JPWO2016147282A1 - Thermal barrier coating and power generation system - Google Patents

Abstract

ADVANTAGE OF THE INVENTION According to this invention, the thermal barrier coating with high durability which can be utilized for the member of the system used under high temperature and a high pressure condition is provided. The thermal barrier coating includes a ceramic layer formed on the surface of a base material via a bonding layer, and the porosity in the vicinity of the bonding layer side interface of the ceramic layer is equal to the bonding of the ceramic layer. It is characterized by being lower than the porosity in the vicinity of the interface opposite to the layer. This thermal barrier coating can also be utilized on the surface of a supercritical CO2 turbine.

Description

  The present invention relates to a turbine device used under conditions of high temperature and high pressure, a thermal barrier coating that can be applied to components thereof, and a power generation system having the thermal barrier coating.

  Conventionally, it has been considered that a thermal barrier coating is applied to the surface of equipment used under high temperature conditions in order to make the equipment less susceptible to damage under high temperature conditions. For example, in equipment such as gas turbines for power generation, the outer surface of parts subjected to high temperature conditions such as combustors, rotor blades, and stationary blades is provided with a thermal barrier coating made of ceramics, etc. The improvement is improved. Improving the durability of such thermal barrier coatings is an important factor in maintaining the durability and reliability of these components themselves.

  In general, a porous material mainly composed of ceramics having a lower thermal conductivity than metal is selected as the material for the thermal barrier coating. Under the high temperature conditions during turbine operation, these porous materials may cause problems such as alteration due to sintering, cracks due to a temperature difference between the front and back surfaces, and delamination due to a difference in thermal expansion from the metal. Therefore, various studies and proposals for improving the durability of the thermal barrier coating have been made.

On the other hand, from the viewpoint of increasing the efficiency of power generation, there is an increasing need for high-temperature and high-pressure operation conditions for power generation turbines. The use of a supercritical CO ₂ turbine for such purposes has been studied. A supercritical CO ₂ turbine mixes fuel such as natural gas, oxygen, and CO ₂ , injects them into a combustor at high pressure and burns them, and rotates the turbine with generated high-temperature and high-pressure combustion gas to generate electric power. Since the supercritical CO ₂ turbine can recover CO ₂ generated by combustion as it is, CO ₂ can be effectively used and NO _X is not discharged, and therefore, it is attracting attention from the viewpoint of protecting the global environment.

However, supercritical CO ₂ turbines and the like are exposed to combustion gas at a very high temperature compared to conventional steam turbines. For this reason, the thermal barrier coating applied to the turbine equipment is also subjected to severer conditions than the conventional coating. As a result, it has become a problem that the thermal barrier coating is easily altered and peeled off.

JP 2012-172610 A

  The present invention has been made in view of the above-described problems, and is intended to provide a thermal barrier coating that is less deteriorated and peeled even when used under high temperature and high pressure conditions and has excellent durability. .

  The thermal barrier coating according to the embodiment includes a ceramic layer formed on the surface of a base material via a bonding layer, and the porosity of the ceramic layer near the bonding layer side interface is The porosity is lower than the porosity in the vicinity of the interface opposite to the bonding layer.

The power generation system according to the embodiment
A combustor for generating combustion gas by burning a fuel mixed with carbon dioxide;
A power generation system including a CO ₂ turbine generator that generates electric power using the combustion gas, wherein the CO ₂ turbine includes a constituent member having the thermal barrier coating on a surface thereof. .

According to the embodiment, a highly durable thermal barrier coating that can be used as a member of a system used under high temperature and high pressure conditions including a supercritical CO ₂ turbine is provided. Such a thermal barrier coating can improve the reliability and operating efficiency of the turbine.

The cross-sectional schematic diagram of the thermal barrier coating by embodiment. The figure which shows the change of the porosity from the coupling layer side interface to the surface side interface of the thermal barrier coating by embodiment. The figure which shows the change of the porosity from the bonding layer side interface to the surface side interface of the other thermal barrier coating by embodiment. The figure which shows the change of the porosity from the bonding layer side interface to the surface side interface of the other thermal barrier coating by embodiment. The cross-sectional schematic diagram of the thermal barrier coating by another embodiment.

  An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a thermal barrier coating according to the embodiment.
The substrate 1 is made of metal or the like. Since the thermal barrier coating according to the embodiment is intended to be used under a high temperature condition, the substrate is generally made of a heat resistant material. Specifically, a constituent member such as a turbine used for a generator or the like serves as a base material. The material of these base materials is not particularly limited, but metals such as superalloys with high nickel and cobalt contents that can withstand high temperature conditions during turbine operation are generally used.

  A bonding layer 2 is formed on the surface of the substrate 1. The bonding layer 2 is provided to improve the adhesion between the ceramic layer 3 and the substrate 1 and the corrosion resistance and oxidation resistance of the substrate 1 under high temperature conditions. The bonding layer 2 is preferably made of a metal material having a high chromium or aluminum concentration, and particularly preferably made of an MCrAlY alloy (M is at least one selected from Ni and Co) having excellent corrosion resistance and oxidation resistance at high temperatures. The thickness of the bonding layer is adjusted as necessary, but the average thickness is generally preferably 0.1 to 0.2 mm.

  In the embodiment, the thermal barrier coating 3 is formed on the bonding layer 2. In FIG. 1, the thermal barrier coating 3 includes a ceramic layer 4 and a hardly sintered layer 5 formed thereon, but the hardly sintered layer 5 is not necessarily essential as will be described later. In the embodiment, the porosity in the vicinity of the bonding layer side interface of the ceramic layer (hereinafter, sometimes referred to as the lower interface for the sake of simplicity) Therefore, the porosity is lower than the porosity in the vicinity of the upper interface).

  In general, when a ceramic layer is formed, the characteristics of the layer are often approximately uniform. For example, it corresponds to a case where a ceramic layer is formed by applying a precursor composition and firing, or a case where a ceramic layer is formed by a simple thermal spraying method.

  When such a uniform ceramic layer is used as a thermal barrier coating, the temperature difference between the front and back surfaces of the ceramic layer 4 becomes large under a high temperature and high pressure environment, and cracks due to a difference in thermal expansion tend to occur.

  In contrast, the thermal barrier coating according to the embodiment has a structure in which the porosity of the ceramic layer increases from the lower interface toward the upper interface. Here, the upper interface is an interface between the ceramic layer and the hard-to-sinter layer when a later-described hard-to-sinter layer is provided, and when not provided, the upper interface is the surface of the ceramic layer exposed to the outside air. is there. Under a high temperature / high pressure environment, the temperature difference between the upper interface and the lower interface of the ceramic layer 3, in other words, between the front and back surfaces becomes large. As a result, the elongation due to the thermal expansion of the upper interface is generally larger than that of the lower interface, and it is common for cracks due to thermal expansion differences to occur easily. However, the thermal barrier coating according to the embodiment has a low porosity in the vicinity of the lower interface at a relatively low temperature relative to the upper interface at a high temperature. As a result, since the porosity in the vicinity of the upper interface is high, the elongation due to thermal expansion is reduced, and the difference in thermal expansion occurring between the upper interface and the lower interface can be reduced. Can be suppressed.

Here, the bonding layer containing a metal material and the ceramic layer generally have different thermal expansion coefficients. For this reason, when the thermal barrier coating is subjected to high-temperature and high-pressure conditions, the dimensional change due to thermal expansion differs between the bonding layer and the ceramic layer, so that shear stress acts and the possibility of delamination at the lower interface is also denied. Can not. However, even if the thermal barrier coating is subjected to high temperature and high pressure conditions, the average temperature of the thermal barrier coating 3 as a whole increases. For this reason, the difference in thermal expansion at the lower interface or the thermal stress resulting therefrom does not increase significantly even at higher temperatures. In addition, the porosity in the vicinity of the lower interface of the ceramic layer can be made equal to that of the conventional thermal barrier coating. For this reason, even when the thermal barrier coating is used under extremely severe conditions, such as a supercritical CO ₂ turbine, cracking or peeling is less than when it is used under normal gas turbine operating conditions. It is not easy to happen. The same applies to the case where the ceramic layer in contact with the bonding layer has a relatively low porosity as in the embodiment.

  As described above, the ceramic layer 4 includes portions having different porosities. Here, the porosity can be measured by taking a photograph of a cross section of the ceramic layer and analyzing the photograph. Here, the porosity in the vicinity of the bonding layer side interface (lower interface) of the ceramic layer and the vicinity of the interface (upper interface) opposite to the bonding layer of the ceramic layer is important. In the embodiment, ideally, the porosity of the lower interface or the upper interface is desirably obtained. However, since the porosity is a ratio of the volume of voids existing in a certain volume, it is difficult to obtain the interface porosity. For this reason, in the embodiment, the vicinity of the lower interface of the ceramic layer refers to a region from the lower interface of the ceramic layer to 1/3 of the thickness of the entire ceramic layer. Similarly, the vicinity of the upper interface of the ceramic layer refers to a 1/3 region of the entire thickness of the ceramic layer from the upper interface of the ceramic layer.

  In the embodiment, the porosity in the vicinity of the upper interface of the ceramic layer needs to be higher than the porosity in the vicinity of the lower interface, but the porosity in the meantime is not particularly limited. However, the porosity distribution of the ceramic layer preferably takes the following pattern.

(I) When a layer having a low porosity and a layer having a high porosity are laminated FIG. 2 shows that a layer having a low porosity is provided on the bonding layer, and a layer having a high porosity is provided thereon. It is a figure which shows the change of the porosity from the lower interface to the upper interface of the ceramic layer which has the laminated structure made. Here, the porosity of the layer formed directly on the bonding layer is p _B, the porosity of the layers stacked thereon is p _A. Here, the relation of p _A > p _B is established. FIG. 2 shows an example in which two layers having different porosities are stacked, but three or more layers may be stacked.

  Since such a structure can be formed by laminating an upper layer having a high porosity on the lower layer, it can be easily manufactured. Further, such a structure is preferable because an interface is formed between the lower layer and the upper layer, and thermal resistance is generated at the interface.

(Ii) When the porosity increases continuously from the lower interface toward the upper interface FIG. 3 shows the lower interface when the porosity of the ceramic layer increases monotonously from the lower interface toward the upper interface. It is a figure which shows the change of the porosity from an upper side interface. This figure shows an example in which the porosity increases in a linear function, but the present invention is not limited to this. That is, the slope of the porosity change may be changed, and there may be a portion where the porosity does not change (the slope is zero).

  Such a structure can be manufactured by a method in which a ceramic layer is formed on a bonding layer while changing formation conditions such as spraying conditions. With such a structure, no interface is formed inside the ceramic layer, so that the risk of peeling or the like can be reduced.

(Iii) Combination of the above (i) and (ii) FIG. 4 shows the case where the porosity does not change in the vicinity of the upper interface and in the vicinity of the lower interface, and the porosity changes continuously in the ceramic layer. It is a figure which shows the change of the porosity from a side interface to an upper side interface. Such a structure can be said to be a combination of the above (i) and (ii).

  In such a structure, after forming a low-porosity layer on the bonding layer, a layer in which the porosity changes from the lower side to the upper side while changing the spraying conditions is further formed. It can be manufactured by a method of stacking high layers. Moreover, after forming a low-porosity layer on the bonding layer, it can also be produced by intermixing the layers when forming the upper layer.

  In these structures, the porosity of the portion having a high porosity (for example, pA) is preferably 15 to 30%. When the porosity of the portion having a high porosity is 15% or more, the thermal conductivity is lowered, and the thermal barrier effect of the thermal barrier coating is increased. On the other hand, when the porosity of the portion having a high porosity is 30% or less, the physical strength of the thermal barrier coating can be maintained high.

  On the other hand, the porosity of the portion having a low porosity (for example, pB) is preferably 5 to 15%. When the porosity of the portion having a low porosity is 15% or less, the difference in thermal expansion caused by the temperature difference between the front and back surfaces of the thermal barrier coating layer can be sufficiently mitigated. In consideration of the porosity range of the high porosity portion, the porosity of the low porosity portion is preferably 5% or more.

  The thickness of the ceramic layer is set so that the substrate is protected as a thermal barrier coating and sufficient thermal barrier is possible. The thickness of the ceramic layer is generally 0.1 to 1.0 mm, preferably 0.2 to 0.5 mm.

  The ceramic material for forming such a ceramic layer is not particularly limited, and can be selected from alumina, magnesia, zirconia, and the like. However, it is preferable to select zirconium oxide for a thermal barrier coating applied to a rotating device such as a turbine, and it is particularly preferable to select zirconium oxide containing a stabilizing material such as magnesium oxide, calcium oxide, yttrium oxide. . This is because zirconium oxide containing a stabilizing material is unlikely to crack the thermal barrier coating due to the phase transformation of the crystal phase at a high temperature.

  Moreover, since the thermal conductivity at room temperature of a general superalloy mainly composed of nickel is 10 W / (m / K) or less, the thermal conductivity at room temperature of the ceramic layer is 5 W / (m / K). The following is preferable. Also from this point, a ceramic layer formed from zirconium oxide is preferable because the thermal conductivity necessary for the thermal barrier coating can be secured.

  A hard-to-sinter layer 5 having an impurity content lower than that of the ceramic layer can be formed on the upper surface of the ceramic layer 4 described above. In a high-temperature and high-pressure turbine, the temperature of the outermost surface becomes high, and thus problems such as a decrease in thermal conductivity and peeling due to sintering become large. The hard-to-sinter layer is preferably provided in order to suppress the occurrence of such problems. As the material of the hard-to-sinter layer, a material having less impurities such as silicon oxide and aluminum oxide having a lower melting point than the material constituting the ceramic layer can be used. Specifically, the impurity content of the ceramic layer described above is generally 1.0 to 3.0% by mass, but the impurity content of the material of the hardly sintered layer is 0.5% by mass or less. Is preferred. Also, rare earth elements such as hafnium oxide, cerium oxide, dysprosium oxide, ytterbium oxide (here, these rare earth elements are not included in impurities) for the purpose of suppressing sintering and stabilizing the crystalline phase of ceramics at high temperatures. Ceramic materials such as zirconium oxide containing can also be used.

  As described above, the porosity of the hardly sintered layer 5 is preferably 15 to 30% for the purpose of relaxing the thermal expansion difference between the front and back surfaces of the thermal barrier coating 3. Moreover, although the thickness of a difficult-to-sinter layer changes according to the objective, generally it is 0.01-0.05 mm.

  For the purpose of suppressing the sintering of the surface, part or all of the ceramic layer can be formed of a material having a low impurity content. In this case, there is no need to further form a hardly sintered layer.

  Further, in the hardly sintered layer 5, for the purpose of relaxing thermal expansion, fine vertical cracks 6 penetrating the layer in the thickness direction may be formed as shown in FIG. By introducing fine vertical cracks, the stress caused by the thermal expansion of the surface can be relaxed, and the effect of reducing the thermal expansion difference between the front and back surfaces of the thermal barrier coating can be obtained.

  The method for forming the thermal barrier coating according to the embodiment will be described as follows.

  First, the base material 1 which provides a thermal barrier coating is prepared.

The material of the base material 1 is not particularly limited, and ceramics such as zirconium oxide, hafnium oxide, aluminum oxide, titanium oxide, tungsten oxide, chromium oxide, gallium oxide, nickel oxide, magnesium oxide or mullite, or nickel, cobalt, iron , Chromium, aluminum, zinc, titanium, copper, yttrium, or an alloy thereof. These base materials are generally molded according to various uses. Although the thermal barrier coating according to the embodiment can be applied to any base material, it is preferable to use a material subjected to high-temperature and high-pressure conditions, for example, a constituent member such as a steam turbine or a supercritical CO ₂ turbine as a base material. . More specifically, a moving blade, a stationary blade, a shroud segment, a transition piece, or the like can be used as a base material.

  Next, the bonding layer 2 is formed on the surface of the substrate. The bonding layer 2 is coated with particles, clusters, or molecules of a metal layer constituent material such as an MCrAlY alloy (M is at least one selected from Ni and Co), for example, by a spraying method, an electron beam evaporation method, or the like. It can be formed by wearing.

  Next, the ceramic layer 4 is formed on the bonding layer 2. Similarly to the bonding layer, the ceramic layer 4 can be formed by depositing particles, clusters, or molecules of ceramic material and depositing it in a uniform film by spraying, electron beam evaporation, or the like. . For the porosity of the ceramic layer, the type of forming method such as thermal spraying or electron beam vapor deposition is appropriately selected. Can be adjusted. The thickness can be adjusted by adjusting the formation time by a thermal spraying method, an electron beam vapor deposition method or the like.

  When the hard-to-sinter layer 5 is formed on the ceramic layer 4, it can be formed using a material having an impurity content lower than that of the ceramic layer under the same or similar conditions as the formation conditions of the ceramic layer.

  Moreover, when forming the longitudinal crack 6 in a hard-to-sinter layer, it can be formed by the conventionally known arbitrary methods. For example, in the case of forming a hardly sintered layer using a thermal spraying method, the thermal spraying temperature, the particle size of the powder, and cooling can be added when forming the ceramic layer. When forming a hard-to-sinter layer using electron beam physical vapor deposition, a vertically cracked structure can be obtained by adjusting the rotation and angle of the substrate during film formation.

  A bonding layer (thickness 0.1 mm) made of MCrAlY alloy was formed on the substrate, and a ceramic layer was formed thereon by thermal spraying using zirconium oxide as a material.

  First, a ceramic layer (thickness 0.2 mm) was formed under a single condition (Comparative Example 1). The porosity of this ceramic layer was 20% both in the vicinity of the bonding layer and in the vicinity of the surface.

  Next, during the formation of the ceramic layer, the spraying conditions were changed midway to form a ceramic layer having a two-layer structure. The thickness was the same as in Comparative Example 1. The porosity of this ceramic layer was 10% near the bonding layer and 20% near the surface.

  These ceramic layers (thermal barrier coatings) were heated until the surface temperature reached 1100 ° C. and the temperature difference between the front and back surfaces reached 250 ° C., and subsequently cooled to room temperature repeatedly to evaluate the durability of the ceramic layers. The ceramic layer of Comparative Example 1 was cracked in the layer after 50 cycles, whereas the ceramic layer of Example 1 was not peeled or cracked even after 50 cycles. The obtained results were as shown in Table 1.

Finally, a turbine used under high temperature and high pressure conditions such as a CO ₂ turbine to which the thermal barrier coating according to the embodiment is applied will be described. For example supercritical CO ₂ turbine components, for example blades, stator blades, the shroud segment, or the transition piece, is a high temperature exceeding 1000 ° C., are exposed to high pressure combustion gases exceeding 30 MPa. Further, since the combustion gas does not directly collide with the combustion gas flow on the bonding layer side of the thermal barrier coating, the temperature difference between the front and rear surfaces becomes very large.

When the thermal barrier coating according to the embodiment is applied to a turbine component subjected to such severe conditions, cracking and peeling of the thermal barrier coating are suppressed, so that the member is directly subjected to high temperature and high pressure. There is nothing. As a result, the member is prevented from being damaged, and the reliability of the member is improved. As a result, the operation efficiency can be improved. The effect of such an embodiment is particularly remarkable in a CO ₂ turbine in which the working fluid has a higher density than air.

  According to at least one embodiment described above, the reliability of members used under high temperature and high pressure conditions can be improved, and the operation efficiency of the apparatus or system can be effectively improved.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Base material 2 Bonding layer 3 Thermal barrier coating 4 Ceramic layer 5 Hard to sinter layer

Claims (14)

  A thermal barrier coating comprising a ceramic layer formed on the surface of a substrate via a bonding layer, wherein the porosity of the ceramic layer in the vicinity of the bonding layer side interface is opposite to the bonding layer of the ceramic layer A thermal barrier coating characterized by a lower porosity than the vicinity of the interface.   The porosity in the vicinity of the bonding layer side interface of the ceramic layer is 5 to 15%, and the porosity of the ceramic layer in the vicinity of the interface opposite to the bonding layer is 15 to 30%. Thermal barrier coating as described.   The thermal barrier coating according to claim 1 or 2, wherein the porosity of the ceramic layer changes in the layer thickness direction and continuously changes from the interface of the bonding layer to the opposite interface.   The thermal barrier coating according to claim 1 or 2, wherein the ceramic layer has a structure in which two or more ceramic layers having different porosities are laminated.   The thermal barrier coating according to any one of claims 1 to 4, wherein the ceramic layer contains zirconium dioxide.   The thermal barrier coating according to claim 5, wherein the zirconium dioxide further comprises a stabilizing material.   7. The hard-to-sinter layer made of a ceramic material having a lower impurity content than the ceramic layer, in the vicinity of or on the interface opposite to the bonding layer of the ceramic layer. Thermal barrier coating as described.   The thermal barrier coating according to claim 7, wherein the porosity of the hardly sintered layer is 15 to 30%.   The thermal barrier coating according to claim 7 or 8, wherein the hardly sintered layer has a plurality of cracks.   The thermal barrier coating according to any one of claims 7 to 9, wherein the hard-to-sinter layer includes zirconium dioxide containing a rare earth element.   The thermal barrier coating according to any one of claims 1 to 10, wherein the base material is a constituent member of a turbine. The thermal barrier coating of claim 11, wherein the turbine is a supercritical CO ₂ turbine. A combustor for generating combustion gas by burning a fuel mixed with carbon dioxide;
A power generation system comprising a CO ₂ turbine generator for generating electric power by the combustion gas, the components the CO ₂ turbine, with the surface of the thermal barrier coating according to any one of claims 1 to 12 A power generation system comprising:   The power generation system of claim 13, wherein the component is selected from the group consisting of a moving blade, a stationary blade, a shroud segment, and a transition piece.

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