阅读说明：本技术 一种低温SiC纤维表面石墨界面的制备方法 (Preparation method of graphite interface on surface of low-temperature SiC fiber ) 是由 王一光 陶鹏飞 于 2019-10-14 设计创作，主要内容包括：本发明涉及一种低温SiC纤维表面石墨界面的制备方法,属于核燃料包壳管制备领域。本发明的目的是为了解决现有制备SiC<Sub>f</Sub>/SiC复合材料采用的PyC界面在高剂量中子辐照后,界面发生退化,界面处产生裂缝,导致材料力学性能和导热性能降低等问题,提供一种低温SiC纤维表面石墨界面的制备方法；该方法首先在SiC纤维预制体表面沉积PyC界面,然后通过强磁场及加热实现PyC界面的石墨化,在维持SiC纤维原有力学性能的同时提高SiC<Sub>f</Sub>/SiC复合材料的高温抗中子辐照能力。本发明利用强磁场辅助加热使PyC界面石墨化,降低石墨化温度,可避免高温加热对SiC纤维的损伤,防止SiC纤维晶粒长大,保持SiC纤维力学强度,也会保证SiC<Sub>f</Sub>/SiC复合材料的力学性能。(the invention relates to a preparation method of a graphite interface on the surface of a low-temperature SiC fiber, belonging to the field of preparation of nuclear fuel cladding tubes. The invention aims to solve the problem of the prior art for preparing SiC f The PyC interface adopted by the/SiC composite material has the problems of degradation of the interface, crack generation at the interface, reduction of the mechanical property and the heat-conducting property of the material and the like after high-dose neutron irradiation, and provides a preparation method of the graphite interface on the surface of the low-temperature SiC fiber; the method comprises the steps of firstly depositing a PyC interface on the surface of a SiC fiber preform, then graphitizing the PyC interface through a strong magnetic field and heating, and improving the original mechanical property of the SiC fiber while maintaining the original mechanical property of the SiC fiber f the high-temperature neutron irradiation resistance of the/SiC composite material. The invention utilizesThe high-intensity magnetic field auxiliary heating graphitizes a PyC interface, reduces the graphitization temperature, can avoid the damage of high-temperature heating to SiC fibers, prevents SiC fiber crystal grains from growing, maintains the mechanical strength of the SiC fibers, and also can ensure that the SiC fibers can be subjected to high-temperature heating f the mechanical property of the/SiC composite material.)

1. A method for preparing a graphite interface on the surface of SiC fiber under low temperature condition is characterized in that: the method comprises the following specific steps:

introducing an interface layer into the SiC fiber preform by adopting a chemical vapor deposition method to prepare the SiC fiber preform; the interface layer is a pyrolytic carbon PyC layer;

ultrasonic cleaning and drying;

And graphitizing the PyC interface by adopting a magnetic field auxiliary heating mode, wherein the magnetic field intensity is 5-10 Tesla, the magnetic field direction is along the radial direction of the fiber, the heating temperature is 1000-1300 ℃, and the time is 30-90 min.

2. The method for preparing the graphite interface on the surface of the SiC fiber under the low-temperature condition according to claim 1, wherein the graphite interface is prepared by the following steps: the thickness of the PyC interface is 60-250 nm.

3. The method for preparing the graphite interface on the surface of the SiC fiber under the low-temperature condition according to claim 1, wherein the graphite interface is prepared by the following steps: the thickness of the graphite interface layer is 50-200 nm.

4. the method for preparing the graphite interface on the surface of the SiC fiber under the low-temperature condition according to claim 1, wherein the graphite interface is prepared by the following steps: the PyC interface is graphitized under the protection of inert gas.

Technical Field

The invention relates to a preparation method of a graphite interface on the surface of a low-temperature SiC fiber, belonging to the field of preparation of nuclear fuel cladding tubes.

Background

For SiC_fThe interface phase of the/SiC composite material should be theoretically adoptedgraphite with anisotropic, layered structure to achieve the effect of deflecting cracks. The graphite layers are bonded by van der waals forces and when the crack tip propagates and meets, deflection occurs between the weakly bonded atomic layers, thereby causing SiC_fthe/SiC material exhibits nonlinear fracture. However, in the practical preparation of interface phase, pyrolytic carbon (PyC) interface is often used to replace graphite, and the existing nuclear grade SiC prepared by Chemical Vapor Infiltration (CVI)_fthe/SiC material mostly adopts a single-layer PyC or a plurality of layers of PyC/SiC as a material interface layer, and the thickness of the interface layer is usually 20-500 nm. The PyC interface is typically deposited on the surface of the fiber preform by a Chemical Vapor Deposition (CVD) process with a gaseous hydrocarbon as precursor. Although PyC has a small neutron absorption cross section, it is nuclear-grade SiC_fthe interface of the/SiC composite material is proved to be seriously damaged by radiation under the condition of high-dose neutron irradiation, so that the SiC composite material has the defect that the PyC interface is seriously damaged by the radiation_fthe/SiC composite material has difficulty in maintaining excellent mechanical properties and fracture toughness. For example, Nozawa et al investigated neutron irradiation (1073K, 7.7dpa) on CVI Hi-Nicalontype S SiC with single-layer PyC and multi-layer (PyC/SiC) n interphase, respectively, by fiber-out test (Push-out test)_fThe influence rule of the interface shear strength of the SiC/SiCcomposite material shows that the reduction range of the interface shear strength of the SiCf/(PyC/SiC) n/SiC composite material after irradiation is larger than that of SiC_fa/PyC/SiC composite material. Ozawa et al separately investigated FCVI TSA3SiC_f/SiC and HNLS SiC_fthe irradiation temperature of the/SiC composite material is 740-750 ℃, and the neutron flux is 3.1 multiplied by 1025n/m respectively²and 1.2X 1026n/m²The change rule of the mechanical property. The results show that: the composite fiber/matrix interface slip stress is significantly reduced. Katoh, Bergquist and the like research that CVI Hi-Nicalon Type S SiC is obtained when the irradiation temperature is 300 ℃, 500 ℃ and 800 ℃ and the irradiation dose is 71-74 dpa_fthe microstructure and the macroscopic property of the/SiC composite material are changed as follows: cracks are found at the PyC interface of the composite material, the interface bonding strength is reduced, and the mechanical property is reduced in different degrees. Koyanagi and Nozawa et al investigated irradiation induced CVI SiC_fThe mechanical property decline mechanism of the/SiC composite material is that when the irradiation dose is 100dpa, the irradiation temperature is 319 ℃ and 629 DEG CIn the process, the PyC interface bonding strength of the composite material becomes stronger and weaker respectively, so that the composite material is brittle and broken, and a large amount of fibers are pulled out from the fracture of the composite material, so that the strength of the composite material is greatly reduced. The present results show that the drug is administered at a high dose of (A)>70dpa) neutron irradiation, PyC is degraded, a disordered graphite structure is converted into a highly carbon-rich amorphous C/Si mixture, the interface phase performance is degraded, stress is generated, the interface debonding is caused, and further SiC is influenced_fThe mechanical and heat-conducting properties of the/SiC composite material under the high-dose neutron irradiation environment.

The PyC interfaces prepared by the chemical vapor deposition method are all in a discontinuous 'graphene-like' structure with a certain orientation and in a 'short-range order' state, so that the PyC interfaces have certain conductivity and can respond to the action of a magnetic field to a certain extent. After being treated by a strong magnetic field, the 'graphene-like' structure can be oriented along the direction of the magnetic field, and the stacked nano graphite sheet layers are parallel to the direction of the magnetic field, so that the PyC is graphitized.

Graphite has a high scattering cross section and an extremely low thermal neutron absorption cross section, has excellent radiation resistance, is often used as a preferred material for a support body of a high-temperature gas cooled reactor, and has excellent heat conduction performance compared with PyC. At the same time, the graphite has a layered structure and a high degree of crystallinity, and is used as SiC_fthe/SiC composite material interface can obtain good crack deflection effect. Generally, graphitization of PyC materials can be achieved by high temperature heat treatment above 1600 ℃, but high temperatures above 1500 ℃ cause grain growth in SiC fibers, resulting in a decrease in the mechanical properties of SiC fibers. If graphite is used as SiC_fThe interface layer of the/SiC composite material needs to solve the following problems: the graphitization temperature (not higher than 1300 ℃) of the PyC material is reduced so as to avoid damaging the mechanics of the SiC fiber and ensure that the chemical property of the fiber is not changed; and secondly, the interface layer is prevented from being oxidized, and the integrity of the interface layer is ensured. Therefore, how to prepare graphite interface on the surface of SiC fiber at lower temperature and improve SiC_fThe radiation resistance, the thermal conductivity and the mechanical property of the/SiC composite material are important.

Disclosure of Invention

The invention aims to solve the problems in the prior artPreparation of SiC_fthe PyC interface adopted by the/SiC composite material has the problems of degradation of the interface, crack generation at the interface, reduction of the mechanical property and the heat-conducting property of the material and the like after high-dose neutron irradiation, and provides a preparation method of the graphite interface on the surface of the low-temperature SiC fiber; the method comprises the steps of firstly depositing a PyC interface on the surface of a SiC fiber preform, then graphitizing the PyC interface through a magnetic field and heating, and improving the original mechanical property of the SiC fiber while maintaining the original mechanical property of the SiC fiber_fThe high-temperature neutron irradiation resistance of the/SiC composite material.

The purpose of the invention is realized by the following technical scheme.

A method for preparing a graphite interface on the surface of SiC fibers under a low-temperature condition comprises the following specific steps:

Step 1, preparation of a PyC interface: introducing an interface layer into the SiC fiber preform by adopting a chemical vapor deposition method to prepare the SiC fiber preform; the interface layer is a pyrolytic carbon PyC layer;

Step 2, cleaning the SiC fiber preform: ultrasonically cleaning and drying the SiC fiber preform;

Step 3, preparing a graphite interface: adopting a strong magnetic field auxiliary heating mode to graphitize a PyC interface;

And 4, cleaning the SiC fiber preform: and ultrasonically cleaning and drying the SiC fiber preform to obtain a graphite interface.

In the step 3, the magnetic field intensity is 5-10 Tesla, the magnetic field direction is along the radial direction of the fiber, the heating temperature is 1000-1300 ℃, and the time is 30-90 min.

The diameter of the SiC fiber is 12-14 mu m.

The thickness of the PyC interface is 60-250 nm.

The thickness of the graphite interface layer is 50-200 nm.

Advantageous effects

1. The method for preparing the graphite interface on the surface of the SiC fiber under the low-temperature condition comprises the steps of introducing a layer of PyC interface on the surface of a SiC fiber preform, and reducing the graphitization temperature of the PyC interface by adjusting the magnetic field intensity, so that the graphite interface with the thickness of 50-200 nm is obtainedIncrease SiC_fthe neutron irradiation resistance of the/SiC composite material.

2. Meanwhile, the magnetic field is used for assisting heating to graphitize a PyC interface, so that the damage of high-temperature heating to SiC fibers can be avoided, SiC fiber crystal grains are prevented from growing, the mechanical strength of the SiC fibers is maintained, and the SiC fibers can be ensured_fthe mechanical property of the/SiC composite material.

Drawings

FIG. 1 is a scanning electron micrograph of a graphite interface prepared by the method;

FIG. 2 is a scanning image of EDS points at the graphite interface prepared by this method;

FIG. 3 is an EDS elemental composition analysis of a graphite layer;

FIG. 4 is an EDS spot scan of a SiC fiber;

FIG. 5 is an EDS elemental composition analysis of SiC fibers;

FIG. 6 is an XRD pattern of a graphite interface-containing SiC fiber preform prepared by the method;

FIG. 7 is a TEM diffraction pattern of the SiC fiber preform having a graphite interface prepared by the method.

Detailed Description

the invention will now be further described with reference to the following examples and drawings.