Composite oxide thermal barrier coating with low thermal inertia and low thermal conductivity

Abstract

A highly complex oxide composition is provided for temperature swing coatings that exhibits low thermal inertia leading to reduced heat losses and improved engine efficiency. The composition includes greater than 5 mol% of at least five constituent oxides. The oxides may form single-phase solid solutions or may form multiple phases. The oxide coating may be mixed with additional phases or have high porosity to further reduce thermal inertia. The oxide may contain at least five of any of the following metals and / or metalloids: Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Ni, Cu, Zn, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, Ba, Al, Ga, Sn, Sb, Tl, Pb, Bi, B, Si, Ge, As, Sb, Te, or Po.

Description

[Technical Field]

[0001] This application claims the benefit and priority of U.S. Provisional Application No. 63 / 134,009, filed on 5 January 2021, the disclosure of which is expressly incorporated herein by reference in its entirety.

[0002] Thermal barrier coatings (TBCs) are ceramic-based coatings that exhibit low thermal conductivity. Generally, it is desirable to minimize thermal conductivity. Exemplary embodiments of this disclosure relate to high-entropy oxide (HEO) materials that exhibit low thermal conductivity with respect to two applications in general: (1) temperature swing coatings used in combustion engines, and (2) TBCs used in aerospace / industrial gas turbine (IGT) components. [Background technology]

[0003] When using high-entropy oxides as temperature-swing coatings for combustion engines, low heat capacity and low thermal conductivity are advantageous. Combustion engines achieve better fuel efficiency when heat loss by the engine block and pistons is minimized. This requires the use of coatings with low thermal conductivity on the internal engine surfaces. Low thermal conductivity layers effectively retain heat in the combustion chamber during combustion events. However, if excessive heat accumulates on the cylinder walls and piston surfaces, the incoming fuel-air mixture is heated upon entering the combustion chamber, potentially causing spontaneous ignition of unburned gases before the flame (knocking) or spontaneous pre-ignition of the fuel-air mixture. This occurs when the coating resists rapid temperature changes, and therefore the temperature distribution of the coating and engine block approaches steady-state conditions during engine operation.

[0004] To prevent the coating temperature from reaching a steady state, the coating also needs to have a low specific heat capacity. The combined low specific heat capacity and thermal conductivity lead to low thermal inertia. Low thermal inertia allows the coating temperature to "swing," meaning the coating surface is hot when a combustion event occurs and cools rapidly before the next stroke of the engine takes in fuel, preventing the fuel / air mixture from overheating. A coating with low thermal inertia limits the amount of heat transferred to the surroundings through the coating, retaining very little heat on the surface walls. In addition to improved fuel efficiency, the coating provides higher hardness, increased cavitation, and wear resistance to coated engine parts.

[0005] When using high-entropy oxides as thermal barrier coatings for aerospace / IGT applications, it is advantageous for the material to possess both high toughness and low thermal conductivity. TBC toughness is typically measured by furnace cycle testing (FCT), in which the coating is subjected to high and low temperature cycles. A tougher coating can withstand a greater number of cycles before failure.

[0006] For TBC applications, high-entropy oxides have been synthesized and proposed. However, the engineering of high-entropy oxides and their use as "temperature swing" coatings are unknown. Furthermore, the concept of thermal inertia engineering in composite oxides for temperature swing properties is unknown. Moreover, the design of high-entropy oxides specifically for low thermal conductivity combined with high toughness is unknown.

[0007] High-entropy oxides encapsulate millions of different potential material compositions and possess specific properties not inherent to high-entropy oxides. Such properties include thermal conductivity, specific heat, and toughness. [Overview of the project] [Problems that the invention aims to solve]

[0008] In exemplary embodiments, the disclosure provides a class of oxide coating compositions that can be applied by thermal spraying technology to engine components of any composition, exhibiting low thermal inertia and effective temperature swing characteristics. The coatings enable improved fuel efficiency in combustion engines. [Means for solving the problem]

[0009] Exemplary embodiments of this disclosure relate to high-entropy oxide (HEO) materials as temperature-swing coatings. In embodiments, the HEO material allows for precise control of chemical, mechanical, and thermal properties for use in specific environments. In embodiments, the HEO material contains at least five oxide components in high concentrations (greater than 5 mol%). Chemical interference in oxide systems generates significant phonon scattering, which in turn leads to inherently low thermal conductivity. Compositional control allows for compositions with low specific heat capacity, and therefore low thermal inertia, defined as the square root of the product of heat capacity, thermal conductivity, and density.

[0010] Compositions that maximize atomic size and mass dispersion provide maximum phonon scattering and lowest thermal conductivity. Compositions with the lowest average atomic mass have the lowest specific heat capacity and density. A suitable combination of low thermal conductivity and low heat capacity provides the disclosed oxide with low thermal inertia and good temperature swing characteristics. [Modes for carrying out the invention]

[0011] In one embodiment, a mixed oxide composition containing at least five different binary oxides in greater than 5 mol% is used as a temperature swing coating for a combustion engine. In one embodiment, the composite oxide is of general formula M x O y This is expressed as follows: where M represents a group of at least five different oxide-forming metal cations, x represents the number of metal cations (M) or atoms, and y represents the number of oxygen anions (O) or atoms.

[0012] In embodiments of this disclosure, at least five different oxide-forming metal cations (M) are: At least one alkaline earth metal containing Be, Mg, Ca, Sr, and Ba, At least one of the following transition metals: Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Ni, Cu, and Zn, preferably at least two, One or more post-transition metals containing Al, Ga, Sn, Sb, Tl, Pb, and Bi, One or more lanthanides containing La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu, and One or more metalloids containing B, Si, Ge, As, Sb, Te, and Po may be included.

[0013] In embodiments, the following metals: (1) alkaline earth metals such as Mg and Ca, (2) transition metals such as Y, Ti, Zr, Hf, Cr, Mo, Mn, Fe, Co, Ni, etc., (3) post-transition metals such as Al and Sn, (4) lanthanides such as La, Ce, Gd, Dy, and Yb, and (j) metalloids such as Si can be used in low-thermal inertia composite oxide TBCs for automobiles.

[0014] In embodiments, the composition may form a single-phase solid solution or a multiphase system. The above composition reduces the thermal conductivity of the coating by using individual atoms with significantly varying sizes and masses and increasing the mass and strain disorder in the sample composition. The calculation of the exact mass and strain dispersion and the average atomic mass for each of over 100,000 compositions of interest is performed using software. The calculated values are then sorted graphically to determine the composition within the space having the minimum thermal inertia.

[0015] The mass scattering value is calculated from Equation (1), where m i is the atomic mass of the i-th element, TIFF0007904832000001.tif3141

[0016] is the average atomic mass of all n elements.

[0017]

Number

[0018] Mass scattering exceeding 35 from the above formula results in a thermal conductivity value below 1 Wm -1 K -1 It can be understood that an aggregate of five or more oxides does not essentially form a single phase, and only three of the eight oxide experiments evaluated showed a single-phase structure.

[0019] In some embodiments, the mass scattering value of the high-entropy oxide composition is 35 or more. In preferred embodiments, the mass scattering value of the high-entropy oxide is at least 40. In more preferred embodiments, the mass scattering value of the high-entropy oxide is 42.5 or more.

[0020] The total scattering value has also been found to be a good predictor of the thermal conductivity of the oxide composition. A higher total scattering value is equal to a lower thermal conductivity value. The total scattering of the oxide composition is calculated as the sum of the above mass scattering value and the strain scattering. The strain scattering δ is calculated from Equation (2), where c i is the composition, r i is the ionic radius of the i-th cation in the oxide system, and n is the total number of cations in the system:

[0021]

Number

[0022] In some embodiments, the total scattering value of the high-entropy oxide composition is 30 or more. In preferred embodiments, the total scattering value of the high-entropy oxide is at least 35. In more preferred embodiments, the total scattering value of the high-entropy oxide is 40 or more.

[0023] To achieve excellent temperature swing characteristics, the coating material should have a thermal conductivity of less than 3.0 Wm -1 K -1 less, preferably less than 1.5 Wm -1 K -1 less, more preferably less than 0.8 Wm -1 K -1 and less.

[0024] In some embodiments, the present disclosure constitutes a "temperature swing" coating. The temperature swing coating is defined as a coating composition having a thermal inertia of less than 3.0 Jm -2 K -1 s -1 / 2 less, preferably less than 2.0 Jm -2 K -1 s -1 / 2 less, more preferably less than 1.5 Jm -2 K -1 s -1 / 2 and less.

[0025] To achieve excellent temperature swing characteristics, the coating material should have a specific heat capacity of less than 900 Jkg -1 K -1 less, preferably less than 600 Jkg -1 K -1 less, more preferably less than 600 Jkg -1 K -1 and low thermal conductivity.

[0026] To achieve excellent toughness characteristics, the alloy should have a tetragonal structure with excellent toughness. However, there are certain limitations to the dopant concentration for common tetragonal oxides such as zirconia, and before that, the structure becomes a cubic structure that is not very tough. A typical dopant concentration is roughly 7 - 10%. However, the high entropy oxide space enables the use of a higher dopant concentration while maintaining the tetragonal structure, but tetragonality is not an inherent feature of high entropy oxides.

[0027] The oxide vacancy concentration has been proposed as a technique for determining the tetragonal crystallinity of oxide materials. In some embodiments, the oxide vacancy concentration is less than 0.05. In preferred embodiments, the oxide vacancy concentration is less than 0.0375. In more preferred embodiments, the oxide vacancy concentration is less than 0.025.

[0028] TBC toughness is typically measured by furnace cycle tests (FCTs) aimed at simulating the cyclic thermal stresses associated with heating and cooling turbine engines. Such FCT tests typically use MCrAlY bond coats to evaluate TBC materials.

[0029] When applied as a thermal barrier coating, the primary composite oxide may be optionally mixed with additional phases such as metal alloys, oxides, and / or carbides. The primary composite oxide may be optionally applied to surfaces at various levels of relative density (i.e., porosity) to reduce thermal inertia. The coating may be applied to the internal cylinder surfaces of homogeneous intake spark ignition (HCSI) and / or stratified intake compression ignition (SCCI) and / or homogeneous intake compression ignition (HCCI) type engines. The engine may be a two-stroke or four-stroke engine. In some embodiments, the coating is applied directly to the piston or engine block. In one embodiment, the oxide coating is applied over an intermediate bond coat (e.g., an MCrAlY composition). The thermal barrier coating topcoat may be applied by spraying techniques such as high-velocity oxygen fuel (HVOF), atmospheric pressure plasma spraying (APS), and physical vapor deposition (PVD), but is not limited to these. [Examples]

[0030] In some embodiments, the HEO TBC is: 50-90% by weight of ZrO2, 0.5-8% by weight of MgO and / or TiO2, It contains 0.5 to 10% by weight of Y2O3, and The remaining total oxides consist of 3-20% by weight of Yb2O3, La2O3, Gd2O3, Dy2O3, HfO2, and CeO2.

[0031] In one embodiment called HEO-4, HEO TBC is: 7.5-11.5% by weight of Y2O3, 13-20% by weight of M2O3 (most preferably Yb2O3), 17-26% by weight of MO2 (most preferably) TiO 2 and / or CeO2), more preferably 5-9 wt% TiO2 and 11-18 wt% CeO2, Contains the remaining ZrO2.

[0032] In another preferred embodiment called HEO-7, the HEO TBC is: 6-9% by weight MO (preferred) Kuha MgO); 0.5-1.5% by weight of Y2O3, More preferably, 2.5 to 4 wt% M2O3 (most preferably M = La or Gd), comprising 1 to 2 wt% La2O3 and 1 to 3 wt% Gd2O3, and Contains the remaining ZrO2.

[0033] In another preferred embodiment called HEO-8, the HEO TBC is: 0.4-0.6% by weight of MO (preferred) Kuha MgO), 1.2-1.8% by weight of Y2O3, More preferably, 5.5 to 9 wt% M2O3 (most preferably M = Yb, La, Gd, or Dy) containing 2 to 4 wt% Yb2O3, 2 to 4 wt% La2O3, and 2 to 3 wt% Dy2O3. 13-21% by weight of MO2 (most preferably CeO2, HfO2, or TiO2), more preferably 2.5-4% by weight of CeO2 and 6.6-9.8% by weight of HfO2, 13-21% by weight of CeO2 or 2.5-4% by weight of TiO2 and 6.6-9.8% by weight of CeO2, and Contains the remaining ZrO2.

[0034] In another preferred embodiment called HEO-12, HEO TBC is 17-26% by weight of M2O3 (most preferably Yb2O3 and Sm2O3), more preferably 12-20% by weight of Yb2O3 and 3-6% by weight of Sm2O3, 13.5 to 20.5% by weight of MO2 (preferably CeO2), and It contains 6-9% by weight of M2O5 (preferably Nb2O5).

[0035] Table 1 below shows the calculated mass scattering values, strain scattering values, total scattering values, and oxide vacancy concentrations for oxides according to exemplary embodiments. As described above, HEO-4, HEO-7, HEO-12, HEO-8A, HEO-8B, and HEO-8C represent exemplary embodiments of the present disclosure. These exemplary embodiments have a novel and non-obvious combination of high total scattering values ​​and low oxide vacancy concentrations that satisfy the technical embodiments of the present disclosure. As shown in Table 1, most of the HEOs tested do not have this combination of properties, and therefore high total scattering and low oxide vacancy concentrations are not inherent properties of high-entropy oxides. Standard thermal barrier coating materials and yttria-stabilized zirconia (YSZ) are also included in Table 1 and do not satisfy the total scattering parameters described herein.

[0036] [Table 1]

[0037] All HEOs shown in Table 1 were manufactured using the same method by spray drying, sintered at 1400°C for 10 hours, and then plasma-sprayed. For all samples, an MCrAlY bond coat was used as the initial layer on the substrate. Then, in one set of experiments, each HEO was directly sprayed onto the bond coat. In a second set of experiments, a standard 8YSZ coating was applied as an intermediate layer on the bond coat, and the HEO coating was applied as the topcoat. The resulting coatings were used in subsequent physical tests, including thermal conductivity before and after sintering and furnace cycle test (FCT) lifetime. The use or absence of the intermediate YSZ layer was related to the FCT lifetime.

[0038] Table 2 below shows the coating properties of oxides according to exemplary embodiments. Thermal conductivity values ​​are expressed in W / mK, and FCT results are expressed in cycles. As shown in Table 2, the excellent toughness of HEO coatings, as demonstrated by the high FCT cycle lifetime, is novel and non-obvious. The high FCT cycle lifetime applies only to HEO compositions with low oxygen vacancy concentrations.

[0039] [Table 2]

[0040] In some embodiments, the HEO coating has an FCT life of more than 200 cycles when sprayed directly onto the bond coat. In preferred embodiments, the HEO coating has an FCT life of more than 250 cycles when sprayed directly onto the bond coat. In even more preferred embodiments, the HEO coating has an FCT life of more than 300 cycles when sprayed directly onto the bond coat.

[0041] In some embodiments, the HEO coating has an FCT life of more than 200 cycles when sprayed on an intermediate 8YSZ layer which is itself sprayed on a bond coat. In preferred embodiments, the HEO coating has an FCT life of more than 500 cycles when sprayed on an intermediate 8YSZ layer which is itself sprayed on a bond coat. In even more preferred embodiments, the HEO coating has an FCT life of more than 900 cycles when sprayed on an intermediate 8YSZ layer which is itself sprayed on a bond coat.

[0042] Furthermore, since the present invention is disclosed herein in a manner that enables the invention to be manufactured and used, for example for simplification or efficiency, by disclosing certain exemplary embodiments, the present invention can be carried out without the presence of any additional elements or structures not specifically disclosed herein.

[0043] It should be noted that the examples described herein are provided for illustrative purposes only and should not be construed as limiting the invention. While the invention has been described with reference to exemplary embodiments, it should be understood that the words used herein are descriptive and illustrative, not limiting. Modifications may be made within the scope of the appended claims, without departing from the scope and spirit of the invention in that aspect, as described and modified. While the invention has been described herein with reference to specific means, materials, and embodiments, the invention is not intended to be limited to the details disclosed herein. Rather, the invention extends to all functionally equivalent structures, methods, and uses, such as those within the scope of the appended claims.

Claims

1. 1.5 Wm －１ K －１ A high-entropy oxide (HEO) material having a lower thermal conductivity, wherein the HEO material contains at least six different binary oxides, The aforementioned HEO material is 0.4 to 0.6% by weight of MO oxide, 1.2 to 1.8% by weight of Y ２ O ３ , 5.5-9% by weight M ２ O ３ oxides, 2.5–4% by weight CeO ２ , 6.6–9.8% by weight of HfO ２ , and Remaining ZrO ２ including In the aforementioned MO oxide, M represents Mg, Said M ２ O ３ The oxide M represents Yb, La, Gd, or Dy, and is an HEO material.

2. 3.0 Jm －２ K －１ s －１／２ The HEO material according to claim 1, further comprising a thermal inertia of less than 1.

3. 900 J kg －１ K －１ The HEO material according to claim 1, further comprising a specific heat capacity of less than 1.

4. The HEO material according to claim 1, wherein more than 90% of the HEO material has a tetragonal structure.

5. The HEO material according to claim 1, having an oxide vacancy concentration of 0.05 or less.

6. The HEO material according to claim 1, further comprising the use of the material for forming a heat-shielding coating.

7. The HEO material according to claim 1, further comprising the use of the material for forming a coating for a combustion chamber.

Images