Electrochemical corrosive agent system for displaying metallographic structures of platinum group alloy samples with various sizes and use method of electrochemical corrosive agent system

Abstract

The invention relates to the technical field of alloy material preparation, and discloses an electrochemical corrosive agent system for displaying metallographic structures of platinum group alloy samples of various sizes and a use method of the electrochemical corrosive agent system, the electrochemical corrosive agent system comprises a direct-current stabilized power supply, the platinum group alloy samples, a graphite crucible, an electrochemical corrosive agent and a magnetic stirrer; wherein the platinum group alloy sample is fixed at one end of the copper strip through the conductive adhesive; the copper strip is bent upwards by 90 degrees at the platinum group alloy sample end slightly larger than the length of the sample. The direct-current power source is used for electrochemical corrosion, the method is suitable for laboratory sample preparation and platinum group alloy samples of various sizes, the problems existing in the existing preparation technology are solved, the process is simple, efficiency is high, applicability is high, repeatability is good, the sample surface quality is high, and the alloy loss mass is small in the corrosion process.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy material preparation. Specifically, it relates to an electrochemical etchant system for displaying the metallographic structures of platinum group alloy specimens of various sizes and a method for using the same. Background Art

[0002] The properties of metal materials are directly affected by their microstructures. By precisely controlling and adjusting process parameters to improve the microstructure, the quality and performance of products can be significantly enhanced. Therefore, metallographic preparation, as a technology that can accurately reflect the microstructure of materials, has become one of the bases for materials science research. Different compositions and heat treatment processes will cause platinum group alloys to form different metallographic structures, thereby affecting the properties of the alloys. In order to ensure that platinum group alloys have the required properties, it is necessary to carefully observe and analyze their metallographic structures, and adjust the alloy composition or treatment process according to the observation results.

[0003] However, platinum group alloys themselves have excellent corrosion resistance, oxidation resistance, high-temperature mechanical properties, and glass infiltration resistance. Under the action of mechanisms such as solid solution strengthening and second-phase strengthening, the corrosion resistance of the alloys is improved, making the metallographic corrosion of platinum group alloys a challenge. Traditional chemical etching methods usually only aqua regia at high temperatures can produce effective etching effects. However, the use of aqua regia not only has complex operations but also releases a large amount of corrosive gases harmful to the human body.

[0004] For example, Patent CN107478481A provides a method for observing the metallographic structure of a platinum-rhodium alloy. Although it can solve the problem to a certain extent, the toxic gases generated during its operation, the change in the concentration of the etching solution, and the requirement for special etching containers limit the application scope of this method and are not suitable for use in laboratories. Potassium cyanide is also an option, but due to its high toxicity, it is hardly used in practice. For alloys added with iridium or rhodium elements, chemical etching methods have poor effects. Electrochemical etching, compared with chemical etching, can obtain a more uniform and delicate etched surface and can more precisely control the etching process.

[0005] In addition, the current electrochemical etching methods are only applicable to large-sized samples. The sample to be etched can be solidified by a curing agent, and one end of the sample is exposed from the curing agent. The exposed part is connected to the electrode for electrolytic etching. However, for samples that need to be observed in a plane and have a small size in the thickness direction, such as thin sheet materials or short wire materials, due to their small thickness, the curing agent cannot be exposed, so electrochemical etching cannot be used. If directly clamped with tools such as tweezers, when using metal products for clamping, the clamping end will be etched prior to the specimen; when using plastic products, the purpose of conducting current cannot be achieved.

[0006] In summary, developing a method for preparing the metallographic structure of platinum group alloys that is safer, faster, more stable, and simpler is not only the key to improving the efficiency of materials science research but also the foundation for promoting the development and application of new materials. Key attention should be paid to finding new combinations of etchants, reducing the limitations of the etching method on sample size, and exploring more environmentally friendly and safe etching techniques to overcome the drawbacks of existing technologies and meet the growing scientific research needs. In this regard, the present invention proposes an innovation based on chemical etching and alternating current etching methods, hoping to develop a method suitable for preparing the metallographic structure of platinum group alloy specimens of various sizes, using direct current electrochemical etching to observe the microstructure of platinum group alloys, and thus providing a basis for the regulation of alloy composition or heat treatment means, ultimately achieving precise control of the structure-property relationship and providing a foundation for the development of new high-temperature structural materials.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] To solve the above technical problems, the basic concept of the technical solution adopted in the present invention is as follows: An electrochemical etchant system for revealing the metallographic structure of platinum group alloy specimens of various sizes, comprising a direct current regulated power supply, a platinum group alloy specimen, a graphite crucible, an electrochemical etchant, and a magnetic stir bar; wherein, the platinum group alloy specimen is fixed to one end of a copper strip by conductive adhesive; the copper strip is bent upward by 90° at a position slightly larger than the specimen length at the end of the platinum group alloy specimen; The negative alligator clip connected to the negative output line of the direct current regulated power supply is clamped on the wall of the graphite crucible; The positive alligator clip connected to the positive output line of the direct current regulated power supply is clamped on the platinum group alloy specimen or the copper strip; The top of the liquid level of the electrochemical etchant shall not exceed the top of the cold inlay material, that is, the electrochemical etchant does not directly contact the copper strip; The electrochemical etchant does not directly contact the positive alligator clip connected to the positive and negative output lines of the direct current regulated power supply; the magnetic stir bar is arranged in the graphite crucible.

[0009] As a preferred embodiment of the present invention, a method for using an electrochemical etchant system for revealing the metallographic structure of platinum group alloy specimens of various sizes is also disclosed, and the method steps are as follows: Step, cut a specimen from a platinum group alloy workpiece, select the metallographic observation plane of the specimen, and polish it successively with sandpapers of coarse to fine mesh numbers; Step, use a mechanical polishing machine to perform rough polishing and fine polishing on the observation surface of the sample polished in Step in sequence to further remove the tiny abrasion marks remaining after the above sandpaper polishing and achieve a bright mirror effect; Step: Prepare an electrolytic etchant by mixing concentrated hydrochloric acid and anhydrous ethanol solution, place it in a graphite crucible. Select the top surface of the polished sample in the step as the anode and the graphite crucible as the cathode. Put the polished platinum group alloy sample into the electrolytic etchant with the polished top surface facing down, and use a DC regulated power supply to pass a DC current and voltage for electrolytic etching at room temperature; Step: Clean the observed surface of the etched sample with anhydrous ethanol and dry it. Place the metallographic observation plane of the platinum group alloy sample under a metallographic microscope to observe the metallographic structure of the platinum group alloy.

[0010] As a preferred embodiment of the present invention, if the platinum group alloy sample in Step is a small-sized sample, the following pretreatment steps need to be added: In Step, after selecting the metallographic observation plane of the sample, take a copper wire or copper flat strip with an appropriate length, bend it at a position greater than the sample length at one end of the copper wire or copper flat strip by °, and use conductive glue to bond and fix the geometric back surface of the observed surface of the platinum group alloy sample to the bent surface of the copper wire or copper flat strip; In Step, embed the small-sized platinum group alloy sample; use a cold embedding liquid and cold embedding powder to embed the platinum group alloy sample.

[0011] In Step, before electrochemical etching, place a magnetic stir bar in the graphite crucible, place the graphite crucible on a magnetic stirrer, adjust the rotation speed to keep the current stable.

[0012] As a preferred embodiment of the present invention, the grinding of the platinum group alloy sample in Step 1: Grind the observed plane of the platinum group alloy sample successively with metallographic sandpapers with particle sizes of 1500#, 2000#, 3000#, and 5000#. Among them, for the grinding with 3000# and 5000# metallographic sandpapers, the water grinding method is adopted. The polishing of the platinum group alloy sample in Step 2: Use a polishing machine to mechanically polish the metallographic observation plane of the platinum group alloy sample after grinding treatment in Step 1 until there are no obvious scratches and contamination points on the metallographic observation plane; the rotation speed of the polishing machine is 900r / min~1400r / min, and the polishing in the mechanical polishing The specific process of the embedding described above is: Place the cut platinum group alloy sample in an embedding mold, and make the metallographic observation plane of the platinum group alloy sample close to the inner bottom surface of the mold. Then mix the cold embedding liquid and cold embedding powder in a certain proportion and inject it around the platinum group alloy sample, and then keep it warm at room temperature for 15min~20min to obtain the embedded platinum group alloy sample. The corrosion of the platinum group alloy sample in Step 3: Place the platinum group alloy sample after mechanical polishing in Step 2 in a graphite container filled with corrosion liquid, and turn on the magnetic stirrer; after corroding for 10min~20min, take out the sample.

[0013] The present invention has the following beneficial effects compared with the prior art: The present invention uses a DC power supply for electrochemical corrosion, which is applicable to the preparation of samples in the laboratory and suitable for platinum group alloy specimens of various sizes, so as to solve the problems existing in the above-mentioned existing preparation technologies. The process is simple, efficient, highly applicable, has good repeatability, high surface quality of the sample, and small mass loss of the alloy during the corrosion process.

[0014] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings. Description of the Drawings

[0015] In the drawings: Figure 1 is a schematic structural diagram of an electrochemical corrosion system; Figure 2 is a schematic diagram of the inlay structure of a small-sized platinum group alloy specimen; Figure 3 is a micrograph of a Pt alloy wire; Figure 4 is a micrograph of a Pt alloy composite material plate.

[0016] In the figure: 1. DC regulated power supply; 2. Positive alligator clip; 3. Negative alligator clip; 4. Graphite crucible; 5. Electrochemical corrosion agent; 6. Magnetic stirrer; 7. Platinum group alloy specimen; 8. Conductive adhesive; 9. Copper strip; 10. Cold inlay material. Specific Embodiments

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments with reference to the accompanying drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention. Embodiment

[0018] As Figures 1 to 3 shown, an electrochemical corrosion agent system for displaying the metallographic structure of platinum group alloy specimens of various sizes includes a DC regulated power supply 1, a platinum group alloy specimen 7, a graphite crucible 4, an electrochemical corrosion agent 5, and a magnetic stirrer 6; wherein, the platinum group alloy specimen 7 is fixed to one end of the copper strip 9 through a conductive adhesive; the copper strip 9 is bent 90° upward at a position slightly larger than the specimen length at the end of the platinum group alloy specimen 7; the negative alligator clip 3 connected to the negative output line of the DC regulated power supply 1 is clamped on the crucible wall of the graphite crucible 4; the positive alligator clip 2 connected to the positive output line of the DC regulated power supply 1 is clamped on the platinum group alloy specimen 7 or the copper strip 9; the top of the liquid level of the electrochemical corrosion agent 5 shall not exceed the top of the cold inlay material 10, that is, the electrochemical corrosion agent 5 does not directly contact the copper strip; the electrochemical corrosion agent 5 does not directly contact the positive alligator clip 2 connected to the positive and negative output lines of the DC regulated power supply 1; the magnetic stirrer 6 is arranged in the graphite crucible 4.

[0019] The present invention also discloses a method for using an electrochemical etching agent system for displaying the metallographic structures of platinum group alloy specimens of various sizes, and the method steps are as follows: Step 1: Cut a specimen from a platinum group alloy workpiece, select the metallographic observation plane of the specimen, and polish it successively with sandpapers of gradually increasing fineness. Step 2: Use a mechanical polishing machine to perform rough polishing and fine polishing on the observation surface of the sample polished in Step 1 in sequence, so as to further remove the tiny abrasion marks remaining after the above sandpaper polishing and achieve a bright mirror surface effect. Step 3: Prepare an electrolytic etching agent by mixing concentrated hydrochloric acid and absolute ethanol solution, place it in a graphite crucible, select the top surface of the sample polished in Step 2 as the anode and the graphite crucible as the cathode, put the polished platinum group alloy specimen into the electrolytic etching agent with the polished top surface facing downwards, and apply a direct current and voltage through a DC regulated power supply for electrolytic etching at room temperature. Step 4: Clean the observation surface of the etched specimen with absolute ethanol and blow it dry, place the metallographic observation plane of the platinum group alloy specimen under a metallographic microscope, and observe the metallographic structure of the platinum group alloy.

[0020] If the platinum group alloy sample in Step 1 is a small-sized specimen, the following pretreatment steps need to be added: In Step 1, after selecting the metallographic observation plane of the specimen, take a copper wire or copper flat strip with an appropriate length, bend it 90° at a position greater than the length of the sample at one end of the copper wire or copper flat strip, and use conductive adhesive to bond and fix the geometric back surface of the observation surface of the platinum group alloy specimen to the bent surface of the copper wire or copper flat strip. In Step 2, perform embedding on the small-sized platinum group alloy specimen; use a cold embedding liquid and cold embedding powder to embed the platinum group alloy specimen.

[0021] In Step 3, before electrochemical etching, place a magnetic stir bar in the graphite crucible, place the graphite crucible on a magnetic stirrer, adjust the rotation speed, and keep the current stable.

[0022] Such as Figures 1 to 4As shown, in the specific implementation, the grinding of the platinum group alloy sample in step 1: The observation plane of the platinum group alloy sample is ground successively with metallographic sandpapers with particle sizes of 1500#, 2000#, 3000# and 5000#. Among them, for the grinding with 3000# and 5000# metallographic sandpapers, the water grinding method is adopted. The polishing of the platinum group alloy sample in step 2: The metallographic observation plane of the platinum group alloy sample after grinding in step 1 is mechanically polished by a polishing machine until there are no obvious scratches and contamination points on the metallographic observation plane; the rotation speed of the polishing machine is 900 r / min to 1400 r / min, and the polishing agent for the mechanical polishing is diamond polishing agent with a particle size of 5 μm. If the platinum group alloy sample is a small-size sample, the specific process of the embedding in step 2 is: Place the cut platinum group alloy sample in the embedding mold, and make the metallographic observation plane of the platinum group alloy sample close to the inner bottom surface of the mold. Then, mix the cold embedding liquid and cold embedding powder in a certain proportion and inject them into the periphery of the platinum group alloy sample, and then keep it warm at room temperature for 15 min to 20 min to obtain the embedded platinum group alloy sample. The corrosion of the platinum group alloy sample in step 3: Place the platinum group alloy sample after mechanical polishing in step 2 in a graphite container filled with corrosion liquid, and turn on the magnetic stirrer; after corroding for 10 min to 20 min, take out the sample. Example

[0023] (1) Prepare the electrolytic corrosion agent: Pipette 20 ml of concentrated hydrochloric acid and 60 ml of absolute ethanol, and pour the concentrated hydrochloric acid into the absolute ethanol at room temperature to prepare an 80 ml mixed solution. (2) Select a Pt alloy wire sample with a diameter of 1.2 mm and a length of 5 mm. Take a section of copper flat strip, bond the Pt alloy wire sample to one end of the copper flat strip with conductive adhesive and cure it, and bend the copper flat strip 90° at 8 mm near the sample end. (3) Place the observation surface facing down and close to the inner bottom surface of the cold embedding mold. Mix the cold embedding liquid and cold embedding powder in a certain proportion and inject them into the periphery of the Pt alloy wire sample, and cure it at room temperature so that the other end of the copper flat strip leaks out of the cold embedding material. (4) Grind the observation plane of the embedded Pt alloy wire sample successively with metallographic sandpapers with particle sizes of 1500#, 2000#, 3000# and 5000#. Among them, the water grinding method is adopted for the grinding with 3000# and 5000# metallographic sandpapers. (5) Use a mechanical polishing machine to polish the observation plane of the formed sample after grinding in step (4) successively for rough polishing and fine polishing. The polishing method is a combination of left-turn polishing and right-turn polishing of the polishing disc. Among them, the polishing fabric for rough polishing is canvas, the rotation speed of the polishing disc is 900 r / min, and the diamond polishing paste of W2 is selected for the polishing paste; the polishing fabric for fine polishing is cashmere, the rotation speed of the polishing disc is 1400 r / min, and the diamond polishing agent of W0.5 is selected for the polishing agent. (6) Using the electrolytic etchant prepared in step (1), select the polished sample observation surface in step (5) as the anode and the graphite crucible as the cathode. Place the polished sample into the electrolytic etchant with the polished surface facing downwards. Turn on the magnetic stirrer and conduct electrolytic etching by applying a direct current and voltage using a DC regulated power supply at room temperature. The power supply parameters are a voltage of 25V. Adjust the magnetic stirrer until the bubbles are uniform and the current is stable. After etching for 20 minutes, immediately take out the specimen; (7) Immediately after the electrolytic etching of the sample observation surface in step (6), perform ultrasonic cleaning with absolute ethanol and then dry it with a hair dryer. Then, the microstructure of the Pt alloy wire can be observed under an optical microscope (as Figure 3 shown). Example

[0024] (1) Prepare the electrolytic etchant: Pipette 20 ml of concentrated hydrochloric acid and 60 ml of absolute ethanol. At room temperature, pour the concentrated hydrochloric acid into the absolute ethanol to prepare an 80 ml mixed solution; (2) Select a Pt alloy composite material plate sample with a length of 8 mm, a width of 5 mm, and a thickness of 1 mm. Select the lower surface of the sample as the observation surface (5 mm * 8 mm). Take a section of copper flat strip and bond the upper surface of the Pt alloy composite material plate sample to one end of the copper flat strip with conductive adhesive and cure it. Bend the copper flat strip 90° at a position 10 mm close to the sample end; (3) Place the lower surface of the sample face downwards closely against the inner bottom surface of the cold mounting mold. Mix the cold mounting liquid and cold mounting powder in a certain proportion and then inject it around the Pt alloy composite material plate sample. Cure it at room temperature to expose the other end of the copper flat strip from the cold mounting material; (4) Successively use metallographic sandpapers with grit sizes of 1500#, 2000#, 3000#, and 5000# to polish the lower surface of the Pt alloy composite material plate sample after embedding. Among them, the 3000# and 5000# metallographic sandpapers are polished using the water grinding method; (5) For the formed sample observation plane polished in step (4), use a mechanical polishing machine to perform rough polishing and fine polishing successively. The polishing method is a combination of left - hand rotation polishing and right - hand rotation polishing of the polishing disc. Among them, the polishing fabric for rough polishing is canvas, the rotation speed of the polishing disc is 900 r / min, and the diamond polishing paste selected is W2; the polishing fabric for fine polishing is cashmere, the rotation speed of the polishing disc is 1400 r / min, and the polishing agent selected is W0.5 diamond polishing agent; (6) Using the electrolytic etching agent prepared in step (1), select the polished sample observation surface in step (5) as the anode and the graphite crucible as the cathode. Place the polished sample into the electrolytic etching agent with the polished surface facing down. Turn on the magnetic stirrer and conduct electrolytic etching by passing a direct current and voltage using a DC regulated power supply at room temperature. The power supply parameters are a voltage of 23V. Adjust the magnetic stirrer until the bubbles are uniform and the current is stable. After etching for 15 minutes, immediately take out the specimen; (7) Immediately after the electrolytic etching of the sample observation surface in step (6), perform ultrasonic cleaning with absolute ethanol and dry it with a hair dryer, and then the microstructure of the Pt alloy composite material plate can be observed under an optical microscope (as Figure 4 shown).

Claims

1. An electrochemical etchant system for displaying the metallographic structure of platinum group alloy samples of various sizes, characterized in that: include: DC regulated power supply, platinum group alloy sample, graphite crucible, electrochemical etchant and magnetic stirring bar; The platinum group alloy sample is fixed to one end of the copper strip by means of a conductive adhesive; the copper strip is bent upward by 90° at a position slightly larger than the length of the sample at the end of the platinum group alloy sample; The negative electrode alligator clip connected to the negative electrode output line of the DC regulated power supply is clamped on the crucible wall of the graphite crucible; The positive alligator clip connected to the positive output line of the DC regulated power supply is clamped on the platinum group alloy sample or the copper strip; The top of the electrochemical corrosive agent liquid level must not be above the top of the cold insert, that is, the electrochemical corrosive agent does not directly contact the copper strip; The electrochemical corrosive agent does not directly contact the positive alligator clip connected to the positive and negative output wires of the DC regulated power supply; A magnetic stirring bar is arranged in the graphite crucible.

2. A method for using an electrochemical etchant system for displaying the metallographic structure of platinum group alloy samples of various sizes, according to claim 1, characterized in that: The method steps are as follows: Step 1, cutting a sample from a platinum group alloy workpiece, selecting a metallographic observation plane of the sample, and polishing it with sandpaper of coarse to fine mesh numbers in sequence; Step 2: Use a mechanical polishing machine to perform rough polishing and fine polishing on the sample observation surface polished in step 1 in sequence, so as to further remove the tiny wear marks remaining from the sandpaper polishing and achieve a bright mirror effect; Step 3, using an electrolytic etchant prepared by mixing concentrated hydrochloric acid and anhydrous ethanol solution, placing it in a graphite crucible, selecting the top surface of the sample polished in step 2 as the anode, and the graphite crucible as the cathode, placing the polished platinum group alloy sample into the electrolytic etchant with the polished top surface facing downward, and using a DC regulated power supply to pass a DC current and voltage at room temperature for electrolytic corrosion; Step 4: clean the observation surface of the sample after corrosion with anhydrous ethanol and blow it dry, place the metallographic observation plane of the platinum group alloy sample under a metallographic microscope, and observe the metallographic structure of the platinum group alloy.

3. The method for using the electrochemical etching agent system for displaying the metallographic structure of platinum group alloy samples of various sizes according to claim 2, characterized in that: If the platinum group alloy sample in step 1 is a small-sized sample, the following pretreatment steps need to be added: In step 1, after selecting the metallographic observation plane of the sample, take a copper wire or copper flat strip of appropriate length, bend it 90° at a position where one end of the copper wire or copper flat strip is greater than the length of the sample, and use conductive glue to bond and fix the geometric back side of the observation surface of the platinum group alloy sample to the bent surface of the copper wire or copper flat strip; In step 2, a small-sized platinum group alloy sample is inlaid; the platinum group alloy sample is inlaid using cold mounting liquid and cold mounting powder.

4. In step 3, before electrochemical corrosion, a magnetic stirrer is placed in the graphite crucible, the graphite crucible is placed on a magnetic stirrer, and the speed is adjusted to keep the current stable.

5. The method for using the electrochemical etching agent system for displaying the metallographic structure of platinum group alloy samples of various sizes according to claim 2, characterized in that: Polishing of the platinum group alloy sample in step 1: The observation plane of the platinum group alloy sample is polished using metallographic sandpapers with particle sizes of 1500#, 2000#, 3000# and 5000# in sequence, wherein the water grinding method is used for polishing with 3000# and 5000# metallographic sandpapers.

6. The method for using the electrochemical etching agent system for displaying the metallographic structure of platinum group alloy samples of various sizes according to claim 1, characterized in that: Polishing of the platinum group alloy sample in step 2: Use a polishing machine to mechanically polish the metallographic observation plane of the platinum group alloy sample after the grinding treatment in step 1 until there are no obvious scratches and contamination points on the metallographic observation plane; the rotation speed of the polishing machine is 900r / min~1400r / min, and the polishing agent for mechanical polishing is a diamond polishing agent with a particle size of 5μm.

7. The method for using the electrochemical etching agent system for displaying the metallographic structure of platinum group alloy samples of various sizes according to claim 1, characterized in that: If the platinum group alloy sample is a small-sized sample, the specific process of the inlay in step 2 is: placing the cut platinum group alloy sample in an inlay mold, with the metallographic observation plane of the platinum group alloy sample close to the inner bottom surface of the mold, and then mixing cold mounting liquid and cold mounting powder in a certain proportion and injecting them into the surrounding side of the platinum group alloy sample, and then keeping it warm at room temperature for 15min~20min to obtain the inlaid platinum group alloy sample.

8. The method for using the electrochemical etching agent system for displaying the metallographic structure of platinum group alloy samples of various sizes according to claim 1, characterized in that: Corrosion of the platinum group alloy sample in step 3: Place the platinum group alloy sample after mechanical polishing in step 2 in a graphite container filled with a corrosive solution, turn on the magnetic stirrer; after corroding for 10 to 20 minutes, take out the sample.

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