Low-thermal-conductivity ceramic powder for thermal barrier coating of ultrahigh-temperature gas turbine, and thermal barrier coating using same

Abstract

The present invention relates to a low-thermal-conductivity ceramic powder for a thermal barrier coating (TBC) of an ultrahigh-temperature gas turbine, and a TBC using same. The presented coating powder is composed of a ceramic top coating powder co-doped with lanthanide rare earth elements, and has a coating layer structure composed of a lower ceramic coating layer (first layer) that has a thickness of approximately 100-150 μm and is coated with a conventional yttria-stabilized zirconium oxide (YSZ, 7-8 wt.%), and an upper ceramic coating layer (second layer) that has a thickness of approximately 400-450 μm and is coated with a mixture (Gd-Yb-Y co-doped ZrO2, YGYZ) of zirconium oxide (ZrO2), which is the TBC powder of the present invention and is co-doped with oxides of gadolinium (Gd), ytterbium (Yb) and yttrium (Y), which are lanthanide rare earth elements.

Description

Low thermal conductivity ceramic powder for ultra-high temperature gas turbine thermal barrier coating and thermal barrier coating using the same

[0001] The present invention relates to a low thermal conductivity ceramic powder for an ultra-high temperature gas turbine thermal barrier coating and a thermal barrier coating using the same, and more particularly, to a low thermal conductivity ceramic powder for an ultra-high temperature gas turbine thermal barrier coating and a thermal barrier coating using the same, which provides improved thermal durability and excellent resistance to CMAS (Calcium - Magnesium - Alumino - Silicate) attack by a ceramic top coating having a co-doped rare earth element.

[0002]

[0003] Gas turbines are widely used in various industrial fields as power engines to drive generators, aircraft, ships, etc., but as gas turbines operate in high-temperature environments, problems such as performance degradation or reduced durability of gas turbine blades, vanes, and other parts due to high-temperature loads frequently occur.

[0004] Conventionally, as a means of protecting gas turbine components from high heat generated in the gas turbine and improving durability, a thermal barrier coating (TBC) is applied to the exterior of the metal base material (S) of the gas turbine components, as shown in Fig. 1.

[0005] A conventional thermal barrier coating (TBC) is composed of a ceramic top coating layer (100) that acts as an insulating layer to block heat applied to a metal base material (S) and a metallic bond coat layer (200) that is applied in the middle to increase the bonding strength between the metal base material (S) and the ceramic coating layer (100). In the process of heat treating after applying a ceramic top coating to the metal base material (S), an aluminum oxide layer (300), which is a thermal growth oxide (TGO), is formed at the interface between the ceramic coating layer (100) and the metallic bond coat layer (200).

[0006] YSZ (Yttria-Stabilized Zirconia), the material of the ceramic coating layer (100), has been widely used as a thermal barrier coating (TBC) material for the past 30 years. However, as the gas turbine temperature has recently been raised to increase gas turbine efficiency, the YSZ material has encountered several material limitations in maintaining the properties of phase stability, thermal conductivity, chemical reactivity, and sintering resistance when used at high temperatures exceeding 1200°C, as described below, making it difficult to use any longer.

[0007] In terms of phase stability, YSZ (yttria-stabilized zirconia) is stable in the cubic phase at room temperature, but when exposed to high temperatures above 1,200°C, the metastable tetragonal prime phase undergoes rapid phase transformation into a monoclinic phase upon cooling, which causes volume change (approximately 4%) and leads to early TBC exfoliation.

[0008] In addition, the turbine inlet temperature (TIT) has gradually increased to increase the efficiency of gas turbines, and the existing single-layer YSZ shows relatively high thermal conductivity compared to recently developed candidate TBC materials, and although the thermal barrier properties are improved when yttria is added, there are limitations such as a decrease in the thermal fatigue durability of the coating layer during operation.

[0009] In addition, in terms of chemical reactivity, YSZ is vulnerable to chemical reactions with certain environmental pollutants, such as CMAS deposits, which can be contaminated by the inflow of air and volcanic ash during gas turbine operation, and thus CMAS attack has the problem that it can lead to coating deterioration, peeling, and performance degradation.

[0010] Specifically, CMAS (Calcium-Magnesium-Aluminum-Silicon oxide) material exists in volcanic ash or sand, melts at about 1,250°C, and then penetrates into the ceramic coating layer (100) of the TBC, reducing porosity. This increases the thermal conductivity of the ceramic coating layer (100) and causes stress generation due to a difference in thermal expansion coefficient, which adversely affects the life and performance of the TBC.

[0011] In addition, in terms of sintering resistance, YSZ tends to rapidly sinter or densify at high temperatures above 1,200°C, which reduces porosity and increases thermal conductivity, but this sintering effect has the problem of damaging the insulating properties of the coating and increasing the risk of coating layer destruction.

[0012] Therefore, there have been various attempts to develop technologies to find alternative materials to YSZ to overcome all limitations for thermal barrier coatings (TBCs) to be used under high-temperature operating conditions exceeding 1,200°C, and to modify the composition and microstructure of ceramic top coats to improve the thermal durability of TBCs.

[0013] One effective approach is to dope zirconia-based ceramic topcoats with rare earth elements. The incorporation of rare earth elements can reduce thermal conductivity and induce phase transformations in the zirconia matrix, thereby enhancing heat resistance and durability. Furthermore, novel ceramic materials, such as pyrochlores, perovskites, hexaaluminates, and defect clusters, have been proposed as alternatives to YSZ for high-temperature applications.

[0014] Among these new ceramic materials, pyrochlores with rare earth zirconate compositions are advantageous as shown in Figure 2, and gadolinium zirconate in particular, which has the lowest thermal conductivity and a coefficient of thermal expansion (CTE) similar to that of a metal bond coating, can be expected to be very promising in high temperature applications considering the same material properties.

[0015] Gadolinium zirconate has very low thermal conductivity, a high melting point of over 2,000℃, and a higher phase transformation temperature than yttria-stabilized zirconia. However, the disadvantages of using gadolinium zirconate include reduced fracture toughness, which leads to easy crack formation and low erosion resistance. In addition, it is known that when Gd2Zr2O7 is applied as a single layer, it tends to easily react with the TGO (Thermally Growth Oxide, Al2O3) layer and preferentially form a porous GdAlO3 layer (Perosvskite phase), which continuously consumes the protective oxide layer and shortens the thermal fatigue cycle life.

[0016] In previous research, NASA developed a powder with significantly lower thermal conductivity by additionally doping another rare earth oxide into the yttria-zirconia composition, and this type of commercial powder was manufactured and sold, but it still had the problem of poor mechanical properties.

[0017] Accordingly, the present invention has been completed by developing a stabilized zirconate by co-doping various rare earth elements for a heat shielding coating exposed to high temperatures of 1,200°C or higher.

[0018]

[0019] The present invention is a solution to the above-mentioned problems, and aims to provide a low thermal conductivity ceramic powder for an ultra-high temperature gas turbine thermal barrier coating that provides improved thermal durability and excellent resistance to CMAS attack by a ceramic top coating having a co-doped rare earth element, and a thermal barrier coating using the same.

[0020]

[0021] A preferred embodiment of the present invention for achieving the above-mentioned task is a low thermal conductivity ceramic powder for ultra-high temperature gas turbine thermal barrier coating characterized by including a mixture of zirconium oxide (ZrO2) co-doped with oxides of La series rare earth elements, as a means for solving the task.

[0022] And, the La series rare earth elements include gadolinium (Gd), ytterbium (Yb) and yttrium (Y), and the ceramic coating powder is characterized in that it is used for the upper ceramic coating of an ultra-high temperature gas turbine thermal barrier coating.

[0023] In addition, the ceramic coating powder contains Gd2O3 1.5 to 3.0 wt%, Yb2O3 2.5 to 22 wt%, Y2O3 23 to 40 wt% and ZrO2Bal., and the ceramic coating powder is characterized by a particle size of -125 +45 μm.

[0024] Meanwhile, another preferred embodiment of the present invention provides a thermal barrier coating for an ultra-high temperature gas turbine comprising a metal bond coating layer, a thermally grown oxide layer (TGO) and a ceramic coating layer on the surface of a metal base material, wherein the ceramic coating layer comprises a lower ceramic coating layer coated on the outer surface of the metal bond layer and an upper ceramic coating layer coated on the outer surface of the lower ceramic coating layer, as another solution to the problem of a low thermal conductivity thermal barrier coating for an ultra-high temperature gas turbine.

[0025] In addition, the material of the lower ceramic coating layer is yttria-stabilized zirconium oxide (YSZ), and the lower ceramic coating layer has a thickness of 100 to 150 μm, which is characterized by increasing the thermal fatigue life of the coating layer and blocking direct reaction between the upper ceramic coating layer and TGO.

[0026] In addition, the material of the upper ceramic coating layer is characterized in that it includes a mixture of zirconium oxide (ZrO2) co-doped with oxides of La series rare earth elements, and the La series rare earth elements include gadolinium (Gd), ytterbium (Yb), and yttrium (Y).

[0027] In addition, the material of the upper ceramic coating layer includes Gd2O3 1.5 to 3.0 wt%, Yb2O3 2.5 to 22 wt%, Y2O3 2 3 to 40 wt% and ZrO2Bal., and the upper ceramic coating layer is characterized by having a thickness of 400 to 450 μm.

[0028]

[0029] The ceramic powder for thermal barrier coating of an ultra-high temperature gas turbine according to the present invention includes a ceramic coating layer containing a co-doped La series rare earth element, and a thermal barrier coating (TBC) using the same has the effect of having improved thermal durability and excellent resistance to CMAS attack by utilizing a multilayer structure.

[0030] In addition, the ceramic powder for thermal barrier coating of ultra-high temperature gas turbines according to the present invention is applicable to power generation gas turbines, aircraft engines and industrial machinery, and provides an effective thermal barrier to reduce heat transfer to basic components and improve durability, and its low thermal conductivity, phase stability and excellent resistance to CMAS attack ensure long-term performance of the thermal barrier coating and have the effect of minimizing maintenance requirements.

[0031] In addition, the present invention provides a thermal barrier coating (TBC) in which the lower ceramic coating layer is yttria-stabilized zirconium oxide (YSZ) having a thickness in the range of about 100 to 150 μm, wherein the YSZ provides a suitable base for the upper ceramic coating layer, which is the upper layer, and has the effect of providing overall heat blocking.

[0032] In addition, the upper ceramic coating layer is composed of co-doped zirconia with added gadolinia (Gd2O3), ytterbia (Yb2O3), and yttria (Y2O3), and has a thickness of approximately 400 to 450 μm. The co-doped zirconia layer lowers the thermal conductivity and suppresses phase transformation into a monoclinic phase, thereby significantly improving the thermal durability of the coating due to volume change according to phase transformation, thereby providing superior heat resistance compared to the existing YSZ coating.

[0033] In addition, while conventionally there was a problem that CMAS deposits composed of calcium, magnesium, aluminum, and silicate compounds could accumulate on turbine parts during operation, which could lead to premature destruction of the thermal barrier coating, the thermal barrier coating (TBC) using the ceramic coating powder according to the present invention has the effect of maintaining the efficiency and reliability of the gas turbine due to the excellent resistance of the coating to CMAS attack.

[0034] Therefore, the thermal barrier coating (TBC) coated with the low thermal conductivity coating powder for the thermal barrier coating of a gas turbine according to the present invention has a great potential to improve the efficiency, reliability and life of gas turbine systems because it has improved insulation and excellent resistance to CMAS attack due to the incorporation of co-doped La series rare earth elements along with a multilayer structure and improved thermal durability.

[0035]

[0036] Figure 1 is a drawing showing the cross-sectional structure of a conventional heat shielding coating.

[0037] Figure 2 is a diagram showing the thermal conductivity and thermal expansion coefficient of examples of heat shielding coatings.

[0038] Figure 3 is a drawing showing the cross-sectional structure of a low thermal conductivity heat shielding coating according to a preferred embodiment of the present invention.

[0039] Figure 4 is a graph showing the results of thermal conductivity measurements by temperature for comparative examples and examples.

[0040] Figure 5 is a graph showing the XRD measurement results for comparing the phase transformation of the comparative example and the example after maintaining at 1,300℃ for 4 hours.

[0041] Figure 6 is an SEM cross-sectional image showing the penetration depth of CMAS components after maintaining at 1,300°C for 4 hours.

[0042] Figure 7 is an SEM cross-sectional image showing the penetration depth of CMAS components after maintaining at 1,300°C for 8 hours.

[0043]

[0044] Hereinafter, the present invention will be described in detail with reference to the attached drawings, according to preferred embodiments of the present invention. However, detailed descriptions of structures and operations easily understood by those skilled in the art will be omitted. Furthermore, it should be noted that the present invention is not necessarily limited to the following embodiments, and that those skilled in the art can make various modifications to the present invention without departing from the technical spirit of the present invention.

[0045] Throughout the description of this specification, the term "including a particular component" may mean that any other component may be included, rather than excluding any other component, unless specifically stated to the contrary.

[0046] A low thermal conductivity ceramic powder for ultra-high temperature gas turbine thermal barrier coating according to a preferred embodiment of the present invention (hereinafter referred to as “ceramic powder for thermal barrier coating”) comprises a mixture of zirconium oxide (ZrO2) co-doped with oxides of La series rare earth elements.

[0047] The ceramic powder for a thermal barrier coating according to the present invention is used for coating an upper ceramic coating layer (10b) in a ceramic coating layer (10) of a thermal barrier coating (TBC) having a structure as shown in FIG. 3.

[0048] Thus, the ceramic powder for thermal barrier coating is composed of a mixture of zirconium oxide (ZrO2) co-doped with oxides of La series rare earth elements, for use as an upper ceramic coating for ultra-high temperature gas turbines, and the La series rare earth elements include gadolinium (Gd), ytterbium (Yb), and yttrium (Y), and the ceramic powder for thermal barrier coating according to the present invention is expressed as Gd2O3-Yb2O3-Y2O3co-doped ZrO2 (YGYZ).

[0049] The ceramic powder (YGYZ) for thermal barrier coating according to the present invention preferably includes Gd2O3 1.5 to 3.0 wt%, Yb2O3 2.5 to 22 wt%, Y2O3 23 to 40 wt%, and ZrO2Bal. as described in Examples 1 and 2 of [Table 1] below. The dopant and its concentration may vary depending on the desired performance characteristics, and as described in [Table 1] below, the appropriate chemical composition content should be maintained and the content of SiO2 (<0.2 wt%), Al2O3 (<0.2 wt%), and impurity elements should be managed at a low level.

[0050] If the composition ratio of the ceramic powder (YGYZ) for heat shielding coating exceeds the above-mentioned limited range, there is a concern that properties such as high-temperature phase stability, resistance to CMAS attack, or high-temperature sintering resistance may deteriorate.

[0051] And, it is preferable that the ceramic powder (YGYZ) for heat shielding coating has a particle size of -125 +45㎛, which is a size suitable for coating, but the particle size is not necessarily limited to the above range and can be adjusted to an appropriate size depending on the conditions of the process, such as the performance of the coating equipment.

[0052] The ceramic powder for heat-shielding coating according to the present invention is a mixture having very stable cubic characteristics, and as confirmed in the examples described below, it was confirmed that it has excellent resistance to CMAS attack and heat resistance.

[0053] Meanwhile, as shown in Fig. 1, the conventional gas turbine thermal barrier coating is a single layer of a ceramic coating layer (100) made of YSZ (7-8 wt% Yttria-Stabilized Zirconia), which blocks heat generated from an ultra-high temperature gas turbine. It is relatively stable in a cubic phase at room temperature and below 1200°C, but when cooled at a high temperature of 1200°C or higher, a metastable tetragonal prime phase undergoes a phase transformation into a monoclinic phase, which causes a volume change (about 4%) and has a serious problem of leading to early TBC peeling.

[0054] A low thermal conductivity thermal barrier coating for an ultra-high temperature gas turbine according to another preferred embodiment of the present invention (hereinafter referred to as a 'thermal barrier coating for a gas turbine') is an improvement over the problem of a conventional gas turbine thermal barrier coating (YSZ) reaching its temperature limit as the turbine temperature increases for efficiency increase, and as shown in FIG. 3, in the ultra-high temperature gas turbine thermal barrier coating comprising a metal bond coating layer (20), a thermally grown oxide layer (TGO) (30), and a ceramic coating layer (10) on the surface of a metal base material (S), the ceramic coating layer (10) includes a lower ceramic coating layer (10a); and an upper ceramic coating layer (10b) coated on the surface of the lower ceramic coating layer (10a).

[0055] Hereinafter, the heat shielding coating of a gas turbine according to the present invention will be described in detail for each layer as follows.

[0056] The ceramic coating layer (10) is composed of a lower ceramic coating layer (10a) (first layer) and an upper ceramic coating layer (10b) (second layer) coated on the surface of the lower ceramic coating layer (10a).

[0057] The lower ceramic coating layer (10a) (first layer) is a layer that comes into contact with a thermally grown oxide layer (TGO) (30) formed during the coating and post-heat treatment process on top of the metal bond coating layer (20), and is made of yttria-stabilized zirconium oxide (YSZ) material. YSZ provides a suitable base for the upper ceramic coating layer (10b) (second layer), which is a subsequent layer coated on the outer surface of the lower ceramic coating layer (10a), and plays a role in increasing the thermal fatigue life of the coating layer and blocking direct reaction between the upper ceramic coating layer and TGO.

[0058] By introducing the lower ceramic layer, the upper ceramic layer component, Pyrochlore (Gd2Zr2O7), easily reacts with TGO to form a porous Perovskite Phase (GdAlO2), thereby solving the problem of easily becoming a starting point for crack propagation during gas turbine operation.

[0059] The thickness of the lower ceramic coating layer (10a) is preferably 100 to 150 μm. If the thickness of the lower ceramic coating layer (10a) is less than the range limited above, there is a concern that the heat blocking effect may be reduced, and if the thickness exceeds the range limited above, the low thermal conductivity effect is relatively reduced and the high temperature stability at 1200°C or higher is rapidly reduced, so there is a concern that the lower ceramic coating layer (10a) may peel off from the metal bond coating layer (20) due to volume expansion during cooling.

[0060] For reference, the thickness of the lower ceramic coating layer (10a) is preferably within the range limited above, but is not necessarily limited to the above range and may be adjusted to an appropriate thickness depending on the process conditions.

[0061] The upper ceramic coating layer (10b) is the outermost layer of the heat shielding coating and acts as a low-thermal-conductivity heat shielding coating for heat transferred from an ultra-high-temperature gas turbine. It is made of a material including a mixture of zirconium oxide (ZrO2) co-doped with oxides of La (lanthanum) series rare earth elements.

[0062] The above La series rare earth metals are characterized by being gadolinium (Gd), ytterbium (Yb), and yttrium (Y).

[0063] The upper ceramic coating layer (10b) (Gd2O3-Yb2O3-Y2O3co-doped ZrO2, YGYZ) layer according to the present invention is a layer coated using ceramic powder containing 1.5 to 3.0 wt% of Gd2O3, 2.5 to 22 wt% of Y2O3, 23 to 40 wt% of Y2O3 and ZrO2Bal. and having a low level of SiO2 (<0.2 wt%), Al2O3 (<0.2 wt.%) and a controlled content of impurity elements to the minimum, which lowers thermal conductivity, suppresses phase transformation into a monoclinic phase, and significantly improves the thermal durability of the coating, thereby providing superior heat resistance and resistance to CMAS attack compared to existing YSZ coatings.

[0064] The thickness of the upper ceramic coating layer (10b) is preferably 400 to 450 μm. If the thickness of the upper ceramic coating layer (10b) is less than the range limited above, there is a concern that the high-temperature phase stability and resistance to CMAS attack may deteriorate, and if the thickness exceeds the range limited above, there is a concern that the thermal fatigue life may deteriorate.

[0065] For reference, the thickness of the upper ceramic coating layer (10b) is preferably within the range limited above, but is not necessarily limited to the above range and may be adjusted to an appropriate thickness depending on the process conditions.

[0066] A gas turbine including an upper ceramic coating layer as described above may be utilized as a gas turbine for power generation.

[0067] The metal bond coating layer (20) and the thermally grown oxide layer (30) constituting the thermal barrier coating of the gas turbine according to the present invention have the same composition as a conventional thermal barrier coating, and the layers are briefly described as follows.

[0068] The metal base material (S) used as a material for gas turbine parts is mainly a super heat-resistant alloy such as a Ni-based alloy or a Co-based alloy, but is not limited thereto, and can be made of various heat-resistant metals or heat-resistant metal alloy materials.

[0069] The metal bond coating layer (20) is made of an oxide or alloy with excellent heat resistance and oxidation resistance, and can typically use a metal powder having a composition formula of MCrAlY (M = Metal). In particular, such powder material has the advantage of being easily film-formed by applying a spraying method.

[0070] The thickness of the metal bond coating layer (20) is preferably formed to be 200 to 250 ㎛, and when the thickness of the coating layer is less than 100 ㎛, there is a concern that the lower ceramic coating layer (10a) coated on the metal base material (S) may not be properly coated, and it is difficult to protect the base metal from high-temperature oxidation during operation, and when the thickness of the coating layer exceeds 300 ㎛, the adhesive properties of the lower ceramic coating layer (10a) coated on the metal base material (S) do not improve in proportion to the increase in the thickness of the coating layer, and there is a concern that an inefficient problem of increased coating costs may occur.

[0071] The thermally grown oxide layer (30) is formed as an aluminum oxide layer at the interface between the metal bond coating layer (20) and the ceramic coating layer (50) through coating or post-heat treatment. At the initial stage of gas turbine operation, the oxide film is formed and has a positive function of protecting the base material from oxidation. However, since oxidation continuously occurs at high temperatures during operation, the thickness thereof gradually increases and becomes brittle, which is ultimately recognized as the main cause of fracture of the thermal barrier coating. Although it is preferable that the thickness is 1 to 2 ㎛ or less, the thickness is not necessarily limited to the above range and may be formed in various thicknesses depending on the materials used and process conditions.

[0072] As described above, the thermal barrier coating of the gas turbine according to the present invention is applied to a high-temperature part of the gas turbine using a thermal spraying technique such as air plasma spraying, as described later in the following examples, using a ceramic coating powder to form a thermal barrier coating.

[0073] Hereinafter, the low thermal conductivity ceramic powder for ultra-high temperature gas turbine heat shielding coating according to the present invention and the heat shielding coating using the same will be specifically described through the following examples, and the present invention is not necessarily limited to the following examples.

[0074]

[0075] 1. Synthesis of low thermal conductivity ceramic powder for heat shielding coating

[0076] A coprecipitation method was used to synthesize co-doped zirconia powder. 99.9% high-purity rare earth element oxides, weighed to have compositions having the same composition ratios as Examples 1 and 2 and Comparative Example 1 in [Table 1] below, were dissolved in hydrochloric acid, and mixed with a solution of zirconium chloride (ZrOCl2) dissolved in distilled water to prepare a precursor solution.

[0077] Ammonia (NH4OH) was slowly added to the above precursor solution while stirring to induce a rapid reaction at pH 11. Afterwards, the solution was dried at 70°C for 24 hours, and in the next step, co-doped zirconia powder was synthesized through a calcination process at 1000°C for 2 hours.

[0078] The zirconia powder co-doped by the above method was spray-dried in a space maintaining a temperature of 60°C using a spray dryer to obtain a coating powder suitable for thermal spray application. The oxide powder was then loaded into a ball mill, and zirconia balls and isopropyl alcohol were used as a mixed medium to wet mix and grind for 24 hours to produce low thermal conductivity ceramic powders for thermal barrier coatings having particle sizes of -125 to +45 μm, as Examples 1 and 2 and Comparative Example 1.

[0079] In [Table 1] below, Comparative Examples 2 and 3 are commercial products with a general-purpose YSZ and a low thermal conductivity powder composition developed by NASA, respectively, purchased from Oerlikon Metco, USA.

[0080] (Unit: wt.%) Classification ZrO2Gd2O3Yb2O3Y2O3La2O3Hf 1) O2SiO2(max.)Al2O3(max.)U&Th(max.)Other Oxides(max)RemarksExample 1Bal.1.5~2.512~2230~40--0.20.20.020.5-Example 2Bal2.0~3.02.5~3.523~35--0.20.20.020.5-Comparative Example 1Bal.2.0~3.03.5~5.56.5~8.5220.20.20.020.5-Comparative Example 2Bal.--7~8------7~8%YSZComparative Example 3Bal.4.7~5.75.1~6.19.0~10.0-1.5~2.0----NASA Development Product 1) Hf is not added forcibly, but is naturally contained in the raw materials during the powder manufacturing process. It's a level.

[0081]

[0082] 2. Thermal barrier coating (TBC) of low thermal conductivity ceramic powder for thermal barrier coating

[0083] A. Thermal barrier coating (TBC) using the ceramic coating powder of Examples 1 and 2 and Comparative Examples 1 and 3

[0084] The surface of the metal base material of a square specimen (50 mm wide × 50 mm long × 5 mm thick) was blasted to form a surface roughness, then washed with acetone to remove surface contaminants, and the surface of the metal base material was preheated to a temperature of 60℃. Then, a metal alloy powder (composition: MCrAlY, M=Metal) was bond-coated to a thickness of approximately 200㎛ on the surface of the metal base material using HVOF (High Velocity Oxygen Fuel) equipment in the air.

[0085] And using the coating powders of Examples 1 and 2 and Comparative Examples 1 and 3, respectively, the lower ceramic coating layer (first layer) of YSZ having a thickness of 100 to 150 ㎛ was coated on the metal bond coating layer using air plasma spray technology, as shown in Fig. 3 below, and then the proposed co-doped zirconate layer having a thickness of 400 to 450 ㎛ was coated as the upper ceramic coating layer (second layer) to perform the thermal barrier coating (TBC). The thermal barrier coating (TBC) is formed by activating the diffusion process through post-heat treatment at a temperature of about 1,000°C (the heat treatment temperature varies depending on the base material), thereby increasing the adhesive strength between the bond coating and the base material and relieving the residual stress generated during the coating. In this process, a fine aluminum oxide layer (30) is formed at the interface between the metal bond coating layer (20) and the ceramic coating layer (50).

[0086] For reference, the substrate specimen used in this experiment was formed by forming a metal bond coating layer (20) with a metal alloy powder (component: MCrAlY, M=Metal) of approximately 200 ㎛ in thickness on top of a metal base material (S) of 5 mm thick aluminum alloy material that is easy to separate by dissolving the coating layer, and coating the lower ceramic coating layer (10a) (first layer) and the upper ceramic coating layer (10b) (second layer) on the outside of the specimen.

[0087] B. Thermal barrier coating (TBC) using the ceramic coating powder of Comparative Example 2

[0088] Unlike the above Examples 1 and 2 and Comparative Examples 1 and 3, the coating of Comparative Example 2 was performed by coating a ceramic coating layer (100) of a single-layer thermal barrier coating (TBC) as shown in FIG. 1 using a ceramic coating powder.

[0089] In the thermal barrier coating (TBC) of Comparative Example 2, the conditions of the metal base material, metal bond coating layer, and thermally grown oxide layer (TGO) are the same as those of the thermal barrier coating (TBC) of Examples 1 and 2 and Comparative Examples 1 and 3, but in the case of Comparative Example 2, the ceramic coating layer (100) was coated as a single layer using a commercial product, 7 to 8 wt% YSZ powder.

[0090] For reference, the thermal barrier coating (TBC) of Comparative Example 2 has a structure composed of a metal base material (S) of aluminum material with a thickness of 5 mm, a metal alloy powder (component: MCrAlY, M=Metal) with a thickness of about 200 μm, a thermally grown oxide layer (300) of aluminum oxide with a thickness of 1 to 2 μm, and a ceramic coating layer (100) with a thickness of about 500 μm, as illustrated in FIG. 1. This is the form in which most thermal barrier coatings are currently applied in the field.

[0091]

[0092] 3. Evaluation of thermal barrier coating (TBC)

[0093] A. Results of thermal conductivity measurement by temperature

[0094] The thermal conductivity was calculated by measuring the thermal diffusivity of the thermal barrier coating layer (TBC) coated using the coating powders of Examples 1 and 2 and Comparative Examples 1 to 3, respectively. The thermal conductivity was measured at various temperatures from room temperature to 1,000°C using the Laser Flash method (ASTM E1461-01). As a result, as shown in Fig. 4, Comparative Example 2 has higher thermal conductivity overall than Examples 1 and 2 and Comparative Examples 1 and 3. It can be confirmed that the thermal conductivity at room temperature is 1.1 W / m·K for Comparative Example 2, which is higher than that of Examples 1 and 2 and Comparative Examples 1 and 3, which are between 0.8 and 0.9 W / m·K.

[0095] In addition, in Examples 1 and 2 and Comparative Examples 1 and 3, the thermal conductivity decreases as the temperature increases from 100°C to 500°C, but it can be confirmed that the thermal conductivity of Comparative Example 2 decreases more rapidly than in Examples 1 and 2 and Comparative Examples 1 and 3.

[0096] In general, Examples 1 and 2 and Comparative Examples 1 and 3, except for Comparative Example 2 (YSZ), maintain low thermal conductivity even at high temperatures, so a superior heat blocking effect can be expected due to low thermal conductivity.

[0097] B. High temperature stability

[0098] The previously used comparative example 2 had a phase transformation (tetragonal → monoclinic) that occurred at a temperature of 1,200℃ or higher, and peeling could easily occur due to the accompanying volume change. As a result of X-ray diffraction analysis for comparing the phase transformation (tetragonal → monoclinic) of Comparative Examples 1 to 3 and Examples 1 and 2 with that of Comparative Examples 1 to 3 after exposure to 1,300℃ for 100 hours, as shown in Fig. 5, it was confirmed that the powders of Examples 1 and 2 and Comparative Examples 1 and 3, except for Comparative Example 2 (YSZ), hardly generated monoclinic even when maintained at high temperatures for a long time, indicating excellent phase stability.

[0099] For reference, Fig. 5 is a graph showing the XRD measurement results for comparing the phase transformation (tetragonal → monoclinic) of the comparative example and the example after exposure at 1,300℃ for 100 hours.

[0100] D. Resistance to CMAS Attack

[0101] CMAS (Ca, Mg, Al, and Si), which can be introduced from the atmosphere or volcanic ash, come into contact with the coating layer at high temperatures and penetrate into the coating layer, creating a low-melting-point phase. This can cause serious damage to the coating layer during gas turbine startup and shutdown.

[0102] As a result of analyzing the SEM images of the cross-sectional microstructures of each sample after applying a certain amount of CMAS component to each thermal barrier coating (TBC) coated using the coating powders of Examples 1 and 2 and Comparative Examples 1 to 3 and then heat-treating them, it can be seen that, as shown in FIGS. 6 and 7, the amount of CMAS component penetrating into the coating layer on the surface of Examples 1 and 2 is small even after heat treatment, thereby proving that the resistance to CMAS attack is excellent.

[0103] For reference, Fig. 6 is an SEM image of the cross-sectional microstructure of the coating layer after the CMAS Test (at 1,300℃ for 4 hours), and Fig. 7 is an SEM image of the cross-sectional microstructure after the CMAS Test (at 1,300℃ for 8 hours). The red dotted line indicates the penetration depth of the CMAS component analyzed through SEM-EDS.

[0104] In this way, the ceramic powder for heat-shielding coating according to the present invention, except for Comparative Example 2 (YSZ), Examples 1 and 2 and Comparative Examples 1 and 3, maintained low thermal conductivity even at high temperatures, and thus showed a superior heat-shielding effect due to low thermal conductivity, and even when maintained at high temperatures for a long time, almost no monoclinic crystals were formed, so that it was confirmed that the phase stability was excellent. However, in the case of Comparative Examples 1 to 3, the resistance to CMAS attack was lower than that of Examples 1 and 2.

[0105] Therefore, examples 1 and 2, which are low thermal conductivity coating powders for thermal barrier coatings of gas turbines according to the present invention, can be expected to lead to significant advancements in the field of thermal barrier coatings (TBCs), and the integration of co-doped La series rare earth elements along with the multilayer structure and improved thermal durability have great potential to improve the efficiency, reliability and life of gas turbine systems, as they possess improved insulation and excellent resistance to CMAS attack.

[0106] As described above, the low thermal conductivity ceramic powder for ultra-high temperature gas turbine thermal barrier coating and the thermal barrier coating using the same according to the preferred embodiment of the present invention have been described, but this is merely an example, and those skilled in the art will understand that various changes and modifications are possible within the scope that does not depart from the technical spirit of the present invention.

[0107]

[0108] Description of the symbol

[0109] 10: Ceramic coating layer

[0110] 10a: Lower ceramic coating layer

[0111] 10b: Upper ceramic coating layer

[0112] 20: Metal bond coating layer

[0113] 30: Thermally grown oxide layer

[0114] S: Metal base material

Claims

1. A low thermal conductivity ceramic powder for ultra-high temperature gas turbine thermal barrier coating, characterized by comprising a mixture of zirconium oxide (ZrO2) co-doped with oxides of La series rare earth elements.

2. In paragraph 1, The above La series rare earth elements are, A low thermal conductivity ceramic powder for ultra-high temperature gas turbine thermal barrier coating, characterized by containing gadolinium (Gd), ytterbium (Yb) and yttrium (Y).

3. In either of paragraphs 1 and 2, The above ceramic coating powder, A low thermal conductivity ceramic powder for use as a top ceramic coating for ultra-high temperature gas turbine thermal barrier coatings, characterized in that it is used as a top ceramic coating for ultra-high temperature gas turbine thermal barrier coatings.

4. In paragraph 3, The above ceramic coating powder, A low thermal conductivity ceramic powder for ultra-high temperature gas turbine thermal barrier coating, characterized by containing 1.5~3.0wt% of Gd2O3, 2.5~22wt% of Yb2O3, 23~40wt% of Y2O3 and ZrO2Bal.

5. In paragraph 4, The above ceramic coating powder, Low thermal conductivity ceramic powder for ultra-high temperature gas turbine thermal barrier coating characterized by particle size of -125 +45㎛.

6. In a thermal barrier coating for ultra-high temperature gas turbines, which is composed of a metal bond coating layer, a thermally grown oxide layer (TGO) and a ceramic coating layer on the surface of a metal base material, A low thermal conductivity thermal barrier coating for an ultra-high temperature gas turbine, characterized by comprising a lower ceramic coating layer coated on the outer surface of a bond coating layer and an upper ceramic coating layer coated on the outer surface of the lower ceramic coating layer.

7. In paragraph 6, The material of the above lower ceramic coating layer is: A low thermal conductivity thermal barrier coating for ultra-high temperature gas turbines characterized by being yttria-stabilized zirconium oxide (YSZ).

8. In paragraph 7, The above lower ceramic coating layer is, A low thermal conductivity thermal barrier coating for ultra-high temperature gas turbines characterized by a thickness of 100 to 150 μm.

9. In paragraph 7, The material of the upper ceramic coating layer is: A low thermal conductivity thermal barrier coating for an ultra-high temperature gas turbine, characterized by comprising a mixture of zirconium oxide (ZrO2) co-doped with oxides of La series rare earth elements.

10. In paragraph 9, The above La series rare earth elements are, A low thermal conductivity thermal barrier coating for an ultra-high temperature gas turbine characterized by containing gadolinium (Gd), ytterbium (Yb) and yttrium (Y).

11. In paragraph 9, The material of the upper ceramic coating layer is: A low thermal conductivity thermal barrier coating for ultra-high temperature gas turbines, characterized by comprising Gd2O3 1.5~3.0wt%, Yb2O3 2.5~22wt%, Y2O3 23~40wt% and ZrO2Bal.

12. In paragraph 9, The upper ceramic coating layer is, A low thermal conductivity thermal barrier coating for ultra-high temperature gas turbines characterized by a thickness of 400 to 450 μm.

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