Preparation method of pre-generated oxidation film on surface of Zr-Nb alloy and alloy product thereof

Abstract

The invention belongs to the technical field of alloy surface oxidation films, and particularly relates to a preparation method of a Zr-Nb alloy surface pre-generated oxidation film and an alloy product thereof, and the preparation method comprises the following steps: carrying out high-temperature oxidation treatment on a Zr-Nb alloy by adopting high-temperature water vapor, and enabling the oxygen content in the high-temperature water vapor to be greater than or equal to 100 mu g / kg so as to form an oxide film on the alloy surface; the problem that the growth quality of an alloy pre-formed film in the prior art is difficult to meet the use requirement of a reactor structural member is solved by oxidizing the water vapor and controlling the rising concentration in the water vapor.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear reactors, and in particular relates to a method for preparing a pre-generated oxide film on the surface of a Zr-Nb alloy and an alloy product thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Against the backdrop of increasingly severe energy crises and environmental problems, nuclear energy, as an efficient and stable clean energy source, is an important choice for optimizing the energy structure and building a clean energy system. After more than 70 years of development, nuclear energy development has established a technical route based on pressurized water reactors, boiling water reactors and heavy water reactors, and has successively developed research reactors, heating reactors and other reactor types to meet the application needs of nuclear energy in different scenarios.

[0004] Zirconium alloy has excellent nuclear properties, with a small thermal neutron absorption cross-section (0.18 barn), excellent resistance to high temperature and high pressure water and steam corrosion, high thermal conductivity, good compatibility with UO2, moderate mechanical properties, and good resistance to neutron irradiation in the reactor. Therefore, zirconium alloy is widely used in structural materials in water-cooled nuclear reactors, such as nuclear fuel element cladding, pressure tubes, positioning grids, and end plugs.

[0005] For example, zirconium-niobium alloy Zr-2.5Nb is one of the current commercial nuclear-grade zirconium alloys. Compared with other zirconium alloys, it has higher strength, better dimensional stability, and lower hydrogen absorption corrosion rate. Therefore, it is used as a high-reliability structural part such as heavy water reactor pressure tubes and research reactor irradiation test circuits. Another important application of nuclear-grade Zr-2.5Nb alloy is biomedical implants. Compared with common titanium alloy implants, it has a small spin magnetic moment and good biocompatibility, which can further enhance the patient experience.

[0006] The above applications all place extremely high demands on long-term wear resistance and corrosion resistance. Since the failure of zirconium alloys caused by factors such as corrosion hydrogen absorption and wear failure mostly starts from its surface, preparing a pre-generated oxide film on the surface of Zr-2.5Nb alloy can effectively inhibit the degradation of material properties and is of great value to further improve the reliability of Zr-2.5Nb alloy in use. There are several existing methods for preparing pre-generated films on the surface of Zr-2.5Nb alloy:

[0007] (1) Electrochemical method. For example, patent CN 115161743 A proposes that a surface oxide layer can be prepared on the surface of Zr-2.5Nb alloy by micro-arc oxidation, anodic oxidation or hard anodic oxidation. The oxide layer prepared by micro-arc oxidation can be 5 to 60 μm thick, the anodic oxide layer can be 10 to 100 μm thick, and the hard anodic oxide layer can be 10 to 200 μm thick.

[0008] (2) High temperature oxidation method. For example, patent CN 111270196 A proposes that an oxidizing gas at a temperature of 550°C to 600°C can be used to form a ceramic oxide film on the surface of the polished Zr-2.5Nb alloy through the oxidation reaction of the alloy. The thickness of the formed ceramic oxide layer is 3 to 7 μm.

[0009] Both of the above methods have their limitations, and therefore cannot be applied to Zr-2.5Nb alloys used in reactor structural parts such as heavy water reactor pressure tubes and research reactor irradiation test loops. The oxide film prepared by the electrochemical method is relatively thick, so the bonding ability between the film layer and the substrate is poor. If used in reactor structural parts such as heavy water reactor pressure tubes, the film layer is more likely to be damaged and peeled off under the action of flow-induced vibration, and loses its protective effect on the substrate. For the high-temperature oxidation method, since the formation temperature of the oxide film is 550℃~600℃, which is higher than the final annealing temperature of the Zr-2.5Nb alloy, it will change the heat treatment state of the Zr-2.5Nb alloy, making the mechanical properties of the Zr-2.5Nb alloy matrix lower than the design requirements. Therefore, there is an urgent need for a new method for preparing a pre-generated oxide film on the surface of a Zr-Nb alloy and its alloy products. Summary of the invention

[0010] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing a pre-grown oxide film on the surface of a Zr-Nb alloy and an alloy product thereof, which improves the density and wear resistance of the pre-grown oxide film on the surface while maintaining the mechanical properties of the Zr-Nb alloy matrix, thereby achieving long-term reliability requirements.

[0011] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a pre-formed oxide film on the surface of a Zr-Nb alloy, comprising:

[0012] The Zr-Nb alloy is subjected to high temperature oxidation treatment by using high temperature steam, wherein the oxygen content in the high temperature steam is greater than or equal to 100 μg / kg, so that an oxide film is formed on the surface of the alloy.

[0013] The present invention performs high-temperature oxidation treatment on the Zr-Nb alloy in high-temperature water vapor and increases the oxygen content in the high-temperature water vapor, so that the alloy is subjected to high-temperature oxidation treatment in an oxygen atmosphere, thereby improving the wear resistance, corrosion resistance and hydrogen absorption corrosion protection capability of the oxide film.

[0014] In some embodiments, the Zr—Nb alloy is subjected to surface mechanical treatment before the high-temperature oxidation treatment, so that the surface of the alloy has a predetermined surface roughness.

[0015] In some embodiments, the surface mechanical treatment is followed by a surface chemical treatment to remove the passivation layer generated by mechanical polishing on the alloy surface.

[0016] In some embodiments, the process further comprises cooling the alloy after the high temperature oxidation treatment to room temperature.

[0017] In some embodiments, the oxygen content in the high temperature steam is 100-1000 μg / kg, preferably 300-800 μg / kg.

[0018] In some embodiments, the surface mechanical treatment is grinding or machining the surface of the Zr—Nb alloy to make the surface roughness Ra of the Zr—Nb alloy reach 0.6-1.0 μm, preferably 0.7-0.9 μm.

[0019] In some embodiments, the Zr—Nb alloy is treated by sandpaper grinding or honing.

[0020] In some embodiments, the alloy after the surface mechanical treatment is pickled or alkali washed, and HNO 3 , H 2 SO 4 The alloy is pickled with a mixed acid aqueous solution of HF and HF.

[0021] In some embodiments, the volume fraction of each component of the mixed acid aqueous solution is: 30% H 2 O, 30% HNO 3 、30%H 2 SO 4 and 10% HF.

[0022] In some embodiments, the alloy is washed with deionized water after the surface mechanical treatment to remove the acid and alkali substances remaining on the surface of the alloy. Preferably, the alloy after the surface chemical treatment is washed in boiling deionized water.

[0023] In some embodiments, the alloy is dried after being washed with deionized water.

[0024] In some embodiments, the Zr-Nb alloy is a Zr-2.5Nb alloy.

[0025] In some embodiments, the alloy is subjected to high temperature oxidation treatment using high temperature steam at 350-450°C, preferably 380-420°C.

[0026] In some embodiments, the high temperature oxidation treatment time is not less than 24 hours, preferably 24-60 hours.

[0027] In some embodiments, the pressure of water vapor is 0.01-12 MPa.

[0028] In some embodiments, the high temperature oxidation treatment is performed in a pressure vessel, preferably an autoclave.

[0029] A second aspect of the present invention provides a Zr-Nb alloy product, the surface of which has an oxide film prepared according to the preparation method of any one of claims 1-9.

[0030] The beneficial effects of the present invention are:

[0031] 1. The present invention prepares a pre-grown oxide film by oxidation on the surface of a Zr-Nb alloy. By regulating the dissolved oxygen content in high-temperature water vapor, the density, wear resistance and other properties of the pre-grown oxide film are improved. At the same time, the diffusion activation energy of the pre-grown oxide film is improved, and the protection capability against hydrogen absorption corrosion of the alloy matrix is ​​further improved. A pre-grown oxide film with better comprehensive performance is prepared on the alloy surface to meet the use needs of reactor internal structural parts such as heavy water reactor pressure tubes.

[0032] 2. The pre-formed oxide film obtained by the present invention has good bonding performance with the alloy matrix; the pre-formed oxide film significantly enhances the surface hardness, can hinder the diffusion of oxygen and hydrogen, and improves the corrosion resistance, hydrogen absorption resistance and wear resistance of the alloy.

[0033] 3. The high-pressure autoclave pre-filming technology adopted in the present invention is simple to operate, low in cost, not limited by the shape of the sample, and has a low process temperature. It is a practical and effective method for improving the performance of zirconium alloys, has good manufacturing economy, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] Figure 1 A flow chart of the preparation of the pre-grown membrane of the present invention;

[0036] Figure 2 This is a typical cross-sectional morphology of the pre-grown film of Example 1 of the present invention. DETAILED DESCRIPTION

[0037] In view of the problem that the growth quality of existing pre-grown films is difficult to meet the use requirements of reactor structural parts, the present invention provides a method for preparing a pre-grown oxide film on the surface of a Zr-Nb alloy and an alloy product thereof.

[0038] The present invention uses water vapor to perform high-temperature oxidation treatment on the alloy surface, thereby reducing the treatment temperature and preventing the alloy from experiencing performance degradation due to excessively high temperature. Since the generation of water vapor mainly depends on the boiling of water vapor, under normal circumstances, the content of dissolved oxygen in water is relatively low. Therefore, the oxygen content in the water vapor of the high-temperature oxidation treatment is generally low, and the oxygen content in the water vapor in the reactor is less than 45 μg / kg. The inventors have found through testing that the performance of the pre-generated oxide film on the surface of the alloy obtained cannot meet the quality requirements of the reactor structure. In the present invention, the water vapor oxidation treatment process is further improved to increase the oxygen content in the warm water vapor, thereby increasing the density and wear resistance of the pre-generated film, and at the same time improving the protection against hydrogen corrosion of the alloy matrix (such as Zr-Nb alloy).

[0039] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail in conjunction with specific embodiments. It should be noted that the raw materials used in the present invention are all common commercially available products. Among them, the Zr-Nb alloy is a nominal composition Zr-2.5Nb alloy, and the alloy inevitably contains some impurities. The alloy is required to contain trace alloy elements such as no more than 1800ppm of O, no more than 1500ppm of Fe, and no more than 120ppm of C.

[0040] Example 1

[0041] This embodiment provides a pre-formed oxide film on the surface of a Zr-Nb alloy, and the specific preparation method thereof is as follows:

[0042] (1) grinding the Zr-2.5Nb alloy with sandpaper of 400 mesh, 800 mesh, 1500 mesh and 2000 mesh in sequence, and ultrasonically cleaning the ground Zr-2.5Nb alloy in anhydrous ethanol for 10-20 min to remove mechanical particles introduced by grinding;

[0043] (2) Prepare the mixed acid according to the following composition and volume fraction: 30% H 2 O, 30% HNO 3 、30%H 2 SO 4 and 10% HF (HF is liquid); pickling the cleaned Zr-2.5Nb alloy with the prepared mixed acid to remove the passivation layer on the surface of the sample;

[0044] (3) The pickled Zr-2.5Nb alloy was boiled in deionized water for 3 times, each time for 15 min, to remove any residual fluoride ions on the alloy surface;

[0045] (4) Dry the sample after boiling and cleaning in an oven at a temperature of 90°C for 1 h;

[0046] (5) The treated Zr-2.5Nb alloy was placed in an autoclave, deionized water was added into the autoclave, the deionized water temperature was heated to 400°C to form steam, the oxygen content in the steam was controlled to be 300 μg / kg, and water vapor oxidation was performed. The steam pressure was controlled at 10.3 MPa, and the oxidation was performed for 24 hours.

[0047] (6) Stop heating the autoclave, wait for the autoclave to cool to room temperature, open the autoclave and take out the Zr-2.5Nb alloy with the pre-formed oxide film.

[0048] Example 2

[0049] This embodiment provides a pre-grown oxide film on the surface of a Zr-Nb alloy, and the specific preparation method thereof is as follows:

[0050] (1) honing the Zr-2.5Nb alloy to a surface roughness of Ra = 0.8 μm, and ultrasonically cleaning the honed Zr-2.5Nb alloy in anhydrous ethanol for 10-20 min to remove mechanical particles introduced by honing;

[0051] (2) Prepare the mixed acid according to the following composition and volume fraction: 30% H 2 O, 30% HNO 3 、30%H 2 SO 4 and 10% HF (HF is liquid); pickling the cleaned Zr-2.5Nb alloy with the prepared mixed acid to remove the passivation layer on the surface of the sample;

[0052] (3) The pickled Zr-2.5Nb alloy was boiled in deionized water for 3 times, each time for 15 min, to remove any residual fluoride ions on the alloy surface;

[0053] (4) Dry the sample after boiling and cleaning in an oven at a temperature of 90°C for 1 h;

[0054] (5) The treated Zr-2.5Nb alloy was placed in an autoclave, deionized water was added into the autoclave, the deionized water temperature was heated to 400°C to form steam, the oxygen content in the steam was controlled to be 500 μg / kg, and water vapor oxidation was performed. The steam pressure was controlled at 2.0 MPa, and the oxidation was performed for 24 hours.

[0055] (6) Stop heating the autoclave, wait for the autoclave to cool to room temperature, open the autoclave and take out the Zr-2.5Nb alloy with the pre-formed oxide film.

[0056] Example 3

[0057] This embodiment provides a pre-grown oxide film on the surface of a Zr-Nb alloy. The difference between the preparation method thereof and that of embodiment 1 is that step (5) is replaced by:

[0058] The treated Zr-2.5Nb alloy was placed in an autoclave, deionized water was added into the autoclave, the deionized water temperature was heated to 400°C to form steam, the oxygen content in the steam was controlled to 800 μg / kg, and water vapor oxidation was performed. The steam pressure was controlled at 12.0 MPa, and the oxidation was carried out for 36 hours.

[0059] Example 4

[0060] This embodiment provides a pre-formed oxide film on the surface of a Zr-Nb alloy. The difference between the preparation method and the embodiment 1 is that step (5) is replaced by: placing the treated Zr-2.5Nb alloy in an autoclave, adding deionized water into the autoclave, heating the deionized water to 450°C to form steam, controlling the oxygen content in the steam to 100 μg / kg, and performing steam oxidation. The steam pressure is controlled at 12.0 MPa, and the oxidation is carried out for 48 hours.

[0061] Example 5

[0062] This embodiment provides a pre-formed oxide film on the surface of a Zr-Nb alloy. The difference between the preparation method and the embodiment 1 is that step (5) is replaced by: placing the treated Zr-2.5Nb alloy in an autoclave, adding deionized water into the autoclave, heating the deionized water to 350°C to form steam, controlling the oxygen content in the steam to 1000 μg / kg, and performing water vapor oxidation. The steam pressure is controlled at 0.01 MPa, and the oxidation is carried out for 36 hours.

[0063] Example 6

[0064] This embodiment provides a pre-formed oxide film on the surface of a Zr-Nb alloy. The difference between the preparation method and the embodiment 1 is that step (5) is replaced by: placing the treated Zr-2.5Nb alloy in an autoclave preheated to 400°C, introducing pre-prepared steam into the pressure vessel, and controlling the oxygen content in the steam to be 320μg / kg. At this time, the steam temperature is about 120°C. In the pressure vessel, the steam is rapidly heated to 400°C for water vapor oxidation. In the pressure vessel, the steam pressure is controlled at 0.36MPa and the oxidation is carried out for 30h.

[0065] Other embodiments of the present invention may also use other pressure vessels that meet the temperature and pressure control accuracy requirements, and can also achieve the same or similar effects.

[0066] Comparative Example 1

[0067] This comparative example provides a pre-generated oxide film on the surface of a Zr-Nb alloy. The difference between its preparation method and that of Example 1 is that in step (5), when the Zr-2.5Nb alloy is subjected to steam oxidation, exhaust gas method is used for deoxidation, and the oxygen content in the steam is less than 45 μg / kg. The remaining steps are the same as those of Example 1.

[0068] Comparative Example 2

[0069] This comparative example provides a pre-generated oxide film on the surface of a Zr-Nb alloy. The difference between its preparation method and that of Example 2 is that when the Zr-2.5Nb alloy is subjected to steam oxidation in step (5), the oxygen content in the steam is controlled to be less than 45 μg / kg, and the remaining steps are the same as those of Example 2.

[0070] Experimental example

[0071] The Zr-2.5Nb alloys with pre-formed oxide films obtained in Examples 1-5 and Comparative Examples 1-2 were observed and tested for performance. The specific tests were as follows:

[0072] (1) Using scanning electron microscopy, the cross section of the Zr-2.5Nb alloy with a pre-formed oxide film was observed to obtain the typical morphology of the pre-formed oxide film. Figure 2 As shown, the average thickness of the pre-grown films formed in Examples 1-5 are 1.0 μm, 1.1 μm, 0.9 μm, 0.10 μm, 0.10 μm and 0.9 μm, respectively, and the average thickness of the pre-grown films obtained in Comparative Examples 1-2 are 2.2 μm and 2.8 μm, respectively. It can be seen that the thickness of the pre-grown films formed in Examples 1-5 is significantly lower than that of Comparative Examples 1 and 2, and the bonding performance of the pre-grown oxide films of Examples 1-5 with the alloy substrate is significantly better than that of Comparative Examples 1 and 2.

[0073] (2) A 6mm spherical silicon carbide grinding head was used to conduct a reciprocating wear test on the pre-grown film. The load of the grinding head was 0.5N and the reciprocating distance was 6mm. The mass wear rate was calculated based on the mass wear amount and the wear scar morphology.

[0074] (3) Measure the diffusion coefficient of hydrogen in the pre-grown film at different temperatures and calculate the diffusion activation energy.

[0075] Table 1 Mass wear rate and diffusion activation energy

[0076]

[0077]

[0078] It can be seen from Table 1 that the alloys with pre-films on the surface obtained in Examples 1-5 have a lower mass wear rate of the oxidized pre-films than those in Comparative Examples 1 and 2, and a significantly higher diffusion activation energy than those in Comparative Examples 1 and 2. It can be seen that the embodiments of the present invention can improve the wear resistance, corrosion resistance and hydrogen absorption corrosion protection of the pre-film by increasing the oxygen content in the water vapor oxidation treatment.

[0079] In the early stage of the research, the inventor developed a method as described in the comparative example, in which the alloy is treated by oxidation with water vapor with a low oxygen content to obtain a pre-grown oxide film, which solves the problem of excessively high temperature during high-temperature oxidation in the existing process, avoids the influence of high temperature on the performance of the alloy matrix, and further reduces the thickness of the pre-grown oxide film, thereby improving the bonding ability between the pre-grown oxide film and the alloy matrix. However, the growth quality of the pre-grown film in the preparation method cannot be effectively controlled, and it is difficult to fully meet the use needs of reactor structural parts. Therefore, the inventor further increased the concentration of oxygen in the water vapor on the basis of the water vapor oxidation treatment, so that the alloy can be oxidized more quickly in the early stage of oxide film formation, and the physical phase of the oxide film is more transformed from the monoclinic system to the triclinic system, thereby improving the density of the oxide film, improving the wear resistance of the pre-grown film, and further improving the protection against hydrogen absorption corrosion, so as to meet the strict requirements of the heavy water reactor pressure tube.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a pre-generated oxide film on the surface of a Zr-Nb alloy, characterized in that: include: The Zr-Nb alloy is subjected to high temperature oxidation treatment by using high temperature steam, wherein the oxygen content in the high temperature steam is greater than or equal to 100 μg / kg, so that an oxide film is formed on the surface of the alloy.

2. The method for preparing a pre-oxidized film on the surface of a Zr-Nb alloy according to claim 1, characterized in that: The Zr-Nb alloy is subjected to surface mechanical treatment before high-temperature oxidation treatment to obtain a predetermined surface roughness on the alloy surface; preferably, the surface mechanical treatment is grinding or machining the surface of the Zr-Nb alloy to treat the surface roughness Ra of the Zr-Nb alloy to 0.6-1.0 μm, more preferably 0.7-0.9 μm.

3. The method for preparing a pre-oxidized film on the surface of a Zr-Nb alloy according to claim 1, characterized in that: After the surface mechanical treatment, the surface chemical treatment is carried out to remove the passivation layer produced by mechanical grinding and polishing on the alloy surface.

4. The method for preparing a pre-oxidized film on the surface of a Zr-Nb alloy according to claim 1, characterized in that: The process also includes cooling the alloy after the high temperature oxidation treatment to room temperature.

5. The method for preparing a pre-oxidized film on the surface of a Zr-Nb alloy according to claim 1, characterized in that: The Zr-Nb alloy is processed by grinding or honing; the Zr-Nb alloy is preferably a Zr-2.5Nb alloy with a nominal composition.

6. The method for preparing a pre-oxidized film on the surface of a Zr-Nb alloy according to claim 1, characterized in that: Pickling or alkali washing the alloy after surface mechanical treatment; Preferably, the pickling formula consists of a mixed acid aqueous solution of HNO3, H2SO4 and HF, and the volume fractions of the components of the mixed acid aqueous solution are: 30% H2O, 30% HNO3, 30% H2SO4 and 10% HF; or, during alkaline washing, the pH of the alkaline washing solution is set to 9-11.

7. The method for preparing a pre-oxidized film on the surface of a Zr-Nb alloy according to claim 1, characterized in that: After the surface mechanical treatment, the alloy is washed with deionized water to remove the acid and alkali substances remaining on the surface of the alloy; preferably, the alloy after the surface chemical treatment is placed in boiling deionized water for washing.

8. The method for preparing a pre-oxidized film on the surface of a Zr-Nb alloy according to claim 1, characterized in that: After washing with deionized water, the alloy is dried.

9. The method for preparing a pre-oxidized film on the surface of a Zr-Nb alloy according to claim 1, characterized in that: The alloy is subjected to high temperature oxidation treatment using high temperature steam at 350-450°C, preferably 380-420°C; Further preferably, the high temperature oxidation treatment time is not less than 24 hours; and the water vapor pressure is 0.01-12 MPa.

10. The method for preparing a pre-oxidized film on the surface of a Zr-Nb alloy according to claim 1, characterized in that: The high temperature oxidation treatment is carried out in a pressure vessel, preferably an autoclave.

11. A Zr-Nb alloy product, characterized in that: Its surface has an oxide film prepared according to the preparation method of any one of claims 1-10.

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