High-temperature stable amorphous oxide-based coatings with environmental barriers

Abstract

High-temperature stable amorphous oxide-based coatings with environmental barriers 1. A high-temperature, non-aqueous environment metallic component, comprising a metallic body and a protective coating applied to an outer surface of said metallic body, said metallic body being intended to come into contact with a non-aqueous working fluid in use, said component comprising: 1. A metallic component for use in high-temperature, non-aqueous environments, wherein the protective coating comprises at least one amorphous aluminum oxide layer, the at least one amorphous aluminum oxide layer comprising at least one doping element uniformly dispersed in the amorphous aluminum oxide layer, the at least one doping element being selected from the group consisting of C, Na, K, Cs, Mg, Ca, Sr, P, Si, Fe, Y, Zr, Mo, W, La, Ce, Er, and Yb.

Description

[Technical Field]

[0001] The present invention relates generally to materials used in high temperature, non-aqueous environments such as industrial processes and energy conversion technologies. [Background technology]

[0002] BACKGROUND OF THE INVENTION In current and future energy conversion technologies and industrial processes, high temperature non-aqueous environments are of great interest for improving energy conversion efficiency and enabling novel manufacturing processes.

[0003] The first and most important example is fourth-generation nuclear reactor technology, which promises broad possibilities for safe, CO2-free energy. Several concepts involve the use of liquid metals (LMs), heavy metal liquids (HLMs), molten salts (MSs), or helium as heat transfer media to extract heat generated from fast fission and fusion reactions in the reactor core. Lead-cooled fast reactors (LFRs), accelerator-driven systems (ADSs), and fusion reactor designs include cooling with liquid metals such as lithium or sodium, as well as heavy metal liquids such as lead, lead-bismuth eutectic (LBE), and lead-lithium eutectic (LLE). Despite the attractive properties of liquid metal coolants, liquid metal corrosion (LME) can dramatically change the microstructure and chemical composition of metal alloy-based structures, resulting in degradation of mechanical properties and a sharp increase in the risk of failure.

[0004] The aforementioned requirements for applications in nuclear systems are met by austenitic and ferritic-martensitic steels. However, these alloys cannot withstand selective dissolution by liquid metals and heavy metal liquids and are subject to liquid metal embrittlement. In addition to nuclear applications, liquid metals, heavy metal liquids, and molten salts are being investigated as working fluids in many thermal management applications and high-temperature energy conversion devices, such as concentrated solar power plants. In these applications, mitigation strategies designed to protect steels from corrosion include the formation of surface alloys and protective coatings. Metal or metal alloy coatings should be pre-oxidized or form a protective oxide layer in situ. However, low reliability and poor controllability of the oxidation process pose additional risks to the implementation of these technologies. Of the proposed ceramic coatings, only amorphous aluminum oxide coatings (a-Al2O3) deposited by pulsed laser deposition (PLD) on stainless steel substrates have been shown to provide protection for the underlying metal from corrosion by liquid metals and heavy metal liquids, as well as corrosion by hydrogen isotope infiltration, while also demonstrating radiation resistance and minimal discrepancy with the substrate in terms of mechanical properties. In particular, although many oxide compounds are stable to reduction by liquid lead, only a-Al2O3 has thermomechanical properties comparable to those of stainless steel.

[0005] As described in US Patent Application Publication No. 2014241485 A1, the exceptional properties of a-Al2O3 coatings are closely related to their integrity, which in turn is related to the stability of the coating's microstructure. All examples of a-Al2O3 coated steel in heavy metal liquids reported in US Patent Application Publication No. 2014241485 A1 were performed at temperatures below 600 °C. Above this temperature, the amorphous phase (ρ ≈ 3.5 g / cm3) is formed. 3 ) to the crystalline phase (3.5 g / cm 3 <ρ<4g / cm3 ), strong crystallization can cause cracking in the film, exposing the underlying support to a corrosive environment. Under the combined effects of radiation fields and high temperatures, stabilization and control of the amorphous-crystalline phase transition is of primary importance for the end application. Indeed, nuclear reactors or other similar thermal systems can have transients that exceed the nominal operating temperature by several hundred degrees for limited periods of time.

[0006] Furthermore, the effect of the radiation field must also be considered. Radiation-enhanced and radiation-induced crystallization are destabilizing mechanisms that affect the crystallization temperature or promote the nucleation of specific crystalline phases, especially in relation to the pure temperature range that can be observed in materials under radiation exposure. As a result, the temperature thresholds for amorphous-crystalline and interphase transitions may shift to strictly lower values.

[0007] In conclusion, the coating microstructure influences the mechanical properties of the film, while phase transformations can lead to densification processes, crack formation, and loss of adhesion and coating integrity. Therefore, fine-tuning and control of coating properties through coating microstructural stabilization will enable the advancement and development of advanced nuclear systems and other high-temperature technologies that use non-aqueous working fluids. Summary of the Invention

[0008] To the above effect, the subject of the present invention is a high-temperature, non-aqueous environment metallic component, intended to come into contact with a non-aqueous working fluid in use, comprising a metallic body and a protective coating applied to the outer surface of said metallic body, the component comprising: The protective coating is a metallic component for use in high-temperature, non-aqueous environments, and includes at least one amorphous aluminum oxide layer, the at least one amorphous aluminum oxide layer including at least one doping element uniformly dispersed in the amorphous aluminum oxide layer, the at least one doping element being selected from the group consisting of C, Na, K, Cs, Mg, Ca, Sr, P, Si, Fe, Y, Zr, Mo, W, La, Ce, Er, and Yb.

[0009] For purposes of this invention, "high temperature" means temperatures above 600°C.

[0010] When the metallic component is steel, particularly austenitic or ferritic-martensitic steel, it is possible to obtain an aluminum oxide-based coating that is composed of an amorphous material and has thermomechanical properties (i.e., Poisson's coefficient, elastic modulus, and thermal expansion coefficient) comparable to those of austenitic and ferritic-martensitic steel. Furthermore, the coating has a higher hardness than stainless steel. As a result, it can withstand the substrate deformations expected in the normal operation of stainless steel components and prevent wear damage to the metallic component.

[0011] The coating of the present invention is able to resist crystallization and crack formation at temperatures up to at least 900°C.

[0012] By virtue of the matrix composed of aluminum oxide, the coating presented here is able to withstand corrosive attack by liquid metals (LM), heavy metal liquids (HLM) or molten salts (MS), and is therefore an effective barrier to prevent corrosion of the stainless steel to which it is applied.

[0013] Furthermore, the homogeneous amorphous coating is an effective barrier to hydrogen isotope penetration by preventing the infiltration of hydrogen isotopes into the coated stainless steel and subsequent embrittlement.

[0014] In conclusion, the coatings disclosed herein can withstand radiation and can withstand high doses without losing their protective properties.

[0015] Stabilization of the amorphous phase of aluminum oxide at high temperatures is desirable for many technological applications requiring resistance to wear, corrosion, and radiation. In particular, improved resistance to crystallization allows the application of aluminum oxide coatings on structural steel coatings in liquid-metal-cooled fast fission reactors. Thus, the qualified performance of aluminum oxide coatings in this field is extended beyond operational conditions (600°C). The primary consequence is increased radiation resistance at currently established operating temperatures. Furthermore, the delayed amorphous-crystalline phase transition allows for increased operating temperature setpoints according to the design, ensuring higher power generation efficiency.

[0016] (Detailed Description of the Invention) Further features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the invention, made with reference to the accompanying drawings, which are provided for illustrative and non-limiting purposes only. [Brief explanation of the drawings]

[0017] [Figure 1]Figure 1 shows the phase diagram of the pseudo-binary system Al2O3-Y2O3, taken from Fabrichnayan et al., Assessment of thermodynamic parameters in the system ZrO2-Y2O3-Al2O3, Zeitschrift fur Metallkunde, 95 (2004). [Figure 2] FIG. 2 is a graph showing the X-ray diffraction patterns of the pure Al2O3 film and the example doped Al2O3 film after the deposition process. [Figure 3] FIG. 3 is a graph showing the X-ray diffraction (XRD) patterns of pure Al2O3 films and example doped Al2O3 films after annealing at 700° C. for 72 hours. [Figure 4] FIG. 4 is a graph showing the X-ray diffraction patterns of pure Al2O3 films and example doped Al2O3 films after annealing at 800° C. for 72 hours. [Figure 5] FIG. 5 is a graph showing the X-ray diffraction patterns of pure Al2O3 films and example doped Al2O3 films after annealing at 900° C. for 72 hours. [Figure 6] Figure 6 shows scanning electron microscope (SEM) images at low magnification (left) and high magnification (right) of a pure Al2O3 film after annealing at 700 °C for 72 h. [Figure 7] FIG. 7 shows scanning electron microscope (SEM) images at low magnification (first row) and high magnification (second row) of pure Al2O3 films and example doped Al2O3 films after annealing at 800 °C for 72 hours. [Figure 8] FIG. 8 shows scanning electron microscope (SEM) images at low magnification (first row) and high magnification (second row) of pure Al2O3 films and example doped Al2O3 films after annealing at 900 °C for 72 hours. DETAILED DESCRIPTION OF THE INVENTION

[0018] We now describe Al2O3-based coatings, which have a thickness between 10 nm and 100 μm, preferably between 0.1 μm and 10 μm, and consist of a homogeneous amorphous layer with a crystalline domain fraction of less than 1% by volume, which is in no case detectable by XRD.

[0019] The coating compositions disclosed herein are characterized by an atomic dispersion of one or more dopants uniformly distributed in an Al2O3 matrix. This dispersion of dopants has the effect of delaying the onset of crystallization in the coating material. Furthermore, once the crystallization threshold is reached, the dopants distributed in the coating material have the secondary effect of delaying grain growth of the first metastable crystalline phase of Al2O3, termed γ-Al2O3, up to higher temperatures than in pure Al2O3 coatings. The advantage in this case is that γ-Al2O3 has a density similar to α-Al2O3 and therefore minimizes mechanical stress upon its formation.

[0020] Dopants considered for stabilizing the amorphous matrix are selected from the group consisting of C, Na, K, Cs, Mg, Ca, Sr, P, Si, Fe, Y, Zr, Mo, W, La, Ce, Er and Yb. Said dopants can be added in the form of pure elements or the relevant most stable oxides. Furthermore, said dopants can be added as single element dopants or multi-element dopants.

[0021] In the first case, the single element dopant is introduced into the Al2O3 matrix in the form of a pure element or a corresponding stable oxide, in the concentrations specified below, with reference to Figure 1. Considering the pseudo-binary phase diagram of the Al2O3-doped oxide system, the C of the first ternary compound present in the phase diagram and containing the highest molar concentration of Al2O3 is TFor the composition of the ternary compound mentioned above, N T The number is defined as the atomic ratio of dopant atoms to aluminum atoms. <N d ≦N T The doping oxide concentration C satisfies d This gives a molar concentration C T The atomic ratio N of the aforementioned ternary compounds is characterized by T In an embodiment of the invention, the condition is 0.001×N T ≦N d ≦0.90×N T In a more preferred embodiment, the condition is further limited to 0.01×N T ≦N d ≦0.70×N T and is limited to:

[0022] An embodiment of the present invention (shown in FIG. 1) is where the single element dopant is yttrium (C T = 37.5 mol%, which corresponds to 57.1 mass% in mass percent), and the concentration of Y2O3 C d may be selected from the range of 0.1-25 mol %, which corresponds to a range of 0.3-43.0 wt % in weight percent concentration, more precisely from the range of 11-22 mol %, which corresponds to a range of 22-38 wt % in weight percent concentration, and even more precisely from the range of 15-20 mol %, which corresponds to a range of 28-35 wt % in weight percent concentration. In the following, reference will be made to concentrations expressed in mol % for simplicity.

[0023] The phase diagram of the Al2O3-Y2O3 pseudobinary system in Figure 1 clarifies the correspondence between the mole fraction of the doped oxide and the doped atomic ratio to aluminum. In particular, N T is the atomic ratio Y / Al characterizing yttrium-aluminum garnet (YAG), while Nd is calculated from the selected molar concentration of Y2O3 and is within the range specified above.

[0024] Thus, the inventors have found that the addition of the doping element in amorphous aluminum oxide allows the coating to be stabilized at temperatures above 600°C. The range of molar concentrations at which stable amorphous aluminum oxide occurs tends to narrow as the temperature to which the coating is exposed increases. For example, in the case where yttrium is used as a dopant for a coating applied to steel, at temperatures below 800°C the amorphous aluminum oxide coating exhibits a C T The inventors have found that coatings having doped oxide concentrations between 11 and 22 mole percent are stable at temperatures between 800 and 900°C.

[0025] Preliminary experiments have shown that the temperature of stability can be raised above 900°C by the addition of one or more additional dopants (always chosen from the elements listed above). In such a situation, a primary dopant will be present, the concentration of which will be defined in the same way as in the case for a single dopant discussed above. The additional dopants will be added in an amount such that each dopant has a molar concentration equal to or less than the oxide of the primary dopant. In the particular case of oxides that form a solid solution with Al2O3, such as ZrO2, the doping oxide concentration is 0.1 mol% < C d It is selected in the range of ≦50 mol %.

[0026] The structure of the coating described above is composed of at least one layer of the above-described Al2O3-based material, but it can also include multiple layers, each characterized by the same or different chemical composition and microstructure. The thickness of each layer is between 10 nm and 100 μm, preferably in the range of 500 nm to 5 μm. For example, in one embodiment of the disclosed invention, the coating will include a single layer having a thickness of 3 μm.

[0027] The combination of an amorphous structure based on an Al2O3 matrix and chemical composition endows the described coating with several properties: resistance to wear, mechanical compatibility with stainless steel, a barrier against penetration by hydrogen isotopes, protection against corrosion by liquid metals (LM), heavy metal liquids (HLM) and molten salts (MS), and resistance to radiation and crystallization.

[0028] The coating can be applied to multiple supports and can be characterized by different geometries. Preferably, the coating is applied to austenitic (e.g., AISI 316 / 316L, 15-15 Ti) and ferritic-martensitic (e.g., reduced activation ferritic martensitic EUROFER) stainless steels. For example, the substrate can be a tube, in particular a fuel cladding tube for a liquid metal (LM), heavy metal liquid (HLM) or molten salt (MS) cooled nuclear reactor.

[0029] The growth of the coating can be obtained by a gas phase method for thin film deposition. For example, the coating is applied to the substrate material by pulsed laser deposition (PLD). Another example of a deposition method is atomic layer deposition (ALD). In one embodiment of the invention, the coating is applied by a deposition technique that does not use auxiliary heating (or support heating), but rather limits the temperature of the coated part to a range from room temperature to several hundred degrees Celsius. The crystallization temperature of the above-described Al2O3-based coating is at least 100°C higher than that of pure Al2O3 coatings. Furthermore, preliminary studies show that the composition of the Al2O3-based coating allows the nucleation of nanometer-sized γ-Al2O3 crystalline domains when the temperature exceeds the crystallization temperature threshold, thereby demonstrating the ability of said coatings to delay the amorphous-crystalline phase transition and control the nucleated crystalline phase within the coating material.

[0030] Furthermore, the chemical composition of the coating is such that it prevents the nucleation of ternary compounds and second phases at high temperatures. As designers of new lead-cooled fast reactors (LFR) and solar thermal systems strive to achieve higher system efficiencies, it is necessary to increase the coolant temperature beyond 650°C. Given the safety margin for operation and the effects of radiation exposure that may cause or accelerate crystallization, it is reasonable to assume that the coating should withstand temperatures up to 800°C.

[0031] The above-described coating materials, due to their compositional and microstructural advantages, can withstand even more extreme conditions up to at least 900° C. and are resistant to crystallization and mechanical failure.

[0032] The integrity of the coating is particularly important in protecting stainless steels from liquid metal (LM) and heavy metal liquid (HLM) corrosion in nuclear reactors, as defect formation (loss of adhesion, bubble formation, crack formation) can expose the substrate and also increase corrosion damage to reactor structural components. [Example]

[0033] This section presents an example of the application of the present invention to stainless steel cladding for a lead-cooled fast reactor (LFR). First, AISI 316 / 316L tubes (10 mm outer diameter, 200 mm long) were polished and then coated with 3 μm thick layers of pure Al2O3 and yttrium-doped Al2O3 obtained by ablation of a mixed target with Y2O3 doping concentrations of 5, 10, 16, and 23 mol% in Al2O3, respectively. Segments 20 mm long were cut from each tube. These samples were subjected to heat treatment in a vacuum furnace at temperatures of 700°C, 800°C, and 900°C for 72 hours. The total pressure measured during the dwell time at the set temperatures was 10 -3Pa: Under these conditions, a small amount of oxygen is still present in the furnace and reacts rapidly with the steel substrate to form oxides of iron and chromium on the uncoated surfaces of the tube segments (ends and uncoated interior surfaces) and on the exterior surfaces where defects in the coating expose the substrate to the furnace environment.

[0034] The X-ray diffraction (XRD) patterns shown in Figures 2-5 illustrate the evolution of the coating from the amorphous to the crystalline phase and the eventual nucleation of the ternary compounds (i.e., yttrium garnet and aluminum garnet (YAG)). Because the onset of crystallization of pure Al2O3 is detected at temperatures around 700 °C, XRD data for the annealed samples are reported at temperatures of 800 °C and 900 °C. While pure Al2O3 is well crystallized as early as 800 °C, XRD detects only the presence of γ-Al2O3, confirming the most significant retardation effect at a doping concentration of 23 mol%. Most of the reflections from the cubic phase γ-Al2O3 disappear, and the detected large peak suggests that the material is in the early stages of crystallization.

[0035] It is noteworthy that at 23 mol % doping oxide, the film rapidly crystallizes in the YAG phase for the sample annealed at 900°C.

[0036] The top-view SEM images shown in Figures 6 through 8 demonstrate the inability of pure Al2O3 films to provide a compact protective barrier to the steel support, as evidenced by crack formation and iron oxide growth. Crack formation was also detected in 5, 10, and 23 mol% doped Al2O3 coatings at 900 °C. The densification process, which occurs through the nucleation and growth of γ-Al2O3 crystals and YAG phases, causes the coating to rupture and allows the substrate to oxidize. Only the sample with 16 mol% dopant was found to be intact and adhered to the underlying steel.

Claims

1. 1. A high-temperature, non-aqueous environment metallic component, comprising a metallic body and a protective coating applied to an outer surface of said metallic body, said metallic body being intended to come into contact with a non-aqueous working fluid in use, said component comprising:

1. A metallic component for use in high-temperature, non-aqueous environments, wherein the protective coating comprises at least one amorphous aluminum oxide layer, the at least one amorphous aluminum oxide layer comprising at least one doping element uniformly dispersed in the amorphous aluminum oxide layer, the at least one doping element being selected from the group consisting of C, Na, K, Cs, Mg, Ca, Sr, P, Si, Fe, Y, Zr, Mo, W, La, Ce, Er, and Yb.

2. containing a single doping element selected from the group consisting of C, Na, K, Cs, Mg, Ca, Sr, P, Si, Fe, Y, Zr, Mo, W, La, Ce, Er and Yb; The doping element is capable of forming a ternary compound with aluminum oxide, and the atomic ratio N of the doping element to aluminum is d is 0 <N d ≦N T is in the range of N T is defined as the mole fraction of the oxide of the doping element in the ternary compound containing the maximum mole fraction of aluminum oxide in the phase diagram of aluminum oxide and the oxide of the doping element, where C T The atomic ratio N corresponds to d or The oxide of the doping element forms a solid solution with aluminum oxide, and the mole fraction C of the oxide of the doping element in the binary system of aluminum oxide and the oxide of the doping element is d is 0.1 mol% <C d ≦50 mol %; The metal member according to claim 1.

3. a plurality of doping elements selected from the group consisting of C, Na, K, Cs, Mg, Ca, Sr, P, Si, Fe, Y, Zr, Mo, W, La, Ce, Er, and Yb, wherein the plurality of doping elements includes a first doping element and at least one second doping element; The first doping element can form a ternary compound with aluminum oxide, and the atomic ratio of the first doping element to aluminum is N d is 0 <N d ≦N T is in the range of N T is defined as the mole fraction of the oxide of the first doping element in the ternary compound containing the maximum mole fraction of aluminum oxide in the phase diagram of aluminum oxide and the oxide of the first doping element, T The atomic ratio N corresponds to d or The oxide of the first doping element forms a solid solution with aluminum oxide, and the mole fraction C of the oxide of the first doping element in the binary system of aluminum oxide and the oxide of the first doping element d is 0.1 mol% <C d ≦50 mol % and the mole fraction of oxide associated with each second doping element is the mole fraction C of oxide of the first doping element. d 2. The metal member according to claim 1, wherein:

4. the atomic ratio of the oxide of the single doping element to aluminum, or the atomic ratio N of the oxide of the first doping element to aluminum d is 0.001 x N T ≦N d ≦0.90×N T , preferably 0.01 x N T ≦N d ≦0.70×N T The metal member according to claim 2 or 3, wherein

5. the single doping element or the first doping element is yttrium, and the mole fraction of yttrium oxide is C d The metal member according to any one of claims 2 to 4, wherein the content of the SiC is 0.1-25 mol%, preferably 11-22 mol%, and more preferably 15-20 mol%.

6. The metal member according to any one of claims 1 to 5, wherein the metal material body is steel.

7. 7. The metal component according to claim 6, wherein the steel is selected from the group consisting of ferritic-martensitic steel and austenitic steel.

8. The metallic component according to any one of claims 1 to 7, wherein the metallic component for use in a high-temperature, non-aqueous environment is a cladding tube for nuclear fuel used in a liquid metal cooled reactor or a molten salt cooled reactor.

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