Anti-oxidation high-precision TG-DSC testing method for high-temperature alloy powder

Abstract

The invention belongs to the technical field of TG-DSC testing of metal powder materials, and particularly relates to an anti-oxidation high-precision TG-DSC testing method of high-temperature alloy powder, which comprises the following steps: placing the high-temperature alloy powder in a furnace body of a TG-DSC instrument, carrying out high-purity argon replacement on the atmosphere in the furnace body by taking high-purity argon as furnace body purging gas, and carrying out high-purity argon replacement on the atmosphere in the furnace body; the initial oxygen content in the furnace body is reduced to 0.1 ppm or below; continuously introducing hydrogen-argon mixed gas as flowing gas into the furnace body, controlling the temperature of the furnace body to be increased to a target temperature, and ending the test to obtain a TG curve and a DSC curve of the to-be-tested high-temperature alloy powder; according to the invention, through physical cleaning of oxygen in the furnace body by circulating vacuumizing before testing and chemical cleaning of oxygen permeating into the furnace body by hydrogen-argon mixed gas in the whole process in the testing process, a dual anti-oxidation barrier is constructed, so that oxidation weight increment and oxidation heat release interference of a powder sample are eliminated fundamentally; therefore, the real mass change and the heat flow signal change of the alloy powder sample in the temperature programming process can be accurately measured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of TG-DSC testing of metal powder materials, and particularly relates to an anti-oxidation high-precision TG-DSC testing method for high-temperature alloy powder. BACKGROUND

[0002] Alloy materials such as nickel-based high-temperature alloys and refractory high-entropy alloys are core materials for manufacturing key hot-end components such as aero-engines and gas turbines. Additive manufacturing using alloy powder as raw material is the mainstream technology for preparing the above complex structural components. Therefore, it is crucial to accurately grasp the thermal physical parameters such as the melting temperature, phase change process and oxidation resistance of alloy powder. Among them, TG-DSC combined technology is a key means to obtain these parameters.

[0003] TG-DSC can monitor the mass change and energy change of alloy powder in the programmed temperature process. In an ideal state, the weight of alloy powder does not change with temperature, and its thermogravimetric curve is a smooth curve. However, even if an inert atmosphere is used for protection during actual testing, oxidation weight gain still occurs. Especially for nickel-based high-temperature alloy powder with a large specific surface area, surface oxidation caused by trace oxygen is difficult to avoid when the temperature is raised to 1200℃, even if high-purity argon is used for protection. This results in abnormal weight gain of the thermogravimetric curve and upward drift, and the differential scanning calorimetry curve is severely distorted due to the superimposed oxidation exothermic peak, which makes it impossible to obtain the true endothermic peak of the sample under test, resulting in serious distortion of the test results. SUMMARY

[0004] In view of the problem of serious distortion of test results caused by oxidation weight gain when TG-DSC testing of high-temperature alloy powder is performed in the prior art, the present application aims to provide an anti-oxidation high-precision TG-DSC testing method for high-temperature alloy powder. The present application fundamentally eliminates the oxidation weight gain and oxidation exothermic interference of metal powder samples by physical cleaning of oxygen before testing and chemical removal of residual trace oxygen during testing, thereby significantly improving the TG-DSC testing accuracy of metal powder.

[0005] To achieve the above purpose, the technical solution adopted by the present application is as follows: An anti-oxidation high-precision TG-DSC testing method for high-temperature alloy powder, comprising the following steps: The high-temperature alloy powder is placed in a furnace of a TG-DSC instrument, high-purity argon is used as furnace purging gas, and the atmosphere in the furnace is replaced by high-purity argon until the initial oxygen content in the furnace is reduced to below 0.1 ppm; then hydrogen-argon mixed gas is continuously introduced into the furnace as flowing gas, the furnace is controlled to be heated to a target temperature, and the test is ended to obtain the TG curve and the DSC curve of the high-temperature alloy powder to be tested; the volume fraction of H2 in the hydrogen-argon mixed gas is 2-4 vol.%.

[0006] In view of the problems of oxidation weight gain and DSC curve distortion of the high-temperature alloy powder in the TG-DSC test process, the furnace is purged by high-purity nitrogen before the sample to be tested is tested to remove oxygen and water vapor in the furnace, and hydrogen-argon mixed gas containing 2-4 vol.% H2 is continuously introduced into the furnace during the heating test to further effectively remove residual oxygen in the furnace and trace oxygen permeated into the furnace from the outside, thereby fundamentally eliminating the oxidation weight gain and oxidation exothermic interference of the alloy powder, the TG curve of the tested sample is relatively stable, and the phase transition peak of the DSC curve is obvious. The test method can effectively prevent the oxidation weight gain of the high-temperature alloy powder in the high-temperature TG-DSC test, so that the real mass change and heat flow signal change of the alloy powder sample in the programmed temperature process can be accurately measured.

[0007] Preferably, the flow rate of the hydrogen-argon mixed gas is 40-60 ml / min.

[0008] During the test, if the flow rate of the hydrogen-argon mixed gas introduced into the furnace is too small, the oxygen removal efficiency in the furnace is low, the residual gas in the furnace and trace oxygen permeated into the furnace from the outside cannot be removed in time, and the alloy powder to be tested still has the problems of oxidation weight gain and unclear phase transition peak in the DSC curve; and if the flow rate of the hydrogen-argon mixed gas is too large, the atmosphere exchange rate in the furnace is too fast, the TG curve has large noise, the heat flow signal of the DSC is interfered, the DSC baseline is unstable, and the phase transition peak is deformed, so the flow rate of the hydrogen-argon mixed gas is preferably 40-60 ml / min, and in this flow rate range, the TG curve and the DSC curve are relatively stable, and the phase transition peak of the DSC curve is relatively clear and has no deformation.

[0009] Preferably, the purity of the high-purity argon is not less than 99.999%.

[0010] Preferably, the heating rate of the furnace is 10-20 ℃ / min, and the target temperature is 600-1500 ℃.

[0011] Preferably, the high-temperature alloy powder includes nickel-based high-temperature alloy powder, cobalt-based high-temperature alloy powder, iron-nickel-based high-temperature alloy powder, and titanium-aluminum alloy powder.

[0012] The test method of the present application shows excellent TG-DSC test curves for nickel-based superalloy powder, cobalt-based superalloy powder, iron-nickel-based superalloy powder and titanium-aluminum alloy powder, and has good universality for superalloy powder.

[0013] Preferably, the superalloy powder is placed in a crucible, compacted and covered with a crucible cover, and then placed in the furnace body of the TG-DSC instrument.

[0014] Compacting the superalloy powder can reduce its specific surface area and reduce its oxygen adsorption capacity; covering the crucible cover also reduces the contact of the test powder sample with the external atmosphere and reduces the oxygen content in the powder sample.

[0015] Preferably, the superalloy powder should be dried before being placed in the furnace body of the TG-DSC instrument.

[0016] Drying the superalloy powder before testing can effectively slow down the instability of the TG curve and the distortion of the DSC curve caused by the evaporation of water vapor from the sample during the heating process.

[0017] Compared with the prior art, the present application has the following advantages: (1) The present application builds a double anti-oxidation barrier through physical cleaning by pre-circulating vacuum and chemical cleaning by hydrogen-argon mixed gas during the test process, which fundamentally eliminates the oxidation weight gain and oxidation exothermic interference of the powder sample. After eliminating the interference of oxidation exothermic, the real thermal effects of the alloy powder itself during heating, such as melting, solidus change, and precipitated phase dissolution, are clearly visible, so that the DSC curve of the same mass as the bulk sample can be measured.

[0018] (2) The TG data of the superalloy powder obtained by the test method of the present application reflects the real mass change of the sample, and the DSC data can be used to accurately determine the characteristic temperature points, providing reliable basis for powder quality control and alloy development.

[0019] (3) The test method of the present application is not only suitable for nickel-based superalloy powder, but also can be extended to other high-activity metal powders sensitive to oxygen, such as high-entropy alloy powder, cobalt-based superalloy powder, iron-nickel-based superalloy powder, titanium-aluminum alloy powder, etc., and has good universality.

[0020] (4) The test method of the present application does not need to modify the main body of the existing TG-DSC instrument, only needs to optimize the test process, and is easy to implement and promote. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 TG-DSC curve of the nickel-based superalloy powder of Example 1; Figure 2 TG-DSC curve of the nickel-based superalloy bulk of Example 1; Figure 3 TG-DSC curve of the nickel-based superalloy powder of Comparative Example 1; Figure 4 TG-DSC curve of the nickel-based superalloy powder of Comparative Example 2; Figure 5 TG-DSC curve of the nickel-based superalloy bulk of Comparative Example 2; Figure 6 TG-DSC curve of the nickel-based superalloy powder of Comparative Example 3; Figure 7 TG-DSC curve of the nickel-based superalloy powder of Comparative Example 4; Figure 8 TG-DSC curve of the refractory high-entropy alloy of Example 3 obtained according to the test method of Example 1; Figure 9 TG-DSC curve of the refractory high-entropy alloy of Example 3 obtained according to the test method of Comparative Example 2. DETAILED DESCRIPTION

[0022] For the purpose of better illustrating the object, technical scheme and advantages of the present application, the present application will be further described in conjunction with specific examples. Those skilled in the art should understand that the specific examples described herein are only used to explain the present application, and are not used to limit the present application. The test methods used in the examples are conventional methods unless otherwise specified; the materials, reagents, etc. used are commercially available unless otherwise specified. Example 1

[0023] This example takes a nickel-based superalloy powder as the sample to be tested, and provides a high-precision TG-DSC test method for a high-temperature alloy powder, comprising the following steps: S1 sample preparation: 10 mg of dry nickel-based superalloy powder to be tested was weighed, put into a crucible, compacted with a tool, and covered with a crucible cover to reduce the specific surface area and contact with the external atmosphere.

[0024] S2 preparation before measurement: The crucible with the nickel-based superalloy powder built-in was placed on the sample holder of the TG-DSC instrument, high-purity argon (≥99.999%) was used as the furnace purging gas, and the furnace was subjected to not less than 5 cycles of vacuum pumping and high-purity argon gas charging replacement to ensure that the initial oxygen content in the furnace chamber was reduced to below 0.1 ppm. Subsequently, hydrogen-argon mixed gas was continuously introduced as the flow gas, and the volume fraction of H2 in the flow gas was 4 vol.%.

[0025] S3 test procedure: The temperature in the furnace cavity is increased from room temperature to 1200℃ at a rate of 10-20℃ / min for TG-DSC test of nickel-based superalloy powder, and hydrogen argon mixed gas is continuously and stably introduced into the furnace cavity as flowing gas during the whole test process, the gas flow of hydrogen argon mixed gas is 50ml / min, and the hydrogen content in hydrogen argon mixed gas is 4vol.%.

[0026] During the heating process, the strong reducing ability of hydrogen in the flowing gas actively removes the trace amount of oxygen entering the furnace cavity from the micro-leakage or released from the furnace body parts during the test, providing "secondary protection" for the whole TG-DSC test process.

[0027] S4 data processing: After the test, the original TG and DSC curves are obtained, as shown in Figure 1 It can be seen that the TG curve presents a smooth and constant straight line, and there is no oxidation weight gain, which truly reflects the possible volatilization, decomposition and other processes of the sample. Without the influence of oxidation weight gain, the DSC phase change peak appears, and the shape, starting point and peak point of the phase change peak have clear indicative significance, which can be accurately read.

[0028] Since the alloy bulk material is almost not affected by oxidation weight gain, the nickel-based superalloy bulk is used as the sample to be tested, and the TG-DSC test method of the embodiment is used for synchronous thermal analysis test, and the result is shown in Figure 2 It can be seen that the TG curve is a smooth straight line, and the sample to be tested does not appear oxidation weight gain during the heating process; and the obvious phase change peak is also obtained.

[0029] The above results show that the TG-DSC test method for metal powder in the embodiment can effectively inhibit the oxidation weight gain phenomenon of metal powder during the test, and achieves the same effect as the bulk test. Comparative Example 1

[0030] The difference between the comparative example and example 1 is that the comparative example uses the conventional test method, and does not involve the oxygen removal before and during the test by the method of cyclic vacuum and hydrogen argon mixed gas in example 1. The comparative example 1 uses argon with purity of more than 99.999% as the furnace purging gas throughout the process, and uses high-purity argon (≥99.999%) with a gas flow rate of 50ml / min as the flowing gas. The specific method is as follows: S1 sample preparation: 10mg of dry nickel-based superalloy powder to be tested is weighed, put into a crucible, compacted with a tool, and covered with a crucible cover to reduce the specific surface area and contact with the external atmosphere.

[0031] S2 preparation before test: Put the crucible with nickel-based superalloy powder inside into the sample holder of the TG-DSC instrument, use high-purity argon (≥99.999%) as the furnace purging gas, and purging for 10 minutes.

[0032] S3 test procedure: Increase the temperature in the furnace cavity from room temperature to 1200°C at a rate of 10-20°C / min for TG-DSC testing of nickel-based superalloy powder, and continuously and stably introduce high-purity argon (≥99.999%) as the flow gas into the furnace cavity throughout the test process, with a gas flow rate of 50 ml / min.

[0033] S4 data processing: After the test, the original TG and DSC curves are obtained, as shown in Figure 3 The TG weight gain of the nickel-based superalloy powder is 18%, and the TG curve drifts significantly upward; the DSC curve also drifts severely due to oxidation, with no obvious phase change peak, resulting in invalid test data.

[0034] From the test results of this comparative example, it can be seen that the metal powder is obviously oxidized and gains weight during the TG-DSC test when using conventional high-purity argon (≥99.999%) as the furnace purging gas before the test and using high-purity argon (≥99.999%) as the flow gas during the test, resulting in invalid test results. Comparative Example 2

[0035] This comparative example provides a TG-DSC testing method for nickel-based superalloy powder. This comparative example uses the pre-test cycle vacuum deoxidization in Example 1, and the only difference from Example 1 is that this comparative example uses high-purity argon (≥99.999%) as the flow gas during the test. The TG-DSC testing method for nickel-based superalloy powder in Comparative Example 2 is as follows: S1 sample preparation: Weigh 10 mg of dry nickel-based superalloy powder to be tested, put it into the crucible, press it with a tool, and cover the crucible cover to reduce the specific surface area and contact with the external atmosphere; S2 preparation before testing: Put the crucible with nickel-based superalloy powder inside into the sample holder of the TG-DSC instrument, use high-purity argon (≥99.999%) as the furnace purging gas, and purging for 10 minutes.

[0036] S3 test procedure: Set the temperature program: from room temperature to 1200℃ at a rate of 10-20℃ / min.

[0037] S4 Data processing: After the test, the original TG and DSC curves were obtained, as shown in Figure 4 The TG weight gain of the nickel-based superalloy powder under the high-purity argon atmosphere was still 13% after the pretreatment of cyclic vacuuming and then replacing with high-purity argon before the test, which had decreased compared to the comparative example 1, but the DSC curve was still severely affected by the oxidation drift, and there was no obvious phase change peak, so the test result was invalid. Figure 4

[0038] According to the TG-DSC test method of the present comparative example, the nickel-based superalloy block was tested as the sample to be tested, and the results are shown in Figure 5 It can be seen that the TG-DSC test result of the nickel-based superalloy block under the pure argon atmosphere also has a trace weight gain of 3%, the TG curve slightly drifts upward, the DSC is not much affected by oxidation, and an obvious phase change peak can be shown, so the test data is basically reliable.

[0039] Comparing the results of example 1 with comparative examples 1 and 2, it can be seen that the present application uses the initial oxygen content in the furnace cavity to be reduced to below 0.1 ppm by cyclic vacuuming and high-purity argon replacement of the furnace body before the test, and then uses 4vol.% hydrogen-argon mixed gas to remove oxygen during the test process, which can effectively inhibit the oxidation weight gain phenomenon of the metal powder during the TG-DSC test process, the TG curve is a smooth straight line, and the DSC appears an obvious phase change peak, so the reliable test result of the metal powder sample can be obtained. Comparative example 3

[0040] The present comparative example uses the nickel-based superalloy powder as the sample to be tested for TG-DSC test, and the difference from example 1 is that the volume fraction of H2 in the hydrogen-argon mixed gas introduced into the furnace cavity of the present comparative example is 0.1vol.%, and the rest is the same as example 1.

[0041] The TG-DSC test result of the nickel-based superalloy powder by the test method of the present example is shown in Figure 6 The nickel-based superalloy powder still has a weight gain of 14% during the test process, and there is no obvious phase change peak, which is similar to the test result of comparative example 2.

[0042] The results show that when the H2 content in the flowing hydrogen-argon mixed gas is low, the oxidation weight gain phenomenon of the nickel-based superalloy powder during the test process cannot be improved. Comparative example 4

[0043] ​This comparative example uses nickel-based superalloy powder as the sample to be tested by TG-DSC. The only difference from Example 1 is that the volume fraction of H2 in the hydrogen-argon mixture introduced into the furnace chamber in this comparative example is 1 vol.%. All other parts are the same as in Example 1.

[0044] The TG-DSC test results of nickel-based superalloy powder obtained by the test method in this embodiment are as follows: Figure 7 As shown, the nickel-based superalloy powder gained 1.4% weight during the test, indicating a significant improvement in the weight gain phenomenon. However, the phase transformation peak remained weak.

[0045] Based on the results of Example 1, Comparative Example 3, and Comparative Example 4, it can be seen that as the H2 content in the flowing gas hydrogen-argon mixture increases, the oxidation weight gain phenomenon of nickel-based superalloy powder during the test process is gradually alleviated, and the phase transition peak becomes more significant.

[0046] Further experiments revealed that when the H2 content in the hydrogen-argon mixture was 2–4 vol.%, the nickel-based superalloy powder showed almost no oxidation weight gain during the test, and the phase transformation peak was also quite obvious, indicating that the test results were valid.

[0047] When the H2 content in the hydrogen-argon mixture exceeds 4 vol.%, it will cause hydrogen corrosion damage to components such as sensors in the TG-DSC testing equipment. Example 2

[0048] The only difference between this embodiment and Embodiment 1 is the flow rate of the flowing gas. In this embodiment, the flow rate of the hydrogen-argon mixture is adjusted to 10 ml / min and 100 ml / min, respectively. When the flow rate is 10 ml / min, the gas flow is relatively small, resulting in low deoxygenation efficiency in the furnace cavity. Residual gas in the furnace cavity and trace amounts of oxygen infiltrating from the outside cannot be removed in time, potentially leading to an increase in local oxygen partial pressure. This results in oxidation weight gain of approximately 10% in the nickel-based superalloy powder sample, and the DSC baseline shows no significant phase transition peak due to oxidation drift.

[0049] When the flow rate of the gas is 100 ml / min, the atmosphere exchange rate is extremely fast, which can most effectively maintain the purity of the atmosphere inside the furnace and quickly remove volatiles. However, it causes significant disturbance to the TG balance, resulting in high noise and severe drift in the TG curve, and a decrease in the measurement accuracy of mass changes. High-speed airflow can also interfere with the heat flux signal of DSC, affecting baseline stability, and at the same time, it can quickly remove heat, causing DCS peak distortion.

[0050] As the flow rate of the hydrogen-argon mixed gas increases, the oxidation and weight gain of the metal powder sample under test gradually improves, and the phase transition peak becomes more significant. However, as the flow rate of the gas increases further, the TG curve becomes noisy and the DSC peak shape is distorted.

[0051] Based on the above test results, the flow rate of the flowing gas is best controlled at 40-60 ml / min. This can suppress the oxidation and weight gain of the high-temperature alloy powder during the TG-DSC test, and also obtain a DSC curve with a significant peak shape, ensuring the authenticity and validity of the test results. Example 3

[0052] In this embodiment, 10 mg of dry refractory high-entropy alloy powder was used as the test sample. TG-DSC testing was performed according to the test method in Example 1. The test results are as follows: Figure 8 As shown, the TG curve is stable, while the DSC curve shows a clear phase transition peak.

[0053] Simultaneously, referring to the test method of Comparative Example 2, TG-DSC testing was performed on the refractory high-entropy alloy powder, and the results are as follows. Figure 9 As shown, without prior cyclic vacuuming and high-purity argon gas replacement, using high-purity argon as the flow gas, the TG weight gain of the high-entropy alloy powder reached 6%, and the DSC curve was severely affected by oxidation, with no obvious phase transition peak.

[0054] The comparison of test results for refractory high-entropy alloys shows that the cyclic vacuuming, flow gas replacement, and selection of a hydrogen-argon mixture with an H2 content of 2-4 vol% in the TG-DSC test method for high-temperature alloy powders in this invention are crucial for obtaining reliable and effective test results.

[0055] In this invention, 10 mg of dry cobalt-based high-temperature alloy powder, iron-nickel-based high-temperature alloy powder, and titanium-aluminum alloy powder were used as test samples, and TG-DSC tests were performed according to the test method of Example 1. All samples obtained stable, drift-free TG curves and DSC curves with obvious phase transition peaks.

[0056] The above results indicate that the TG-DSC testing method of the present invention has good universality for high-temperature alloy powder samples.

Claims

1. A high-precision TG-DSC test method for oxidation resistance of high-temperature alloy powder, characterized in that, Includes the following steps: The high-temperature alloy powder was placed in the furnace of the TG-DSC instrument. High-purity argon was used as the furnace purging gas to replace the atmosphere in the furnace with high-purity argon until the initial oxygen content in the furnace dropped to below 0.1 ppm. Then, a hydrogen-argon mixture was continuously introduced into the furnace as the flowing gas to control the furnace temperature to the target temperature. The test was then completed, and the TG curve and DSC curve of the high-temperature alloy powder to be tested were obtained. The volume fraction of H2 in the hydrogen-argon mixture is 2–4 vol.%.

2. The TG-DSC testing method according to claim 1, characterized in that, The flow rate of the hydrogen-argon mixture is 40–60 ml / min.

3. The TG-DSC testing method according to claim 1, characterized in that, The purity of the high-purity argon gas is not less than 99.999%.

4. The TG-DSC testing method according to claim 1, characterized in that, The furnace body heating rate is 10-20℃ / min, and the target temperature is 600-1500℃.

5. The TG-DSC testing method according to claim 1, characterized in that, The high-temperature alloy powder includes nickel-based high-temperature alloy powder, cobalt-based high-temperature alloy powder, iron-nickel-based high-temperature alloy powder, and titanium-aluminum alloy powder.

6. The TG-DSC testing method according to claim 1, characterized in that, After compacting the high-temperature alloy powder in a crucible and covering it with a crucible lid, it is placed inside the furnace of the TG-DSC instrument.

7. The TG-DSC testing method according to claim 1, characterized in that, The high-temperature alloy powder should be dried before being placed in the furnace of the TG-DSC instrument.

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