A method for determining the content of oxygen and nitrogen in high-temperature alloy powder for additive manufacturing

Abstract

The present invention belongs to the alloy trace element analysis technology, and discloses a detection method for determining the oxygen and nitrogen content in high-temperature alloy powder for additive manufacturing. The pulse heating program temperature rise method is used to realize the separation and determination of the adsorbed oxygen / nitrogen and combined oxygen / nitrogen contents in the powder, and at the same time, the accurate determination of the total content of oxygen and nitrogen elements in the high-temperature alloy powder is realized. It includes the following 6 steps: (1) blank test and blank subtraction (2) instrument calibration before analyzing the sample; (3) separation of adsorbed oxygen / nitrogen and combined oxygen / nitrogen in the powder; (4) determination of adsorbed oxygen and combined oxygen; (5) determination of adsorbed nitrogen and combined nitrogen; (6) calculation of total oxygen content and total nitrogen content. The method of the present invention improves the accuracy and precision of the total oxygen and total nitrogen determination results, and solves the problem of determining the adsorbed oxygen / nitrogen and combined oxygen / nitrogen contents in alloy powder for additive manufacturing.

Description

Technical Field

[0001] The present invention belongs to alloy trace element analysis technology, and relates to a method for determining the content of gas elements in alloy powder, and in particular to a method for determining the content of oxygen and nitrogen elements in high-temperature alloy powder for additive manufacturing. Background Art

[0002] Additive manufacturing (3D printing) of metal materials has many advantages over traditional "subtractive manufacturing" technology, so it has attracted more and more attention from the design and manufacturing industries of aerospace engine parts in the field of aerospace engines. Metal powder is one of the most important raw materials for additive manufacturing. Compared with bulk materials, the specific surface area of ​​powder increases significantly, and its adsorption of gas also increases significantly accordingly. At the same time, the powder changes when it comes into contact with air during use. The cost of most powder raw materials is very expensive, but the utilization rate of powder in the additive manufacturing process is low. In the actual production process, the finer the particle size of metal powder, the greater its utilization rate. Therefore, in order to improve the utilization rate of metal powder and reduce costs, the particle size of metal powder used in additive manufacturing is usually between 15μm-53μm, and it needs to be reused many times. However, during repeated use, metal powder will undergo obvious oxygenation. The finer the particle size of the powder, the more serious the oxygenation, which has a serious impact on the quality and performance of powder raw materials and finished products.

[0003] As the raw material for high-temperature alloy additive manufacturing, the properties of high-temperature alloy powder directly affect the organizational characteristics of the bulk material after hot consolidation and hot processing, thereby affecting the service performance of the material. Gaseous elements have an important influence on the mechanical properties of castings. Therefore, it is of great significance to accurately determine the oxygen and nitrogen content in high-temperature alloy powder for additive manufacturing and distinguish the adsorption and compound state of oxygen and nitrogen elements on the powder surface, which will provide a data basis for the monitoring and improvement of additive manufacturing production processes and related mechanism research. However, the current analysis methods for the oxygen and nitrogen content in high-temperature alloy powder for additive manufacturing are all based on the analysis methods of bulk samples. In actual analysis, there is a problem that the measurement results fluctuate too much and the oxygen and nitrogen content in alloy powder for additive manufacturing cannot be accurately determined; at the same time, the existing analysis methods for oxygen and nitrogen elements in high-temperature alloy powder for additive manufacturing measure the total content of each element, and cannot distinguish between the surface adsorption amount and the compound amount. Summary of the invention

[0004] In view of the above-mentioned situation of the prior art, the purpose of the present invention is to provide a method for accurately determining the total content of oxygen and nitrogen in high-temperature alloy powder for additive manufacturing, and at the same time determining the adsorbed oxygen / nitrogen and combined oxygen / nitrogen content in the powder.

[0005] A detection method for determining the oxygen and nitrogen content in a high-temperature alloy powder for additive manufacturing of the present invention comprises: a graphite crucible and a flux blank test and a calibration of a measuring instrument; separation of adsorbed oxygen / nitrogen and combined oxygen / nitrogen in the high-temperature alloy powder for additive manufacturing by a programmed temperature pulse heating method; determination of the adsorbed oxygen and combined oxygen contents by an infrared detector, and determination of the adsorbed nitrogen and combined nitrogen contents by a thermal conductivity detector; and finally, obtaining the total oxygen content and the total nitrogen content in the high-temperature alloy powder for additive manufacturing by the adsorbed oxygen / nitrogen content and the combined oxygen / nitrogen content.

[0006] The method specifically comprises the following steps:

[0007] Step 1, blank test: graphite crucible blank test - according to the working conditions selected by the oxygen and nitrogen analyzer, place an empty crucible to measure the oxygen and nitrogen contents, and subtract the blank; nickel capsule or nickel box blank test - according to the working conditions selected by the oxygen and nitrogen analyzer, measure the oxygen and nitrogen contents of the nickel capsule or nickel box, obtain the measured values ​​of the oxygen and nitrogen contents in the nickel capsule or nickel box, and subtract the blank;

[0008] Step 2: Calibration of measuring instruments: Before analyzing the sample, calibrate the measuring instrument with a standard substance that has the same or similar composition as the powder sample and whose oxygen and nitrogen contents are close to those in the powder sample;

[0009] Step 3, separation and determination of adsorbed oxygen / nitrogen: weigh a certain mass of powder sample and put it into a capsule or box-shaped flux, first keep the powder sample at the first analysis temperature for a first time, and release the adsorbed oxygen and adsorbed nitrogen in the powder in the form of CO / CO2 and N2 respectively; make the gas released by the powder sample pass through a copper catalyst first, and convert all the CO in it into CO2, and then analyze the adsorbed oxygen content therein by an infrared detector, and the adsorbed oxygen in the original powder sample is separated and determined in the form of CO2, and only remove CO2 and H2O in the gas passing through the infrared detector, and then analyze the adsorbed nitrogen content therein by a thermal conductivity detector, and the adsorbed nitrogen in the original powder is separated and determined in the form of N2;

[0010] Step 4, separation and determination of combined oxygen / nitrogen: the powder sample is kept at a second analysis temperature higher than the first analysis temperature for a second time, and the combined oxygen and combined nitrogen in the powder are released in the form of CO / CO2 and N2, respectively; the gas released from the powder sample is first passed through a copper catalyst to convert all the CO therein into CO2, and then the combined oxygen content therein is analyzed by an infrared detector, and the combined oxygen in the original powder sample is separated and determined in the form of CO2; after only CO2 and H2O in the gas passing through the infrared detector are removed, the combined nitrogen content therein is analyzed by a thermal conductivity detector, and the combined nitrogen in the original powder is separated and determined in the form of N2;

[0011] Step 5. Calculation of total oxygen content and total nitrogen content: Add the adsorbed oxygen content and the combined oxygen content to obtain the total oxygen content in the powder sample; add the adsorbed nitrogen content and the combined nitrogen content to obtain the total nitrogen content in the powder sample.

[0012] The first analysis temperature is 550° C. to 1200° C., and the second analysis temperature is 1900° C. to 2300° C. In addition, the first time is 30s to 45s to ensure sufficient release of adsorbed oxygen / nitrogen, and the second time is 80s to 95s to ensure sufficient release of combined oxygen / nitrogen.

[0013] The graphite crucible is a sleeve graphite crucible made of high-purity graphite, and the oxygen content and nitrogen content are ≤0.0001% (mass percentage based on 1g).

[0014] The capsule-shaped or box-shaped flux is a nickel capsule or a nickel box, preferably a high-purity nickel capsule or a nickel box, and the mass content of oxygen per gram is ≤0.0010%, and the mass content of nitrogen is ≤0.0002%. The standard substance described in step 2 is a certified standard substance.

[0015] The removal of CO2 and H2O is achieved by alkali asbestos and anhydrous magnesium perchlorate.

[0016] The mass of the powder sample is 0.2-0.5 g. When the oxygen content or nitrogen content in the powder sample is high, the mass of the sample is appropriately reduced. When the oxygen content or nitrogen content in the powder sample is low, the mass of the sample is appropriately increased.

[0017] In addition, the infrared detector is required to be able to detect an oxygen content of 0.0001%, and the thermal conductivity detector is required to be able to detect a nitrogen content of 0.0001%.

[0018] The method of the present invention can accurately determine the total content of oxygen and nitrogen in ultrafine high-temperature alloy powder for additive manufacturing, making up for the deficiency of excessive fluctuation in the measurement results of existing analytical methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a spectrum of the oxygen content in the high temperature alloy powder for additive manufacturing using the method of the present invention.

[0020] Figure 2 It is a spectrum of determination of nitrogen content in high temperature alloy powder for additive manufacturing using the method of the present invention. DETAILED DESCRIPTION

[0021] In order to more clearly understand the purpose, technical solutions and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0022] Example: Determination of oxygen and nitrogen content in high temperature alloy powder for additive manufacturing (particle size 15μm to 53μm)

[0023] 1. Blank test:

[0024] 1.1 Graphite crucible blank test: According to the working conditions selected by the oxygen and nitrogen analyzer, measure the oxygen and nitrogen contents of the graphite crucible. The measured values ​​of the oxygen and nitrogen contents of the high-purity graphite crucible should be less than 0.0001%;

[0025] 1.2 Nickel capsule or nickel box blank test: According to the working conditions selected by the oxygen and nitrogen analyzer, measure the oxygen and nitrogen content of the high-purity nickel capsule or nickel box, obtain the measured values ​​of the oxygen and nitrogen content in the nickel capsule or nickel box, and deduct the blank. The measured value of the oxygen content of the high-purity nickel capsule or nickel box should be less than 0.0010%, and the measured value of the nitrogen content should be less than 0.0002%.

[0026] 2 Calibration of oxygen and nitrogen measuring instrument: Use standard materials with the same or similar composition as the sample and oxygen and nitrogen contents close to those in the sample (502-898 from LECO, USA, oxygen content 0.0090% ± 0.0005%; nitrogen content 0.0072% ± 0.0002%) to calibrate the instrument. Perform 3 to 5 analyses under the selected working conditions. When the measured values ​​are within the allowable error range of the standard material, the calibration coefficient is obtained; then use another standard material, 502-893 from LECO, USA (oxygen content 0.0039% ± 0.0006%, nitrogen content 0.0021% ± 0.0003%) for verification. When the measured values ​​are within the allowable error range of the standard material, the sample can be measured.

[0027] 3. Separation and determination of adsorbed oxygen / nitrogen: Weigh 0.4g~0.5g of powder sample into a nickel capsule or nickel box (accurate to 0.0001g), first keep the powder sample at 995℃ for 40s, and the adsorbed oxygen and adsorbed nitrogen in the powder are released in the form of CO / CO2 and N2 respectively; let the gas released from the powder sample pass through a copper catalyst first to convert all the CO in it into CO2, and then analyze the adsorbed oxygen content therein by an infrared detector, and the adsorbed oxygen in the original powder sample is separated and determined in the form of CO2; then let the gas pass through alkali asbestos and anhydrous magnesium perchlorate, remove CO2 and H2O in the gas passing through the infrared detector, and then analyze the adsorbed nitrogen content therein by a thermal conductivity detector, and the adsorbed nitrogen in the original powder is separated and determined in the form of N2;

[0028] 4. Separation and determination of combined oxygen / nitrogen: The above powder sample is kept at 2125°C for 80 seconds, and the combined oxygen and combined nitrogen in the powder are released in the form of CO / CO2 and N2 respectively; the gas released from the powder sample is first passed through a copper catalyst to convert all the CO in it into CO2, and then the combined oxygen content therein is analyzed by an infrared detector, and the combined oxygen in the original powder sample is separated and determined in the form of CO2; the gas is then passed through alkali asbestos and anhydrous magnesium perchlorate to remove CO2 and H2O in the gas passing through the infrared detector, and then the combined nitrogen content therein is analyzed by a thermal conductivity detector, and the combined nitrogen in the original powder is separated and determined in the form of N2;

[0029] Figure 1 and Figure 2 They are respectively the determination spectra of oxygen content and nitrogen content in high-temperature alloy powder for additive manufacturing using the method of the present invention.

[0030] Table 1 Contents of adsorbed and combined oxygen and nitrogen in powder samples

[0031]

[0032] As shown in Table 1, the adsorbed oxygen and combined oxygen contents in the powder sample are 0.0008% and 0.0141% respectively, and the determination results are stable (RSD < 10%). The adsorbed nitrogen and combined nitrogen contents in the powder sample are 0.0003% and 0.0022% respectively, and the determination results are stable (RSD < 20%).

[0033] 5 Calculation of total oxygen content and total nitrogen content: Add the adsorbed oxygen content and the combined oxygen content to obtain the total oxygen content in the powder sample; add the adsorbed nitrogen content and the combined nitrogen content to obtain the total nitrogen content in the powder sample.

[0034] Table 2 Determination results of total oxygen and nitrogen content in powder samples

[0035]

[0036] As shown in Table 2, the total contents of oxygen and nitrogen in the powder sample are 0.0149% and 0.0025% respectively. The determination results are stable (RSD < 5%), which is significantly better than the traditional pulse heating constant temperature method (total oxygen content RSD > 20%).

[0037] It can be seen from Table 1 and Table 2 that the method of the present invention has the advantages of high accuracy and good precision, and is conducive to popularization and application.

Claims

1. A method for determining the oxygen and nitrogen content in a high-temperature alloy powder for additive manufacturing, comprising: Graphite crucible and capsule or box flux blank tests and measurement instrument calibration; Through the step-by-step programmed temperature pulse heating method, the high-temperature alloy powder sample is kept at a first analysis temperature and a second analysis temperature higher than the first analysis temperature for a certain period of time, respectively, to achieve the separation of adsorbed oxygen / nitrogen and combined oxygen / nitrogen in the high-temperature alloy powder for additive manufacturing; the adsorbed oxygen and combined oxygen contents are determined by an infrared detector, and the adsorbed nitrogen and combined nitrogen contents are determined by a thermal conductivity detector; finally, the total oxygen content and total nitrogen content in the high-temperature alloy powder for additive manufacturing are obtained through the adsorbed oxygen / nitrogen content and the combined oxygen / nitrogen content. The specific steps are as follows: Step 1, blank test: Graphite crucible blank test - according to the working conditions selected by the oxygen and nitrogen analyzer, place the graphite crucible to measure the oxygen and nitrogen content, and subtract the blank; Capsular or box-shaped flux blank test - according to the working conditions selected by the oxygen and nitrogen analyzer, measure the oxygen and nitrogen content of the capsule or box-shaped flux, obtain the measured values ​​of the oxygen and nitrogen content in the capsule or box-shaped flux, and subtract the blank; Step 2: Calibration of measuring instruments: Before analyzing the sample, calibrate the measuring instrument with a standard substance that has the same or similar composition as the powder sample and whose oxygen and nitrogen contents are close to those in the powder sample; Step 3, separation and determination of adsorbed oxygen / nitrogen: Weigh a certain mass of powder sample into a capsule-shaped or box-shaped flux, keep the powder sample at the first analysis temperature for a first time, and release the adsorbed oxygen and adsorbed nitrogen in the powder in the form of CO / CO2 and N2 respectively; make the gas released from the powder sample pass through a copper catalyst first, convert all the CO in it into CO2, and then analyze the adsorbed oxygen content therein by an infrared detector; After removing only CO2 and H2O from the gas that passes through the infrared detector, the adsorbed nitrogen content is analyzed by a thermal conductivity detector; Step 4, separation and determination of combined oxygen / nitrogen: the powder sample is kept at a second analysis temperature higher than the first analysis temperature for a second time, and the combined oxygen and combined nitrogen in the powder are released in the form of CO / CO2 and N2 respectively; the gas released from the powder sample is first passed through a copper catalyst to convert all the CO therein into CO2, and then the combined oxygen content therein is analyzed by an infrared detector; only CO2 and H2O in the gas passing through the infrared detector are removed, and then the combined nitrogen content therein is analyzed by a thermal conductivity detector; Step 5. Calculation of total oxygen content and total nitrogen content: Add the adsorbed oxygen content and the combined oxygen content to obtain the total oxygen content in the powder sample; add the adsorbed nitrogen content and the combined nitrogen content to obtain the total nitrogen content in the powder sample.

2. The method according to claim 1, wherein the first analysis temperature is 550°C to 1200°C, and the second analysis temperature is 1900°C to 2300°C.

3. The method according to claim 1 or 2, wherein the first time is 30s to 45s, and the second time is 80s to 95s.

4. The method according to claim 1, wherein the graphite crucible is a sleeve graphite crucible made of high-purity graphite.

5. The method according to claim 1, wherein the capsule-shaped or box-shaped flux is a nickel capsule or a nickel box.

6. The method according to claim 5, wherein the nickel capsule or nickel box is a high-purity nickel capsule or nickel box, and the oxygen mass content per gram is ≤0.0010%, and the nitrogen mass content is ≤0.0002%.

7. The method according to claim 1, wherein the removal of CO2 and H2O is achieved by alkali asbestos and anhydrous magnesium perchlorate.

8. The method according to claim 1, wherein the mass of the powder sample is 0.2-0.5 g, and when the oxygen content or nitrogen content in the powder sample is high, the mass of the sample is appropriately reduced, and when the oxygen content or nitrogen content in the powder sample is low, the mass of the sample is appropriately increased.

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