Nuclear fuel cladding composite material and preparation method thereof

Abstract

The invention mainly provides a nuclear fuel cladding composite material and a preparation method thereof. The nuclear fuel cladding composite material comprises a zirconium alloy matrix, the niobium-rich diffusion barrier layer is formed on the surface of the zirconium alloy matrix; the Cr coating covers the niobium-rich diffusion barrier layer; and an Al-rich layer formed on the surface of the Cr coating. The preparation method comprises the following steps: firstly, carrying out surface pretreatment on the zirconium alloy matrix; a niobium-rich diffusion barrier layer is formed on the surface of the zirconium alloy matrix through ion implantation; then depositing a Cr coating on the niobium-rich layer; and finally, an Al element is injected into the surface of the Cr coating, and an Al-rich layer is formed so that an Al2O3 protective layer can be formed under the high-temperature working condition. According to the technical scheme, interface mutual diffusion can be effectively inhibited, the stability of the coating is improved, meanwhile, the Cr coating structure is optimized, the oxidation process is delayed, a gradient protection system is constructed, and the oxidation resistance of a high-temperature material is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of coating preparation and surface treatment, in particular to a composite coating material formed by ion implantation of niobium and aluminum and high-power pulsed magnetron sputtering using a zirconium alloy as a substrate and a preparation method thereof. Background Art

[0002] At present, zirconium alloys are widely used in the field of nuclear fuel cladding for water-cooled reactors due to their advantages such as small thermal neutron absorption cross section, good thermal conductivity, good irradiation stability, water-side corrosion resistance, good mechanical properties and easy processing. However, under the condition of a reactor loss of coolant accident, zirconium alloys will undergo a violent oxidation reaction with high-temperature steam, releasing a large amount of heat and hydrogen, causing an explosion, leading to a large-scale release of radioactive substances and causing catastrophic consequences. Therefore, it is very necessary to improve the ability of nuclear fuel cladding to resist reactor accidents, that is, to improve its resistance to high-temperature steam oxidation.

[0003] The preparation of anti-oxidation coating on the surface of commercial mature zirconium alloy cladding has the advantages of short R&D cycle and low cost, showing great potential for engineering application. Metal Cr can generate denser and more protective Cr in oxidizing medium. 2 O 3 The film layer is compatible with the zirconium alloy matrix, so it has become one of the preferred materials for the cladding surface coating. However, there are some problems that need to be optimized. First, the Zr-Cr interface is prone to mutual diffusion, especially in the coating-substrate interface area under high temperature. 2 Interdiffusion layer, ZrCr 2 It is a brittle Laves phase, which has a great negative impact on the mechanical properties of the coating material. It also causes the loss of Cr coating material, thereby reducing the protective effect of the coating and even causing it to fail.

[0004] On the other hand, as a protective coating for nuclear fuel accident tolerance cladding, there are certain requirements for thickness, generally about 15um, which is already a relatively thick coating for magnetron sputtering technology. The metal pure Cr coating prepared by magnetron sputtering usually shows a growth morphology of columnar crystals. The continuous grain boundary of coarse columnar crystals is a defect, which is easy to cause cracking and peeling of the coating under the action of external force. In addition, this grain boundary is easy to diffuse oxygen elements to the substrate, causing the failure of the coating. In order to obtain a dense coating, if only the substrate bias is increased, the internal stress of the coating will be greatly increased, which is easy to cause the coating to stick and peel off. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a nuclear fuel cladding composite material, comprising: Zirconium alloy matrix; A niobium (Nb)-rich diffusion barrier layer formed on the surface of the zirconium alloy substrate; A Cr coating overlying the niobium-rich diffusion barrier layer; and an Al-rich layer formed on the surface of the Cr coating.

[0006] Furthermore, the niobium-rich diffusion barrier layer has a thickness of 50-200 nm and forms a solid solution structure with the zirconium alloy matrix.

[0007] Furthermore, the Cr coating has a thickness of 10-15 μm and is prepared by high-power pulsed magnetron sputtering. The grains grow in a dense and fine straight columnar shape with a grain size of 50-200 nm.

[0008] Furthermore, the Al-rich layer has a thickness of 50-100 nm and covers the columnar grain boundaries on the surface of the Cr coating to form a continuous and dense oxygen diffusion barrier layer.

[0009] The present invention also provides a method for preparing a nuclear fuel cladding composite material, comprising the following steps: Performing surface pretreatment on the zirconium alloy substrate; A niobium-rich diffusion barrier layer is formed on the surface of the zirconium alloy substrate by ion implantation; depositing a Cr coating on the niobium-rich layer; Al element is implanted into the surface of Cr coating.

[0010] Furthermore, the ion implantation energy to form the niobium-rich diffusion barrier layer is 50-150keV; the implantation dose is 1×10¹ 6 -5×10¹ 7 ions / cm².

[0011] Furthermore, in the deposition step of the Cr coating, high-power pulsed magnetron sputtering is used, the sputtering power is 5-7KW, the working gas is argon, and the deposition time is 8-10h.

[0012] Furthermore, the implantation energy of Al element is 30-80 keV; the implantation dose is 5×10¹ 6 -2×10¹ 8 ions / cm².

[0013] Furthermore, before the Al element injection step, the Cr coating is subjected to vacuum annealing at a temperature of 500-800° C. for 1-3 h.

[0014] Therefore, the beneficial effects of the present invention are: 1. Inhibit interfacial diffusion and improve coating stability. By ion implanting on the surface of the zirconium alloy matrix to form a niobium (Nb)-rich diffusion barrier layer, the interdiffusion of Zr and Cr in high temperature environments is effectively blocked. Nb forms a solid solution structure with the Zr matrix, and its high melting point and compatibility with Cr significantly inhibit the brittle ZrCr2 The formation of Laves phase improves the coating-substrate interface bonding strength and avoids the problem of coating peeling failure caused by mutual diffusion. At the same time, Nb has a low neutron absorption cross section (1.16 barns), which has little impact on the neutron economy of the reactor.

[0015] 2. Optimize the structure of the Cr coating and slow down the oxidation process. The Cr coating prepared by high-power pulsed magnetron sputtering (HiPIMS) has a fine columnar crystal structure, and its high ionization rate process significantly reduces the density of grain boundary defects. Compared with traditional magnetron sputtering, HiPIMS technology increases the density of the coating by more than 20%, and the connectivity of the grain boundary as an oxygen diffusion channel is effectively blocked, thereby slowing down the penetration rate of oxygen into the substrate in a high-temperature water vapor environment.

[0016] 3. Build a gradient protection system to enhance high-temperature anti-oxidation ability. The surface of the Cr coating is treated with Al ion implantation and high-temperature oxidation to form a dense Al 2 O 3 Oxide film. 2 O 3 The thermal stability of the film at 1200℃ is better than that of Cr 2 O 3 Its oxygen diffusion coefficient is only less than 1 / 5 of that of pure Cr coating, which can block the columnar grain boundary defects of Cr coating and form a dual protection mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Surface structure diagram of the coating of the present invention.

[0018] Figure 2 This is a cross-sectional morphology diagram of the coating of the present invention.

[0019] Figure 3 Cross-sectional SEM image of the coating of the present invention after polishing.

[0020] Figure 4 This is a cross-sectional view of the membrane-substrate interface of Example 3 after being subjected to a 1200°C high-temperature steam oxidation test for 1 hour.

[0021] Figure 5 This is a scratch test comparison chart. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, please refer to the accompanying drawings and embodiments to further describe the present invention in detail. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] Example 1

[0024] Embodiment 1 provided by the present invention is a nuclear fuel cladding composite material, comprising a zirconium alloy substrate, a niobium (Nb)-rich diffusion barrier layer formed on the surface of the zirconium alloy substrate by ion implantation, a Cr coating covering the niobium-rich diffusion barrier layer, and an Al coating formed on the surface of the Cr coating. 2 O 3 The thickness of the niobium-rich diffusion barrier layer is 50-200 nm, and it forms a solid solution structure with the zirconium alloy matrix. The thickness of the Cr coating is 10-15 μm, and it is prepared by high-power pulsed magnetron sputtering. The grains grow in a columnar shape with a grain size of 50-200 nm. 2 O 3 The thickness of the oxide film is 50-100 nm, and it covers the columnar grain boundaries on the surface of the Cr coating, forming a continuous and dense oxygen diffusion barrier.

[0025] Example 2

[0026] Embodiment 2 provided by the present invention proposes a method for preparing a nuclear fuel cladding composite material, comprising the following steps: Step 1: Matrix pretreatment: Use zirconium alloy (Zr-4) plate, mechanically polish it to Ra≤0.1 μm, and ultrasonically clean it to remove surface contaminants.

[0027] Step 2: Nb ion implantation: In an ion implanter, 150 keV energy and 5×10¹ 7 ions / cm² dose was implanted into Nb to form a Nb-rich layer with a thickness of about 180 nm. Scanning electron microscopy (SEM) showed that the Nb element formed a gradient distribution on the surface of the matrix and formed a solid solution structure with the Zr matrix.

[0028] Step 3: Cr coating deposition: HiPIMS process was used, with a Cr target purity of 99.99%, a sputtering power of 6 KW, an argon pressure of 0.5 Pa, and a deposition time of 8 h to obtain a Cr coating with a thickness of 14.5 μm and an average columnar crystal size of about 150 nm.

[0029] Step 4: Vacuum annealing: annealing at 700℃ for 2 h to eliminate the internal stress of the coating. The scratch test showed that the film-base bonding strength was increased to 85 N.

[0030] Step 5: Al ion implantation and oxidation: 80 keV energy, 1×10¹ 8 ions / cm² dose is implanted into Al to form an Al-rich layer about 90nm thick outside the Cr layer.

[0031] After 1200℃ steam oxidation for 1 h, the oxidation weight gain was 3.2 mg / cm², the thickness of the oxide layer was uniformly about 3.8 μm, and the ZrCr at the interface between the substrate and the Cr coating 2The thickness of the diffusion layer is only 0.6 μm, which is 82% lower than the 3.5 μm diffusion layer of the sample without Nb barrier layer. The coating hardness is 10.6 GPa (pure Cr coating is 7.8 GPa), and the fracture toughness is increased by 30%.

[0032] Example 3

[0033] Embodiment 3 provided by the present invention proposes a method for preparing a nuclear fuel cladding composite material, comprising the following steps: Step 1: Matrix pretreatment: The surface of the zirconium alloy tube is sandblasted (Ra≈0.5 μm), and then quickly enters the ion implantation process after pickling and activation.

[0034] Step 2: Nb ion implantation: Dynamic scanning mode, implantation energy 80 keV, dose 1×10¹ 7 ions / cm², forming a Nb-rich layer with a thickness of about 80 nm, and the time consumed is 40% shorter than that in Example 1.

[0035] Step 3: Cr coating deposition: The HiPIMS sputtering power was reduced to 6.5 KW, and the deposition time was 7 h, resulting in a Cr coating with a thickness of 13.6 μm. TEM observation showed that the columnar crystal size was about 50 nm, and the grain boundary density was reduced by 15%.

[0036] Step 4: Al implantation optimization: using dual beam implantation technology (Al+O co-implantation), energy 50 keV, dose 5×10¹ 7 ions / cm², and a 50 nm thick amorphous Al-O transition layer was formed directly by irradiation.

[0037] Step 5: Post-treatment: vacuum annealing at 500 °C for 1 h to eliminate interface stress.

[0038] After 1100℃ steam oxidation for 1h, the oxidation weight gain was 2.4mg / cm², and the Al-O layer was converted into dense Al 2 O 3 The HiPIMS process is mature, the film quality is stable, and it is suitable for continuous production of tubular cladding. Neutron economic analysis shows that reducing the thickness of the Nb layer reduces the thermal neutron absorption loss to 0.3%.

[0039] The experimental results are shown in the following table:

[0040] Therefore, the technical solution of the present invention has the following advantages: 1. Inhibit interfacial diffusion and improve coating stability By ion implanting the zirconium alloy matrix surface to form a niobium (Nb) rich diffusion barrier layer, the mutual diffusion of Zr and Cr in high temperature environment is effectively blocked. Nb forms a solid solution structure with the Zr matrix, and its high melting point (2469℃) and compatibility with Cr (Zr-Nb eutectic temperature 1740℃) significantly inhibit the brittle ZrCr 2 The formation of Laves phase increases the coating-substrate interface bonding strength by more than 30%, avoiding the problem of coating peeling failure caused by mutual diffusion. At the same time, Nb has a low neutron absorption cross section (1.16 barns), which has little impact on the neutron economy of the reactor.

[0041] 2. Optimize the Cr coating structure and delay the oxidation process The Cr coating prepared by high-power pulsed magnetron sputtering (HiPIMS) has a fine columnar crystal structure (grain size 50-200 nm), and its high ionization rate process significantly reduces the density of grain boundary defects. Compared with traditional magnetron sputtering, HiPIMS technology increases the density of the coating by more than 20%, and the connectivity of the grain boundary as an oxygen diffusion channel is effectively blocked, thereby slowing down the penetration rate of oxygen into the substrate in a high-temperature water vapor environment.

[0042] 3. Build a gradient protection system to enhance high temperature antioxidant capacity The surface of the Cr coating is implanted with Al ions, and a continuous and dense Al 2 O 3 Oxide film (thickness 50-100 nm, density ≥98%). Al 2 O 3 The thermal stability of the film at 1200℃ is better than that of Cr 2 O 3 Its oxygen diffusion coefficient is only less than 1 / 5 of that of pure Cr coating, which can block the columnar grain boundary defects of Cr coating and form a double protection mechanism: the outer layer Al 2 O 3 The membrane acts as the main barrier to block the oxidizing medium, and the inner Cr coating provides structural support. The synergistic effect of the two reduces the oxidation weight gain of the composite material to ≤5 mg / cm² after 1 hour of water vapor oxidation at 1200℃, which is more than 80% lower than that of traditional Cr coating.

[0043] 4. Strong process compatibility and potential for engineering applications This technology uses a combination of mature surface modification processes such as ion implantation and magnetron sputtering. It does not require complex equipment modification, and can achieve precise design of coating performance through parameter control (such as injection energy and sputtering power). After vacuum annealing (500-800℃), the residual stress of the coating decreases by 50%-70%, and the film-base bonding strength reaches more than 80 N (scratch test results), meeting the mechanical performance requirements of nuclear fuel assemblies for long-term irradiation service.

[0044] In summary, the present invention breaks through the performance bottleneck of traditional Cr coating in high-temperature oxidation environment through the multi-level protection strategy of "interface diffusion inhibition-coating structure optimization-surface oxidation enhancement", and provides a reliable solution for the engineering application of nuclear fuel cladding.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A nuclear fuel cladding composite material, characterized in that: include: Zirconium alloy matrix; A niobium (Nb)-rich diffusion barrier layer formed on the surface of the zirconium alloy substrate; A Cr coating covering the niobium-rich barrier diffusion layer; And an Al-rich layer formed on the surface of the Cr coating.

2. A nuclear fuel cladding composite material according to claim 1, characterized in that: The niobium-rich diffusion barrier layer has a thickness of 50-200 nm and forms a solid solution structure with the zirconium alloy matrix.

3. The nuclear fuel cladding composite material according to claim 1, characterized in that: The Cr coating has a thickness of 10-15 μm and is prepared by high-power pulsed magnetron sputtering. The grains grow in a columnar shape and the grain size is 50-200 nm.

4. The nuclear fuel cladding composite material according to claim 1, characterized in that: The Al-rich layer has a thickness of 50-100 nm and covers the columnar grain boundaries on the surface of the Cr coating to form a continuous and dense oxygen diffusion barrier layer.

5. A method for preparing a nuclear fuel cladding composite material according to any one of claims 1 to 4, characterized in that: The following steps are involved: Performing surface pretreatment on the zirconium alloy substrate; forming a niobium-rich diffusion barrier layer on the surface of the zirconium alloy substrate by ion implantation; depositing a Cr coating on the niobium-rich layer; Al element is injected into the surface of Cr coating to form Al-rich layer.

6. The preparation method according to claim 5, characterized in that: The ion implantation energy for forming the niobium-rich diffusion barrier layer is 50-150 keV; the implantation dose is 1×10¹ 6 -5×10¹ 7 ions / cm².

7. The preparation method according to claim 5, characterized in that: In the deposition step of the Cr coating, high-power pulsed magnetron sputtering is used, the sputtering power is 5-7 KW, the working gas is argon, and the deposition time is 8-10 hours.

8. The preparation method according to claim 5, characterized in that: The Al element is implanted with an implantation energy of 30-80 keV and an implantation dose of 5×10¹ 6 -2×10¹ 8 ions / cm².

9. The preparation method according to claim 5, characterized in that: Before the Al element injection step, the Cr coating is subjected to vacuum annealing treatment at a temperature of 500-800° C. for 1-3 h.

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