A method for testing the combustion dynamics performance of bulk refractory metals

Abstract

The present invention relates to a method for testing the combustion dynamics performance of bulk refractory metals, and belongs to the technical field of material performance testing. A bulk refractory metal sample is clamped and placed in a quartz tube; a laser emitter and a high-speed camera are arranged outside the quartz tube; gas is introduced circumferentially from the bottom of the quartz tube; the laser emitter is turned on to emit laser to burn the sample, and the whole combustion process is recorded by a high-speed camera; performance indicators for evaluating the combustion dynamics of refractory metals are quantitatively obtained according to the results of the high-speed camera. By adopting a thin sheet sample with a thickness of 0.05-2 mm, the ignition and self-sustaining combustion of bulk refractory metals in a laboratory environment can be achieved, and the combustion dynamics performance such as ignition delay time, critical oxygen concentration for combustion, self-sustaining combustion line combustion speed and self-sustaining combustion volume combustion speed can be obtained, which can be used to evaluate the combustion performance of energetic structural materials and applied to their material selection.

Description

Technical Field

[0001] The invention relates to a method for testing the combustion dynamics performance of a block refractory metal, and belongs to the technical field of material performance testing. Background Art

[0002] Alloys composed of refractory elements such as Ti, Zr, Hf, Nb, and Ta are expected to be used in energetic structural materials such as fragments, shells, and liners due to their excellent mechanical properties and high combustion calorific values. Under normal storage conditions, the structure remains intact and the performance is stable; after colliding with the target at high speed, a combustion reaction occurs to release a large amount of heat, causing secondary chemical damage to the target. In addition to the combustion heat, the energy release effect of refractory metals in the service environment is closely related to the combustion kinetic properties of the material itself, such as the ignition threshold and self-sustaining combustion performance. Therefore, the evaluation of the combustion kinetic properties of bulk refractory metals is crucial to the selection of energetic structural materials.

[0003] At present, the testing of the combustion kinetics of bulk metal materials is mainly focused on titanium alloys and magnesium alloys that are prone to disasters such as "titanium fire / magnesium fire" in the application of aerospace structural materials. Due to the differences in material properties and application fields, there are two problems in directly applying the combustion kinetics test method suitable for titanium / magnesium alloys to refractory metals: 1) Titanium / magnesium alloys are more active than refractory metals. They can usually be ignited using blocks or columns with a thickness of millimeters, while refractory metals of the same size are difficult to ignite and maintain self-sustaining combustion in a laboratory environment, and thus combustion kinetics cannot be obtained; 2) Existing test devices pay more attention to the flame retardant properties of the sample, such as the ignition point, and less attention to the self-sustaining combustion performance of the sample after ignition, such as the burning speed. Therefore, it is necessary to propose a test and evaluation method that can be applied to the combustion kinetics of bulk refractory metals. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a method for testing the combustion dynamics performance of bulk refractory metals.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] A method for testing the combustion kinetics performance of bulk refractory metals, the method steps comprising:

[0007] (1) Clamp a bulk refractory metal sample and place it vertically in a quartz tube; the sample thickness is 0.05~2mm, the width is 2~5mm, and the length is greater than or equal to 2mm; the melting point of the refractory metal is above 1500℃;

[0008] (2) A laser emitter is set outside the quartz tube to ensure that the light spot is irradiated on the bottom of the sample, and a high-speed camera is set outside the quartz tube to ensure that the shooting picture includes the entire sample; the power of the laser emitter is 20~100W; the spatial resolution of the high-speed camera is less than or equal to 100μm, and the frame rate is 5000-20000fps;

[0009] (3) introducing gas from the bottom of the quartz tube in a circumferential direction, wherein the gas is oxygen or a mixture of oxygen and nitrogen; the gas flow rate is 2-10 L / min;

[0010] (4) Turn on the laser transmitter to emit laser so that the sample is ignited and continues to burn after leaving the heat source, and record the entire combustion process with a high-speed camera;

[0011] (5) Quantitatively obtain performance indicators for evaluating the combustion dynamics of refractory metals based on the high-speed camera results.

[0012] Furthermore, the refractory metal includes metal elements of Groups IVB to VIB in the periodic table and alloys thereof.

[0013] Furthermore, the laser transmitter is a CO2 laser, a fiber laser or a solid laser.

[0014] Furthermore, a combustion product collection bucket is placed at the bottom of the quartz tube and below the sample, and air holes are evenly distributed circumferentially at the bottom of the quartz tube and between the combustion product collection bucket and the quartz tube.

[0015] Furthermore, the performance indicators of the combustion dynamics include ignition delay time, critical combustion oxygen concentration, self-sustaining combustion line combustion speed and self-sustaining combustion volume combustion speed.

[0016] Furthermore, the ignition delay time is obtained according to the change in video brightness during the ignition stage; the self-sustaining combustion line combustion speed and the self-sustaining combustion volume combustion speed are obtained according to the combustion process video recorded by the high-speed camera combined with the calibration photo processing.

[0017] A device for testing the combustion dynamics performance of bulk refractory metals comprises a fixture, a quartz tube, a laser emitter, a high-speed camera, and an atmosphere control structure; wherein the fixture is used to clamp the bulk refractory metal sample, the laser emitter and the high-speed camera are arranged outside the quartz tube, the position of the laser emitter ensures that the light spot is irradiated on the bottom end of the sample; the position of the high-speed camera ensures that the shooting picture includes the entire sample; the atmosphere control mechanism is connected to the bottom of the quartz tube through a connecting seat, and the bottom of the quartz tube is evenly distributed with air holes in a circumferential direction.

[0018] Furthermore, the device also includes a calibration device arranged above the sample, which is used to calibrate the length of a unit pixel in the combustion video taken by the high-speed camera.

[0019] Furthermore, the atmosphere control mechanism includes an oxygen cylinder, a nitrogen cylinder and a three-way air pipe. A gas outlet is provided at the bottom of the connecting seat. The three-way air pipe is respectively connected to the oxygen cylinder, the nitrogen cylinder and the gas outlet; a flow meter is provided on the connecting pipeline between the oxygen cylinder, the nitrogen cylinder and the three-way air pipe.

[0020] Furthermore, a combustion product collection bucket is placed at the bottom of the quartz tube and below the sample, and air holes are evenly distributed circumferentially at the bottom of the quartz tube and between the combustion product collection bucket and the quartz tube.

[0021] Beneficial Effects

[0022] The present invention provides a method for testing the combustion kinetics performance of bulk refractory metals. By strictly controlling experimental conditions, including heat source and ambient atmosphere, the ignition and self-sustaining combustion of bulk refractory metals in a laboratory environment can be achieved, thereby obtaining their combustion kinetics performance.

[0023] The present invention provides a method for testing the combustion kinetics of bulk refractory metals, which can quantitatively characterize two types of combustion kinetics of materials: the ignition threshold and the self-sustaining combustion performance. The ignition threshold includes the ignition delay time and the critical oxygen concentration for combustion; the self-sustaining combustion performance includes the linear combustion velocity and the volumetric combustion velocity. The combustion kinetics of the material can be evaluated by different parameters according to the evaluation requirements. It is beneficial to the rapid acquisition and evaluation of the combustion kinetics data of refractory metals, which can be used in the selection and evaluation of energetic structural materials, and provide a basis for the composition optimization of refractory metals and the selection of energetic structural materials.

[0024] The invention provides a device for testing the combustion dynamics performance of bulk refractory metals. The device is simple, has good feasibility, and low experimental cost, and is convenient for obtaining a large amount of data and conducting systematic analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a structural schematic diagram of a bulk refractory metal combustion dynamics performance testing device described in the present invention; in the figure, 1-clamp, 2-calibration device, 3-bulk refractory metal sample, 4-high-speed camera, 5-laser transmitter, 6-quartz tube, 7-combustion product collection barrel, 8-connecting seat, 9-gas guide port, 10-oxygen cylinder, 11-nitrogen cylinder, 12-flow meter, 13-three-way gas guide pipe.

[0026] Figure 2 The change of the image brightness over time during the combustion process of pure Nb with a thickness of 0.45 mm in Example 1.

[0027] Figure 3 This is a screenshot of the video of the combustion process of the 0.33 mm thick TiNb alloy sheet in a pure O2 environment in Example 2.

[0028] Figure 4The combustion conditions of TiZrHfTa in Example 3 under different oxygen concentrations. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with specific embodiments.

[0030] like Figure 1 As shown, a device for testing the combustion dynamics performance of bulk refractory metals comprises a fixture 1, a calibration device 2, a quartz tube 6, a laser emitter 5, a high-speed camera 4, and an atmosphere control structure; wherein, the fixture 1 is used to clamp the calibration device 2 and the bulk refractory metal sample 3, the laser emitter 5 and the high-speed camera 4 are arranged outside the quartz tube 6, and the position of the laser emitter 5 ensures that the light spot is irradiated on the bottom end of the sample 3; the position of the high-speed camera 4 ensures that the shooting picture includes the entire sample 3; the atmosphere control mechanism is connected to the bottom of the quartz tube 6 through a connecting seat 8, and the bottom of the quartz tube 6 is evenly distributed with pores in a circumferential direction.

[0031] Furthermore, the fixture 1 is used to clamp the calibration device 2 and the bulk refractory metal sample 3, and the calibration device 2 is used to calibrate the length of the bulk refractory metal sample 3 per unit pixel in the combustion video.

[0032] Furthermore, the atmosphere control mechanism includes an oxygen cylinder 10, a nitrogen cylinder 11 and a three-way air pipe 13. A gas port 9 is provided at the bottom of the connecting seat 8. The three-way air pipe 13 is respectively connected to the oxygen cylinder 10, the nitrogen cylinder 11 and the gas port 9; a flow meter 12 is provided on the connecting pipelines between the oxygen cylinder 10, the nitrogen cylinder 11 and the three-way air pipe 13.

[0033] Furthermore, a combustion product collection barrel 7 is placed at the bottom of the quartz tube 6 and below the sample, and air holes are evenly distributed circumferentially at the bottom of the quartz tube 6 and between the combustion product collection barrel 7 and the quartz tube 6 .

[0034] Before the test, the sample 3 was subjected to surface treatment, including manual or mechanical grinding with sandpaper to remove the surface oxide scale, and grinding to the same roughness as the sandpaper or grinding wheel used.

[0035] Example 1

[0036] A method for testing the combustion kinetics of Nb, the method steps comprising:

[0037] (1) A pure Nb thin slice with a length of 40 mm, a width of 3 mm, and a thickness of 0.5 mm was obtained by wire cutting. After being polished by a grinding wheel and 400# sandpaper, the surface was smooth. The thickness of the polished sample 3 was 0.45 mm. The sample 3 was clamped by a fixture 1 and placed in a quartz tube 6 with a diameter of 42 mm × 150 mm and a wall thickness of 2 mm, and the sample 3 was ensured to be vertical;

[0038] (2) Turn on the red light in the laser emitter 5, adjust the position and angle of the optical fiber to ensure that the red light spot can be at the center position of the lowest end of the sample 3 and can fully irradiate the sample 3. Among them, the laser emitter 5 uses a CO2 laser emitter to provide high-energy laser with a constant power of 100 W, and the diameter of the laser spot is 2 mm, which can ensure that it all falls on the sample with a width of 3 mm.

[0039] (3) Turn on the low-light mode of the high-speed camera 4 (select the Phantom VEO 410L high-speed camera), adjust the camera resolution to 512×800, ensure that the picture includes the entire sample 3, adjust the aperture to 2.5 after focusing, and take pictures in the low-light mode for later calibration. Then turn off the low-light mode of the high-speed camera 4, and adjust the sampling frequency to 10000 fps and the exposure time to 1 µs.

[0040] (4) Adjust the flowmeter to control the flow rate of pure oxygen gas to be 2 L / min, and ventilate for more than 1 min to ensure that the air flow in the whole device is uniform and stable.

[0041] (5) Turn off the red light of the laser emitter, adjust the laser power to 100 W and turn on the laser, and at the same time turn on the high-speed camera to record the whole combustion process. During the combustion process, droplets may drip from the lower end of the sample 3, and the combustion product collection bucket 7 collects the dripping combustion products while ensuring a stable air flow into the quartz tube 6, avoiding the ignition of the gas transmission pipe by high-temperature molten droplets and causing a fire.

[0042] (6) According to the change of the video brightness in the ignition stage of the pure Nb combustion video recorded by the high-speed camera, obtain the ignition delay time. Specifically: The laser starts to be loaded at 0 s. Select the stage from the laser loading to the moment when the pure Nb starts to spread upward. Use the PCC software自带的高速摄像 to export the video as a color photo, then use Matlab to convert all color photos into grayscale photos, and calculate the grayscale sum in the rectangular area of 140 < x < 260, 640 < y < 750 in the bottom ignition area of each photo as the brightness of this photo. Finally, count the change of the pure Nb brightness with time to obtain the ignition delay time.

[0043] Figure 2 For the change of the combustion video brightness of pure niobium with a thickness of 0.45 mm over time under a pure oxygen atmosphere of 2 L / min and a 100 W laser load, it can be seen that the picture is very dark when the laser is just loaded at 0 s. Then the pure niobium absorbs the laser heat and quickly warms up and brightens. After the surface is oxidized, the reflectivity decreases and the picture brightness slightly decreases. And there is a sudden change in brightness at the moment of ignition and sparks appear at the edge. The ignition delay time of pure Nb is 0.705 s.

[0044] Example 2

[0045] A test method for the combustion kinetics performance of TiNb, the method steps include:

[0046] (1) A TiNb alloy sheet with a length of 30 mm, a width of 3 mm, and a thickness of 0.33 mm is obtained by wire cutting and grinding. The sample 3 is clamped by a fixture 1 and placed in a quartz tube 6 with a diameter of 42 mm × 150 mm and a wall thickness of 2 mm, and the sample 3 is ensured to be vertical;

[0047] (2) Turn on the red light in the laser emitter 5, adjust the position and angle of the optical fiber, and ensure that the red light spot can be at the center of the lower end of the sample 3 and can be completely irradiated on the sample 3. The laser emitter 5 uses a CO2 laser emitter to provide a high-energy laser with a constant power of 100 W. The diameter of the laser spot is 2 mm, which can ensure that the red light spot falls on the sample with a width of 3 mm.

[0048] (3) Turn on the low-light mode of high-speed camera 4 (Phantom VEO 410L high-speed camera) and adjust the camera resolution to 384×600 to ensure that the image includes the entire sample 3. Take photos in low-light mode for later calibration. Then turn off the low-light mode of high-speed camera 4, adjust the sampling frequency to 15,000 fps, the exposure time to 1 s, and the camera aperture to 3.

[0049] (4) Adjust the flow meter to control the pure oxygen gas flow rate to 2L / min, and ventilate for more than 1 minute to ensure uniform and stable airflow throughout the device.

[0050] (5) Turn off the red light of the laser transmitter, adjust the laser power to 100W and turn on the laser, and turn on the high-speed camera to record the entire combustion process. During the combustion process, droplets from the lower end of the sample 3 may drip, and the combustion product collection bucket 7 collects the dripping combustion products while ensuring that the air flow is smoothly input into the quartz tube 6, so as to prevent the high-temperature molten droplets from igniting the gas pipeline and causing a fire.

[0051] (6) Data processing is performed based on the TiNb alloy combustion video recorded by the high-speed camera to evaluate the self-sustaining combustion performance. The actual length represented by a unit pixel in the combustion video is calculated by the calibration device 2, and the sample combustion speed is calculated using the measurement function in the PCC software adapted for the high-speed camera. Figure 3 As shown in Figure 2, the average burning velocity in the 10-25 mm stage of stable combustion is selected to represent the self-sustaining combustion performance of the TiNb alloy. The linear burning velocity and volume burning velocity of the TiNb alloy are 33.20 mm / s and 32.87 mm / s, respectively. 3 / s.

[0052] Example 3

[0053] A method for testing the combustion kinetics performance of TiZrHfTa, the method steps comprising:

[0054] (1) A series of TiZrHfTa alloy sheets with a length of 40 mm, a width of 3 mm, and a thickness of 0.3-0.33 mm were obtained by wire cutting and surface grinding. Sample 3 was clamped by fixture 1 and placed in a quartz tube 6 with a diameter of 42 mm × 150 mm and a wall thickness of 2 mm, and the sample 3 was ensured to be vertical;

[0055] (2) Turn on the red light in the laser emitter 5, adjust the position and angle of the optical fiber, and ensure that the red light spot can be at the center of the lower end of the sample 3 and can be completely irradiated on the sample 3. The laser emitter 5 uses a CO2 laser emitter to provide a high-energy laser with a constant power of 100 W. The diameter of the laser spot is 2 mm, which can ensure that the red light spot falls on the sample with a width of 3 mm.

[0056] (3) Turn on the low-light mode of high-speed camera 4 (Phantom VEO 410L high-speed camera), adjust the camera resolution to 512×800, ensure that the image includes the entire sample 3, and take photos in low-light mode for later calibration. Then turn off the low-light mode of high-speed camera 4, adjust the sampling frequency to 5000 fps, the exposure time to 1 s, and the camera aperture to 3.

[0057] (4) Adjust the flow meter to control the total gas flow rate of oxygen and nitrogen to 5L / min, and ventilate for more than 1 minute to ensure uniform and stable airflow throughout the device.

[0058] (5) Turn off the red light of the laser transmitter, adjust the laser power to 100W and turn on the laser, and turn on the high-speed camera to record the entire combustion process. During the combustion process, droplets from the lower end of the sample 3 may drip, and the combustion product collection bucket 7 collects the dripping combustion products while ensuring that the air flow is smoothly input into the quartz tube 6, so as to prevent the high-temperature molten droplets from igniting the gas pipeline and causing a fire.

[0059] (6) The oxygen ratio was continuously adjusted to 100%, 80%, 70%, 60%, 68%, and 66%, and the critical oxygen concentration for maintaining self-sustaining combustion of TiZrHfTa alloy with a length of 40 mm, a width of 3 mm, and a thickness of 0.30-0.33 mm was tested.

[0060] (7) Based on the alloy combustion video recorded by a high-speed camera, the critical oxygen concentration for combustion of TiZrHfTa alloy was evaluated.

[0061] TiZrHfTa alloy burns at different oxygen concentrations. The combustion photos are shown in Figure 4 When the oxygen ratio is higher than 68%, the alloy can self-sustain combustion to the root. At an oxygen concentration of 66%, the alloy first partially burns and melts, and the combustion stops when it burns to near the midpoint of the sample. Therefore, the critical oxygen concentration for self-sustaining combustion of TiZrHfTa alloy with a thickness of 0.30-0.33 mm is between 66-68%.

[0062] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A method for testing the combustion kinetics of bulk refractory metals, characterized in that: The method steps include: (1) Clamp a bulk refractory metal sample and place it in a quartz tube; the sample thickness is 0.05~2mm, the width is 2~5mm, and the length is greater than or equal to 2mm; the melting point of the refractory metal is above 1500℃; the size of the quartz tube is Ф42 mm×150 mm, and the wall thickness is 2mm; (2) A laser emitter is set outside the quartz tube to ensure that the light spot is irradiated on the bottom of the sample, and a high-speed camera is set outside the quartz tube to ensure that the shooting picture includes the entire sample; the power of the laser emitter is 20~100W; the spatial resolution of the high-speed camera is less than or equal to 100μm, and the frame rate is 5000~20000fps; (3) introducing gas from the bottom of the quartz tube in a circumferential direction, wherein the gas is a mixture of oxygen and nitrogen; the gas flow rate is 2-10 L / min; (4) Turn on the laser transmitter to emit laser so that the sample is ignited and continues to burn after leaving the heat source, and record the entire combustion process with a high-speed camera; (5) Quantitatively obtain performance indicators for evaluating the combustion dynamics of refractory metals based on high-speed camera results; A combustion product collection bucket is placed at the bottom of the quartz tube and below the sample, and air holes are evenly distributed in the circumferential direction at the bottom of the quartz tube and between the combustion product collection bucket and the quartz tube; The performance indicators of the combustion dynamics include ignition delay time, critical combustion oxygen concentration, self-sustaining combustion line combustion speed and self-sustaining combustion volume combustion speed; The ignition delay time is obtained according to the change of video brightness in the ignition stage. The critical oxygen concentration of combustion is obtained according to the combustion process video recorded by the high-speed camera. The linear combustion velocity and volumetric combustion velocity are obtained according to the combustion process video recorded by the high-speed camera combined with the calibration photo processing.

2. A method for testing the combustion dynamics performance of bulk refractory metals according to claim 1, characterized in that: The refractory metals include metal elements of Groups IVB to VIB in the periodic table and alloys thereof.

3. A method for testing the combustion dynamics performance of bulk refractory metals according to claim 1, characterized in that: The laser transmitter is a CO2 laser, a fiber laser or a solid laser.

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