Preparation method of chromium-containing metal thin coating and its application

Abstract

The present invention discloses a preparation method and application of a chromium-containing metal thin coating, and relates to the technical field of metal coatings. The method comprises depositing a chromium-containing target material on the surface of a substrate using an ultrafast laser to form a metal pre-layer on the substrate surface, and then scanning the metal pre-layer using a continuous laser to react in situ on the metal pre-layer to prepare a chromium-containing metal thin coating. By using a chromium-containing target material as the raw material of the chromium-containing metal thin coating, the prepared chromium-containing metal thin coating has better mechanical properties and better corrosion resistance. The target material is then ablated by an ultrafast laser to form a metal pre-layer on the substrate surface. The metal pre-layer and a very small part of the workpiece substrate are melted and solidified, and the interface metallurgical bonding occurs, resulting in extremely high bonding strength. Continuous laser scanning is then performed to react in situ on the metal pre-layer to form a chromium-containing metal thin coating, which is beneficial to improving the mechanical properties and corrosion resistance of the chromium-containing metal thin coating.

Description

Technical Field

[0001] The present invention relates to the technical field of metal coatings, and in particular to a preparation method of a chromium-containing metal thin coating and application thereof. Background Art

[0002] Surface damage caused by wear and corrosion is the primary cause of long-term failure of mechanical components, severely reducing the overall performance and service life of mechanical equipment. Wear, corrosion, and other damage primarily originate at the surface interface of components. Therefore, surface protection technology is an important way to enhance the wear and corrosion resistance of component surfaces, while also improving component strength and overall performance. Therefore, surface protection technology holds significant theoretical research significance and enormous engineering application value in extending component life, conserving resources, and improving economic efficiency.

[0003] Metal coating is one of the most widely used methods of component surface protection. Different service conditions also put forward different requirements for the type and performance of metal coatings. For example, in the field of micro-nano imprinting, in order to ensure the shape of the product, the shape of the mold needs to be finely carved. However, traditional alloy molds are not only difficult to meet the requirements of micro-nano imprinting in terms of grain size, but also cause large damage to the mold during the micro-nano imprinting process. Therefore, there is an urgent need to provide a metal coating on the mold surface that meets the requirements of micro-nano imprinting. However, the finer the component, the higher the requirements for the morphology of the coating in order to ensure that the shape of the component surface is not covered by the coating. The method for preparing a qualified coating is also more stringent. For another example, the components in nuclear fuel units are usually in a liquid environment of high temperature, high pressure, high flow rate, and strong radiation for a long time. The more complex the reaction environment, the more stringent the performance requirements of the components of the nuclear fuel unit. In order to extend the service life of the components of the nuclear fuel unit and enhance their performance parameters, there is also an urgent need to provide a metal coating that meets the use requirements of the nuclear fuel unit.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a chromium-containing metal thin coating and its application.

[0006] The present invention is achieved in that:

[0007] In a first aspect, the present invention provides a method for preparing a chromium-containing metal thin coating, comprising using an ultrafast laser to deposit a chromium-containing target material on the surface of a substrate to form a metal pre-layer on the surface of the substrate, and then using a continuous laser to scan the metal pre-layer to produce a chromium-containing metal thin coating by an in-situ reaction on the metal pre-layer.

[0008] In a second aspect, the present invention provides an application of the preparation method according to any one of the aforementioned embodiments in micro-nano imprinting or nuclear fuel units.

[0009] The present invention has the following beneficial effects:

[0010] The present invention provides a preparation method and application of a chromium-containing metal thin coating. By using a chromium-containing target material as the raw material of the chromium-containing metal thin coating, the prepared chromium-containing metal thin coating has better mechanical properties and better corrosion resistance. The target material is then ablated by ultrafast laser to form a metal pre-layer on the surface of a substrate. The metal pre-layer and a very small part of the workpiece substrate are melted and solidified, and the interface is metallurgically bonded with extremely high bonding strength. Continuous laser scanning is then performed to generate a chromium-containing metal thin coating by in-situ reaction on the metal pre-layer, which is beneficial to improving the mechanical properties, corrosion resistance, etc. of the chromium-containing metal thin coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0012] Figure 1 A schematic structural diagram of an apparatus for preparing a thin chromium-containing metal coating provided by the present invention;

[0013] Figure 2 This is a scanning electron microscope image of the dense thin film pre-deposited layer provided in Example 1 of the present invention;

[0014] Figure 3 A transmission electron microscope image of the dense thin film pre-deposited layer provided in Example 1 of the present invention;

[0015] Figure 4 This is a transmission Kikuchi diffraction pattern of the chromium-containing metal thin coating provided in Example 1 of the present invention;

[0016] Figure 5 A transmission Kikuchi diffraction pattern of the contact interface between the chromium-containing metal thin coating and the substrate provided in Example 1 of the present invention;

[0017] Figure 6 This is a scanning electron microscope image of the loose nanopowder pre-layer provided in Example 3 of the present invention;

[0018] Figure 7 A transmission electron microscope image of a loose nanopowder pre-deposited layer provided in Example 3 of the present invention;

[0019] Figure 8Scanning electron microscope image of the chromium-containing metal thin coating corresponding to the continuous laser process change provided in Experimental Example 1 of the present invention;

[0020] Figure 9 Scanning electron microscope image of the chromium-containing metal thin coating corresponding to the continuous laser process change provided in Experimental Example 2 of the present invention;

[0021] Figure 10 Scanning electron microscope image of the chromium-containing metal thin coating corresponding to the continuous laser process change provided in Experimental Example 3 of the present invention;

[0022] Figure 11 This is a scanning electron microscope image of the chromium-containing metal thin coating corresponding to the continuous laser process changes provided in Experimental Example 4 of the present invention.

[0023] Explanation of the main component symbols: 100 - device for preparing a thin chromium-containing metal coating; 110 - control unit; 120 - reaction unit; 121 - target fixing mechanism; 122 - substrate fixing mechanism; 123 - vacuum reaction chamber; 130 - ultrafast laser; 140 - continuous laser; 151 - first galvanometer; 152 - second galvanometer. DETAILED DESCRIPTION

[0024] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0025] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0026] In a first aspect, the present invention provides a method for preparing a chromium-containing metal thin coating, comprising using an ultrafast laser to deposit a chromium-containing target material on the surface of a substrate to form a metal pre-layer on the surface of the substrate, and then using a continuous laser to scan the metal pre-layer to produce a chromium-containing metal thin coating by an in-situ reaction on the metal pre-layer.

[0027] It should be noted that the above preparation method can be applied to Figure 1 The device 100 for preparing a thin chromium-containing metal coating includes a control unit 110, a reaction unit 120, an ultrafast laser 130, a continuous laser 140, and an optical path adjustment unit.

[0028] The optical path adjustment unit includes a first galvanometer mirror 151 and a second galvanometer mirror 152 .

[0029] The first galvanometer mirror 151 is located between the ultrafast laser 130 and the reaction unit 120 and is used to guide the laser light emitted by the ultrafast laser 130 to the reaction unit 120 to ablate the chromium-containing target.

[0030] The second galvanometer mirror 152 is located between the continuous laser 140 and the reaction unit 120 and is used to guide the laser light emitted by the continuous laser 140 to the reaction unit 120 to scan the metal pre-layer.

[0031] Preferably, the first galvanometer mirror 151 and the second galvanometer mirror 152 are respectively located on the left and right sides of the reaction unit 120 to facilitate control of the laser light path.

[0032] Furthermore, the reaction unit 120 includes a vacuum reaction chamber 123, a target fixing mechanism 121 and a substrate fixing mechanism 122. The target fixing mechanism 121 and the substrate fixing mechanism 122 are both connected to the vacuum reaction chamber 123, and the target fixing mechanism 121 can be used to fix and rotate the chromium-containing target, and the substrate fixing mechanism 122 can be used to fix and rotate the substrate to ensure that the reaction proceeds smoothly.

[0033] The control unit 110 is in communication connection with the reaction unit 120 , the ultrafast laser 130 , the continuous laser 140 , the first galvanometer 151 and the second galvanometer 152 to achieve effective control of the ultrafast laser process and the continuous laser process.

[0034] Preferably, the control unit 110 can be any device such as an industrial computer, a computer, etc.

[0035] Preferably, the above Figure 1 The working principle of the device 100 for preparing a thin chromium-containing metal coating is as follows:

[0036] First, the target is fixed on the target fixing mechanism 121 in the vacuum reaction chamber 123, and the substrate is fixed on the substrate fixing mechanism 122 in the vacuum reaction chamber 123. The control unit 110 controls the vacuum degree in the vacuum reaction chamber 123 to be within the range required for the reaction.

[0037] When the pressure within vacuum reaction chamber 123 meets the reaction conditions, control unit 110 controls ultrafast laser 130 to emit laser light. The laser light is then transmitted through first galvanometer mirror 151 to the chromium-containing target within vacuum reaction chamber 123. The ultrafast laser light ablates the chromium-containing target, depositing it on the substrate surface to form a metal pre-layer. Control unit 110 then controls ultrafast laser 130 to shut off and continuous laser 140 to emit laser light. Second galvanometer mirror 152 transmits the laser light to the metal pre-layer on the substrate surface within vacuum reaction chamber 123, causing the metal pre-layer to react in situ to form a thin chromium-containing metal coating with an ultrafine grain structure.

[0038] Furthermore, according to actual needs, the control unit 110 can control the ultrafast laser 130 and the continuous laser 140 to emit lasers alternately to form multiple layers of chromium-containing metal thin coatings with ultrafine grain structure on the surface of the substrate.

[0039] Furthermore, the inventors discovered that although ultrafast laser ablation of chromium-containing targets is also used, the metal pre-layers formed are different depending on the deposition gas pressure in the reaction chamber where the reaction occurs. The metal pre-layers include either a dense thin film pre-layer or a loose nanopowder pre-layer.

[0040] Specifically, the deposition pressure of the dense thin film pre-layer is ≤8×10 -3 Pa, the dense thin film pre-layer prepared by adopting the deposition gas pressure can be used for depositing target materials of metal or non-metal materials.

[0041] Under the above-mentioned deposition pressure, the present invention adopts ultrafast laser to ablate chromium-containing target materials. Through the nonlinear, non-equilibrium absorption and non-thermal phase change characteristics of the ultrafast laser, the target surface of the chromium-containing target material is excited to form plasma / atoms / clusters. These particles continue to interact with the laser and expand directionally in the cavity to form a regionalized high-temperature and high-pressure plasma plume. Under high vacuum conditions, the plume is directly deposited on the surface of the substrate, thereby forming a dense thin film pre-layer on the surface of the substrate.

[0042] After the dense thin film pre-layer is irradiated by continuous laser, the material at the interface between the dense thin film and the substrate undergoes thermal diffusion, thereby improving the bonding strength between the chromium-containing metal thin coating and the substrate. The formed chromium-containing metal thin coating is a low-diffusion coating with good smoothness and good fidelity of the coating's own components, reducing the possibility of impurity formation.

[0043] The deposition pressure of the loose nano-powder pre-layer is 10-20 Pa. The loose nano-powder pre-layer is generally used for depositing targets of metal materials.

[0044] Under the above-mentioned deposition gas pressure, the present invention adopts ultrafast laser to ablate chromium-containing target materials. Through the nonlinear, non-equilibrium absorption and non-thermal phase change characteristics of the ultrafast laser, the target surface is stimulated to form plasma / atoms / clusters. Since the inert gas fills the entire cavity, the feather collides with the inert gas during the transmission process to form nano-crystals, and the nano-crystals grow and crystallize on the substrate, thereby forming a loose nano-powder pre-layer on the substrate surface.

[0045] After the loose nano-powder pre-layer is clad by a continuous laser process, the loose nano-powder of the pre-layer and a very small part of the substrate melt and solidify, eventually forming a diffusion-type coating - a thin chromium-containing metal coating. The interface between the coating and the substrate achieves metallurgical bonding with extremely high bonding strength.

[0046] Preferably, the deposition pressure forming process of the loose nanopowder pre-layer includes: firstly evacuating the reaction chamber, and controlling the pressure of the reaction chamber to 2×10 -3 Pa, and then an inert gas, such as argon, is introduced into the reaction chamber as a protective gas. When the inert gas is filled into the reaction chamber to a pressure in the range of 10 to 20 Pa, ultrafast laser ablation of the chromium-containing target can be used.

[0047] In an optional embodiment, the chromium-containing target material includes pure chromium metal or a chromium-containing alloy, and the chromium-containing alloy includes any one of CrFeNi high entropy alloy and CrNi alloy.

[0048] Preferably, in order to ensure the performance of the chromium-containing metal thin coating, the target material for preparing the dense thin film pre-layer includes pure chromium metal or a chromium-containing alloy; the target material for preparing the loose nanopowder pre-layer is a chromium-containing alloy.

[0049] In an optional embodiment, the ultrafast laser deposition parameters include: target-substrate distance of 40-50 mm, ultrafast laser power of 280-320 kHz, laser deposition scan times of 120-180 times, and single pulse energy of 100-150 μJ.

[0050] The scanning parameters of the continuous laser include: continuous laser power of 25 to 35 W, laser scanning speed of 15 to 50 mm / s, and defocusing amount of 32 to 48 mm.

[0051] Preferably, in some embodiments, the chromium-containing metal thin coating provided by the present invention includes at least the following three preparation methods:

[0052] 1. When the chromium-containing target material for preparing a dense thin film pre-layer is pure chromium metal, that is, when preparing a pure chromium low-diffusion coating, the pure chromium target material is first ablated by ultrafast laser to obtain a dense thin film pre-layer of pure chromium material on the surface of the substrate, and then the dense thin film pre-layer of pure chromium material is irradiated by continuous laser to form a pure chromium metal coating on the surface of the substrate.

[0053] Among them, the deposition parameters of the ultrafast laser include: target-substrate distance of 40 to 50 mm, ultrafast laser power of 280 to 320 kHz, laser deposition scan times of 120 to 180 times, and single pulse energy of 100 to 150 μJ.

[0054] The scanning parameters of the continuous laser include: continuous laser power of 25 to 35 W, laser scanning speed of 30 to 50 mm / s, and defocus of 42 to 48 mm.

[0055] 2. When the target material for preparing a dense thin film pre-layer is a chromium-containing alloy, that is, when preparing a low-diffusion coating of a chromium alloy, the target material of the chromium-containing alloy is first ablated by an ultrafast laser to obtain a dense thin film pre-layer of the chromium alloy on the surface of the substrate, and then a continuous laser is used to irradiate the dense thin film pre-layer of the chromium alloy to form a metal coating containing a chromium alloy on the surface of the substrate.

[0056] Among them, the deposition parameters of the ultrafast laser include: target-substrate distance of 40 to 50 mm, ultrafast laser power of 280 to 320 kHz, laser deposition scan times of 120 to 180 times, and single pulse energy of 100 to 150 μJ.

[0057] The scanning parameters of the continuous laser include: continuous laser power of 25 to 35 W, laser scanning speed of 35 to 45 mm / s, and defocusing amount of 35 to 45 mm.

[0058] 3. When the target material for preparing the loose nano-powder pre-layer is a chromium-containing alloy, that is, when preparing a chromium alloy diffusion-type coating, the chromium-containing alloy target material is first ablated by ultrafast laser to obtain a loose nano-powder pre-layer of chromium alloy material on the substrate surface, and then the loose nano-powder pre-layer of chromium alloy material is melted by continuous laser cladding to form a chromium alloy metal coating on the substrate surface.

[0059] Among them, the deposition parameters of the ultrafast laser include: target-substrate distance of 40 to 50 mm, ultrafast laser power of 280 to 320 kHz, laser deposition scan times of 120 to 180 times, and single pulse energy of 100 to 150 μJ.

[0060] The scanning parameters of the continuous laser include: continuous laser power of 25 to 35 W, laser scanning speed of 15 to 25 mm / s, and defocus of 32 to 38 mm.

[0061] In an optional embodiment, in order to ensure the performance of the coating, multiple layers of thin chromium-containing metal coatings may be deposited on the surface of the substrate. Therefore, ultrafast laser and continuous laser may be used for alternating scanning.

[0062] Preferably, the number of layers of the chromium-containing metal thin coating on the surface of the substrate is 2 to 4 layers, more preferably 3 layers.

[0063] In an optional embodiment, the substrate can be selected according to different application requirements, as long as good compatibility between the substrate and the coating is ensured. The substrate includes any one of a zirconium substrate and a stainless steel substrate, preferably a zirconium substrate. The zirconium substrate can be used as the material of the AFT nuclear fuel cladding of the nuclear fuel unit. The chromium-containing metal thin coating of the present invention is deposited on its surface, which can be applied to the complex service conditions of the nuclear fuel unit.

[0064] Preferably, the zirconium substrate is a Zr-4 zirconium alloy substrate.

[0065] In a second aspect, the present invention provides an application of the preparation method according to any one of the aforementioned embodiments in micro-nano imprinting or nuclear fuel units.

[0066] In an optional embodiment, the application of the preparation method in a nuclear fuel unit includes using the preparation method to prepare a mechanical structure in the nuclear fuel unit, and the mechanical structure includes any one of AFT nuclear fuel cladding and film preparation.

[0067] The components of nuclear fuel units are exposed to high-temperature, high-pressure, high-flow, and highly radioactive hydrochemical environments for extended periods, placing even higher demands on their performance. They must ensure corrosion resistance against high-temperature, high-pressure water under irradiation conditions. Furthermore, during operation within the reactor, fuel assemblies are subject to axial and lateral flow from the high-velocity coolant flow, causing fluid-induced vibrations (FIVs) in the fuel rods. Therefore, components within nuclear fuel units must also possess excellent resistance to FIVs.

[0068] The applicant proposes that the metal coating prepared by the preparation method provided by the present invention can be applied to nuclear fuel units as a coating material for components therein. It can not only ensure good bonding between the coating and the substrate, but also the chromium-containing metal thin coating prepared by the present invention has excellent corrosion resistance and good mechanical properties, which can meet the long-term use of nuclear fuel units, especially AFT nuclear fuel cladding.

[0069] Preferably, the application of the preparation method in micro-nano imprinting includes preparing an alloy mold by using the preparation method.

[0070] Micro-nano imprinting technology uses photoresist to transfer micro-nano structures from a mold to the material being processed. Because the micro-nano patterns on the mold surface are extremely fine, the grain size of conventional alloy molds is much larger than the feature size of the micro-nano imprinted patterns. This causes uneven mold deformation during the imprinting process, reducing imprint quality and limiting the application of micro-nano imprinted alloy molds.

[0071] Therefore, the applicant proposed to apply the chromium-containing metal thin coating obtained by the preparation method provided by the present invention to the field of micro-nano embossing, and to coat a layer of chromium-containing metal thin coating on the surface of the alloy mold to improve the matching degree between the grain size of the alloy mold and the graphic feature size of the micro-nano embossing. At the same time, the setting of the metal coating is also beneficial to extend the life of the alloy mold and reduce the wear of the mold.

[0072] Example 1

[0073] This embodiment provides a method for preparing a thin chromium-containing metal coating, and the specific steps are as follows:

[0074] The pure chromium target and the Zr-4 zirconium alloy substrate were fixed in the reaction chamber, the reaction chamber was closed, and the reaction chamber was evacuated by a mechanical pump and a molecular pump until the pressure in the reaction chamber was 2×10 -3 Pa.

[0075] The target material is a round cake with a diameter of 50 mm and a thickness of 5 mm, and the zirconium alloy base is a cube with a size of 15 mm × 15 mm × 5 mm.

[0076] The gas pressure in the reaction chamber is maintained, and an ultrafast laser is first used to ablate a pure chromium target to obtain a dense thin film pre-layer of pure chromium material on the surface of the substrate. Then, a continuous laser is used to irradiate the dense thin film pre-layer to form a low-diffusion pure chromium metal coating on the surface of the substrate.

[0077] Among them, ultrafast laser and continuous laser are alternately emitted three times to form three layers of pure chromium metal coating on the surface of Zr-4 zirconium alloy substrate.

[0078] The ultrafast laser deposition parameters for each deposition were as follows: target-substrate distance of 45 mm, ultrafast laser power of 300 kHz, laser deposition scan times of 150 times, and single pulse energy of 120 μJ.

[0079] The scanning parameters of each continuous laser scan include: continuous laser power of 30W, laser scanning speed of 30mm / s, and defocus of 45mm.

[0080] The dense thin film pre-layer of pure chromium material prepared in this embodiment was placed under a scanning electron microscope (SEM) for observation, and the following was obtained: Figure 2 The results shown by Figure 2 It can be seen that the dense thin film pre-deposited layer made of pure chromium material in this embodiment is tightly bonded to the substrate, and the coating has no cracks.

[0081] Furthermore, the dense thin film pre-deposited layer of pure chromium material prepared in this embodiment was observed using a transmission electron microscope (TEM), showing the overall morphology of the pre-deposited layer, as shown below: Figure 3 Results shown.

[0082] The low diffusion type pure chromium metal coating prepared in this embodiment was tested by transmission Kikuchi diffraction (TKD), and the following results were obtained: Figure 4 Results shown.

[0083] From the phase diagram ( Figure 4 a) It can be seen that the coating is composed of body-centered cubic Cr structure, and its corresponding inverse pole figure ( Figure 4 b) shows that the coating grain size is between 100 and 300 nanometers, and all are equiaxed crystals.

[0084] In order to further understand the characteristics of the interface between the low-diffusion pure chromium metal coating and the Zr substrate prepared in this example, TEM was used to observe the interface and the following results were obtained: Figure 5 Results shown.

[0085] Depend on Figure 5 It can be seen that Figure 5 a is the overall morphology of the interface between the pure chromium metal coating and the Zr substrate. In the middle area of ​​the coating, b can be observed that the coating is mainly composed of equiaxed crystal structure ( Figure 5 b), consistent with TDK test results.

[0086] Example 2

[0087] This embodiment provides a method for preparing a thin chromium-containing metal coating, and the specific steps are as follows:

[0088] The CrFeNi high entropy alloy target and the Zr-4 zirconium alloy substrate were fixed in the reaction chamber, the reaction chamber was closed, and the reaction chamber was evacuated by a mechanical pump and a molecular pump until the pressure in the reaction chamber was 2×10 -3 Pa.

[0089] The target material is a round cake with a diameter of 50 mm and a thickness of 5 mm, and the zirconium alloy substrate is a cube with a size of 15 mm × 15 mm × 5 mm.

[0090] The gas pressure in the reaction chamber is maintained, and the CrFeNi high-entropy alloy target is first ablated by ultrafast laser to obtain a dense thin film pre-layer of CrFeNi high-entropy alloy material on the surface of the substrate. Then, the dense thin film pre-layer is irradiated by continuous laser to form a low-diffusion CrFeNi high-entropy alloy coating on the surface of the substrate.

[0091] Among them, ultrafast laser and continuous laser are alternately emitted three times to form a three-layer CrFeNi high-entropy alloy coating on the surface of the Zr-4 zirconium alloy substrate.

[0092] The ultrafast laser deposition parameters for each deposition were as follows: target-substrate distance of 45 mm, ultrafast laser power of 300 kHz, laser deposition scan times of 150 times, and single pulse energy of 120 μJ.

[0093] The scanning parameters of each continuous laser scan include: continuous laser power of 30W, laser scanning speed of 40mm / s, and defocus of 35mm.

[0094] Example 3

[0095] This embodiment provides a method for preparing a thin chromium-containing metal coating, and the specific steps are as follows:

[0096] The CrFeNi high entropy alloy target and the Zr-4 zirconium alloy substrate were fixed in the reaction chamber, the reaction chamber was closed, and the reaction chamber was evacuated by a mechanical pump and a molecular pump until the pressure in the reaction chamber reached 2×10 -3 Pa, and then argon is introduced into the reaction chamber as a protective gas. When the argon is filled to the pressure in the reaction chamber to reach 15 Pa, subsequent operations can be carried out.

[0097] The target material is a round cake with a diameter of 50 mm and a thickness of 5 mm, and the zirconium alloy base is a cube with a size of 15 mm × 15 mm × 5 mm.

[0098] The gas pressure in the reaction chamber is maintained, and the CrFeNi high-entropy alloy target is first ablated by ultrafast laser to obtain a loose nano-powder pre-layer of CrFeNi high-entropy alloy material on the surface of the substrate. Then, the loose nano-powder pre-layer is melted by continuous laser to form a diffused CrFeNi high-entropy alloy coating on the surface of the substrate.

[0099] Among them, ultrafast laser and continuous laser are alternately emitted three times to form a three-layer CrFeNi high-entropy alloy coating on the surface of the Zr-4 zirconium alloy substrate.

[0100] The ultrafast laser deposition parameters for each deposition were as follows: target-substrate distance of 45 mm, ultrafast laser power of 300 kHz, laser deposition scan times of 150 times, and single pulse energy of 120 μJ.

[0101] The scanning parameters of each continuous laser scan include: continuous laser power of 30W, laser scanning speed of 20mm / s, and defocus of 35mm.

[0102] The loose nano-powder pre-layer of CrFeNi high entropy alloy prepared in this embodiment was placed under a scanning electron microscope (SEM) for observation, and the following was obtained: Figure 6 The results are shown. Figure 6 It can be seen that the loose nano-powder pre-layer of the CrFeNi high entropy alloy material of this embodiment is uniform and loose. The loose nano-powder pre-layer of the CrFeNi high entropy alloy material prepared in this embodiment is observed using a transmission electron microscope (TEM), and the following is obtained: Figure 7 The results are shown. Figure 7 It can be seen that the diameter size distribution of CrFeNi high-entropy alloy nanoparticles ranges from tens of nanometers to hundreds of nanometers, and a large number of crystal defects can be seen inside the nanoparticles. The nanometal particles have a large specific surface energy, and the large number of crystallographic defects inside increase the internal stress of the metal nanoparticles, making them in a high-energy state. Under the condition of external energy interference, they can tend to transform to a low-energy state and release their own internal energy.

[0103] Test Example 1

[0104] Based on the preparation method of Example 1, the defocus distance (DF) and laser scanning speed (s) in the continuous laser scanning parameters are changed, and the morphology of the low-diffusion pure chromium metal coating obtained is as follows: Figure 8 The coating conditions are shown in Table 1.

[0105] Figure 8 In the figure, a is the cross-sectional morphology of the coating when DF = 35 mm, s = 50 mm / s; b is the cross-sectional morphology of the coating when DF = 35 mm, s = 40 mm / s; c is the cross-sectional morphology of the coating when DF = 35 mm, s = 30 mm / s; d is the cross-sectional morphology of the coating when DF = 40 mm, s = 50 mm / s; e is the cross-sectional morphology of the coating when DF = 40 mm, s = 40 mm / s; f is the cross-sectional morphology of the coating when DF = 40 mm, s = 30 mm / s; g is the cross-sectional morphology of the coating when DF = 45 mm, s = 50 mm / s; h is the cross-sectional morphology of the coating when DF = 45 mm, s = 40 mm / s; i is the cross-sectional morphology of the coating when DF = 45 mm, s = 30 mm / s.

[0106] Table 1 Status of low-diffusion pure chromium metal coating

[0107] s=50mm / s s=40mm / s s=30mm / s DF=35mm crack crack crack DF=40mm crack crack crack DF=45mm No cracks No cracks No cracks

[0108] Depend on Figure 8 As shown in Table 1, at low defocus, that is, DF≤40mm, cracks appeared in the prepared coatings. When the defocus was 45mm and the laser scanning rate was 30-50mm / s, a high-quality, low-diffusion pure chromium metal coating with no heat-affected zone, diffusion layer, or defects was obtained.

[0109] Test Example 2

[0110] Based on the preparation method of Example 2, the defocus distance (DF) and laser scanning speed (s) in the continuous laser scanning parameters are changed, and the morphology of the low-diffusion CrFeNi high-entropy alloy coating obtained is as follows: Figure 9 The coating thickness and state are shown in Table 2.

[0111] Figure 9In the figure, a is the cross-sectional morphology of the coating when DF = 25 mm, s = 40 mm / s; b is the cross-sectional morphology of the coating when DF = 25 mm, s = 20 mm / s; c is the cross-sectional morphology of the coating when DF = 25 mm, s = 10 mm / s; d is the cross-sectional morphology of the coating when DF = 30 mm, s = 40 mm / s; e is the cross-sectional morphology of the coating when DF = 30 mm, s = 20 mm / s; f is the cross-sectional morphology of the coating when DF = 30 mm, s = 10 mm / s; g is the cross-sectional morphology of the coating when DF = 35 mm, s = 40 mm / s; h is the cross-sectional morphology of the coating when DF = 35 mm, s = 20 mm / s; i is the cross-sectional morphology of the coating when DF = 35 mm, s = 10 mm / s.

[0112] Table 2 Thickness and state of low-diffusion CrFeNi high-entropy alloy coating

[0113] s=40mm / s s=20mm / s s=10mm / s DF=25mm 14.6μm (crack) 15.5μm (crack) 23.0μm DF=30mm 14.7μm (crack) 18.7μm (crack) 21.2μm DF=35mm 6.5μm 10.2μm 23.1μm

[0114] Depend on Figure 9 As shown in Table 2, under the condition of low laser scanning rate, that is, s = 10mm / s, there is no crack at the interface between the diffusion zone below the coating and the substrate, but the coating thickness is relatively large, at about 23.0μm. When the scanning rate increases and the defocus is ≤30mm, cracks appear in the coating due to thermal stress. When the scanning rate is 20mm / s and the defocus is 35mm, although there is no crack in the coating, the coating thickness is still relatively thick, at 10.2μm. When the defocus and scanning rate meet the requirements, Figure 9 The coating thickness shown in g is 6.5 μm.

[0115] Test Example 3

[0116] Based on the preparation method of Example 3, the defocus distance (DF) and laser scanning speed (s) in the continuous laser scanning parameters are changed, and the morphology of the obtained diffusion type CrFeNi high entropy alloy coating is as follows: Figure 10 The coating thickness and state are shown in Table 3.

[0117] Figure 10In the figure, a is the cross-sectional morphology of the coating when DF = 25 mm, s = 40 mm / s; b is the cross-sectional morphology of the coating when DF = 25 mm, s = 20 mm / s; c is the cross-sectional morphology of the coating when DF = 25 mm, s = 10 mm / s; d is the cross-sectional morphology of the coating when DF = 30 mm, s = 40 mm / s; e is the cross-sectional morphology of the coating when DF = 30 mm, s = 20 mm / s; f is the cross-sectional morphology of the coating when DF = 30 mm, s = 10 mm / s; g is the cross-sectional morphology of the coating when DF = 35 mm, s = 40 mm / s; h is the cross-sectional morphology of the coating when DF = 35 mm, s = 20 mm / s; i is the cross-sectional morphology of the coating when DF = 35 mm, s = 10 mm / s.

[0118] Table 3 Thickness and state of diffusion-type CrFeNi high-entropy alloy coating

[0119] s=40mm / s s=20mm / s s=10mm / s DF=25mm 13.3μm (crack) 15.1μm (crack) 19.9μm DF=30mm 13.8μm (crack) 15.9μm 17.1μm DF=35mm 10.8μm (crack) 13.7μm 20.3μm

[0120] Depend on Figure 10 As shown in Table 3, under the condition of low laser scanning rate, that is, s = 10mm / s, there is no crack at the interface between the diffusion zone below the coating and the substrate, but the thickness of the coating is relatively large, ranging from 17.1 to 20.3μm. When the scanning rate is higher, that is, s = 40mm / s, cracks will appear regardless of how the defocus is adjusted within the range of 0 to 35mm. When the scanning rate is 20mm / s, the defocus is ≤ 25mm, and the coating will crack; when the defocus is 30, the coating is thicker. When the defocus and scanning rate meet the requirements, Figure 10 The coating thickness shown in h is 13.7 μm.

[0121] Test Example 4

[0122] Based on the preparation method of Example 3, the target material was adjusted to a pure chromium target material for preparing a diffusion-type pure chromium metal coating. The remaining steps and parameters were the same as those of Example 3. The only difference was that the defocus distance (DF) and the laser scanning speed (s) in the continuous laser scanning parameters were changed. The morphology of the obtained diffusion-type pure chromium metal coating is shown in FIG. Figure 11 The coating conditions are shown in Table 4.

[0123] Figure 11 In the figure, a is the cross-sectional morphology of the coating when DF = 20 mm, s = 40 mm / s; b is the cross-sectional morphology of the coating when DF = 20 mm, s = 20 mm / s; c is the cross-sectional morphology of the coating when DF = 20 mm, s = 10 mm / s; d is the cross-sectional morphology of the coating when DF = 25 mm, s = 40 mm / s; e is the cross-sectional morphology of the coating when DF = 25 mm, s = 20 mm / s; f is the cross-sectional morphology of the coating when DF = 25 mm, s = 10 mm / s.

[0124] Table 4 Status of diffusion type pure chromium metal coating

[0125] s=40mm / s s=20mm / s s=10mm / s DF=20mm crack Cracks and lack of fusion Cracks and lack of fusion DF=25mm crack Unfused Cracks and lack of fusion

[0126] Depend on Figure 11 As shown in Table 4, it is difficult to prepare a defect-free coating material from a diffused pure chromium metal coating obtained by continuous laser treatment of a loose nanopowder pre-layer prepared by ultrafast laser ablation of a pure chromium target.

[0127] An embodiment of the present invention provides a method for preparing a chromium-containing metal thin coating and its application. The method uses ultrafast laser deposition of a metal pre-layer, and then uses continuous laser ablation of the metal pre-layer to generate an in-situ reaction of the chromium-containing metal thin coating. The above analysis shows that the heat input of the continuous laser treatment causes the extremely fine nano-grains in the laser-deposited metal pre-layer to grow and form equiaxed grains on the scale of hundreds of nanometers. After the continuous laser treatment, the bonding strength between the chromium-containing metal thin coating and the substrate is improved.

[0128] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a thin chromium-containing metal coating, characterized in that: The method comprises depositing a chromium-containing target material on the surface of a substrate using an ultrafast laser to form a metal pre-layer on the substrate surface, and then scanning the metal pre-layer using a continuous laser to react in situ on the metal pre-layer to produce a chromium-containing metal thin coating; the substrate is a zirconium substrate; The chromium-containing target material includes pure chromium metal or a chromium-containing alloy, and the chromium-containing alloy includes any one of a CrFeNi high entropy alloy and a CrNi alloy; The metal pre-layer includes at least one of a dense thin film pre-layer and a loose nano powder pre-layer; The deposition pressure of the dense thin film pre-layer is ≤8×10 -3 Pa, the deposition pressure of the loose nano powder pre-layer is 10-20 Pa; The target material for preparing the dense thin film pre-layer includes pure chromium metal or a chromium-containing alloy; The target material for preparing the loose nano powder pre-layer is a chromium-containing alloy; When the target material of the dense thin film pre-deposited layer is pure chromium metal, the ultrafast laser deposition parameters include: target-substrate distance of 40-50 mm, ultrafast laser power of 280-320 kHz, laser deposition scan times of 120-180 times, and single pulse energy of 100-150 μJ; The scanning parameters of the continuous laser include: continuous laser power of 25~35W, laser scanning speed of 30~50mm / s, and defocus of 42~48mm; When the target material of the dense thin film pre-deposition layer is a chromium-containing alloy, the ultrafast laser deposition parameters include: target-substrate distance of 40-50 mm, ultrafast laser power of 280-320 kHz, laser deposition scan times of 120-180 times, and single pulse energy of 100-150 μJ; The scanning parameters of the continuous laser include: continuous laser power of 25~35W, laser scanning speed of 35~45mm / s, and defocus distance of 35~45mm; When a chromium-containing alloy is used as a target material to prepare the loose nanopowder pre-layer, the ultrafast laser deposition parameters include: a target-substrate distance of 40-50 mm, an ultrafast laser power of 280-320 kHz, a laser deposition scan number of 120-180 times, and a single pulse energy of 100-150 μJ; The scanning parameters of the continuous laser include: continuous laser power of 25~35W, laser scanning speed of 15~25mm / s, and defocus distance of 32~38mm.

2. The preparation method according to claim 1, characterized in that The ultrafast laser and the continuous laser are scanned alternately to form multiple layers of the chromium-containing metal thin coating on the surface of the substrate.

3. The preparation method according to claim 2, characterized in that The number of layers of the chromium-containing metal thin coating on the surface of the substrate is 2 to 4 layers.

4. The preparation method according to claim 2, characterized in that The number of layers of the chromium-containing metal thin coating on the surface of the substrate is 3.

5. The preparation method according to claim 1, characterized in that The zirconium matrix is ​​a Zr-4 zirconium alloy matrix.

6. Use of the preparation method according to any one of claims 1 to 5 in micro-nano imprinting or nuclear fuel units.

7. The use according to claim 6, characterized in that The application of the preparation method in the nuclear fuel unit includes preparing AFT nuclear fuel cladding by adopting the preparation method.

8. The use according to claim 7, characterized in that The application of the preparation method in the micro-nano imprinting includes preparing an alloy mold by adopting the preparation method.

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