阅读说明：本技术 一种液态铅铋合金中金属材料疲劳裂纹扩展速率测试方法 (Method for testing fatigue crack propagation rate of metal material in liquid lead-bismuth alloy ) 是由 何西扣 李骥 杨钢 赵吉庆 包汉生 许斌 方才顺 吴冰洁 于 2021-06-22 设计创作，主要内容包括：一种液态铅铋合金中金属材料疲劳裂纹扩展速率测试方法,属于核材料的性能测试技术领域。以倒置式疲劳试验机为基础,利用金属反应釜和陶瓷坩埚盛装高温铅铋合金液提供了实验环境,并利用覆盖进行密封,通过反力架、试样结构夹具,装夹三点弯曲断裂韧性试样,将测试部分整体浸入高温铅铋共晶合金液中,利用卧式三点弯曲试样,开口方向向上,在施加载荷过程中,通过高温引伸计测量裂纹扩展速率,从而判断材料在液态金属中的裂纹扩展情况,进而实现在苛刻的高温铅铋环境下测量材料韧性性能,为铅铋快中子反应堆结构材料的选则提供支持。优点在于,避免了引伸计受到腐蚀,降低了实验成本,延长使用寿命。(A method for testing the fatigue crack propagation rate of a metal material in a liquid lead-bismuth alloy belongs to the technical field of performance test of nuclear materials. Based on an inverted fatigue testing machine, an experimental environment is provided by utilizing a metal reaction kettle and a ceramic crucible to contain high-temperature lead-bismuth alloy liquid, the high-temperature lead-bismuth alloy liquid is sealed by utilizing a cover, a three-point bending fracture toughness sample is clamped by a reaction frame and a sample structure clamp, a testing part is wholly immersed into the high-temperature lead-bismuth eutectic alloy liquid, a horizontal three-point bending sample is utilized, the opening direction is upward, and in the loading process, the crack propagation rate is measured by a high-temperature extensometer, so that the crack propagation condition of the material in liquid metal is judged, the toughness performance of the material is measured under the harsh high-temperature lead-bismuth environment, and support is provided for selection of the lead-bismuth fast neutron reactor structural material. The advantages are that the corrosion of the extensometer is avoided, the experiment cost is reduced, and the service life is prolonged.)

1. A method for testing the fatigue crack propagation rate of a metal material in a liquid lead-bismuth alloy is characterized by comprising the following specific measurement steps:

1) a reaction frame support (4), a reaction frame base (8) and a sample base (9) are arranged on a cross beam of the fatigue testing machine, and the sample base (9) is contacted with the midpoint of a sample (7); the sample (7) should be kept with the opening upward, and the lower surface of the loading rod (5) is connected with two ends of the sample (7) to form a couple of three-point bending. A central rod of the fatigue testing machine is connected with a loading rod (5) to form a closed force application system;

2) an opening of the sample 7 is connected with a ceramic rod (6), and the other end of the ceramic rod is connected with the foot part of the high-temperature extensometer (1) to form an opening measuring system;

3) putting a ceramic crucible (11) into a metal kettle body (12), putting a lead bismuth alloy ingot into the ceramic crucible (11) for testing, and heating to melt the lead bismuth alloy ingot;

4) immersing a reaction frame support (4), a reaction frame base (8), a sample base (9), a sample (7), a loading rod (5) and a ceramic rod (6) in the step 1) into a ceramic crucible, and sealing a metal kettle body (12) by using a kettle cover (3) and a sealing ring (2);

5) step 2), the lower part of the high-temperature extensometer 1 is arranged in the metal kettle body (12), and the upper part of the high-temperature extensometer is arranged outside the kettle cover (3);

6) the liquid level of the lead-bismuth alloy in the step 1) is higher than the upper surface of the sample (7) by 5 mm;

7) the kettle cover (3) and the metal kettle body (12) are kept sealed, after the temperature is constant, the frequency is selected in the range of 0-30HZ of the fatigue testing machine, a sine wave loading mode is adopted, a three-point bending test is carried out when the stress ratio R is 0.1, and the crack propagation rate is measured through the high-temperature extensometer 1.

Technical Field

The invention belongs to the technical field of performance test of nuclear materials, and particularly relates to a method for testing crack propagation and fracture toughness of a stacking structure material.

Background

The lead bismuth pile is a reactor taking liquid lead bismuth eutectic alloy (LBE) as a coolant, adopts a closed fuel circulation mode, and is one of six main pile types in a future fourth generation nuclear energy system. The latest release fourth generation nuclear energy system technology roadmap of the international forum organization GIF for the fourth generation nuclear energy system shows that the lead bismuth stack is expected to be the first to become the fourth generation nuclear energy system for realizing industrial demonstration and commercial application. LBE has good neutronics, low chemical activity, good heat transfer characteristics and intrinsic safety, and is a prime candidate for lead-based stack coolants. Although LBE has many advantages, under the operating condition of a reactor, the structural material is subjected to continuous scouring of LBE with high temperature and high flow rate, and different types of corrosion such as dissolution, oxidation, erosion, fretting wear and the like occur, so that the structural material is embrittled, and the service material fails. The synergistic effect of liquid metal and stress can lead to that the risk of LME (liquid metal embrittlement) of the structural material is greatly increased, and the LME fracture failure process comprises the nucleation and growth of cracks, wherein the crack core is formed on the solid-liquid wetting surface firstly, and then the crack is expanded until the fracture failure. When the material is corroded, the material composition, the medium oxygen concentration, the temperature, the flow rate and the like can have important influence on the material corrosion. Therefore, the research on the crack propagation condition of the material in the lead-bismuth environment and how to reduce the crack propagation rate and the improvement of the crack propagation resistance of the material have important significance on promoting the development of the lead-bismuth pile.

In the last decade, research on the influence of LME effect on the mechanical properties of structural materials has gradually become an international research hotspot. In order to evaluate the brittleness of the structural material in an LBE service environment, related organizations at home and abroad modify respective equipment, and the influence of medium environmental factors on the mechanical property of the structural material in the LBE environment is researched by adopting stress corrosion methods such as slow strain rate stretching, constant load stretching and the like in a high-temperature lead bismuth environment. The method reflects the influence of LME on the plasticity of the material through the elongation numerical side of the tensile sample, but cannot visually reflect the toughness index of the material, and has a few reports on the research on the crack propagation rate and the fracture toughness of the material in a high-temperature lead-bismuth environment. A few research works on fracture toughness firstly adopt an LBE pre-wetting mode, and then experiments are carried out in an Ar gas environment, and the difference between the test environment and the actual service environment of the material is large. At present, no experimental conditions for meeting the fracture toughness and the crack propagation rate in a high-temperature lead bismuth environment exist at home and abroad, and the crack propagation amount cannot be measured by adopting an LVDT (linear variable differential transformer) mode to measure the resistance due to the conductivity of liquid lead bismuth. Meanwhile, corrosion of the liquid lead bismuth to the extensometer can not effectively measure the relative displacement.

The crack propagation measurement test method under the liquid lead bismuth environment has strong innovation, and the toughness performance and the fatigue crack propagation rate of the material can be more visually tested by using the method.

Disclosure of Invention

The invention aims to provide a method for testing the fatigue crack propagation rate of a metal material in a liquid lead-bismuth alloy, which can realize the measurement of the crack propagation rate and the fracture toughness under different experimental conditions (temperature, strain rate and strain quantity).

The invention is based on an inverted fatigue testing machine (an upper seat moving cylinder), provides an experimental environment by utilizing a metal reaction kettle and a ceramic crucible to contain high-temperature lead bismuth alloy liquid, utilizes a cover to seal, clamps a three-point bending fracture toughness sample through a reaction frame and a sample structure clamp, entirely immerses a testing part into the high-temperature lead bismuth eutectic alloy liquid, utilizes a horizontal three-point bending sample, has an upward opening direction, and measures the crack propagation rate through a high-temperature extensometer in the process of applying a load, thereby judging the crack propagation condition of the material in liquid metal, further realizing the measurement of the toughness property of the material in a harsh high-temperature lead bismuth environment, and providing support for the selection of a lead bismuth fast neutron reactor structure material. The specific measurement steps are as follows:

(1) a reaction frame pillar 4, a reaction frame base 8 and a sample base 9 are arranged on a cross beam of the fatigue testing machine, and the sample base 9 is contacted with the midpoint of a sample 7; the sample 7 should be kept open upward, and the two ends of the sample 7 are connected below the loading rod 5 to form a three-point bending couple. A central rod of the fatigue testing machine is connected with the loading rod 5 to form a closed force application system;

(2) an opening of a sample 7 is connected with a ceramic rod 6, and the other end of the ceramic rod is connected with a foot part of a high-temperature extensometer 1, so that an opening measuring system is formed;

(3) putting the ceramic crucible 11 into the metal kettle body 12, putting a lead bismuth alloy ingot into the ceramic crucible 11 for testing, and heating to melt the lead bismuth alloy ingot;

(4) immersing the reaction frame support 4, the reaction frame base 8, the sample base 9, the sample 7, the loading rod 5 and the ceramic rod 6 in the step (1) into a ceramic crucible, and sealing the metal kettle body 12 by using the kettle cover 3 and the sealing ring 2;

(5) the lower part of the high-temperature extensometer 1 is arranged in the metal kettle body 12, and the upper part is arranged outside the kettle cover 3;

(6) the liquid level of the lead-bismuth alloy in the step (1) is 5mm higher than the upper surface of the sample 7;

(7) the kettle cover 3 and the metal kettle body 12 are kept sealed, after the temperature is constant, the frequency is selected in the range of 0-30HZ of the fatigue testing machine, a sine wave loading mode is adopted, a three-point bending test is carried out when the stress ratio R is 0.1, and the crack propagation rate is measured through the high-temperature extensometer 1.

After loading, acting force and reacting force between the loading rod and the sample base are utilized to enable the sample to be subjected to repeated acting force of one-way bending, the opening is enabled to be constantly changed, displacement is recorded along with the change of the load through the ceramic rod and the extensometer, crack propagation rate and stress intensity factors are calculated through the opening of the load and the cutting edge, then the crack propagation speed is measured under the high-temperature lead bismuth environment, and the crack propagation resistance of the material under the high-temperature lead bismuth environment is analyzed.

Compared with the prior art, the invention has the following advantages:

1. the method can directly measure the fracture toughness and the fatigue crack propagation rate of the material in the liquid lead bismuth environment, and has more intuitive representation on the toughness performance of an analysis sample;

2. the invention realizes different medium environments in the kettle body through the heating device;

3. the invention can achieve good sealing effect in low-temperature or high-temperature environment, can simulate special medium environment, and simultaneously can prevent lead-bismuth alloy steam from volatilizing in a sealing way;

4. according to the invention, the extensometer is connected with the ceramic, so that the extensometer is prevented from being corroded, the experiment cost is reduced, and the service life is prolonged.

Drawings

FIG. 1 is a schematic illustration of the experimental procedure for testing fatigue crack growth rate using the method of the present invention.

Fig. 2 is an enlarged view of a pattern portion.

In the figure, a high-temperature extensometer 1, a sealing ring 2, a kettle cover 3, a reaction frame support 4, a loading rod 5, a ceramic rod 6, a sample 7, a reaction frame base 8, a sample base 9, a lead-bismuth alloy liquid 10, a ceramic crucible 11, a metal kettle body 12, a heating coil 13 and heat-preservation cotton 14.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clearly apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the detailed description and specific examples, while indicating the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

As shown in figure 1, a method for testing the fatigue crack propagation rate of a metal material in a liquid lead-bismuth alloy is characterized in that a fatigue testing machine needs to be improved properly, a cross beam of the fatigue testing machine is connected with a reaction frame support 4, the lower end of the reaction frame support 4 is connected with a reaction frame base 8, a sample base 9 is installed on the reaction frame base 8, the center of a sample 7 is located at the position of a boss at the center of the sample base, the sample 7 needs to keep an opening upward, two ends of a loading rod 5 are in contact with two ends of the sample 7, and the upper end of the loading rod is connected with a central driving shaft of the original fatigue testing machine. Because the three-point bending experiment needs to be carried out in lead bismuth, the high-temperature extensometer 1 used for measuring the crack propagation rate is only high-temperature resistant but is not lead bismuth corrosion resistant, so that the ceramic rod 6 is connected to the foot part of the high-temperature extensometer 1, the other end of the ceramic rod 6 is clamped at the cutting edge position of the sample 7, the opening displacement is convenient to measure in real time, and the upper part of the high-temperature extensometer 1 is kept outside the sealing ring of the reaction kettle.

A metal kettle body 12 is arranged on a base of an original fatigue testing machine, a heating coil 13 and heat insulation cotton 14 are wrapped on the periphery of the metal kettle body, and a ceramic crucible 11 is embedded inside the metal kettle body. Putting a lead bismuth alloy ingot into a ceramic crucible 11, heating to enable a lead bismuth alloy liquid 10 to be in a molten state, integrally immersing a reaction frame support 4, a loading rod 5, a ceramic rod 6, a sample 7, a reaction frame base 8 and a sample base 9 into the lead bismuth alloy liquid 10, then closing a kettle cover 3 and a metal kettle body 12, sealing a high-temperature extensometer 1, the reaction frame support column 4 and the loading rod 5 by a sealing ring 2, forming a sealed environment inside the kettle, and reducing the overflow of gas volatilized by the lead bismuth alloy from the upper part of the kettle cover 3 as much as possible.

The heating coil 13 is wound at the outer part and the bottom of the kettle body and used for heating the kettle body, and the outer part of the heating coil is insulated by heat insulation cotton 14 made of aluminum silicate materials with heat insulation effect, so that the test temperature can be adjusted conveniently, and the fatigue crack propagation measurement experiment of lead and bismuth at different temperatures can be carried out.

Example (b): testing the fatigue crack propagation rate under the lead bismuth environment of 350 DEG C

And a sample 7 with prefabricated cracks is arranged between the sample base 9 and the loading rod 5, the opening of the sample 7 is upward, the opening is connected with the ceramic rod 6, and the other end of the ceramic rod is connected with the foot part of the high-temperature extensometer 1. The method comprises the steps of putting a lead bismuth eutectic alloy ingot into a ceramic crucible 11, putting the ceramic crucible 11 into a metal kettle body 12, heating and melting the lead bismuth alloy ingot through a heating coil 13 until the temperature is 350 ℃ to obtain a lead bismuth alloy liquid 10, preserving heat for a period of time, immersing a reaction frame support 4, a loading rod 5, a ceramic rod 6, a sample 7, a reaction frame base 8 and a sample base 9 into the lead bismuth alloy liquid 10 integrally, wherein the liquid level of the lead bismuth alloy is 5mm higher than the upper surface of the sample 7, covering the liquid level with a kettle cover 3, and sealing the liquid level with a sealing ring 2. And starting loading when the overall temperature of the sample 7 and the lead-bismuth alloy liquid 10 is uniform, and forming three-point bending stress with the center upward and two ends downward through the loading rod 5 and the sample base 9. The loading frequency is 1HZ, the loading mode adopts a sine wave, the stress ratio R is 0.1 for loading, the reading and the load of the high-temperature extensometer 1 are recorded, and the crack propagation rate under the environment is further explained.

The preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.