An accident-tolerant Cr / Nb nanomultilayer coating and its preparation method

Abstract

The present invention discloses an accident-tolerant Cr / Nb nano-multilayer coating and a preparation method thereof. The Cr / Nb nano-multilayer coating is deposited on a clean silicon substrate by magnetron sputtering. The principle is that Ar gas generates high-density Ar+ after glow discharge. Under the action of the electric field, the Ar+ is strongly attracted to the negative electrode and bombards the metal Cr DC target and the metal Nb DC target at a high rate, forming a collision cascade process to sputter target atoms and secondary electrons. The Cr and Nb atoms ultimately move in opposite directions to deposit on the silicon substrate at the anode. The secondary electrons move in an orthogonal electromagnetic field in a direction perpendicular to the electric and magnetic fields, circulating in the form of cycloids, increasing the ionization rate of Ar, the ion density and energy, and thus achieving high-rate sputtering. The method regulates the microstructure of the accident-tolerant Cr / Nb nano-multilayer coating by controlling the modulation ratio, thereby improving the oxidation resistance of the Cr / Nb nano-multilayer coating.

Description

Technical Field

[0001] The invention belongs to the field of material surface modification, and in particular relates to an accident-tolerant Cr / Nb nano multilayer coating and a preparation method thereof. Background Art

[0002] Pure Cr metal coatings have become the first choice for light water reactor cladding materials due to their good corrosion resistance, high melting point, excellent mechanical strength and wear resistance, as well as good chemical inertness, high-temperature oxidation performance and substrate adhesion. Currently, there are many preparation methods for depositing pure Cr metal coatings. Among them, magnetron sputtering is a relatively mature coating preparation technology due to its low energy, controllable deposition rate and good process repeatability. However, the pure Cr metal coatings prepared by magnetron sputtering usually show a columnar crystal growth morphology. The continuous grain boundaries of the columnar crystals are a defect. Under the action of external forces, they can easily cause cracking and peeling of the coating, making it difficult to achieve multifunctional and efficient protection. Therefore, the continuous growth of columnar crystals is not conducive to improving the performance of the metal Cr coating. By introducing a heterogeneous interface, the continuous growth of columnar crystals in the entire film thickness direction can be destroyed, and the stress-oriented multifunctional protection of the multilayer film coating can be achieved. Nb and Cr are both BCC metals, and metallic Nb coatings have good radiation resistance and a small thermal neutron absorption cross section. They also have a high melting point, high thermal strength and certain corrosion resistance. Therefore, Cr and Nb are selected as target materials. Combining the advantages of the two materials, magnetron sputtering is used to prepare Cr / Nb nano-multilayer coatings with different modulation ratios.

[0003] Modulation parameter changes significantly affect the preferred growth direction during the deposition and growth of metallic Cr / Nb nanostructured multilayer coatings, thereby determining the coating's microstructure. Adjusting the modulation parameters can improve and enhance the coating's quality and performance. To provide effective protection in extreme environments such as high-temperature oxidation, Cr / Nb nanostructured multilayer coatings must possess a uniform, dense microstructure and excellent performance, which relies heavily on the fabrication techniques and process parameters employed. Current research focuses on selecting the optimal magnetron sputtering process and modulation parameters to manipulate the coating's microstructure and produce Cr / Nb nanostructured multilayer coatings with superior oxidation resistance. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides an accident-tolerant Cr / Nb nano-multilayer coating and a preparation method thereof, so as to achieve the regulation of the microstructure of the Cr / Nb nano-multilayer coating.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing an accident-tolerant Cr / Nb nano-multilayer coating comprises the following steps:

[0007] Step 1, ultrasonically cleaning and drying the surface of the silicon substrate;

[0008] Step 2: Under vacuum, DC magnetron co-sputtering is performed on a silicon substrate using a Cr target and a Nb target. The deposition power of the Cr target and the Nb target are both 200 W, the deposition pressure is 0.3 Pa, and the rotation speed of the silicon substrate is 10 r / min. After sputtering and deposition to a predetermined thickness, the coating is cooled to room temperature in the furnace to obtain a Cr / Nb nano-multilayer coating.

[0009] During the magnetron co-sputtering process, the sum of the thicknesses of the Cr layer and the Nb layer formed in each modulation period is the same, and the modulation ratio of the thickness of the Cr layer to the Nb layer formed in each modulation period is 0.1-9.0.

[0010] Preferably, in step 1, the silicon substrate is first polished, and then the polished silicon substrate is ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes respectively and then dried to remove impurities on the surface of the silicon substrate.

[0011] Preferably, the vacuum degree of the vacuum environment in step 2 is 1.0×10 -4 Below Pa.

[0012] Preferably, in step 2, under vacuum, Ar + The silicon substrate is etched by ions and then pre-sputtered;

[0013] The etching power is 200 W, the etching pressure is 1.0 Pa, and the etching time is 5 min.

[0014] Preferably, the argon ventilation time before the pre-sputtering is at least 30 seconds, and the pre-sputtering time is at least 10 seconds, so as to remove adsorbed substances on the surface of the target material.

[0015] Preferably, the total time of the magnetron co-sputtering in step 2 is 16460s-18280s, and in each modulation cycle, the sputtering time of the Cr target is 74-667s, and the sputtering time of the Cr target is 770-86s.

[0016] Preferably, the argon gas flow rate during the deposition process is set to 40 sccm.

[0017] An accident-tolerant Cr / Nb nano-multilayer coating, wherein when the modulation ratio is less than 1.00, the grain morphology of the Cr / Nb nano-multilayer coating is triangular pyramidal columnar crystals;

[0018] When the modulation ratio is ≥1.00, the grain morphology of the Cr / Nb nano multilayer coating is worm-like columnar crystals.

[0019] Preferably, the thickness of the Cr / Nb nano multilayer coating is 2 μm, and the total thickness of the Cr layer and the Nb layer in each modulation period is the same and is 100 nm.

[0020] Preferably, the hardness of the Cr / Nb nano multilayer coating is 5.0 GPa to 7.0 GPa.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] The present invention provides a method for preparing an accident-tolerant Cr / Nb nano-multilayer coating. The Cr / Nb nano-multilayer coating is deposited on a clean silicon substrate via magnetron sputtering deposition. First, impurities on the silicon substrate surface are removed to improve the coating's bonding strength to the substrate. Ar gas is then glow-discharged to produce high-density Ar+. Under the action of an electric field, the Ar+ is strongly attracted to the negative electrode and bombards a Cr and Nb DC target at a high rate, transferring some of its kinetic energy to target atoms. The target atoms then collide with other target atoms, forming a cascade process. During this cascade process, target atoms near the surface gain sufficient kinetic energy to move outward, sputtering target atoms and secondary electrons. Cr and Nb atoms ultimately move in the opposite direction to deposit on the silicon substrate at the anode. The secondary electrons, in an orthogonal electromagnetic field, move perpendicularly to the electric and magnetic fields, circulating in a cycloidal pattern. This increases the Ar ionization rate, ion density, and energy, thereby achieving high-rate sputtering. Finally, the coating is cooled to room temperature in a vacuum coating chamber to avoid coating flaking caused by a slight temperature rise during sputtering and the different thermal expansion coefficients between the coating and the substrate. As a result, the final deposited coating has few defects and strong adhesion. The present invention regulates the microstructure of the accident-tolerant Cr / Nb nano-multilayer coating by controlling the modulation ratio. Changes in the modulation ratio affect changes in the coating's surface morphology and, at the same time, its performance. By controlling the modulation ratio to regulate the coating's microstructure, a Cr / Nb nano-multilayer coating with a modulation ratio of 3 achieves optimal oxidation resistance in 1000°C water vapor.

[0023] Furthermore, after the deposition is completed, the coating is placed in a high vacuum coating chamber for furnace cooling to avoid thermal stress caused by the different thermal expansion coefficients of the coating and the substrate, which may cause the coating to fall off the substrate, and to prevent the coating from oxidizing under high temperature conditions.

[0024] A fault-tolerant metallic Cr / Nb coating features columnar grains with a stable nanocrystalline size and triangular pyramidal and vermicular structures on the surface. The coating's microstructure changes with the modulation ratio: at low modulation ratios, the coating exhibits large grains and a loose structure. As the modulation ratio increases, the coating's grain size decreases and then increases, while the structural density increases and then decreases. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a SEM photo of the accident-tolerant Cr / Nb nano-multilayer coating prepared by magnetron sputtering of the present invention;

[0026] Figure 2 This is an indentation hardness curve of the accident-tolerant Cr / Nb nano multilayer coating of the present invention;

[0027] Figure 3 This is a graph showing the weight gain per unit area of the accident-tolerant Cr / Nb nano multilayer coating of the present invention after oxidation in water vapor at 1000°C for 10 minutes. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the accompanying drawings, which are intended to explain rather than limit the present invention.

[0029] A method for preparing an accident-tolerant Cr / Nb nano-multilayer coating comprises the following steps:

[0030] Step 1), ultrasonically cleaning and drying the surface of the silicon substrate;

[0031] Specifically, the silicon substrate is polished on one side, and then ultrasonically cleaned in acetone and ethanol for 15 minutes respectively, and then quickly dried, so that the surface of the silicon substrate is clean, free of stains and dust, and has a roughness of less than 0.8 nm.

[0032] The silicon substrate is fixed on the base plate and sent into the vacuum coating chamber, and the back vacuum is then pumped to 1.0×10 -4 Below Pa.

[0033] Step 2) In a high vacuum environment, use Ar + Ions are used to etch and remove impurities on the substrate surface, followed by magnetron sputtering deposition to obtain a metal Cr / Nb coating with a nano-multilevel structure. The metal Cr and Nb targets use a DC power supply with a power of 200W and a target purity of not less than 99.95wt.%; the deposition pressure is 0.3Pa and the deposition temperature is room temperature.

[0034] Specifically, the etching power is 200 W, the etching pressure is 1.0 Pa, and the etching time is 5 min; the argon gas is introduced for 30 s before pre-sputtering, the pre-sputtering time is 10 s, and the silicon substrate rotation speed during the deposition process is 10 r / min.

[0035] like Figure 1As shown in the figure, the modulation ratio is the ratio of the thickness of the Cr layer to the Nb layer. The grain morphology of the prepared accident-tolerant Cr / Nb nano-multilayer coating appears as triangular pyramidal columnar crystals at low modulation ratios (η<1.00), while it appears as worm-shaped columnar crystals at high modulation ratios (η≥1.00), and the grain size is stable in the nanocrystalline range; the microstructure of the coating changes with the change of the modulation ratio: at low modulation ratios, the grain size of the coating is larger and the structure is relatively loose; as the modulation ratio increases, the grain size of the coating first decreases and then increases, and the structural density first increases and then slightly decreases.

[0036] A method for preparing an accident-tolerant Cr / Nb nano-multilayer coating is provided. First, a polished Si(111) substrate is placed in an acetone solution and an anhydrous ethanol solution for ultrasonic cleaning for 15 minutes respectively to remove surface stains and dust and improve the bonding strength between the coating and the substrate. The Cr / Nb nano-multilayer coating is deposited on a clean silicon substrate by magnetron sputtering deposition. The principle is that Ar gas generates high-density Ar ions after glow discharge. Ar + Under the action of the electric field, it is strongly attracted to the negative electrode and bombards the target material at a high rate, and transfers part of the kinetic energy to the target atoms, after which the target atoms collide with other target atoms to form a cascade process. In this cascade process, target atoms near certain surfaces obtain sufficient kinetic energy to move outward, so that the target atoms and secondary electrons are sputtered out, and the Cr atoms and Nb atoms eventually move in the opposite direction to deposit on the silicon substrate of the anode, while the secondary electrons move in the direction of motion of the orthogonal electromagnetic field perpendicular to the electric field and the magnetic field, and circulate in the form of a cycloid, thereby increasing the ionization rate of Ar, increasing the ion density and energy, and thus achieving high-rate sputtering. The present invention uses a DC target to magnetron sputter deposit an accident-tolerant Cr / Nb nano-multilayer coating, with a deposition power of 200W. The same deposition pressure and different deposition times are used to regulate the microstructure of the Cr / Nb nano-multilayer coating. Finally, the coating is cooled to room temperature in a vacuum coating chamber to avoid coating peeling due to a small temperature rise during sputtering and the different thermal expansion coefficients of the coating and the substrate. Therefore, an accident-tolerant Cr / Nb nano-multilayer coating with few defects and strong adhesion is finally deposited.

[0037] Example 1

[0038] A method for preparing an accident-tolerant Cr / Nb nano-multilayer coating comprises the following steps:

[0039] S1, the polished Si (111) substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 15 min respectively and then dried to remove impurities on the surface of the silicon substrate; then the silicon substrate was fixed on the base plate and automatically conveyed into the magnetron sputtering vacuum coating chamber, and the back vacuum was evacuated to 1.0×10 -4 Pa, the etching power is 200W, the etching pressure is 1.0Pa, and the time is 5min.

[0040] S2. Start magnetron sputtering deposition of Cr / Nb nano-multilayer coating. First, introduce argon for 30 seconds, pre-sputter for 10 seconds, and use metal Cr DC target and metal Nb DC target (purity is 99.95wt.%) for co-deposition. The deposition power is 200W, the substrate rotation speed is 10r / min, the deposition pressure is set to 0.3Pa, the argon flow rate is 40sccm, the deposition temperature is room temperature, the single-layer Cr thickness is set to 10nm, the single-layer Nb thickness is set to 90nm, the number of cycles is 20, that is, the total film thickness is 2μm.

[0041] In step S3, the sample was allowed to cool naturally in the vacuum coating chamber for 2-3 hours to room temperature before being removed, resulting in a Cr / Nb nano-multilayer coating with a thickness of approximately 2.00 μm. Microstructural characterization of the prepared Cr / Nb nano-multilayer coating revealed triangular pyramidal columnar crystals with a stable size within the nanocrystalline range. The grains were large and had a relatively loose structure.

[0042] Example 2

[0043] A method for preparing an accident-tolerant Cr / Nb nano-multilayer coating comprises the following steps:

[0044] S1, the polished Si (111) substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 15 min respectively and then dried to remove impurities on the surface of the silicon substrate; then the silicon substrate was fixed on the base plate and automatically conveyed into the magnetron sputtering vacuum coating chamber, and the back vacuum was evacuated to 1.0×10 -4 Pa, the etching power is 200W, the etching pressure is 1.0Pa, and the time is 5min.

[0045] S2, start magnetron sputtering deposition of Cr / Nb nano-multilayer coating, first introduce argon for 30s, pre-sputter for 10s, and use metal Cr DC target and metal Nb DC target (purity is 99.95wt.%) for co-deposition, the deposition power is 200W, the substrate rotation speed is 10r / min, the deposition pressure is set to 0.3Pa, the argon flow rate is 40sccm, the deposition temperature is room temperature, the single layer Cr thickness is set to 25nm, the single layer Nb thickness is 75nm, the number of cycles is 20, that is, the total film thickness is 2μm.

[0046] After the sample was naturally cooled in the vacuum coating chamber for 2-3 hours to room temperature, it was removed from the vacuum coating chamber, resulting in a Cr / Nb nano-multilayer coating with a thickness of approximately 2.13 μm. Microstructural characterization of the prepared Cr / Nb nano-multilayer coating revealed triangular pyramidal columnar crystals with a stable size within the nanocrystalline range. The grains were large and the structure was relatively loose.

[0047] Example 3

[0048] A method for preparing an accident-tolerant Cr / Nb nano-multilayer coating comprises the following steps:

[0049] S1, the polished Si (111) substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 15 min respectively and then dried to remove impurities on the surface of the silicon substrate; then the silicon substrate was fixed on the base plate and automatically conveyed into the magnetron sputtering vacuum coating chamber, and the back vacuum was evacuated to 1.0×10 -4 Pa, the etching power is 200W, the etching pressure is 1.0Pa, and the time is 5min.

[0050] S2, start magnetron sputtering deposition of Cr / Nb nano-multilayer coating, first introduce argon for 30s, pre-sputter for 10s, and use metal Cr DC target and metal Nb DC target (purity is 99.95wt.%) for co-deposition, the deposition power is 200W, the substrate rotation speed is 10r / min, the deposition pressure is set to 0.3Pa, the argon flow rate is 40sccm, the deposition temperature is room temperature, the single layer Cr thickness is set to 50nm, the single layer Nb thickness is 50nm, the number of cycles is 20, that is, the total film thickness is 2μm.

[0051] After the sample was naturally cooled in the vacuum coating chamber for 2-3 hours to room temperature, it was removed from the vacuum coating chamber, resulting in a Cr / Nb nano-multilayer coating with a thickness of approximately 2.17 μm. Microstructural characterization of the prepared Cr / Nb nano-multilayer coating revealed vermicular columnar crystals with stable columnar crystal size within the nanocrystalline range. The grains were large and the structure was relatively loose.

[0052] Example 4

[0053] A method for preparing an accident-tolerant Cr / Nb nano-multilayer coating comprises the following steps:

[0054] S1, the polished Si (111) substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 15 min respectively and then dried to remove impurities on the surface of the silicon substrate; then the silicon substrate was fixed on the base plate and automatically conveyed into the magnetron sputtering vacuum coating chamber, and the back vacuum was evacuated to 1.0×10 -4 Pa, the etching power is 200W, the etching pressure is 1.0Pa, and the time is 5min.

[0055] S2, start magnetron sputtering deposition of Cr / Nb nano multilayer coating, first introduce argon for 30s, pre-sputter for 10s, use metal Cr DC target and metal Nb DC target (purity is 99.95wt.%) for co-deposition, the deposition power is 200W, the substrate rotation speed is 10r / min, the deposition pressure is set to 0.3Pa, the argon flow rate is 40sccm, the deposition temperature is room temperature, the single layer Cr thickness is set to 75nm, the single layer Nb thickness is 25nm, the number of cycles is 20, that is, the total film thickness is 2μm.

[0056] After the sample was naturally cooled in the vacuum coating chamber for 2-3 hours to room temperature, it was removed from the vacuum coating chamber, resulting in a Cr / Nb nano-multilayer coating with a thickness of approximately 2.23 μm. Microstructural characterization of the prepared Cr / Nb nano-multilayer coating revealed vermicular columnar crystals with stable columnar crystal size within the nanocrystalline range. The grain size was small, and the structure was densely packed.

[0057] Example 5

[0058] A method for preparing an accident-tolerant Cr / Nb nano-multilayer coating comprises the following steps:

[0059] S1, the polished Si (111) substrate was ultrasonically cleaned in acetone and anhydrous ethanol for 15 min respectively and then dried to remove impurities on the surface of the silicon substrate; then the silicon substrate was fixed on the base plate and automatically conveyed into the magnetron sputtering vacuum coating chamber, and the back vacuum was evacuated to 1.0×10 -4 Pa, the etching power is 200W, the etching pressure is 1.0Pa, and the time is 5min.

[0060] S2, start magnetron sputtering deposition of Cr / Nb nano-multilayer coating, first introduce argon for 30s, pre-sputter for 10s, and use metal Cr DC target and metal Nb DC target (purity is 99.95wt.%) for co-deposition, the deposition power is 200W, the substrate rotation speed is 10r / min, the deposition pressure is set to 0.3Pa, the argon flow rate is 40sccm, the deposition temperature is room temperature, the single layer Cr thickness is set to 90nm, the single layer Nb thickness is set to 10nm, the number of cycles is 20, that is, the total film thickness is 2μm.

[0061] After the sample was naturally cooled in the vacuum coating chamber for 2-3 hours to room temperature, it was removed from the vacuum coating chamber, resulting in a Cr / Nb nano-multilayer coating with a thickness of approximately 2.19 μm. Microstructural characterization of the prepared Cr / Nb nano-multilayer coating revealed vermicular columnar crystals with a stable size within the nanocrystalline range. The grain size was small, and the structural density was reduced.

[0062] The present invention discloses an accident-tolerant metal Cr / Nb nano-multilayer coating and its preparation method. The metal Cr / Nb coating is deposited on a clean silicon substrate by magnetron sputtering deposition. The principle is that Ar gas generates high-density Ar after glow discharge. + ,Ar + Under the action of the electric field, it is strongly attracted to the negative electrode and bombards the metal Cr DC target and metal Nb DC target at a high rate, and transfers part of the kinetic energy to the target atoms, and then the target atoms collide with other target atoms to form a cascade process. In this cascade process, some target atoms near the surface obtain enough kinetic energy to move outward, so the target atoms and secondary electrons are sputtered out, and the Cr atoms and Nb atoms eventually move in the opposite direction to deposit on the silicon substrate of the anode, and the movement direction of the secondary electrons in the orthogonal electromagnetic field is perpendicular to the electric field and magnetic field, and circulates in the form of cycloids, which increases the ionization rate of Ar, increases the ion density and energy, and thus achieves high-rate sputtering. Figure 1 As shown in the figures, the microstructures of the accident-tolerant Cr / Nb nano-multilayer coatings prepared at different modulation ratios are different. Therefore, the modulation ratio can be controlled to provide an experimental reference for regulating the microstructure of the Cr / Nb nano-multilayer coating, thereby preparing an accident-tolerant Cr / Nb nano-multilayer coating with excellent performance.

[0063] The above content is only for explaining the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an accident-tolerant Cr / Nb nano-multilayer coating, characterized in that: The following steps are involved: Step 1, ultrasonically cleaning and drying the surface of the silicon substrate; Step 2: Under vacuum, a silicon substrate is subjected to DC magnetron co-sputtering using a Cr target and a Nb target. The deposition power of the Cr target and the Nb target are both 200 W, the deposition pressure is 0.3 Pa, the silicon substrate rotation speed is 10 r / min, the argon flow rate is 40 sccm, and the deposition temperature is room temperature. After sputtering and deposition to a predetermined thickness, the coating is cooled to room temperature in the furnace to obtain a Cr / Nb nano-multilayer coating. The total time of the magnetron co-sputtering was 16460s-18280s, and in each modulation cycle, the sputtering time of the Cr target was 74-667s, and the sputtering time of the Cr target was 770-86s; During the magnetron co-sputtering process, the sum of the thicknesses of the Cr layer and the Nb layer formed in each modulation period is the same, and the modulation ratio of the thickness of the Cr layer to the Nb layer formed in each modulation period is 0.1 to 9.0; When the modulation ratio is less than 1.00, the grain morphology of the Cr / Nb nano multilayer coating is triangular pyramidal columnar crystals; When the modulation ratio is ≥1.00, the grain morphology of the Cr / Nb nano-multilayer coating is worm-like columnar crystals; The thickness of the Cr / Nb nano multilayer coating is 2 μm, and the total thickness of the Cr layer and the Nb layer in each modulation period is the same and is 100 nm; The hardness of the Cr / Nb nano multilayer coating is 5.0 GPa to 7.0 GPa.

2. The method for preparing an accident-tolerant Cr / Nb nano multilayer coating according to claim 1, characterized in that: In step 1, the silicon substrate is first polished, and then the polished silicon substrate is ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes respectively and then dried to remove impurities on the surface of the silicon substrate.

3. The method for preparing an accident-tolerant Cr / Nb nano-multilayer coating according to claim 1, characterized in that: The vacuum degree of the vacuum environment in step 2 is 1.0×10 -4 Below Pa.

4. The method for preparing an accident-tolerant Cr / Nb nano multilayer coating according to claim 1, characterized in that: In step 2, under vacuum, first use Ar + The silicon substrate is etched by ions and then pre-sputtered; The etching power is 200 W, the etching pressure is 1.0 Pa, and the etching time is 5 min.

5. The method for preparing an accident-tolerant Cr / Nb nano-multilayer coating according to claim 4, characterized in that: The argon ventilation time before the pre-sputtering is at least 30 seconds, and the pre-sputtering time is at least 10 seconds, so as to remove the adsorbed substances on the surface of the target material.

Images