the purpose of forming said powder particles. Method according to any one of claims 1-6, characterized in that the first and second ceramic TBC layers (4, 5) have the same chemical composition. Process according to any one of claims 1-7, characterized in that the TBC coating comprises stabilized zirconia, preferably dysprosium oxide stabilized zirconia. Method according to any one of claims 1-8, characterized in that the diameter of the powder particles is 10-150 micrometers. Method according to any one of claims 1-9, characterized in that the diameter of the powder grains which form said powder particles is 0.5-5 micrometers, preferably 1-2 micrometers. A method according to any one of claims 1-10, characterized in that the TBC coating is applied by plasma spraying.