Temperature gradient optimization method for high-temperature confocal microscope sample
By welding thermocouples onto the specimens in a high-temperature confocal microscope and adjusting the specimen height, the temperature gradient problem was solved, achieving temperature uniformity and observation accuracy. This method is applicable to various metal materials and equipment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIUQUAN IRON & STEEL (GRP) CO LTD
- Filing Date
- 2026-03-05
- Publication Date
- 2026-04-28
AI Technical Summary
The high-temperature confocal microscope specimen has a temperature gradient problem during the heating process, which leads to inaccurate observation results and makes it difficult to meet the requirements of rapid heat treatment process simulation. Existing technologies lack accurate measurement and quantitative evaluation methods.
A calibration thermocouple is welded onto the upper surface of the sample. Combined with the existing temperature control thermocouple in the equipment, the sample height is adjusted by a three-stage extraction and release furnace atmosphere control method to establish a correspondence between the temperature gradient and the height, and the sample size is optimized to reduce the temperature gradient.
It achieves uniform temperature distribution of the sample, ensuring the accuracy of observation and the reliability of data, meeting the requirements of rapid heat treatment process simulation, and is applicable to a variety of metal materials and equipment.
Smart Images
Figure CN121933331A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metallurgical materials technology, and specifically relates to a method for optimizing the temperature gradient of samples for high-temperature confocal microscopes. Background Technology
[0002] High-Temperature Confocal Laser Scanning Microscopy (HT-CLSM) is an advanced characterization device capable of observing the microstructure evolution of materials in real time under high-temperature conditions. It is widely used in research fields such as solidification processes, phase transformation behavior, grain growth, and inclusion behavior in metallic materials. This device employs infrared radiation heating and focuses the light source onto the sample surface using the principle of elliptical focusing, enabling rapid and uniform heating. The maximum heating rate can reach over 300℃ / min, providing a powerful tool for studying the microstructure evolution of materials during rapid heat treatment.
[0003] In practical applications, the test sample is typically placed in an Al2O3 or other material crucible, which is then placed in the heating chamber of a high-temperature furnace. Because the lower surface of the sample is in direct contact with the bottom of the crucible, while the upper surface is exposed to the furnace's radiant environment, this asymmetrical heating and cooling condition inevitably leads to a temperature gradient along the sample's height. This temperature gradient manifests primarily as a significant temperature difference between the upper and lower surfaces of the sample, and as an uneven temperature distribution between the sample's surface and interior.
[0004] Temperature gradients have a significant impact on materials research and performance testing. First, in phase transformation process studies, the presence of a temperature gradient can lead to asynchronous phase transformations in different regions of the sample, making the observed microstructure evolution process unable to truly reflect the intrinsic properties of the material. Second, in thermophysical property testing, temperature gradients can affect the accuracy and repeatability of measurement results. Furthermore, for certain temperature-sensitive phase transformation processes (such as martensitic transformation and precipitation behavior), excessively large temperature gradients can even cause different regions of the sample to acquire completely different microstructures, severely affecting the reliability of experimental data.
[0005] To address the issue of temperature gradient in samples, existing technologies primarily employ two methods for control: one is to reduce the heating rate, allowing sufficient time for heat to conduct uniformly within the sample; the other is to extend the holding time, enabling the temperature across different parts of the sample to converge through prolonged thermal equilibrium. For example, reducing the heating rate to 10-20℃ / min or extending the holding time to over 30 minutes can reduce the temperature gradient to some extent. However, these methods have significant drawbacks: slow heating cannot meet the demands of modern materials research for simulating rapid heat treatment processes, making it difficult to reflect the microstructural evolution under rapid heating conditions in actual industrial production; while prolonged holding can easily induce chemical changes such as oxidation and decarburization on the sample surface, altering the sample surface state, affecting the accuracy of in-situ observations, and even causing deviations between observed results and actual application conditions.
[0006] Furthermore, existing technologies lack precise methods for measuring and quantitatively assessing the temperature gradient of samples. Most researchers control the temperature gradient indirectly by adjusting heating parameters, making it difficult to accurately determine the actual temperature differences within the sample, and even more difficult to optimize sample size to minimize the temperature gradient for specific materials and equipment conditions. Therefore, how to accurately measure, quantitatively assess, and effectively reduce the temperature gradient of samples in high-temperature confocal microscopy has become a pressing technical problem in the field of in-situ research on material microstructure. Summary of the Invention
[0007] This invention aims to solve the temperature gradient problem of high-temperature laser confocal microscope samples during heating, and provides an optimized method that can accurately measure, quantitatively evaluate and effectively reduce the temperature gradient of the sample. Under the premise of avoiding sample surface oxidation and ensuring heat treatment efficiency, it achieves uniform temperature distribution of the sample during the heating and cooling process, thereby obtaining reliable in-situ observation data of microstructure.
[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for optimizing the temperature gradient of a sample for high-temperature confocal microscopy includes the following steps: (1) Prepare a cylindrical sample, polish its upper surface, and firmly weld the calibration thermocouple to the surface using a spot welding machine; the sample diameter is 6 mm and the height is adjustable in the range of 3 mm to 4 mm. (2) Place the sample with the thermocouple welded on it in the Al2O3 crucible in the high-temperature furnace of the high-temperature confocal microscope, and expose the upper surface of the sample to the furnace environment. (3) Perform at least three vacuuming-argon filling cycles on the high-temperature furnace cavity. After each vacuuming, fill the cavity with argon gas of 99.999% purity to remove residual oxygen-containing gas in the furnace cavity, prevent the sample surface from oxidizing at high temperature, and ensure the accuracy of temperature measurement. (4) The sample is heated according to the preset heat treatment regime, including the heating, holding and cooling processes, and the surface of the sample is observed in situ through a high-temperature confocal microscope during the heating process to monitor the surface condition; the heat treatment regime is as follows: starting from room temperature, heating to 200℃ at a heating rate of 50℃ / min; then heating to 1200℃ at a heating rate of 200℃ / min; holding at 1200℃ for 10 minutes; and finally cooling to room temperature at a cooling rate of -200℃ / min. (5) During the 1200℃ heat preservation stage, after confirming that there was no oxidation on the sample surface by high temperature confocal microscope, the following two sets of temperature data were collected respectively: a) the actual temperature value measured by the thermocouple welded to the upper surface of the sample; b) the temperature value of the lower surface area of the sample measured by the high temperature furnace temperature control thermocouple. (6) Based on the two sets of temperature data in step (5), calculate the temperature difference between the upper and lower surfaces of the sample, and in conjunction with the sample height, calculate the temperature gradient of the sample along the height direction using the following formula: TG = ΔT / d Where TG is the temperature gradient, in °C / mm; ΔT is the temperature difference between the upper and lower surfaces, in °C; and d is the sample height, in mm. (7) Adjust the height of the sample, repeat steps (1) to (6), record the temperature gradient data at different heights, and establish the correspondence between sample height and temperature gradient; (8) Based on the correspondence established in step (7), select the sample height with the smallest absolute value of temperature gradient as the optimized sample size for subsequent high-temperature confocal microscopy experiments, so as to achieve uniform temperature distribution of the sample during the heating and cooling process.
[0009] Furthermore, the adjustment of the sample height in step (7) specifically includes testing the temperature gradient at heights of 4.0 mm, 3.5 mm, and 3.0 mm, respectively, and selecting the height with the absolute value of the temperature gradient closest to 0 ℃ / mm as the optimized size by comparing the temperature difference and the temperature gradient value.
[0010] Furthermore, the method is applicable to the optimization of temperature gradients for samples of different metallic materials. By establishing the height-temperature gradient relationship curves for different materials, the selection of sample size for high-temperature confocal microscopy experiments can be guided.
[0011] Compared with the prior art, the present invention has the following beneficial effects: First, by directly welding a calibration thermocouple onto the upper surface of the sample and combining it with the existing temperature-controlling thermocouple in the equipment, the present invention enables simultaneous measurement of the temperature of the upper and lower surfaces of the sample. This allows for precise quantification of the temperature gradient along the height direction of the sample, providing a reliable data basis for the evaluation and optimization of the temperature gradient.
[0012] Secondly, by adjusting the sample height, this invention establishes a correspondence between sample height and temperature gradient, thereby enabling the selection of the optimal sample height with the smallest temperature gradient for specific materials and equipment conditions, fundamentally reducing the problem of uneven temperature distribution of the sample during the heating process.
[0013] Third, the present invention adopts a three-stage extraction and three-stage release furnace atmosphere control method, which effectively avoids the oxidation of the sample surface at high temperature, ensures the authenticity of in-situ observation and the accuracy of temperature measurement, and overcomes the defect of traditional long-term heat preservation methods that easily lead to surface oxidation.
[0014] Fourth, the method of the present invention can be carried out at a high heating and cooling rate (up to 200°C / min), which meets the needs of rapid heat treatment process simulation and solves the problem that traditional slow heating methods cannot reflect actual industrial production conditions.
[0015] Fifth, the method of the present invention is simple to operate, requires low equipment, and has a short test cycle. It is not only applicable to temperature gradient optimization of 45 steel, but can also be extended to other metal materials, and has good versatility and practical value.
[0016] Sixth, the sample size optimized by the method of this invention can ensure that the sample is in a uniform temperature state during the heating and cooling process, and the obtained microstructure evolution data is more real and reliable, providing a scientific basis for the formulation and optimization of material heat treatment process. Attached Figure Description
[0017] Figure 1 A schematic diagram of the thermocouple connection inside the high-temperature confocal microscope of this invention.
[0018] Figure 2 This is a schematic diagram of the connection between the sample of the present invention and the thermocouple.
[0019] Figure 3 This is a physical diagram of the sample of the present invention connected to a thermocouple.
[0020] In the figure: 1-sample, 2-Al2O3 crucible, 3-thermocouple welded to the upper surface of the sample, 4-temperature measuring thermocouple (temperature control thermocouple) of the lower surface of the sample. Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Example
[0022] This embodiment uses No. 45 steel as the research object and optimizes the temperature gradient of its sample using the method of the present invention.
[0023] The specific operating steps are as follows: Step 1: Sample preparation and thermocouple welding The 45# steel sample was machined into a cylinder with a diameter of 6 mm and a height of 4 mm. The upper surface of the sample was polished to meet the surface finish requirements for in-situ observation using a high-temperature confocal microscope. A calibrated thermocouple (S-type or K-type) was then firmly welded to the center of the upper surface of the sample using a spot welding machine, ensuring good contact between the thermocouple and the sample surface to accurately reflect the actual temperature of the sample's upper surface. The welded sample... Figure 2 and Figure 3 As shown.
[0024] Step 2: Loading the sample into the furnace The sample with the thermocouple welded to it was placed in an Al2O3 crucible inside the high-temperature furnace of a high-temperature confocal microscope, such as... Figure 3 As shown. The lower surface of the sample is in contact with the bottom of the crucible, and the upper surface of the sample is exposed to the radiation environment of the furnace cavity. The thermocouple leads welded to the upper surface of the sample are led out through the channels reserved in the furnace wall and connected to an external temperature recorder.
[0025] Step 3: Furnace Atmosphere Control Close the furnace door and evacuate the high-temperature furnace cavity. Once the required vacuum level is reached, fill the cavity with 99.999% high-purity argon gas. Repeat the evacuation-argon filling operation three times (i.e., three evacuations and three purgings) to remove residual air, moisture, and oxygen from the furnace cavity as much as possible, preventing oxidation of the sample surface during high-temperature heating and ensuring the accuracy of subsequent temperature measurements and the authenticity of in-situ observations.
[0026] Step 4: Implementation of heat treatment procedures The specific parameters are as follows: starting from room temperature, the sample is heated to 200℃ at a heating rate of 50℃ / min; then heated to 1200℃ at a heating rate of 200℃ / min; held at 1200℃ for 10 minutes; and finally cooled to room temperature at a cooling rate of -200℃ / min. Throughout the heating process, the sample surface is observed in situ using a high-temperature confocal microscope to monitor changes in the sample surface condition in real time.
[0027] Step 5: Temperature Data Acquisition During the 1200℃ holding stage, the absence of oxidation on the sample surface was first confirmed using a high-temperature confocal microscope. Assuming the sample surface was in good condition, two sets of temperature data were simultaneously collected: one set was the temperature measured by a thermocouple welded to the upper surface of the sample, and the other set was the temperature of the lower surface region of the sample measured by a thermocouple controlling the temperature in the high-temperature furnace. Both sets of data were recorded synchronously using a temperature recorder. In this embodiment, for a sample with a height of 4.0 mm, the measured temperature of the upper surface was 1221℃, and the temperature displayed by the thermocouple controlling the temperature on the lower surface was 1200.1℃.
[0028] Step 6: Temperature gradient calculation Based on the temperature data collected in step five, calculate the temperature difference ΔT between the upper and lower surfaces of the sample. For a sample with a height of 4.0 mm, ΔT = 1221 - 1200.1 = 20.9℃. Combining this with the sample height d = 4.0 mm, calculate the temperature gradient TG using the following formula: TG = ΔT / d = 20.9 / 4.0 = 5.225℃ / mm.
[0029] Step 7: Adjust the sample height and repeat the test. The sample height was gradually reduced, and samples with heights of 3.5 mm and 3.0 mm were prepared respectively. Steps one through six were repeated, and temperature data at different heights were recorded and the temperature gradient was calculated. The experimental results are summarized in Table 1: Table 1. Temperature gradient results under different sample heights (3~4 mm) Step 8: Determine the optimal sample height Comparing the temperature gradient and temperature difference data at different heights, it can be seen that: when the sample height is 4.0 mm, the temperature difference between the upper and lower surfaces reaches 20.9℃, and the temperature gradient is as high as 5.225℃ / mm, indicating extremely uneven temperature distribution; when the sample height is reduced to 3.5 mm, the temperature difference decreases to 10.4℃, and the temperature gradient drops to 2.971℃ / mm, showing some improvement in uniformity; when the sample height is further reduced to 3.0 mm, the temperature difference between the upper and lower surfaces is only -1.4℃ (the negative value indicates that the temperature of the upper surface is slightly lower than that of the lower surface, but the absolute value is very small), and the absolute value of the temperature gradient is only 0.467℃ / mm, indicating that the temperature distribution of the sample tends to be more uniform.
[0030] Therefore, for the 45 steel sample used in this embodiment, the optimal sample height is 3.0 mm under existing equipment conditions. Using a sample of this height for subsequent high-temperature confocal microscopy experiments can maintain good temperature uniformity during the heating and cooling process, and obtain more realistic and reliable data on microstructure evolution.
[0031] This embodiment uses 45# steel as an example to illustrate the method of the present invention in detail, but the present invention is not limited thereto. For other metallic materials, such as different grades of steel, aluminum alloys, titanium alloys, high-temperature alloys, etc., the method of the present invention can be used for temperature gradient optimization. In specific operation, it is only necessary to adjust the heat treatment parameters according to the characteristics of the material, and determine the optimal sample height by establishing the height-temperature gradient correspondence curve for that material.
[0032] Furthermore, the method of this invention can also be used to calibrate the temperature field characteristics between different models of high-temperature confocal microscopes. By testing the temperature gradient of standard samples, the heating uniformity of different devices can be evaluated, providing a basis for equipment calibration and optimization of experimental conditions.
[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various improvements and modifications without departing from the spirit and principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for optimizing the temperature gradient of a sample for a high-temperature confocal microscope, characterized in that, Includes the following steps: (1) Prepare a cylindrical sample, polish its upper surface, and firmly weld the calibrated thermocouple to the surface using a spot welding machine; (2) Place the sample with the thermocouple welded on it in the Al2O3 crucible in the high-temperature furnace of the high-temperature confocal microscope, and expose the upper surface of the sample to the furnace environment. (3) Perform at least three vacuuming-argon filling cycles on the high-temperature furnace cavity. After each vacuuming, fill the cavity with argon gas of 99.999% purity to remove residual oxygen-containing gas in the furnace cavity and prevent the sample surface from oxidizing at high temperature. (4) The sample is heated according to the preset heat treatment system, including the heating, holding and cooling processes, and the surface of the sample is observed in situ through a high-temperature confocal microscope during the heating process to monitor the surface condition. (5) During the heat preservation stage, collect the following two sets of temperature data respectively: a) The actual temperature value measured by welding a thermocouple to the upper surface of the sample; b) Temperature values of the lower surface region of the sample measured by the temperature control thermocouple of the high-temperature furnace; (6) Based on the two sets of temperature data in step (5), calculate the temperature difference between the upper and lower surfaces of the sample, and in conjunction with the sample height, calculate the temperature gradient of the sample along the height direction using the following formula: TG = ΔT / d Where TG is the temperature gradient, in °C / mm; ΔT is the temperature difference between the upper and lower surfaces, in °C; and d is the sample height, in mm. (7) Adjust the height of the sample, repeat steps (1) to (6), record the temperature gradient data at different heights, and establish the correspondence between sample height and temperature gradient; (8) Based on the correspondence established in step (7), select the sample height with the smallest absolute value of temperature gradient as the optimized sample size for subsequent high-temperature confocal microscopy experiments, so as to achieve uniform temperature distribution of the sample during the heating and cooling process.
2. The method according to claim 1, characterized in that, The cylindrical sample mentioned in step (1) has a diameter of 6 mm and a height that is adjustable from 3 mm to 4 mm.
3. The method according to claim 1, characterized in that, The heat treatment process described in step (4) is as follows: Starting from room temperature, heat to 200°C at a heating rate of 50°C / min; Then heat to 1200℃ at a heating rate of 200℃ / min; Keep warm at 1200℃ for 10 minutes; Finally, the temperature was lowered to room temperature at a cooling rate of -200℃ / min.
4. The method according to claim 1, characterized in that, The heat preservation stage in step (5) is to keep the sample at 1200℃ for 10 minutes. After confirming that there is no oxidation on the sample surface by using a high-temperature confocal microscope during this stage, temperature data is then collected.
5. The method according to claim 1, characterized in that, In step (6), the temperature difference ΔT in the temperature gradient calculation is the absolute value of the difference between the measured temperature of the sample's upper surface and the measured temperature of the temperature-controlled thermocouple, or retains the positive or negative sign to reflect the direction of temperature distribution.
6. The method according to claim 1, characterized in that, The sample height with the smallest absolute value of temperature gradient in step (8) is determined in the following way: For the 45 steel sample, the temperature gradient is tested at heights of 4.0 mm, 3.5 mm and 3.0 mm respectively, and the height with the absolute value of temperature gradient closest to 0℃ / mm is selected as the optimized size.
7. The method according to any one of claims 1 to 6, characterized in that, The method is applicable to the optimization of temperature gradients for samples of different metallic materials. By establishing the height-temperature gradient relationship curves for different materials, it guides the selection of sample size for high-temperature confocal microscopy experiments.