KR20240077166A - Method for forming a protective coating film having excellent oxidation resistance and products comprising the oxidation resistance protective coating film formed thereby - Google Patents

Abstract

The present invention relates to a method for forming a protective coating film with excellent oxidation resistance and a product comprising the oxidation-resistant protective coating film formed thereby.
The present invention supplies a chromium source, an inert gas, and a nitrogen gas, respectively, and forms an oxidation-resistant protective coating film including a polycrystalline mixed layer of cubic structure in which polycrystals of chromium and chromium nitride are mixed on the top of the object to be treated by arc ion plating method. It provides a method of forming an oxidation-resistant protective coating film including the step of:

Description

Method for forming a protective coating film having excellent oxidation resistance and products comprising an oxidation resistance protective coating film formed thereby {Method for forming a protective coating film having excellent oxidation resistance and products comprising the oxidation resistance protective coating film formed thereby}

The present invention relates to a method for forming a protective coating film with excellent oxidation resistance and a product comprising the oxidation-resistant protective coating film formed thereby.

In general, nuclear fuel cladding tubes used as protection tubes for nuclear fuel are manufactured using zirconium alloy materials with low neutron absorption ability and excellent corrosion resistance and mechanical properties. However, the zirconium alloy carries the risk of rapidly oxidizing and generating a large amount of hydrogen gas when an accident occurs at a nuclear power plant or when exposed to a high-temperature water vapor atmosphere.

Previously, in order to improve the high-temperature oxidation resistance of the nuclear fuel cladding tube as described above, a method was used to improve the oxidation resistance of the zirconium alloy itself or to coat the surface of a product made of zirconium alloy with a material with excellent oxidation resistance. there is. As new coating materials with excellent long-term oxidation resistance, SiC composites, FeCrAl composites, and Mo composites are being developed. In the short term, coating technology for oxidation-resistant materials to strengthen the accident resistance of zirconium-clad pipes is a method using chromium and chromium alloys. It is being used.

Previously, in order to form a protective film on a zirconium clad tube, cold spray coating using chromium-based powder, high-energy pulse sputtering (HiPIMS) using a chromium alloy target in a vacuum, and chromium alloy in a vacuum were used. Arc ion plating (AIP), which melts and deposits metal by inducing an arc discharge to the target, is used.

The low-temperature spray coating method has the advantage of a high deposition rate, but has the disadvantage of forming a coating film with a somewhat low yield, low density of the coating film, and low coating uniformity and adhesion.

The high-energy pulse sputtering method has the advantage of being able to form a high-purity film and having almost no defects in the coating film, but the deposition rate is slow, adhesion, and fine columnar phases due to the low energy of neutral incident atoms during the deposition process. There is a disadvantage in that the columnar structure grain growth does not restrict the movement of oxidizing substances.

On the other hand, the arc ion plating method has the advantage of being able to form a coating film with higher density and purity than the pulse sputtering method, the adhesion of the coating film is high due to the reaction of ions, and the deposition rate is higher than the pulse sputtering method. There is a risk of defects occurring due to droplets resulting from discharge, and there is a problem of growth of crystal grains with a columnar structure.

Accordingly, a method has previously been proposed to form a chromium or chromium alloy coating film on a zirconium clad tube to form a columnar structure and an isotropic structure using the arc ion plating method. Specifically, previously, during the coating film deposition process, the bias voltage was basically applied to -50V and then periodically increased to -400V to partially form an isotropic structure, resulting in grain growth with a mixture of columnar and isotropic structures. A method for forming a coating film with a structure has been proposed.

However, in the arc ion plating process, which typically uses argon, an inert gas, to induce evaporation of the chrome alloy target, the columnar structure is mainly dominant, and partial destruction of the columnar crystal grains may occur due to ion shock due to an increase in bias. However, there is a problem that changes in the columnar structure that occur during the growth process of the entire film do not occur easily, and because of this, oxidation resistance cannot be significantly improved, so research on methods to complement this is necessary.

Document 1: Korean Patent No. 10-2161584 (Publication Date: 2020.04.09)

Document 1: Jung-Hwan Park, Hyun-Gil Kim, Jeong-yong Park, Yang-Il Jung, Dong-Joon Park, Yang-Hyun Koo, "High temperature steam-oxidation behavior of arc ion plated Cr coatings for accident tolerant fuel claddings", Surface & Coatings Technology, 280 (2015) 256-259 Document 2: Shengfa Zhu, Lin Chen, Yanping Wu, Yin Hu, Tianwei Liu, Kai B. Tang, Qiang Wei, "Microstructure and corrosion resistance of Cr/Cr2N multilayer lm deposited on the surface of depleted uranium", Corrosion Science, 82 (2014) 420-425 Document 3: G. Greczynski, J.Lu, O. Tengstrand, I.Petrov, J.E. Greene, L.Hultman, “Nitrogen-doped bcc-Cr films: Combining ceramic hardness with metallic toughness and conductivity”, Scripta Materialia, 122 (2016) 40-44 Literature 4: C. C. Wang, W. P. Hsieh, M. H. Shiao, J. H. Lin, and F. S. Shieu, “Microstructural Evolution in the Oxidized Chromium Nitride Coatings Prepared by Unbalanced Magnetron Sputtering", Journal of The Electrochemical Society, 150 (5) B199-B204 (2003)

Therefore, an embodiment of the present invention to solve the problems of the prior art described above is a competition growth method that uses nitrogen to hinder crystal growth of a columnar structure and promote crystal growth of polycrystalline structures having different shapes. ) to form a polycrystalline mixed layer with a cubic structure, thereby significantly suppressing the movement of oxidizing substances, thereby providing technical details on how to form a protective coating film with excellent oxidation resistance.

The technical problem to be achieved by the present invention is not limited to the technical problem mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the description below. There will be.

In one embodiment of the present invention for achieving the above-described object of the present invention, a chromium source, an inert gas, and a nitrogen gas are respectively supplied for arc discharge, and chromium and chromium nitride are placed on the top of the object to be treated by an arc ion plating method. It provides a method of forming an oxidation-resistant protective coating film comprising: forming an oxidation-resistant protective coating film comprising a polycrystalline mixed layer of cubic structure in which polycrystals are mixed.

According to one embodiment, the polycrystalline mixed layer is characterized in that it contains chromium and chromium nitride of the following formula (1) (however, in the following formula (1), X is 0.5 < X < 1.0).

[Formula 1]

CrN _1-X

In the chromium nitride of Formula 1, nitrogen penetrates and partially replaces the chromium crystal lattice (BCC), thereby inducing lattice deformation. That is, nitrogen affects the lattice structure of chromium and does not completely change the phase, but partially produces chromium nitride, and the polycrystalline mixed layer forms a polycrystal in which chromium and chromium nitride coexist. Such polycrystals have a lattice structure that is different from chromium nitride compounds such as Cr ₂ N and CrN, which have HCP or FCC lattice structures, due to phase change occurring when nitrogen is substituted into the crystal lattice.

According to one embodiment, the step of forming the oxidation-resistant protective coating film may include supplying the inert gas and nitrogen gas at a volume ratio of 10:1 to 1:1, respectively, to form the polycrystalline mixed layer, and applying an arc current of 30 A or more. The polycrystalline mixed layer can be formed by applying a bias voltage of -10 to -1,000 V, and the polycrystalline mixed layer can be formed at a temperature of 250 to 400°C.

According to one embodiment, the polycrystalline mixed layer may have a thickness of 0.01 to 100 ㎛.

According to one embodiment, forming the oxidation-resistant protective coating further includes forming an adhesion-enhancing layer on the object to be treated before forming the polycrystalline mixed layer, and forming the adhesion-enhancing layer. may supply the chromium source and the inert gas respectively and form an adhesion-enhancing layer on the top of the object to be treated by an arc ion plating method, and the adhesion-enhancing layer may have a thickness of 1 to 10 ㎛.

According to one embodiment, forming the oxidation-resistant protective coating further includes forming the polycrystalline mixed layer and then forming a surface protective layer on top of the polycrystalline mixed layer, and forming the surface protective layer. may supply the chromium source and the inert gas respectively and form a surface protective layer on top of the polycrystalline mixed layer by an arc ion plating method, and the surface protective layer may have a thickness of 1 to 10 ㎛.

According to one embodiment, the object to be treated may be a base material containing zirconium or a zirconium alloy.

Meanwhile, according to one embodiment, a product is provided that is formed by the method described above and includes a polycrystalline mixed layer of cubic structure in which polycrystals of chromium and chromium nitride are mixed on the top as an oxidation-resistant protective coating film.

According to one embodiment, the polycrystalline mixed layer is characterized by including chromium nitride of the following formula (1) (where, in the following formula (1), X is 0.5 < X < 1.0).

[Formula 1]

CrN _1-X

According to one embodiment, the oxidation-resistant protective coating film may further include an adhesion improvement layer formed on the lower part of the polycrystalline mixed layer and a surface protective layer formed on the upper part of the polycrystalline mixed layer, and the product is made of zirconium or zirconium. It may be a base material containing an alloy.

The method of forming a protective coating film with excellent oxidation resistance according to an embodiment uses nitrogen to inhibit crystal growth of a columnar structure and induce competition growth that promotes crystal growth of a polycrystalline structure with different shapes. By forming a polycrystalline mixed layer with a cubic structure, the movement of oxidizing substances can be greatly inhibited, thereby forming a protective coating film with excellent oxidation resistance.

The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

Figure 1 is a cross-sectional view showing the structure of a protective coating film formed by a method of forming a protective coating film according to an embodiment.
Figure 2 shows a chromium layer (Cr layer), a first chromium nitride layer (CrN layer), and a second chromium nitride layer (Cr ₂ N layer) formed on the surface of a zirconium specimen using the method of forming a protective coating film according to an embodiment. This is the result of measuring adhesion.
Figure 3 shows (a) a chromium layer (Cr layer), (b) a polycrystalline mixed layer (N-doped Cr or CrN _1-X ), and (c) a second chromium nitride layer formed by an arc ion plating method according to an embodiment. (Cr ₂ N layer) and (d) an electron microscope image of a cross section of the first chromium nitride layer (CrN layer).
Figure 4 shows the results of XRD pattern analysis of a thin film formed by the arc ion plating method according to an example.
Figure 5 shows the amount of bias current by trapping ions formed by bias voltage during the process of depositing a chromium layer using only argon in the coating method according to the embodiment and the process of depositing the chromium nitride layer by simultaneously supplying argon and nitrogen. This is the result of measurement.
Figure 6 shows the results of an electropotential polarization test for pure zirconium (Zr), a chromium layer (Cr layer), and a first chromium nitride layer (CrN layer) according to an example.
Figure 7 shows the results of an electropotential polarization test for pure zirconium (Zr), a chromium layer (Cr layer), a second chromium nitride layer (CrN ₂ layer), and a polycrystalline mixed layer (CrN _1-X ) according to an example.
Figure 8 shows that in the arc ion plating method according to an embodiment, arc currents of (a) 60 A and (b) 50 A are applied, and bias voltages are 0 V, -50 V, -75 V, and -100 V, respectively. , This is an electron microscope image of the cross section and surface of the chromium layer formed after adjusting and applying -125 V.
Figure 9 shows bias voltages of 0 V, -50 V, and -75 V under the conditions of (a) an arc current of 60 A and a process pressure of 5 Pa and (b) an arc current of 50 A and a process pressure of 5 Pa, depending on the embodiment. , This is the result of XRD pattern analysis of the chrome layer formed by adjusting to -100 V and -125 V.
Figure 10 shows bias voltages of 0 V, -50 V, and -75 V under the conditions of (a) an arc current of 60 A and a process pressure of 5 Pa and (b) an arc current of 50 A and a process pressure of 5 Pa, depending on the embodiment. , This is the result of analyzing the grain size of the chrome layer formed by adjusting -100 V and -125 V.
Figure 11 is a microscope image of a cross-section of a coating layer formed on the surface of a zirconium clad tube by a method according to an example.

Hereinafter, the present invention will be described with reference to the attached drawings. However, the present invention may be implemented in various different forms and, therefore, is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts unrelated to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

Throughout the specification, when a part is said to be "connected (connected, contacted, combined)" with another part, this means not only "directly connected" but also "indirectly connected" with another member in between. "Includes cases where it is. Additionally, when a part is said to “include” a certain component, this does not mean that other components are excluded, but that other components can be added, unless specifically stated to the contrary.

The terms used in this specification are merely used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

The method of forming a protective coating film according to an embodiment can prevent the movement of oxidizing substances by suppressing the growth of the columnar structure and inducing the tissue growth of the granular structure by applying the arc ion plating method. It relates to a method of forming a protective coating film with excellent oxidation resistance.

Growth of the cubic structure can be achieved through crystal grain refinement by incorporating heterogeneous materials, especially nitrogen, a reactive gas, to induce polycrystal competition growth of metal and metal nitride.

Polycrystal competitive growth using heterogeneous elements as described above is a technology that maximizes the properties of the material by inducing the nanoization of crystal grains. When chromium crystal grains grow in the structure, an amorphous phase caused by chromium nitride grows simultaneously, thereby hindering crystal growth. It has the characteristic of growing a polycrystalline mixed layer with a nano-sized cubic structure.

The polycrystalline protective coating film minimizes the occurrence of columnar defects, pinholes, and voids in the columnar structure and can block the movement path of oxidizing substances diffusing from the coating surface through defects, showing excellent oxidation resistance.

In addition, it not only suppresses the deposition of metal compounds at the interface, especially oxides, resulting from the initially contaminated target during the protective coating film formation process, but also suppresses the formation of metal compounds at the interface, improving the adhesion between the protective coating film and the surface of the coating object. It can be improved.

The protective coating film as described above may have a multilayer structure including a single layer of a polycrystalline mixed layer, a metal layer-polycrystalline mixed layer, a polycrystalline mixed layer-metal layer, or a metal layer-polycrystalline mixed layer-metal layer.

In addition, the method of forming the oxidation-resistant protective coating film 200 according to the embodiment includes a vacuum chamber, a bias voltage control device for applying a negative voltage or pulse alternating voltage to the object 100, and an arc cathode device for evaporating the chromium source. , the coating film can be formed using a conventional arc ion plating device having a structure including a gas supply device for supplying an inert gas and a reactive gas, respectively.

In the formation of the polycrystalline mixed layer 210 using the arc ion plating device, argon gas is supplied to form an argon atmosphere and nitrogen gas is supplied together to dissolve and evaporate the chromium source in the arc cathode device and treat the object 100. A thin film is formed on the surface, and a polycrystalline mixed layer 210 of cubic structure is formed.

In addition, the adhesion improvement layer 230 and the surface protection layer 250 each use the arc ion plating device, supply argon gas to form an argon atmosphere, and dissolve and evaporate the chromium source in the arc cathode device, It can be formed by forming a thin film on the surface of the object to be treated 100 or the upper surface of the polycrystalline mixed layer 210.

Hereinafter, the method of forming the oxidation-resistant protective coating film 200 according to the embodiment will be described in more detail with reference to the drawings.

Figure 1 is a cross-sectional view showing the structure of an oxidation-resistant protective coating film 200 formed by a method of forming the oxidation-resistant protective coating film 200 according to an embodiment.

Referring to FIG. 1, a method of forming an oxidation-resistant protective coating film 200 according to an embodiment includes forming an oxidation-resistant protective coating film 200 including a polycrystalline mixed layer 210.

The polycrystalline mixed layer 210 can be formed into a cubic structure in which polycrystals of chromium and chromium nitride are mixed on the upper part of the object to be treated 100 by supplying a chromium source, an inert gas, and nitrogen gas, respectively, and using an arc ion plating method. there is.

Specifically, the polycrystalline mixed layer 210 applies the arc ion plating method and incorporates heterogeneous materials, especially nitrogen, a reactive gas, to suppress the growth of the columnar structure and promote the growth of the granular structure. When chromium crystal grains grow through competitive growth of polycrystals, the amorphous phase caused by chromium nitride grows at the same time, thereby hindering crystal growth, thereby forming a nano-sized cubic structure within the structure, and forming defects, pinholes, and voids in the columnar structure. By minimizing the occurrence of etc., the movement path of oxidizing substances diffusing from the coating surface through defects can be blocked, thereby greatly improving the oxidation resistance of the object.

The object to be treated 100 may be manufactured from various common materials that require improved oxidation resistance. In particular, the object to be treated 100 may be a base material containing zirconium or a zirconium alloy. Specifically, the object to be treated 100 may be a representative example of a zirconium clad tube or a zirconium plate for nuclear fuel.

The chromium source may utilize a variety of common materials used to deposit chromium on the surface of the object 100 to be treated using an arc ion plating method.

The inert gas may be argon (Ar) gas, helium (He) gas, xenon (Xe) gas, or a mixture thereof. In particular, the inert gas may be argon (Ar) gas.

The reactive nitrogen gas may be a variety of common gases used for thin film growth. In particular, the reactive gas may be nitrogen (N ₂ ) gas.

In this step, the polycrystalline mixed layer 210 can be formed by supplying inert gas and nitrogen gas at a volume ratio of 10:1 to 1:1, respectively. In particular, in this step, inert gas and nitrogen gas can be supplied at a volume ratio of 10:2 to 1:3, respectively.

If the content of the nitrogen gas is low, the formation of a columnar structure may be difficult due to the low production amount of chromium nitride crystals, and if the content of the nitrogen gas is high, the columnar structure may be formed again on the surface of the object 100 to be treated. There is a problem.

Typically, a chromium nitride compound layer such as Cr ₂ N or CrN has a structure of a close-packed hexagonal lattice (HCC) or a face-centered cubic lattice (FCC) by inducing a phase change as nitrogen is substituted into the crystal lattice. However, in the method of forming an oxidation-resistant protective coating layer according to the embodiment, nitrogen affects the body-centered cubic (BCC) structure of chromium, and although it does not completely change the phase, it partially forms a chromium nitride compound to form a polycrystalline structure. . The polycrystalline mixed layer 210 may include chromium nitride (Cr) and chromium nitride having the structure of the following formula (1) (where X is 0.5 < X < 1.0).

[Formula 1]

CrN _1-X

The polycrystalline mixed layer 210 containing chromium nitride of Chemical Formula 1 as described above forms a cubic structure rather than a columnar crystal structure.

That is, the polycrystalline mixed layer 210 is a mixed layer of chromium (Cr) and chromium nitride (Cr ₂ N), but it is not necessary for crystals of chromium nitride (Cr ₂ N) to be grown. The polycrystalline mixed layer 210 may include second chromium nitride (CrN _1-X ) capable of changing phase depending on nitrogen concentration. The second chromium nitride may contain nitrogen at a rate of 5 to 25 at%, and preferably may have a structure containing 10 to 20 at% nitrogen, and is a mixture of chromium and chromium nitride. The polycrystalline mixed layer 210 having such a nitrogen concentration forms a cubic structure structure, so that defects such as columnar defects or pinholes do not occur, and oxidation resistance, that is, corrosion resistance, can be strengthened.

Additionally, in this step, the polycrystalline mixed layer 210 can be formed by applying an arc current of 30 A or more and a bias voltage of -10 to -1,000 V.

The arc current can be adjusted depending on the size of the arc target, and when the size of the arc increases, the arc current can also increase. In particular, the arc discharge current may range from 30 to 1000 A and is not limited thereto.

Additionally, the bias voltage can be adjusted considering the deposition rate.

For reference, the object to be treated 100 is heated by arc discharge first through a heating device mounted in a vacuum chamber. Second, the heat contained in the coating material by the micro droplets (solid state) and macro droplets (molten state) generated from the arc discharge is conducted to the object to be treated (100). Third, there is heating due to kinetic energy conversion in radiation caused by hot electrons of arc discharge and particularly important ions moving to the object to be treated (100). When a bias is applied, ions according to the bias voltage are accelerated by electric potential and are further heated by the received electric potential energy and impact energy. Fourth, due to the bias current, high-resistance metal alloys such as zirconium-clad tubes or stainless steels with relatively high electrical resistance are further heated due to additional Joule heating.

In an actual arc ion plating experiment, as the arc current changes, the process temperature rises to 352 ℃ at 80 A and the temperature measured by the thermocouple in the absence of bias increases to 370 ℃ when a bias is applied. In a process where the arc current is 60 A, the temperature rises to about 290 ℃ in the process without a bias applied, and it rises to 310 ℃ when the bias is applied. Under 50 A conditions, the temperature rises to approximately 270 to 290 °C. Accordingly, it is heated to approximately 20° C. or higher by the bias voltage. When the arc current is 80 A, the temperature rises to 370°C, but it is difficult to measure the temperature heated by bias using a thermocouple. Therefore, in the experiment, the color development according to temperature was measured using a thermal sheet (NiGK Co. G-1, G-2 model) to determine what the temperature reached was. As a result, the temperature was 414 ℃ or higher depending on the bias current. It is observed that the temperature rises by approximately 45°C or more, and it is analyzed that the temperature rises above the recrystallization temperature of zirconium. Therefore, in the process of applying the bias voltage, the arc current must be adjusted to be below the recrystallization temperature of the zirconium clad tube.

Accordingly, in this step, the chrome layer can be formed by applying an arc current of 50 to 70 A and a bias voltage of -30 to -125 V. Preferably, an arc current of 60 A and a bias voltage of -75 V can be applied.

And, in this step, the chromium layer can be formed at a temperature of 250 to 400 °C. For reference, in the case of zirconium alloy, the recrystallization temperature is 400°C, so it is important to maintain the process temperature below the recrystallization temperature. The arc ion plating process generates an arc in the object 100 to heat the molten droplets and ions in the object 100 at a heating rate of 10°C/min. The temperature can be increased to over 200°C.

Additionally, in the above step, the polycrystalline mixed layer 210 can be formed to a thickness of 0.01 to 100 ㎛. In particular, the polycrystalline mixed layer 210 can be formed to a thickness of 0.1 to 10 ㎛, preferably 5 to 7 ㎛.

Additionally, the oxidation-resistant protective coating film 200 may have a single-layer structure including only the polycrystalline mixed layer 210, or it may have a multi-layer structure including a chromium layer and a polycrystalline mixed layer 210.

When the oxidation-resistant protective coating film 200 is a multilayer film, the chromium layer and the polycrystalline mixed layer 210 can each be formed to have a thickness of 0.1 to 3 ㎛.

Meanwhile, forming the oxidation-resistant protective coating film 200 may further include forming an adhesion-enhancing layer on the top of the object to be treated 100 before forming the polycrystalline mixed layer 210.

The adhesion enhancement layer 230 is formed between the object to be treated 100 and the polycrystalline mixed layer 210 and serves to improve the adhesion of the polycrystalline mixed layer 210 to the surface of the object to be treated 100.

Specifically, the polycrystalline mixed layer 210 is grown by introducing nitrogen, and the chromium nitride layer is a high hardness thin film of 17 GPa or more. On the other hand, when the object to be treated (100) is zirconium, the hardness of zirconium is less than 1 GPa, and the difference in hardness between the chromium nitride layer and the object to be treated (100) is large, so the adhesive strength may be greatly reduced. The chromium layer deposited by the arc ion plating method varies depending on the bias conditions, but has a hardness in the range of 3 to 7 GPa, which is higher than that of the object to be treated (100) but does not show a very significant difference. In the case of the polycrystalline mixed layer 210, the hardness is as high as 15 to 20 GPa, so a problem may occur in which the polycrystalline mixed layer 210 is easily peeled off due to stress difference.

Therefore, an adhesion improvement layer can be formed on the surface of the object to be treated 100 to provide a hardness gradient between the object to be treated 100 and the polycrystalline mixed layer 210 to improve adhesion.

The adhesion improvement layer as described above can be formed to have a thickness of 1 to 10 ㎛, preferably 3 to 5 ㎛, and the thickness of the adhesion improvement layer can be adjusted depending on the thickness of the polycrystalline mixed layer 210.

The adhesion improvement layer 230 may be formed on the top of the object 100 by supplying the chromium source and inert gas, respectively, and using an arc ion plating method.

Additionally, in this step, the adhesion improvement layer 230 can be formed by applying an arc current of 30 A or more and a bias voltage of -10 to -1,000 V. In particular, the adhesion improvement layer 230 can be formed by applying an arc current of 50 to 70 A and a bias voltage of -30 to -125 V. Preferably, an arc current of 60 A and a bias voltage of -75 V can be applied.

Meanwhile, the method of forming the oxidation-resistant protective coating film 200 according to the embodiment aims to improve oxidation resistance by forming a polycrystalline mixed layer 210.

However, a nitride film layer is formed as a nitrogen contamination layer on the surface of the chromium source of the arc cathode due to nitrogen gas generated during the process for forming the polycrystalline mixed layer 210, or the chromium source of the arc cathode is exposed to the atmosphere. When exposed, an oxide layer is formed, and there is a problem that the adhesion of the coating is reduced due to the deposition of foreign substances at the interface of the object to be treated 100 during the arc evaporation and deposition process on the surface of the chromium source on which the nitride layer and the oxide layer are formed. That is, the surface protection layer forms a polycrystalline mixed layer 210 and then restricts the introduction of nitrogen into the chromium source surface of the arc cathode and the object to be treated 100 and introduces only argon gas to perform arc discharge, thereby, Pure chromium is exposed and deposited on the surface of the chrome source of the arc cathode and the surface of the object to be treated (100).

Accordingly, in the method of forming the oxidation-resistant protective coating film 200 according to the embodiment, a nitride film is formed on the surface of the chromium source of the arc cathode and the surface of the object 100 generated by nitrogen in the process of forming the polycrystalline mixed layer 210. The layers are removed at the same time and a surface protection layer 250 of a columnar crystal structure is formed on top of the polycrystalline mixed layer 210.

To this end, forming the oxidation-resistant protective coating film 200 may further include forming the polycrystalline mixed layer 210 and then forming a surface protective layer 250 on top of the polycrystalline mixed layer 210. You can.

The surface protective layer 250 may be formed on the upper part of the polycrystalline mixed layer 210 by supplying the chromium source and inert gas, respectively, and using an arc ion plating method.

The surface protective layer 250 is a chrome layer and can be formed by applying an arc current of 30 A or more and a bias voltage of -10 to -1,000 V. In particular, in this step, it can be formed by applying an arc current of 50 to 70 A and a bias voltage of -30 to -125 V. Preferably, an arc current of 60 A and a bias voltage of -75 V can be applied.

The surface protection layer may be deposited to a thickness of 1 to 10 ㎛. Preferably, the surface protection layer may be deposited to a thickness of 3 to 5 ㎛.

The method of forming the oxidation-resistant protective coating film 200 according to the above-described embodiment has been described as forming the adhesion enhancement layer 230, the polycrystalline mixed layer 210, and the surface protection layer 250 once each, but is limited to this. In order to form an oxidation-resistant protective coating film 200 suitable for the desired thickness, the steps of forming the adhesion improvement layer 230, polycrystalline mixed layer 210, and surface protection layer 250 as described above are performed at least twice. It can be performed repeatedly.

The method of forming a protective coating film with excellent oxidation resistance according to the above-described embodiment is a competition growth method that uses nitrogen to hinder crystal growth of a columnar structure and promote crystal growth of polycrystalline structures having different shapes. ) is induced to form a polycrystalline mixed layer with a cubic structure, which can greatly inhibit the movement of oxidizing substances, forming a protective coating film with excellent oxidation resistance.

Meanwhile, the product including the oxidation-resistant protective coating film 200 according to the embodiment is formed by the method described above and includes a polycrystalline mixed layer 210 having a cubic structure in which polycrystals of chromium and chromium nitride are mixed on the top.

In addition, the oxidation-resistant protective coating film 200 further includes an adhesion enhancement layer 230 formed on the lower part of the polycrystalline mixed layer 210 and a surface protective layer 250 formed on the upper part of the polycrystalline mixed layer 210. can do.

The product may be a base material containing zirconium or zirconium alloy for nuclear fuel. Specifically, the product may be a zirconium clad pipe or a zirconium plate.

Hereinafter, the present invention will be described in more detail through examples.

The presented examples are only specific examples of the present invention and are not intended to limit the technical scope of the present invention.

<Example 1> Formation of a single layer protective coating film with cubic structure using arc ion plating method

Zirconium clad tubes, zirconium plates, and silicon wafers for analysis were prepared as specimens. The prepared specimen was ultrasonically cleaned with acetone and alcohol, loaded into the equipment, evacuated, heated, and maintained at 100°C. Next, to clean the surface of the specimen, argon gas was introduced and plasma cleaning was performed under a pressure condition of 3 Pa.

Next, the first chromium nitride layer (CrN layer), the second chromium nitride layer (Cr ₂ N layer), and the polycrystalline mixed layer (N-doped Cr or CrN _1-X ) were each applied to the surface of the specimen using the arc ion plating method. Argon gas was introduced to grow a chromium film on the surface of zirconium, and nitrogen gas was simultaneously introduced to form it. At this time, the coating material for forming the chromium nitride-based film was formed using chromium (GFE, Germany) with a purity of 99.9%.

The equipment used to form the chromium nitride film is a rotatable system equipped with 8 rotating jigs (diameter 135 mm) on a rotating plate with a diameter of 600 mm. There are 12 arc guns, 3 on each of the 4 sides, A reactor capable of forming chromium and chromium nitride was used, with an effective coating zone of 850 mm in the longitudinal direction and a maximum length of 1 m.

Next, in the arc deposition process, the pressure was adjusted to 1 to 5 Pa, the arc current was set to 50 to 80A, and the bias was adjusted to -125 to 0V to form a chromium nitride-based film. The chromium nitride-based film was formed by first introducing only a chromium source and argon gas to grow a chromium film on the surface of the specimen, and then introducing nitrogen and argon gas as reaction gases to nitride the chromium film.

The first chromium nitride layer (CrN layer), the second chromium nitride layer (Cr ₂ N layer), and the polycrystalline mixed layer (N-doped Cr or CrN _1-X ) are controlled by arc current, bias voltage, argon gas, and nitrogen gas, respectively. It was formed by controlling the flow rate. At this time, the polycrystalline mixed layer (N-doped Cr or CrN _1-X ) was formed by supplying nitrogen and argon at a volume ratio of 2:1, respectively, thereby forming a polycrystalline mixed layer.

<Example 2> Formation of a multilayer protective coating film

Using the method used in Example 1, a chromium layer was formed on the surface of the specimen to improve adhesion, a polycrystalline mixed layer was formed on the upper surface of the chrome layer, and then chromium was added to the upper surface of the polycrystalline mixed layer to remove nitrogen and protect the surface. Additional layers were formed to form a multi-layer protective coating film with a triple-layer structure.

<Experimental example>

(1) Evaluation of adhesion of chromium layer and chromium nitride layer

A chromium layer (Cr layer), a first chromium nitride layer (CrN layer), and a second chromium nitride layer (Cr ₂ N layer) were each grown on the surface of the zirconium specimen, and then the adhesion between the specimen and the coating layer was evaluated. As a result, is shown in Figure 2. The adhesion of the coating layer was evaluated using the scratch analysis method (maximum indentation load 30N).

Figure 2 shows a chromium layer (Cr layer), a first chromium nitride layer (CrN layer), and a second chromium nitride layer (Cr ₂ N layer) formed on the surface of a zirconium specimen using the method of forming a protective coating film according to an embodiment. This is the result of measuring adhesion.

As shown in Figure 2, as a result of evaluating the adhesion of the coating layer, it was confirmed that the adhesion of the chrome layer was the best because no cracks occurred in the coating layer even when the pressure exceeded 30N. On the other hand, in the case of the first chromium nitride layer, the time point (Lc2) at which the crack occurred was approximately 19N, and in the case of the second chromium nitride layer, the time point (Lc2) at which the crack occurred was confirmed to be approximately 7N.

Accordingly, the chrome layer (Cr layer) had the best adhesion to the zirconium specimen, so the chrome layer was selected as the first coating layer.

(2) Cross-sectional shape and crystal structure analysis of the coating layer thin film

The cross-sectional shape and crystal structure of the chromium layer (Cr layer), the first chromium nitride layer (CrN layer), the second chromium nitride layer (Cr ₂ N layer), and the polycrystalline mixed layer (CrN _1-X ) were analyzed, and the results were analyzed. It is shown in Figure 3.

Figure 3 shows (a) a chromium layer (Cr layer), (b) a polycrystalline mixed layer (N-doped Cr or CrN _1-X ), and (c) a second chromium nitride layer formed by an arc ion plating method according to an embodiment. (Cr ₂ N layer) and (d) an electron microscope image of a cross section of the first chromium nitride layer (CrN layer).

Referring to FIG. 3, it was confirmed that the chromium layer (Cr layer), the first chromium nitride layer (CrN layer), and the second chromium nitride layer (Cr ₂ N layer) all grew in a columnar structure, but were polycrystalline. In the case of the mixed layer (N-doped Cr, CrN _1-X ), no defects were identified in crystal growth due to the mixed cubic amorphous structure.

(3) Evaluation of the impact of reactive gas and inert gas supply amount

In order to evaluate the effect of the supply amount of nitrogen gas and inert gas when forming a polycrystalline mixed layer (CrN _1-X ), the supply amount of argon gas was set to 200 sccm, and the supply amount of nitrogen gas was set to 0, 50, 100, and 150, respectively. , 200, and 300 sccm were adjusted to form a thin film. XRD pattern analysis of the formed thin film was performed to confirm the composition of the thin film, and the results are shown in Figure 4.

As shown in Figure 4, when the flow rates of argon gas and nitrogen gas are 200 sccm and 50 sccm, respectively, crystals of CrN _1-X are formed in the tissue, and the supply ratio of argon gas and nitrogen gas for crystal growth of cubic structure is set to I was able to confirm.

(4) Contamination of the arc cathode chrome source and contamination of the deposition layer

After performing the arc ion plating process, the vacuum is broken and the equipment is exposed to the atmosphere for a certain period of time to detach and detach the sample. At this time, the arc cathode chrome source is exposed to oxygen and an oxide layer is formed on the surface. When the arc cathode chrome source is a pure chromium layer, the oxide layer formed on the surface forms a very thin and dense structure. However, when a chromium nitride layer is formed on the surface of the arc cathode chrome source, nitride and chromium are mixed on the surface, so a mixed layer of nitride and oxide is formed when exposed to air. In addition, the diffusion thickness of nitrogen is significant on the arc cathode chrome source surface, showing a tendency for nitrogen to diffuse and penetrate from the target surface to a thickness of 50 to 100 ㎛.

Figure 5 shows the amount of bias current by trapping ions formed by bias voltage during the process of depositing a chromium layer using only argon in the coating method according to the embodiment and the process of depositing the chromium nitride layer by simultaneously supplying argon and nitrogen. This is the result of measurement.

As shown in Figure 5, when the chromium layer was deposited by supplying only argon gas, the normal bias current was measured within 1 minute after the arc discharge was initiated. When nitrogen was supplied during the arc discharge process, it was confirmed that the amount of bias current changed depending on the amount of nitrogen supplied. In other words, it was confirmed that a low bias current amount was shown after the arc discharge was initiated, but that a normal current amount was shown as the arc discharge time elapsed. A low current amount initially after the start of arc discharge means that nitride or oxide with high resistance has been formed on the surface of the thin film, and it was confirmed that when nitrogen diffuses deeply into the surface of the thin film, the time to return to the normal current amount becomes longer. At such a low current amount, chromium, nitride, and oxide are simultaneously melted and radiated through arc discharge of the thin film, and eventually chromium, nitride, and oxide are simultaneously deposited on the object to be treated.

(5) Evaluation of corrosion resistance of thin films

The corrosion resistance of the chrome layer (Cr layer) and the polycrystalline mixed layer (CrN _1-X ) was evaluated. Corrosion resistance evaluation was performed through a potentiodynamic polarization test, and the counter electrode was composed of Pt and the reference electrode was Ag/AgCl in a 3.5% NaCl (25℃) electrolyte solution, and the electrode was measured in the range of -1 V to 1.5 V. It was performed under conditions of 2 mV/sec.

The electropotential polarization test was first conducted on zirconium specimens, the substrate on which the protective film is formed. At this time, the surface of the zirconium specimen was easily oxidized, so a polished surface was used.

First, a chromium layer (Cr layer), a first chromium nitride layer (CrN layer), a second chromium nitride layer (Cr ₂ N layer), and a polycrystalline mixed layer (CrN _1-X ) were deposited on the surface of the zirconium specimen, respectively. Next, an electropotential polarization test was performed on the coating layer of the zirconium specimen with each coating layer formed, and the results are shown in FIG. 6.

Figure 6 shows the results of an electropotential polarization test for pure zirconium (Zr), a chromium layer (Cr layer), and a first chromium nitride layer (CrN layer) according to an example.

Figure 7 shows the results of an electropotential polarization test for pure zirconium (Zr), a chromium layer (Cr layer), a second chromium nitride layer (CrN ₂ layer), and a polycrystalline mixed layer (CrN _1-X ) according to an example.

Referring to Figure 6, in the case of zirconium, the corrosion potential is -617 mV vs. It was found to be Ag/AgCl, and when a chromium layer was formed on the surface of the zirconium specimen, the corrosion potential was -173 mV vs. It was confirmed that it appeared as Ag/AgCl and showed a potential difference of 444 mV.

Additionally, when the first chromium nitride layer (CrN) was formed on the surface of the zirconium specimen, the corrosion potential was -143 mV vs. It was confirmed to be Ag/AgCl, and it was confirmed that the difference in corrosion potential was not significant when a chromium layer (Cr) was formed on the surface of the zirconium specimen.

In addition, referring to Figure 7, when a second chromium nitride layer (Cr ₂ N) is formed on the surface of the zirconium specimen (CrN layer), the difference in corrosion potential is also the case when a chromium layer (Cr) is formed on the surface of the zirconium specimen. It was confirmed that it was not large, but when a polycrystalline mixed layer (CrN _1-X ) was formed on the surface of the zirconium specimen, the corrosion potential was greatly improved and the potential difference was confirmed to show a larger deviation.

(6) Evaluation of the effects of arc current and bias voltage

A chromium layer was formed on the surface of a zirconium clad tube with a diameter of 800 mm using an arc ion plating process. At this time, the arc current was set to 50 A and 60 A, the bias was adjusted to 0 V, -50 V, -75 V, -100 V, and -125 V, respectively, and the process time was adjusted to create an arc with a thickness of 20 ㎛. A chrome layer was formed, and the cross-section and surface of the chrome layer formed by controlling different process conditions were evaluated, and the results are shown in Figure 8.

As shown in Figure 8, it was confirmed that the main variable in the process of removing columnar voids or defects in the process of forming the chrome layer is the bias voltage.

Specifically, it was confirmed that a dense film was formed under the condition of applying a bias voltage of -100 V or more at an arc current of 50 A. Additionally, when the arc current was 60 A, a dense film was formed at a bias voltage of -75 V or higher. In other words, it was confirmed that the higher the arc current, the more dense the film became, and that the film tended to become more dense as the bias voltage increased.

Therefore, it was confirmed that the growth structure of the film could be controlled by controlling the arc current and bias voltage.

(7) Evaluation of the influence of arc current and bias voltage on crystal growth

In addition, crystal growth characteristics were evaluated according to arc current and bias voltage, and the results are shown in Figure 9.

Figure 9 shows bias voltages of 0 V, -50 V, and -75 V under the conditions of (a) an arc current of 60 A and a process pressure of 5 Pa and (b) an arc current of 50 A and a process pressure of 5 Pa, depending on the embodiment. , This is the result of XRD pattern analysis of the chrome layer formed by adjusting to -100 V and -125 V.

As shown in Figure 9(a), it was confirmed that Cr(110) crystals grow in the main growth direction from 0 V to -50 V and grow most strongly at -50 V. However, when the bias was -75 V, it was confirmed that Cr(110) crystal growth was limited and changes occurred. At this time, rather than changing the preferential growth direction to Cr(211), it was determined that the preferential growth of Cr(110) was limited and polycrystallized. In addition, it was confirmed that after the bias of -100 V, polycrystalline growth occurred without overall preferential growth.

Additionally, as shown in Figure 9(b), it was confirmed that the preferential growth direction was limited to Cr(110) at -50 V under the conditions of arc current of 50 A and process pressure of 5 Pa. Although there is a slight difference in the arc current between 60 A and 50 A, it is clear that the phase changes starting at -50 V, and it was confirmed that polycrystals of Cr(110) and Cr(211) appear.

(8) Evaluation of the influence of arc current and bias voltage on grain size

In addition, the grain size was measured using the XRD pattern analysis results, and the results are shown in Figure 11.

Figure 10 shows bias voltages of 0 V, -50 V, and -75 V under the conditions of (a) an arc current of 60 A and a process pressure of 5 Pa and (b) an arc current of 50 A and a process pressure of 5 Pa, depending on the embodiment. , This is the result of analyzing the grain size of the chromium layer formed by adjusting to -100 V and -125 V.

As shown in Figure 10, when no bias was applied, the average size of crystal grains formed in the chrome layer was confirmed to be 208.9 nm when the arc current was 60 A and 190.0 nm when the arc current was 50 A. When a bias voltage is applied, crystal growth is promoted, and when the arc current is 60 A, the average size of the crystal grains tends to increase from approximately 270 nm to 308 nm. When the arc current is 50 A, the bias voltage tends to increase. Even in the case of rise, it was confirmed that the size of the crystal grains was approximately 260 nm to 270 nm, showing little increase in the size of the grains.

(9) Thickness evaluation

Figure 11 is a microscope image of a cross-section of a coating layer formed on the surface of a zirconium clad tube by the method according to the example.

As shown in Figure 11, it was confirmed that a coating layer with an average thickness of approximately 20 ㎛ was formed on the surface of the zirconium clad tube through the arc ion plating process.

Although the technical idea of the present invention described above has been described in detail in preferred embodiments, it should be noted that the above-described embodiments are for illustrative purposes only and are not intended for limitation. Additionally, those of ordinary skill in the technical field of the present invention will understand that various embodiments are possible within the scope of the technical idea of the present invention. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the attached claims.

100: object to be treated
200: Oxidation-resistant protective coating film
210: polycrystalline mixed layer
230: Adhesion improvement layer
250: Surface protective layer

Claims (11)

Supplying a chromium source, an inert gas, and nitrogen gas, respectively, and forming an oxidation-resistant protective coating film including a polycrystalline mixed layer of a cubic structure in which polycrystals of chromium and chromium nitride are mixed on the top of the object to be treated by an arc ion plating method; A method of forming an oxidation-resistant protective coating film comprising. According to paragraph 1,
A method of forming an oxidation-resistant protective coating film, wherein the polycrystalline mixed layer includes chromium nitride of the following formula (1) (wherein in the formula (1), X has a range of 0.5 < X < 1.0).
[Formula 1]
CrN _1-X According to paragraph 1,
The step of forming the oxidation-resistant protective coating film is a method of forming an oxidation-resistant protective coating film, characterized in that the polycrystalline mixed layer is formed by applying an arc current of 30 A or more and a bias voltage of -10 to -1,000 V. According to paragraph 1,
The step of forming the oxidation-resistant protective coating film,
A method of forming an oxidation-resistant protective coating film, characterized in that forming the polycrystalline mixed layer at a temperature of 250 to 400 ° C. According to paragraph 1,
A method of forming an oxidation-resistant protective coating film, characterized in that the polycrystalline mixed layer has a thickness of 0.01 to 100 ㎛. According to paragraph 1,
The step of forming the oxidation-resistant protective coating film,
Further comprising forming an adhesion improvement layer on top of the object to be treated before forming the polycrystalline mixed layer,
The step of forming the adhesion improvement layer is,
A method of forming an oxidation-resistant protective coating film, comprising supplying the chromium source and the inert gas respectively and forming an adhesion-enhancing layer on the top of the object to be treated by an arc ion plating method. According to paragraph 1,
The step of forming the oxidation-resistant protective coating film,
Forming the polycrystalline mixed layer and then forming a surface protective layer on top of the polycrystalline mixed layer,
The step of forming the surface protective layer is,
A method of forming an oxidation-resistant protective coating film, characterized in that supplying the chromium source and the inert gas respectively and forming a surface protective layer on the upper part of the polycrystalline mixed layer by an arc ion plating method. According to paragraph 1,
A method of forming an oxidation-resistant protective coating film, characterized in that the object to be treated is a base material containing zirconium or zirconium alloy for nuclear fuel. A product comprising an oxidation-resistant protective coating film formed by the method according to any one of claims 1 to 8 and including a polycrystalline mixed layer of cubic structure in which polycrystals of chromium and chromium nitride are mixed on the top. According to clause 10,
The polycrystalline mixed layer is a product characterized in that it contains chromium nitride of the following formula (1) (however, in the following formula (1),
[Formula 1]
CrN _1-X According to clause 10,
The oxidation-resistant protective coating film,
An adhesion improvement layer formed on the lower part of the polycrystalline mixed layer, and
A product characterized in that it further comprises a surface protection layer formed on top of the polycrystalline mixed layer.