Environmental barrier coatings based on high temperature stable amorphous oxides

Abstract

A metallic component for high temperature non-aqueous environments, comprising a metallic material body and a protective coating applied to an outer surface of the metallic material body, the protective coating being intended for contacting a non-aqueous working fluid wherein the protective coating comprises at least one layer of amorphous alumina, the at least one layer of amorphous alumina comprises at least one doping element uniformly distributed in the amorphous alumina layer, and the at least one doping element is 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 generally relates to materials used in high temperature non-aqueous environments, such as in industrial processes and energy conversion technologies. Background Art

[0002] In modern and future energy conversion technologies and industrial processes, high-temperature non-aqueous environments are of great significance for improving energy conversion efficiency and realizing new production processes.

[0003] The first and most important example is Generation IV nuclear reactor technology, which promises to provide widespread access to safe, CO2-free energy. Several concepts involve using liquid metal (LM), heavy liquid metal (HLM), molten salt (MS), or He as heat carriers to extract heat from the fast fission and fusion reactions in the reactor core. Designs for lead-cooled fast reactors (LFRs), accelerator-driven systems (ADSs), and fusion reactors involve the use of LM (e.g., lithium or sodium), HLM (e.g., lead), lead-bismuth eutectic (LBE), and lead-lithium eutectic (LLE) for cooling. Despite the attractive properties of LM coolants, liquid metal corrosion (LMC) can significantly alter the microstructure and chemical composition of structural components based on metal alloys, leading to a degradation of mechanical properties and ultimately an increased risk of failure.

[0004] Austenitic steels and ferritic / martensitic steels can meet the application requirements of the above-mentioned nuclear systems. However, these alloys cannot resist the selective dissolution of LM and HLM and are subject to liquid metal embrittlement (LME). In addition to nuclear applications, LM, HLM and molten salts are being investigated as working fluids in many thermal management applications and high-temperature energy conversion devices (e.g., concentrated solar power plants). In these applications, mitigation strategies designed to protect steel from corrosion include the formation of surface alloys and protective coatings. The metal coating or metal alloy coating should be pre-oxidized or an oxide protective layer should be formed in situ. However, the poor reliability and control of the oxidation process bring additional risks to the implementation of these technologies. Among the proposed ceramic coatings, only amorphous aluminum oxide coatings (a-Al2O3) deposited on stainless steel substrates by pulsed laser deposition (PLD) have been shown to provide protection of the underlying metal from LM and HLM corrosion and hydrogen isotope permeation, while also exhibiting radiation resistance and minimal differences in mechanical properties from the substrate. In particular, while many oxide compounds are stable to the reduction of liquid lead, only α-Al2O3 has thermomechanical properties that match those of stainless steel.

[0005] As described in US2014241485A1, the excellent performance of α-Al2O3 coatings is closely related to their integrity. This integrity, in turn, is related to the stability of the coating microstructure. All examples of α-Al2O3 coated steel in HLM described in US2014241485A1 were conducted at temperatures of 600°C or below. Above this temperature, the density decreases from the amorphous phase (ρ≈3.5 g / cm 3 ) increased to the crystalline phase (3.5 g / cm 3 <ρ<4g / cm 3 ), strong crystallization can cause cracking in the film, exposing the underlying support to corrosive environments. Stabilizing and controlling the amorphous-to-crystalline phase transition under the combined effects of radiation fields and high temperatures is crucial for the end application. Indeed, nuclear reactors and other similar thermal systems can experience transients exceeding the rated operating temperature by up to several hundred degrees for limited periods of time.

[0006] Furthermore, the effects of the radiation field should be considered. In particular, radiation-enhanced crystallization and radiation-induced crystallization are destabilization mechanisms that can affect the crystallization temperature of a material under irradiation or promote the nucleation of specific crystalline phases relative to what might be observed in a purely thermal mechanism. Consequently, the temperature thresholds for amorphous-crystalline and phase-phase transitions can be rigidly shifted to lower values.

[0007] In summary, the coating microstructure affects the mechanical properties of the film, and phase transformations can lead to densification, crack formation, and loss of adhesion and coating integrity. Therefore, stabilizing the coating microstructure to fine-tune and control the coating's properties will contribute to the advancement and development of advanced nuclear systems and other high-temperature technologies using non-aqueous working fluids. Summary of the Invention

[0008] To achieve the above-mentioned objectives, the subject of the present invention is a metal component for use in high-temperature non-aqueous environments, comprising a body of metal material and a protective coating applied to the outer surface of the body of metal material, said protective coating being intended for use in contact with a non-aqueous working fluid,

[0009] Wherein, the protective coating comprises at least one layer of amorphous aluminum oxide, and the at least one layer of amorphous aluminum oxide comprises at least one doping element uniformly distributed in the amorphous aluminum oxide layer, and the at least one doping element is 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.

[0010] For the purposes of this invention, "high temperature" refers to temperatures above 600°C.

[0011] In the case where the metal component is steel, in particular austenitic or ferritic-martensitic steel, it is possible to obtain an alumina-based coating composed of an amorphous material whose thermomechanical properties (i.e., Poisson's coefficient, elastic modulus, and thermal expansion coefficient) are compatible with those of austenitic and ferritic-martensitic stainless steels. Furthermore, the coating has a higher hardness than the stainless steel. Therefore, it can withstand the deformation of the substrate expected during normal operation of the stainless steel component and prevent wear damage to the metal component.

[0012] The coatings of the present invention resist crystallization and crack formation at high temperatures (at least up to 900°C).

[0013] Since the substrate is composed of aluminum oxide, the coating of the present invention can resist the corrosive effects of liquid metal (LM), heavy liquid metal (HLM) or molten salt (MS). Therefore, it is an effective barrier to prevent corrosion of the stainless steel to which it is applied.

[0014] Furthermore, the uniform and amorphous coating acts as an effective barrier against hydrogen isotope penetration by preventing their penetration into the interior of the coated stainless steel and subsequent embrittlement.

[0015] In summary, the coatings disclosed herein are radiation resistant and can withstand high doses without losing their protective properties.

[0016] The stability of amorphous aluminum oxide's phase at high temperatures is ideal for applications in many technical fields requiring resistance to wear, corrosion, and radiation. In particular, the enhanced resistance to crystallization allows the use of aluminum oxide coatings on structural steel in the field of liquid-metal-cooled fast fission reactors. Consequently, the qualified performance of aluminum oxide coatings in this field can be extended to temperatures above operating conditions (600°C). The result is, first of all, improved radiation resistance at currently defined operating temperatures. Furthermore, the delayed amorphous-crystalline transition allows for higher operating temperature setpoints depending on the design, ensuring higher power generation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings, which are provided for purely illustrative and non-limiting purposes.

[0018] Figure 1 The phase diagram of the pseudo-binary system Al2O3-Y2O3 is shown, adapted from Fabrichnayanet al., Assessment of thermodynamic parameters in the system ZrO2–Y2O3–Al2O3, Zeitschrift für Metallkunde, 95, 2004;

[0019] Figure 2 is a graph showing X-ray diffraction patterns of a pure Al2O3 film and a doped Al2O3 film according to an embodiment after the deposition process;

[0020] Figure 3 is a graph showing X-ray diffraction (XRD) patterns of a pure Al2O3 film and an Al2O3 film doped in an embodiment after annealing at 700°C for 72h;

[0021] Figure 4 is a graph showing X-ray diffraction patterns of a pure Al2O3 film and an Al2O3 film doped in an embodiment after annealing at 800°C for 72h;

[0022] Figure 5 is a graph showing X-ray diffraction patterns of a pure Al2O3 film and an Al2O3 film doped in an embodiment after annealing at 900°C for 72h;

[0023] Figure 6 Shown are scanning electron microscopy (SEM) images of a pure Al2O3 film after annealing at 700℃ for 72h at low magnification (left) and high magnification (right);

[0024] Figure 7 Shows scanning electron microscope (SEM) images of pure Al2O3 film and doped Al2O3 film in the example after annealing at 800℃ for 72h at low magnification (first row) and high magnification (second row);

[0025] Figure 8 Scanning electron microscope (SEM) images of pure Al2O3 films and doped Al2O3 films in Examples after annealing at 900°C for 72 h at low magnification (first row) and high magnification (second row) are shown. DETAILED DESCRIPTION

[0026] The coatings based on Al2O3 are now described. The coatings consist of an amorphous homogeneous layer with a thickness of 10 nm to 100 μm, preferably 0.1 μm to 10 μm, with a crystalline domain fraction of less than 1% by volume and in any case not detectable by XRD.

[0027] The coating compositions disclosed herein are characterized by an atomic dispersion of one or more dopants, the dopants being uniformly distributed throughout the Al2O3 matrix. This dispersion of the dopants has the effect of delaying the onset of crystallization in the coating material. Furthermore, once the crystallization threshold is reached, the dopants distributed throughout the coating material have a secondary effect, delaying the grain growth of the first metastable crystalline phase of Al2O3 (i.e., γ-Al2O3) to a higher temperature than that of a pure Al2O3 coating. An advantage in this case is that γ-Al2O3 has a similar density to α-Al2O3, so its formation is subject to minimal mechanical stress.

[0028] The dopant used to stabilize the amorphous matrix is ​​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 dopant can be added in pure elemental form or in the form of the most stable oxide compound thereof. Furthermore, the dopant can be added as a single element dopant or a multi-element dopant.

[0029] In the first case, the single element dopant is introduced into the Al2O3 matrix in pure elemental form or in the form of the relevant stable oxide, with a concentration according to Figure 1 According to the pseudo binary phase diagram of Al2O3-oxide doping system, determine the first ternary compound in the phase diagram and the C containing the highest molar concentration of Al2O3 T For the composition of the above ternary compound, the number N T It is defined as the atomic ratio of dopant atoms to Al atoms. The coating material described herein has a <N d ≤N T Conditional doping oxide concentration C d , thereby disclosing the atomic ratio of dopant atoms to Al atoms, which is less than the atomic ratio of the dopant atoms to the Al atoms at a molar concentration of C T The atomic ratio N of the above ternary compound is characterized by T In the embodiment of the present invention, the condition is limited to 0.001*N T ≤N d ≤0.90*N T In a preferred embodiment, this condition is further limited to 0.01*N T ≤N d ≤0.70*N T .

[0030] In the embodiments of the present invention (such as Figure 1 As shown), the single element dopant is yttrium (C T =37.5% mol, equivalent to a weight concentration of 57.1% wt), the concentration of Y2O3 C dThe concentration is selected within the range of 0.1-25% mol (equivalent to a weight concentration within the range of 0.3-43.0% wt), more precisely within the range of 11-22% mol (equivalent to a weight concentration within the range of 22-38% wt), and more precisely within the range of 15-20% mol (equivalent to a weight concentration within the range of 28-35% wt). For simplicity, the concentrations hereinafter will be expressed in % mol.

[0031] Figure 1 The pseudo-binary Al2O3-Y2O3 system phase diagram illustrates the corresponding relationship between the mole fraction of the doped oxide and the doping atomic ratio on Al. T is the atomic ratio Y / Al that characterizes yttrium aluminum garnet (YAG), while N d It is calculated based on the selected Y2O3 molar concentration and is within the above range.

[0032] Therefore, the inventors have found that adding doping elements to amorphous alumina can make the coating stable at temperatures above 600°C. As the temperature to which the coating is subjected increases, the molar concentration range of the amorphous alumina within which stable amorphous alumina occurs tends to narrow. For example, in the case of yttrium as a dopant for a coating applied to steel, the inventors have found that at temperatures below 800°C, for amorphous alumina less than or equal to C T =37.5 mol% amorphous alumina coatings are stable at any value of dopant oxide concentration. Coatings with dopant oxide concentrations between 11 mol% and 22 mol% are stable at temperatures between 800°C and 900°C.

[0033] Preliminary experiments have shown that the stability temperature can be increased to above 900°C by adding one or more additional dopants (always selected from the elements listed above). In this case, a first doping element is present, and its concentration is defined in the same way as discussed above for a single dopant. The additional dopants are added in amounts such that the molar concentration of each dopant is less than or equal to the molar concentration of the oxide of the first doping element.

[0034] For the specific case of oxides that form a solid solution with Al2O3 (e.g. ZrO2), the concentration of the doped oxide is 0.1% mol ≤ C d Select within the range of ≤50% mol.

[0035] The coating structure is composed of at least one layer of the aforementioned Al2O3-based material. However, the coating structure may also include multiple layers, each layer being 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 present invention, the coating comprises a single layer having a thickness of 3 μm.

[0036] The combination of the amorphous structure and chemical composition of the Al2O3 matrix gives the above coating materials a variety of properties, namely wear resistance, mechanical compatibility with stainless steel, hydrogen isotope permeation barrier, protection against LM, HLM and MS corrosion, radiation resistance and anti-crystallization.

[0037] The coating can be applied to a variety of support materials characterized by different geometries. Preferably, the coating is applied to austenitic stainless steels (e.g., AISI 316 / 316L, 15-15Ti) and ferritic / martensitic stainless steels (e.g., low-activation ferritic martensitic EUROFER). For example, the substrate can be a tube, particularly a cladding tube for LM, HLM, or MS cooling of nuclear reactor fuel.

[0038] The coating can be grown using vapor-phase thin film deposition techniques. For example, the coating is applied to the substrate material by pulsed laser deposition (PLD). Another example of a deposition technique is atomic layer deposition (ALD). In one embodiment of the present invention, the coating is applied using a deposition technique that does not utilize support heating but rather limits the temperature of the component to be coated to a range of room temperature to several hundred degrees Celsius.

[0039] The crystallization temperature of the Al2O3-based coatings is at least 100°C higher than that of pure Al2O3 coatings. Furthermore, as shown in preliminary studies, the composition of the Al2O3-based coatings allows the nucleation of nanosized γ-Al2O3 domains when the temperature exceeds the threshold temperature for crystallization, demonstrating the coating's ability to induce a delayed amorphous-to-crystalline transition and control the nucleated crystalline phase within the coating material.

[0040] Furthermore, the coating's chemical composition prevents the nucleation of ternary compounds and secondary phases at high temperatures. As designers of new LFR and solar thermal systems strive to achieve higher system efficiencies, it becomes necessary to increase coolant temperatures above 650°C. Considering operational safety margins and radiation effects that may induce or accelerate crystallization, it is reasonable to assume that the coating should be able to withstand temperatures up to 800°C.

[0041] The coating material, by virtue of its composition and microstructure, is able to withstand more extreme conditions, resisting crystallization and mechanical failure at temperatures of at least up to 900°C.

[0042] In particular, coating integrity is crucial for protecting stainless steels in nuclear reactors from LM and HLM corrosion, as defect initiation (loss of adhesion, blister formation, crack formation) can expose the substrate and increase corrosion damage to reactor structural components.

[0043] Example

[0044] An embodiment of the application of the present invention in LFR stainless steel cladding is now presented. An AISI 316 / 316L tube (outer diameter 10 mm, length 200 mm) is first polished and then coated with a 3 μm thick pure Al2O3 layer and an Al2O3 layer doped with Y atom dispersion, the Al2O3 layer doped with Y atom dispersion being obtained by a mixed target sputtering method, with Y2O3 doping concentrations in Al2O3 being 5% mol, 10% mol, 16% mol and 23% mol, respectively. 20 mm long sections are cut from each tube. These samples are heat treated in a vacuum furnace at 700°C, 800°C and 900°C for 72 hours. During the dwell time at the set value temperature, the measured total pressure is 10 -3 Pa: Under these conditions, a small amount of oxygen is still present in the furnace and reacts rapidly with the steel substrate to form iron oxides and chromium oxides on the uncoated surfaces (edges and uncoated inner surfaces) and outer surfaces (defects in the coating expose the substrate to the furnace environment) of the pipe cut sections.

[0045] Figure 2-5 The XRD patterns shown depict the coating's evolution from an amorphous to a crystalline phase, and the eventual nucleation of ternary compounds (i.e., yttrium garnet and aluminum garnet - YAG). Crystallization of pure Al2O3 is detected at temperatures around 700°C, so XRD data for the annealed sample are reported for temperatures of 800°C and 900°C. Pure Al2O3 crystallizes well as early as 800°C, while the most pronounced delayed effect is observed at a doping concentration of 23% mol%, at which point only the presence of γ-Al2O3 can be detected by XRD. Most of the reflections of the cubic γ-Al2O3 phase disappear, and the large peak detected indicates that the material is in the early stages of crystallization.

[0046] It is noteworthy that the film crystallizes rapidly in the YAG phase in the sample annealed at 900 °C with 23 mol% doped oxide.

[0047] Figures 6 to 8The top SEM image shown demonstrates that the pure Al2O3 film is unable to provide a tight, protective barrier to the steel support, as evidenced by crack formation and the resulting iron oxide growth. Crack formation was also detected at 900°C in Al2O3 coatings doped with 5%, 10%, and 23% mol%. Densification processes caused by γ-Al2O3 crystallization and nucleation and growth of the YAG phase led to cracking of the coating and oxidation of the substrate. Only the sample with 16% mol% dopant was intact and adhered to the underlying steel.

Claims

1. A metal component for use in a high-temperature non-aqueous environment, the metal component comprising a main body of metal material and a protective coating applied to an outer surface of the main body of metal material, the protective coating being intended for contact with a non-aqueous working fluid; in, The protective coating comprises at least one layer of amorphous aluminum oxide, wherein the at least one layer of amorphous aluminum oxide comprises at least one doping element uniformly distributed in the amorphous aluminum oxide layer, and the at least one doping element is 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. The metal component according to claim 1, comprising 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; in, The doping element can form a ternary compound with aluminum oxide, and the atomic ratio between the doping element and aluminum is N d 0 <N d ≤N T , where N T corresponds to the maximum mole fraction C T The atomic ratio N d Value, C T Defined as the mole fraction of the dopant element oxide in the ternary compound containing the highest mole fraction of alumina in the alumina-dopant element oxide phase diagram; or Wherein, the doping element oxide forms a solid solution with aluminum oxide, and in the binary system of aluminum oxide-doping element oxide, the molar fraction of the doping element oxide C d 0.1% mol <C d ≤50% mol.

3. The metal component according to claim 1 , comprising a plurality of doping elements, the plurality of doping elements 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, the plurality of doping elements comprising a first doping element and at least one second doping element; in, The first doping element can form a ternary compound with aluminum oxide, and the atomic ratio between the first doping element and aluminum is N d 0 <N d ≤N T , where N T corresponds to the maximum mole fraction C T The atomic ratio N d Value, C T is defined as the mole fraction of the first doping element oxide in the ternary compound containing the highest mole fraction of aluminum oxide in the aluminum oxide-first doping element oxide phase diagram; or The first doping element oxide forms a solid solution with aluminum oxide. In the binary system of aluminum oxide and the first doping element oxide, the molar fraction of the first doping element oxide C d 0.1% mol <C d ≤50% mol; and The molar fraction of the oxide of each second doping element is lower than or equal to the molar fraction of the oxide of the first doping element C. d .

4. The metal component according to claim 2 or 3, wherein the atomic ratio N between the single doping element oxide and aluminum, or between the first doping element oxide and aluminum, is d 0.001*N T ≤N d ≤0.90*N T , preferably 0.01*N T ≤N d ≤0.70*N T .

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

6. A metal component according to any one of the preceding claims, wherein the metal material is steel.

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

8. The metal component according to any one of the preceding claims, wherein the metal component is a cladding tube for liquid metal or molten salt cooled reactor nuclear fuel.

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