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

Abstract

Compositions of highly complex oxides for variable temperature coatings are provided that exhibit low thermal inertia, which results in reduced heat loss and increased engine efficiency. The compositions include at least five constituent oxides greater than 5 mol%. The oxides can form a single phase solid solution, or can form multiple phases. The oxide coating can be mixed with additional phases, or have high porosity, to further reduce thermal inertia. The oxides can include at least five of any of the following metals and / or semimetals: 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

[0001] Cross citation of mutual statement

[0002] This application claims the benefit and priority of U.S. Provisional Application No. 63 / 134,009, filed January 5, 2021, the disclosure of which is expressly incorporated herein by reference in its entirety. Technical Field

[0003] Thermal barrier coatings (TBCs) are ceramic-based coatings exhibiting low thermal conductivity. It is generally desirable to minimize thermal conductivity. Example embodiments of this disclosure generally relate to high entropy oxide (HEO) materials exhibiting low thermal conductivity for two applications: (1) temperature-varying coatings for internal combustion engines, and (2) TBCs for aerospace / industrial gas turbine (IGT) components. Background Technology

[0004] When high-entropy oxides are used as variable-temperature coatings for internal combustion engines, they advantageously possess low heat capacity and low thermal conductivity. Lower fuel efficiency in internal combustion engines is achieved by minimizing heat losses through the engine block and piston. This necessitates the use of coatings with low thermal conductivity on the internal engine surfaces. Low thermal conductivity layers effectively retain heat within the combustion chamber during combustion events. However, if excessive heat accumulates on the cylinder walls and piston surfaces, the incoming fuel-air mixture becomes heated upon entering the combustion chamber, potentially leading to spontaneous ignition of unburned gases before the flame (knock) or spontaneous pre-ignition of the fuel-air mixture. This occurs when the coating resists rapid temperature changes, allowing the temperature profiles of the coating and engine block to approach steady-state conditions during engine operation.

[0005] To prevent the coating from reaching a steady temperature, it must also have a low specific heat capacity. The combination of low specific heat capacity and low thermal conductivity results in low thermal inertia. Low thermal inertia allows the coating's temperature to "fluctuate" – meaning the coating surface is hot when combustion occurs and cools rapidly before fuel is drawn in during the engine's next stroke, preventing the fuel / air mixture from being heated. A coating with low thermal inertia both limits the heat transferred through the coating to the surrounding environment and retains very little heat on its surface. In addition to improved fuel efficiency, the coating provides greater stiffness, increased cavitation, and wear resistance to the coated engine components.

[0006] When using high-entropy oxides as thermal barrier coatings for aerospace / IGT applications, the materials advantageously possess both high toughness and low thermal conductivity. TBC toughness is typically measured via furnace cycle testing (FCT), which subjectes the coating to cycling at hot and cold temperatures. Tougher coatings can withstand many cycles before failure.

[0007] High-entropy oxides have been synthesized and proposed for TBC applications. However, the engineering of high-entropy oxides and their use as "temperature-variable" coatings are unknown. Furthermore, the concept of thermal inertia engineering in temperature-variable composite oxides is also unknown. Additionally, the design of high-entropy oxides combining low thermal conductivity and high toughness is also unknown.

[0008] It is understandable that high-entropy oxides encompass millions of different potential material compositions, and possess certain properties that are not inherent to high-entropy oxides. Such properties include thermal conductivity, specific heat, and toughness. Summary of the Invention

[0009] In exemplary embodiments, this disclosure provides a class of oxide coating compositions that can be applied to engine components of any composition via thermal spraying technology, exhibiting low thermal inertia and effective temperature-dependent properties. The coating allows for improved fuel efficiency of internal combustion engines.

[0010] This disclosure relates to an example embodiment of a high-entropy oxide (HEO) material as a temperature-variable coating. In this embodiment, the HEO material allows for precise tunability of its chemical, mechanical, and thermal properties for specific environments. In this embodiment, the HEO material comprises at high concentrations (>5 mol%) of at least five oxide components. Chemical disorder in the oxide system produces significant phonon scattering, which results in inherently low thermal conductivity. Control of the composition allows the composition to have a low specific heat capacity and therefore low thermal inertia, defined as the square root of the product of heat capacity, thermal conductivity, and density.

[0011] Compositions that maximize variations in atomic size and mass provide the most phonon scattering and the lowest thermal conductivity. Compositions with the lowest average atomic mass have the lowest specific heat capacity and density. The appropriate combination of low thermal conductivity and low heat capacity provides the disclosed oxides with low thermal inertia and good temperature-dependent properties. Detailed Implementation

[0012] In one embodiment, a composition comprising more than 5 mol% of at least five different binary oxides is used as a variable-temperature coating in an internal combustion engine. In one embodiment, the composite oxide is composed of general formula M x O y The expression indicates that M represents a group of at least 5 different metal cations that form oxides, x represents the number of metal cations (M) or atoms, and y represents the number of oxygen anions (O) or atoms.

[0013] In embodiments of this disclosure, at least five different metal cations (M) that form oxides may include:

[0014] At least one alkaline earth metal, including Be, Mg, Ca, Sr and Ba;

[0015] At least one, preferably at least two, 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;

[0016] One or more post-transition metals, including Al, Ga, Sn, Sb, Tl, Pb, and Bi;

[0017] One or more lanthanide elements, including La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu; and

[0018] One or more half-metals, including B, Si, Ge, As, Sb, Te, and Po.

[0019] In the implementation scheme, the following metals may be used in low thermal inertia composite oxide automotive TBCs: (1) alkaline earth metals, such as Mg and Ca; (2) transition metals, such as Y, Ti, Zr, Hf, Cr, Mo, Mn, Fe, Co, Ni; (3) post-transition metals, such as Al and Sn; (4) lanthanides, such as La, Ce, Gd, Dy and Yb; and (5) half-metals, such as Si.

[0020] In the embodiments, the composition may form a single-phase solid solution or a multiphase system.

[0021] The thermal conductivity of the coating is reduced by increasing the mass and strain disorder in the sample composition using individual atoms of significantly varying size and mass. With the aid of software, precise mass and strain variations and average atomic masses are calculated for each of >100,000 compositions of interest. The calculated values ​​can then be graphically sorted to determine the composition with the lowest thermal inertia in space.

[0022] The mass scattering value is calculated from formula (1), hence m i Let m_i be the atomic mass of the i-th element, and m_ be the average atomic mass of all n elements.

[0023]

[0024] It has been found that when the oxide is a single phase, mass scattering greater than 35 from the above formula yields less than 1 W / m. - 1 K -1 The thermal conductivity values. It is understandable that a collection of five or more oxides does not inherently form a single phase, and only three of the eight oxides evaluated in the experiment exhibited a single-phase structure.

[0025] In some embodiments, the mass scattering value of the high-entropy oxide composition is 35 or higher. In a preferred embodiment, the mass scattering value of the high-entropy oxide is 40 or higher. In a more preferred embodiment, the mass scattering value of the high-entropy oxide is 42.5 or higher.

[0026] It has been found that total scattering is also a good predictor of the thermal conductivity of oxide compositions. A higher total scattering value is equivalent to a lower thermal conductivity value. The total scattering of oxide compositions is calculated as the sum of the mass scattering value and the strain scattering value mentioned above. The strain scattering δ is calculated from formula (2), where c i As a composition, r i Let be the ionic radius of the i-th cation in the oxide system, and n be the total number of cations in the system.

[0027]

[0028] In some embodiments, the total scattering value of the high-entropy oxide composition is 30 or higher. In a preferred embodiment, the total scattering value of the high-entropy oxide is 35 or higher. In a more preferred embodiment, the total scattering value of the high-entropy oxide is 40 or higher.

[0029] To achieve excellent temperature-dependent properties, the coating material should have a strength of less than 3.0 W / m². -1 K -1 Preferably less than 1.5W m -1 K -1 More preferably less than 0.8W m -1 K -1 Thermal conductivity.

[0030] In some embodiments, this disclosure constitutes a "temperature-variable" coating. A temperature-variable coating is defined as having a thermal inertia of less than 3.0 J / m. - 2 K -1 s -1 / 2 Preferred concentration is less than 2.0 J / m. -2 K -1 s -1 / 2 And more preferably less than 1.5 Jm -2 K -1 s -1 / 2 Coating composition.

[0031] To achieve excellent temperature-dependent properties, the coating material should have a strength of less than 900 J / kg. -1 K -1 Preferred weight is less than 600 J / kg. - 1 K -1 And more preferably less than 600 J kg -1 K -1 It has a high specific heat capacity and low thermal conductivity.

[0032] To achieve excellent toughness, the alloy should have a tetragonal structure, which is known for its superior toughness. However, there are limitations on the dopant concentration for common tetragonal oxides (such as zirconium oxide), before the structure becomes a less tough cubic structure. Typical dopant concentrations are roughly 7-10%. However, the dimensionality of high-entropy oxides allows for higher dopant concentrations while maintaining a tetragonal structure, although tetragonality is not an inherent characteristic of high-entropy oxides.

[0033] Oxide vacancy concentration is presented as a technique for determining the tetragonality of oxide materials. In some embodiments, the oxide vacancy concentration is less than 0.05. In a preferred embodiment, the oxide vacancy concentration is less than 0.0375. In a more preferred embodiment, the oxide vacancy concentration is less than 0.025.

[0034] TBC toughness is typically measured via furnace cycle test (FCT), which is designed to simulate the cyclic thermal stresses associated with the heating and cooling of turbine engines. In such an FCT test, the TBC material is usually evaluated using an MCrAlY binder coating.

[0035] When applied as a thermal barrier coating, the primary composite oxide may optionally be mixed with other phases, such as metallic alloys, oxides, and / or carbides. The primary composite oxide may optionally be applied to surfaces with varying levels of relative density (i.e., porosity) to reduce thermal inertia. The coating may be applied to the internal cylinder surfaces of homogeneous charge-spark ignition (HCSI) and / or stratified charge-compression ignition (SCCI) and / or homogeneous charge-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 on top of an intermediate binder coating (e.g., an MCrAlY composition). The thermal barrier top coating may be applied using thermal spraying techniques, such as, but not limited to, high-velocity oxygen fuel (HVOF), atmospheric plasma spraying (APS), physical vapor deposition (PVD), etc.

[0036] Example

[0037] In some implementations, HEO TBC includes:

[0038] 50-90% by weight ZrO2;

[0039] 0.5-8 wt% MgO and / or TiO2;

[0040] 0.5-10 wt% Y₂O₃; and

[0041] All remaining oxides include 3-20% by weight of Yb₂O₃, La₂O₃, Gd₂O₃, Dy₂O₃, HfO₂, and CeO₂.

[0042] In a preferred embodiment designated HEO-4, the HEO TBC includes:

[0043] 7.5-11.5% by weight Y₂O₃;

[0044] 13-20% by weight of M2O3 (Yb2O3 is the most preferred);

[0045] 17-26 wt% MO2 (most preferably Ti2O2 and / or CeO2), more preferably 5-9 wt% TiO2 and 11-18 wt% CeO2; and

[0046] The balance of ZrO2.

[0047] In another preferred embodiment, designated HEO-7, the HEO TBC includes:

[0048] 6-9% by weight MO (preferably MgO);

[0049] 0.5-1.5% by weight Y₂O₃;

[0050] 2.5-4 wt% M₂O₃ (most preferably M = La or Gd), more preferably including 1-2 wt% La₂O₃ and 1-3 wt% Gd₂O₃; and

[0051] The balance of ZrO2.

[0052] In another preferred embodiment, designated HEO-8, the HEO TBC includes:

[0053] 0.4-0.6% by weight of MO (preferably MgO);

[0054] 1.2-1.8 wt% Y₂O₃;

[0055] 5.5-9 wt% M2O3 (most preferably M = Yb, La, Gd or Dy), more preferably including 2-4 wt% Yb2O3, 2-4 wt% La2O3 and 2-3 wt% Dy2O3;

[0056] 13-21 wt% MO2 (most preferably CeO2, HfO2 or TiO2), more preferably 2.5-4 wt% CeO2 and 6.6-9.8 wt% HfO2, 13-21 wt% CeO2, or 2.5-4 wt% TiO2 and 6.6-9.8 wt% CeO2; and

[0057] The balance of ZrO2.

[0058] In another preferred embodiment, designated HEO-12, the HEO TBC includes:

[0059] 17-26 wt% M2O3 (most preferably Yb2O3 and Sm2O3), more preferably 12-20 wt% Yb2O3 and 3-6 wt% Sm2O3;

[0060] 13.5-20.5% by weight MO2 (preferably CeO2); and

[0061] 6-9% by weight of M2O5 (preferably Nb2O5).

[0062] Table 1 below shows the calculated mass scattering, strain scattering, total scattering, and oxide vacancy concentration of oxides according to example embodiments. As discussed above, HEO-4, HEO-7, HEO-12, HEO-8A, HEO-8B, and HEO-8C represent exemplary embodiments of this disclosure. These exemplary embodiments have a novel and non-obvious combination of high total scattering and low oxide vacancy concentration that satisfies the technical embodiments of this disclosure. As shown in Table 1, most of the tested HEOs do not have such a combination of properties; therefore, high total scattering and low oxide vacancy concentration are not inherent properties of high-entropy oxides. Standard thermal barrier coating materials and yttrium-stabilized zirconia (YSZ) are also included in Table 1 and do not satisfy the total scattering parameters described herein.

[0063] Table 1

[0064] HEO-1 42.6 10.9 53.5 0.25 HEO-2 44.3 9.1 53.4 0.25 HEO-3 26.4 9.9 36.3 0.2 HEO-4 33.4 10.2 43.6 0.06 HEO-5 50.2 12.7 62.9 0.25 HEO-6 46.5 10.7 57.2 0.2 HEO-7 36.1 4.8 40.9 0.11 HEO-8 28.9 7.7 36.6 0.04 HEO-9 44 13 57 0.15 HEO-10 52.4 10.2 62.6 0.29 HEO-11 20.6 12.2 32.8 0.33 HEO-12 27.4 9.1 36.5 0.01 HEO-8A 23.6 7.5 31.1 0.03 HEO-8B 25.7 8 33.7 0.03 HEO-8C 23.3 7.6 30.9 0.03 YSZ 0.7 5.5 6.2 0.02

[0065] All HEOs presented in Table 1 were manufactured in a similar manner via spray drying, sintered at 1400°C for 10 hours, and plasma-sprayed onto the substrate. In all samples, an MCrAlY binder coating was used as the initial layer on the substrate. Then, in one set of experiments, each HEO was directly sprayed onto the binder coating. In a second set of experiments, a standard 8YSZ coating was applied as an intermediate layer onto the binder coating, and the HEO coating was applied as the top layer. The resulting coatings were used for 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 correlated with FCT lifetime.

[0066] The coating properties of the oxides according to the example embodiments are shown in Table 2 below. Thermal conductivity values ​​are expressed in W / mK, and FCT results are expressed in cycles. As shown in Table 2, the high FCT cycle life demonstrates the excellent toughness of the HEO coating, which is novel and not obvious. The high FCT cycle life corresponds only to HEO compositions with low oxygen vacancy concentrations.

[0067] Table 2

[0068] 1 1.22 <20 <20 2 1.3 <20 <20 3 1.21 <20 <20 4 0.77 <20 <20 5 1.29 <20 20-60 6 1.04 <20 <20 7 0.93 96-116 60-96 8 0.91 240-260 370-390 9 1.26 104 <20 10 1.18 <20 <20 11 1 100 85 12 0.95 1035 20 8A 1 920+ 73 8B 1 1050+ 477 8C 1 950+ 53

[0069] In some embodiments, the HEO coating has an FCT life of over 200 cycles when directly sprayed onto the adhesive coating. In a preferred embodiment, the HEO coating has an FCT life of over 250 cycles when directly sprayed onto the adhesive coating. In a more preferred embodiment, the HEO coating has an FCT life of over 300 cycles when directly sprayed onto the adhesive coating.

[0070] In some embodiments, the HEO coating exhibits an FCT lifetime of over 200 cycles when sprayed onto the intermediate 8YSZ layer, which itself is then sprayed onto the adhesive coating. In a preferred embodiment, the HEO coating exhibits an FCT lifetime of over 500 cycles when sprayed onto the intermediate 8YSZ layer, which itself is then sprayed onto the adhesive coating. In a more preferred embodiment, the HEO coating exhibits an FCT lifetime of over 900 cycles when sprayed onto the intermediate 8YSZ layer, which itself is then sprayed onto the adhesive coating.

[0071] Furthermore, at least because the invention is disclosed herein in a manner that enables its manufacture and use, the invention can be practiced without any additional elements or structures not specifically disclosed herein, for example, for simplicity or efficiency, based on the disclosure of specific exemplary embodiments.

[0072] It should be noted that the foregoing embodiments are for illustrative purposes only and should not be construed as limiting the invention. While the invention has been described with respect to exemplary embodiments, it should be understood that the terms used herein are descriptive and explanatory, not limiting. Variations and modifications, as described herein and modified, may be made in various aspects without departing from the scope and spirit of the invention within the scope of the appended claims. Although the invention has been described herein with respect to specific means, materials, and embodiments, the invention is not intended to be limited to the details disclosed herein; rather, the invention extends to structures, methods, and uses that are functionally equivalent as defined in the appended claims.

Claims

1. A high-entropy oxide (HEO) material, said HEO material containing less than 1.5 W / m -1 K -1 The thermal conductivity, characterized in that The HEO material comprises: 0.4-0.6% by weight of MO oxide; 1.2-1.8% by weight of Y₂O₃; 5.5-9% by weight of M2O3 oxides; 13-21% by weight of MO2; and The remaining ZrO2, Where M represents a group of at least 5 different metal cations that form oxides. The total scattering value of the HEO material is 36.6 or higher, and The HEO material described therein has a furnace cycle life of 370-390 cycles when directly sprayed onto the adhesive layer.

2. The HEO material of claim 1, wherein the HEO material further comprises less than 3.0 J / m³. -2 K -1 s -1 / 2 Specific heat capacity.

3. The HEO material of claim 1, wherein the HEO material further comprises less than 900 J kg. -1 K -1 Specific heat capacity.

4. The HEO material of claim 1, wherein more than 90% of the HEO material is tetragonal.

5. The HEO material of claim 1, wherein the HEO material has an oxide vacancy concentration of 0.05 or less.

6. The HEO material of claim 1, further comprising the use of the material for forming a thermal barrier coating.

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

8. The HEO material of claim 1, wherein the HEO material is composed of general formula M x O y The expression indicates that M represents a group of at least 5 different metal cations that form oxides, x represents the number of metal cations (M) or atoms, and y represents the number of oxygen anions (O) or atoms.

9. The HEO material of claim 1, wherein the HEO material is composed of general formula M x O y The expression is represented as follows: M represents at least one member of Group II of the periodic table, x represents the number of metal cations (M) or atoms, and y represents the number of oxygen anions (O) or atoms.

10. The HEO material of claim 1, wherein the HEO material is composed of general formula M x O y The expression indicates that M represents at least one lanthanide element, x represents the number of metal cations (M) or atoms, and y represents the number of oxygen anions (O) or atoms.

11. The HEO material of claim 1, wherein the HEO material is composed of general formula M x O y The expression indicates that M represents at least one transition metal, x represents the number of metal cations (M) or atoms, and y represents the number of oxygen anions (O) or atoms.

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