A method for preparing ultrafine metal powder cross-section specimen

Abstract

The present invention proposes a method for preparing a cross-sectional sample of ultrafine metal powder, which belongs to the technical field of metallographic structure inspection and is used to solve the technical problems of low powder adhesion, easy falling off and deviation in dynamic hardness measurement in the ultrafine metal powder cross-sectional sample prepared by the existing method. The present invention comprises the following steps: dispersing ultrafine metal powder in a dispersant to obtain a dispersion liquid, dripping the dispersion liquid onto a carrier and drying it, so that the ultrafine metal powder is dispersed on the carrier; using an electric soldering iron to heat the welding wire to perform drip welding on the ultrafine metal powder dispersed on the carrier, and then pressing the welding drop into a welding block; using a hot embedding process to embed the welding block to obtain an embedded sample; grinding and polishing the embedded sample to obtain an ultrafine metal powder cross-sectional sample. The sample prepared by the present invention has a low powder shedding rate, uniform powder dispersion, and high phase contrast, and can be used for observing the microstructure in the powder and performing dynamic hardness measurement on the powder.

Description

Technical Field

[0001] The invention belongs to the technical field of metallographic structure inspection, and in particular relates to a method for preparing an ultrafine metal powder cross-section sample. Background Art

[0002] Metal-bonded diamond abrasives have strong abrasive bonding capabilities, good toughness, high load-bearing capacity, and low raw material prices. They have stable production processes and high forming rates, making them suitable for manufacturing products of various complex shapes and widely used in forming grinding, precision, and ultra-precision grinding of complex surfaces of brittle and hard materials. The consumption of metal-bonded diamond tools far exceeds that of resin-bonded and ceramic-bonded diamond tools, and they play an irreplaceable role in diamond tools. The copper-based bond system is one of the main metal bond systems, and the copper-tin bond is the most common copper-based bond. The copper-tin bond has good thermal conductivity, can reduce the grinding temperature, and prevent surface burns. It is mostly used in fields such as diamond abrasives and stone cutting saw blades.

[0003] As a key raw material, alloy powder's performance directly impacts the quality of metal-bonded superhard abrasive tools. Therefore, observation of powder structure and hardness measurement are crucial. Using bulk metallographic mounting methods, it's extremely difficult to secure fine-grained metal powders securely through thermosetting resin mounting. This is because the interfacial bonding between metal and organic mounting materials is typically weak, held together by mechanical mounting forces. The smaller the metal sample, the greater the specific surface area, and the more interfacial weak zones present, making it more susceptible to fallout. Therefore, conventional thermosetting mounting methods are ineffective for obtaining secure and reliable metallographic samples of metal powders with extremely large specific surface areas. A mounting method for ultrafine metal powders with secure particle fixation and high contrast would facilitate more accurate and convenient dynamic hardness measurements and microstructure observation. By observing the phase content and distribution within the powder microstructure, as well as the dynamic hardness differences between different particle sizes, the variations in mechanical properties of powders with varying particle sizes can be studied, providing guidance for the production of copper-tin alloys. Therefore, exploring a method for preparing cross-sectional samples of ultrafine metal powders for dynamic hardness measurement has significant engineering value and practical significance.

[0004] Currently, there are two main powder inlay methods. Patent publication number CN202210321829 describes a method for preparing ceramic powder cross-section inlay samples. Ceramic powder and tin powder are added to deionized water, mixed, ultrasonically oscillated, and then dried and pressed. However, due to the high hardness of metal alloy powder, this method is not suitable for metal alloy powder. Patent publication number CN20190764739 describes a method for displaying the microstructure of fine powder cross-sections. Fine powder and hot inlay powder are mixed, sampled, and polished. The method is simple, but the powder shedding rate is high, there are certain requirements for powder particle size, and the powder utilization rate is low. The firmness of the bonding and the related inlay powder may affect the dynamic hardness. Summary of the Invention

[0005] In response to the technical problems of low powder adhesion, easy falling off and deviation in dynamic hardness measurement in ultrafine metal powder cross-section samples prepared by existing methods, the present invention proposes a method for preparing ultrafine metal powder cross-section samples. The samples prepared by this method have low powder shedding rate, uniform powder dispersion, high phase contrast, and stable dynamic hardness measurement data.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for preparing a cross-section sample of ultrafine metal powder mainly comprises the following steps:

[0008] Step 1: Select ultrafine metal powder and low melting point welding wire; the ultrafine metal powder is copper powder, copper-tin alloy powder, high entropy alloy powder or other metal powder.

[0009] Step 1.1: The preparation method of metal ultrafine powder is gas atomization powder making, and the powder particle size is less than 60μm.

[0010] Step 1.2: The selected welding wire has a hardness close to that of the metal ultrafine powder and good wettability; preferably a lead-tin welding wire with a mass fraction of lead of 33% and a mass fraction of tin of 67%; or an Ag-Sn welding wire.

[0011] Step 2: Use an ultrasonic resonance disperser to clean and disperse the metal ultrafine powder;

[0012] Step 2.1: The dispersant used in the cleaning and dispersion process is ethanol, propanol or acetone, and the dispersion time of the ultrasonic resonance disperser is 3-5 minutes to obtain a dispersion liquid; the dispersion liquid is dropped onto a carrier and the dispersant is dried, and the dried metal ultrafine powder is dispersed on the carrier, which is a glass slide.

[0013] The concentration of the ultrafine metal powder in the dispersion is 0.1-0.5 g·mL -1 .

[0014] Step 3: Use an electric soldering iron to heat the soldering wire and perform drip welding on the dispersed ultrafine metal powder. The molten solder droplets fall on the ultrafine metal powder, causing the ultrafine metal powder to adhere to and embed on the surface of the solder droplets. The drip welding is then pressed.

[0015] Step 3.1: Pay attention to the amount and position of the droplet during the drop welding process. Try to select a position with a higher dispersion of ultrafine metal powder for welding. Immediately press the droplet with a hot press at a pressure of 80KN and a pressing time of 8-10s.

[0016] Step 4: After the solder block cools down, use the inlay powder to inlay the solder block, heat and melt it to make an inlay sample;

[0017] Step 4.1: During the mounting process, pay attention to the orientation of the powder in the solder block, ensuring that the powder side faces downward. The mounting powder is a standard metallographic mounting powder, preferably bakelite powder or electric jade powder, but other combinations of mounting powders are also acceptable. The mounting temperature is 145-155°C, and the mounting time is 10-15 minutes.

[0018] Step 5: Polish the hot-mounted specimen using water-sandpaper of different grits;

[0019] Step 5.1: The weld block is soft after welding, so you need to pay attention to the strength and the order of sandpaper during the grinding process.

[0020] Step 6: Polish the hot-mounted sample using diamond slurry with different abrasive grit sizes;

[0021] Step 6.1: Diamond polishing liquid is used as the polishing liquid, and the particle size of the polishing liquid is gradually reduced.

[0022] Finally, an ultrafine metal powder cross-section specimen is obtained. This specimen can be directly used for dynamic hardness measurement and microstructure observation. However, in order to more clearly observe the microstructure of the ultrafine metal powder, the ultrafine metal powder cross-section specimen can be corroded with an etching solution before observing its microstructure. The etching solution is selected according to the type of ultrafine metal powder.

[0023] Beneficial effects of the present invention:

[0024] (1) The present invention uses drop welding to embed ultrafine metal powder on the surface of the welding droplet. The prepared sample can be used to observe the microstructure inside the powder and perform dynamic hardness measurement on the powder, providing a new method for metallographic sample preparation of ultrafine metal powder and dynamic hardness measurement of powder;

[0025] (2) The sample prepared by the present invention has a low powder shedding rate, uniform powder dispersion, high phase contrast, stable data when used for dynamic hardness measurement, and a smooth force-displacement curve.

[0026] (3) The hardness of the selected welding wire is close to that of the powder, making sample preparation and grinding more convenient; it saves powder, and only a small amount of powder is needed to disperse to obtain its metallographic sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 The figure is a schematic flow chart of the preparation method of the present invention.

[0029] Figure 2 This is the microstructure of copper-tin alloy under light microscopy conditions.

[0030] Figure 3 Dynamic hardness indentation of copper-tin alloy powder.

[0031] Figure 4 This is the force-displacement curve during dynamic hardness measurement. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] A method for preparing a cross-section sample of ultrafine metal powder, the process is as follows Figure 1 As shown, the following steps are included:

[0035] Experimental preparation: Copper-tin alloy powder with a particle size less than 60 μm, containing 85% copper and 15% tin by mass, and a spherical powder morphology. The copper-tin alloy powder needs to be dried before mounting. The solder used is lead-tin solder with a lead content of 33% by mass, an electric soldering iron, alcohol, and hot mounting powder. The equipment used includes an ultrasonic disperser, a hot press, a hot mounting machine, and a metallographic polishing machine.

[0036] Disperse the copper-tin alloy powder: Select 5 g of powder, place the copper-tin alloy powder in 50 mL of alcohol solution, use an ultrasonic resonance disperser to clean and disperse the powder, then use a rubber-tipped dropper to absorb part of the dispersion onto a slide, and dry the alcohol on the slide.

[0037] To drip solder copper-tin alloy powder, heat the soldering iron to 250°C, then melt the lead-tin solder wire, allowing the molten solder to drip onto the copper-tin alloy powder. The solder droplets are then quickly pressed using a hot press at a pressure of 80 kN for 11 seconds. This press increases the contact area between the copper-tin alloy powder and the solder droplet, allowing the droplet to weld onto more powder and improving weld strength.

[0038] Mount the solder blocks: Use 25g of hot mounting powder, set the mounting temperature to 150°C, and mount for 14 minutes. To improve the success rate of sample grinding, hot mount several solder blocks onto a single hot mount. During mounting, pay attention to the orientation of the solder blocks: the powdered side should face downward.

[0039] Grinding of inlaid specimens: Due to the low hardness of welding wire, attention should be paid to the grinding and polishing time. The sandpaper used is water sandpaper. Water sandpaper with grit sizes of 150 mesh, 400 mesh, 800 mesh, 1500 mesh, and 2500 mesh is used to grind the inlaid specimens. The grinding and polishing time of each grit sandpaper is 5 minutes. During the grinding process, attention should be paid to the water flow rate. Too much water flow rate will affect the grinding efficiency. Too little water flow rate will easily cause scratches. The water flow rate should be controlled at 100 mL min -1 , polish until no scratches are visible under an optical microscope.

[0040] Polishing of the inlaid specimens: Diamond polishing fluid was used, and diamond polishing fluids with diamond particle sizes of 6 μm, 3 μm, 1 μm, and 0.5 μm were used for polishing in sequence. The polishing time was 5 min to obtain ultrafine metal powder cross-section specimens.

[0041] First, a dynamic hardness test was conducted on the cross-section sample of the ultrafine metal powder. The test pressure was 10 gf, the loading time was 30 s, and the unloading time was 5 s. The final measured dynamic hardness (Martens hardness) was 1364.27 N·mm -2 ; Dynamic hardness indentation of copper-tin alloy powder Figure 2 As shown by Figure 2 It can be seen that the powder indentation is clear, the powder adhesion is good, the phase is uniform, the contrast is high, and it is easy to grind and polish. The force-displacement curve during the dynamic hardness measurement is as follows Figure 3 As shown by Figure 3 It can be seen that the sample loading curve is stable and the force-displacement curve is smooth, indicating that the prepared sample is suitable for dynamic hardness measurement.

[0042] In order to further observe the microstructure of copper-tin alloy powder, the cross-section sample of ultrafine metal powder was corroded. The corrosive solution used was FeCl3 alcohol solution with a ratio of FeCl3: alcohol = 5g: 30ml and the corrosion time was 10s. The microstructure of the copper-tin alloy under optical microscopy is as follows: Figure 4 As shown by Figure 4 It can be seen that the metallographic specimens of the prepared ultrafine metal powder have a low powder shedding rate during the grinding and polishing process, high contrast, and clear microscopic morphology inside the powder.

[0043] Example 2

[0044] A method for preparing a cross-section sample of ultrafine metal powder, the process is as follows Figure 1 As shown, the following steps are included:

[0045] Experimental preparation: Pure copper powder with a particle size of 50-60 μm and an overall spherical shape. The pure copper powder needs to be dried before mounting. The solder used is a lead-tin solder with a lead content of 33% by mass, an electric soldering iron, acetone, and hot mounting powder. The equipment used includes an ultrasonic disperser, a hot press, a hot mounting machine, and a metallographic polishing machine.

[0046] Disperse the copper-tin alloy powder: Select 5 g of powder, put the copper-tin alloy powder into 30 mL of acetone solution, use an ultrasonic resonance disperser to clean and disperse the powder, then use a rubber-tipped dropper to draw part of the dispersion onto a slide, and dry the acetone on the slide.

[0047] To drip solder pure copper powder: Heat the soldering iron to 250°C, then melt the lead-tin solder wire, allowing the molten solder to drip onto the pure copper powder. The solder droplets are then quickly pressed using a hot press at a pressure of 80 kN for 11 seconds. This press increases the contact area between the pure copper powder and the solder droplet, allowing the droplet to weld onto more powder and improving weld strength.

[0048] Mount the solder blocks: Use 25g of hot mounting powder, set the mounting temperature to 145°C, and mount for 10 minutes. To improve the success rate of sample grinding, hot mount several solder blocks onto a single hot mounting sample. During mounting, pay attention to the orientation of the solder blocks: the powdered side of the solder blocks should face downward.

[0049] Grinding of the inlaid specimens: Due to the low hardness of the welding wire, attention should be paid to the grinding and polishing time. The sandpaper used is water sandpaper. The inlaid specimens are polished with water sandpaper of 150 mesh, 400 mesh, 800 mesh, 1500 mesh, and 2500 mesh in sequence. The grinding and polishing time of each grit sandpaper is 7 minutes. During the grinding process, attention should be paid to the water flow rate. Too much water flow rate will affect the grinding efficiency. Too little water flow rate will easily cause scratches. The water flow rate should be controlled at 300 mL min-1 , polish until no scratches are visible under an optical microscope.

[0050] The inlaid specimens were polished: diamond polishing fluid was used, and diamond polishing fluids with diamond particle sizes of 6 μm, 3 μm, 1 μm, and 0.5 μm were used for polishing in sequence. The polishing time was 10 min to obtain ultrafine metal powder cross-section specimens.

[0051] The dynamic hardness test of the ultrafine metal powder cross-section sample was carried out with a test pressure of 10gf, a loading time of 30s, and an unloading time of 5s. The final measured dynamic hardness (Martens hardness) was 1101.38N·mm -2 .

[0052] Example 3

[0053] A method for preparing a cross-section sample of ultrafine metal powder, the process is as follows Figure 1 As shown, the following steps are included:

[0054] Experimental preparation: Copper-tin alloy powder with a particle size less than 60 μm, containing 67% copper and 33% tin by mass, and an overall spherical powder morphology. The copper-tin alloy powder needs to be dried before mounting. The solder used is Ag-Sn solder wire, a soldering iron, propanol, and hot mounting powder (including Bakelite powder). The equipment used includes an ultrasonic disperser, a hot press, a hot mounting machine, and a metallographic polishing machine.

[0055] Disperse the copper-tin alloy powder: Select 5 g of powder, place the copper-tin alloy powder in a 10-propanol solution, use an ultrasonic resonance disperser to clean and disperse the powder, then use a rubber-tipped dropper to draw part of the dispersion onto a slide, and dry the propanol on the slide.

[0056] To perform drop soldering on copper-tin alloy powder, heat the soldering iron to 250°C, then melt the Ag-Sn solder wire so that it reaches the surface of the copper-tin alloy powder. The solder droplet is then quickly pressed using a hot press at a pressure of 80 kN for 11 seconds. This press increases the contact area between the copper-tin alloy powder and the solder droplet, allowing the droplet to weld to a larger area of ​​powder while also improving weld strength.

[0057] Mount the solder blocks: Use 25g of hot mounting powder, set the mounting temperature to 155°C, and mount for 10 minutes. To improve the success rate of sample grinding, hot mount several solder blocks onto a single hot mount. During mounting, pay attention to the orientation of the solder blocks: the powdered side of the solder blocks should face downward.

[0058] Grinding of inlaid specimens: Due to the low hardness of welding wire, attention should be paid to the grinding and polishing time. The sandpaper used is water sandpaper. Water sandpaper with grit sizes of 150 mesh, 400 mesh, 800 mesh, 1500 mesh, and 2500 mesh is used to grind the inlaid specimens. The grinding and polishing time of each grit sandpaper is 10 minutes. During the grinding process, attention should be paid to the water flow rate. Too much water flow rate will affect the grinding efficiency. Too little water flow rate is more likely to cause scratches. The water flow rate should be controlled at 400 mL min -1 , polish until no scratches are visible under an optical microscope.

[0059] The inlaid specimens were polished: diamond polishing fluid was used, and diamond polishing fluids with diamond particle sizes of 6 μm, 3 μm, 1 μm, and 0.5 μm were used for polishing in sequence. The polishing time was 7 min, and ultrafine metal powder cross-section specimens were obtained.

[0060] The dynamic hardness test of the ultrafine metal powder cross-section sample was carried out with a test pressure of 10gf, a loading time of 30s, and an unloading time of 5s. The final measured dynamic hardness (Martens hardness) was 1809.30N·mm -2 .

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a cross-section sample of ultrafine metal powder, characterized in that: The following steps are involved: (1) Dispersing ultrafine metal powder in a dispersant to obtain a dispersion liquid, dropping the dispersion liquid on a glass slide and drying it, so that the ultrafine metal powder is dispersed on the glass slide; (2) Using an electric soldering iron to heat the solder wire to melt it, the molten solder droplets fall onto the ultrafine metal powder, causing the ultrafine metal powder to adhere to and embed on the surface of the solder droplets. The solder droplets are then quickly pressed into solder blocks using a hot press. (3) The solder block is mounted using a hot mounting process to prepare a mounted sample, wherein the solder block is placed with the powder side facing downward, the mounting temperature is 145-155°C, and the mounting time is 10-15 minutes; (4) Grinding and polishing the embedded sample to obtain an ultrafine metal powder cross-section sample; The particle size of the ultrafine metal powder is ≤60μm; The concentration of the ultrafine metal powder in the dispersion is 0.1-0.5 g·mL -1 ; The welding wire is a lead-tin welding wire or a silver-tin welding wire.

2. The method for preparing a cross-section specimen of ultrafine metal powder according to claim 1, characterized in that: The ultrafine metal powder is prepared by adopting a gas atomization powder making process.

3. The method for preparing a cross-section specimen of ultrafine metal powder according to claim 1 or 2, characterized in that: In the step (1), the ultrafine metal powder is added to the dispersant and dispersed and cleaned using an ultrasonic disperser.

4. The method for preparing a cross-section specimen of ultrafine metal powder according to claim 3, characterized in that: The dispersant is ethanol, propanol or acetone.

5. The method for preparing a cross-section sample of ultrafine metal powder according to claim 4, characterized in that: The inlay powder used in the hot inlay process is bakelite powder or electric jade powder.

6. The method for preparing a cross-section specimen of ultrafine metal powder according to claim 1, characterized in that: In the step (4), the embedded sample is polished with sandpaper, wherein the sandpaper is water-based sandpaper; after the polishing is completed, the embedded sample is polished with a polishing liquid.

7. The method for preparing a cross-section specimen of ultrafine metal powder according to claim 1, characterized in that: The cross-section specimen of the ultrafine metal powder was obtained by etching with the etching solution in step (4).

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