Metallographic corrosive agent for molybdenum / steel composite material and corrosion method

Abstract

The invention discloses a metallographic corrosive agent for a molybdenum / steel composite material and a corrosion method, the metallographic corrosive agent comprises a molybdenum metal corrosive agent and a steel corrosive agent, the molybdenum metal corrosive agent is composed of a ferricyanide aqueous solution and a sodium hydroxide aqueous solution, and the steel corrosive agent is composed of copper chloride, a hydrochloric acid solution, a sulfuric acid solution and an ethanol solution; according to the corrosion method, the surface of the molybdenum / steel composite material is wiped and corroded by adopting a steel corrosive agent and then adopting a molybdenum metal corrosive agent. According to the metallographic corrosive agent, the molybdenum metal corrosive agent and the steel corrosive agent have a good corrosive effect on matrixes on the corresponding sides by controlling the composition ratio of the two corrosive agents, and have no corrosive effect on matrixes on the other sides, so that a connecting interface and a matrix metallographic structure of a molybdenum / steel composite material are clearly shown; the step-by-step corrosion method is stable in corrosion process, easy to operate and suitable for the field of metallographic sample preparation, and the use sequence of different corrosive agents is not required.

Description

Technical Field

[0001] The invention belongs to the technical field of metallographic sample preparation, and in particular relates to a metallographic etchant and an etching method for a molybdenum / steel composite material. Background Art

[0002] Molybdenum metal has important applications in aerospace, nuclear energy, metallurgy, chemistry and other fields due to its excellent physical and chemical properties. Its high temperature strength, oxidation resistance, electrical conductivity and corrosion resistance make it have great advantages in extreme environments. Steel is a metal alloy made of iron and a small amount of carbon. It is widely used in construction, transportation, manufacturing, energy and other fields. Its good strength, hardness, plasticity and corrosion resistance make it a pillar material of modern industry. Molybdenum steel composite material is a composite material made of molybdenum and steel through composite technology. It combines the excellent high temperature performance, radiation resistance and electrical conductivity of molybdenum. Molybdenum steel composite material has a wide range of applications in extreme environments such as high temperature, high pressure and corrosion resistance.

[0003] Since the material undergoes microstructural changes during the composite process, and the organization at the interface of the composite material changes greatly, the internal organization structure of the metal material can determine the mechanical properties of the material, and metallographic observation is a relatively simple and effective method. The principle of metallographic corrosion is to selectively corrode the metal surface through chemical or electrochemical reactions, so that different phases or grain boundaries of the metal material show different contrasts under the microscope, thereby revealing its microstructure. Good metallographic corrosion can obtain a clear metallographic structure, see obvious grain boundaries and organizational changes at the interface of the composite material, and then analyze the influence of the organization on the mechanical properties.

[0004] At present, for the corrosion of dissimilar materials, the step-by-step corrosion method is often used to corrode different alloys. However, due to the influence of factors such as corrosive agent composition, concentration and time, it is difficult to simultaneously etch out the metallographic structure of dissimilar metal composite materials. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a metallographic etchant for molybdenum / steel composite materials in view of the above-mentioned deficiencies of the prior art. The metallographic etchant controls the composition ratio of the two etchants so that the molybdenum metal etchant and the steel etchant both have good corrosion effects on the corresponding side substrates and have no corrosion effects on the other side substrates, thereby making the connection interface and the substrate metallographic structure of the molybdenum / steel composite materials clearly visible, solving the problem that the dissimilar metals molybdenum and steel in the molybdenum / steel composite materials cannot be corroded at the same time and the corrosion interference between the etchants.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a metallographic etchant for molybdenum / steel composite materials, characterized in that it includes a molybdenum metal etchant and a steel etchant, and the molybdenum metal etchant is composed of a ferrocyanide aqueous solution with a mass concentration of 10% and a sodium hydroxide aqueous solution with a mass concentration of 10% in a volume ratio of 1:1, and the steel etchant is composed of cupric chloride, analytically pure hydrochloric acid, analytically pure sulfuric acid and ethanol, and the mass ratio of cupric chloride to the volume of analytically pure hydrochloric acid, analytically pure sulfuric acid and ethanol is 5:80:10-20:100, the mass unit is g, and the volume unit is mL, wherein the mass fraction of analytically pure hydrochloric acid is 36%-38%, and the mass fraction of analytically pure sulfuric acid is 95%-98%.

[0007] The present invention finds that during the corrosion process of molybdenum / steel composite materials, due to the irregular arrangement of grain boundary atoms and high free energy, the grain boundaries are susceptible to corrosion and appear as pits under a microscope. Different materials have different chemical properties, which makes it difficult for the same corrosive agent to corrode composite materials with large differences in chemical properties. In this regard, the metallographic etchant developed by the present invention comprises a molybdenum metal etchant and a steel etchant. The molybdenum metal etchant is controlled to be composed of an aqueous solution of ferricyanide with a mass concentration of 10% and an aqueous solution of sodium hydroxide with a mass concentration of 10% in a volume ratio of 1:1, and the oxidation effect of ferricyanide is used to cooperate with the alkaline dissolution effect of sodium hydroxide to efficiently remove the oxide layer on the surface of molybdenum metal, including pure molybdenum and molybdenum alloys, and preferentially corrode grain boundaries or defective areas, so that its microstructure is exposed. Since steel contains chromium, a dense chromium oxide (Cr2O3) passivation film will spontaneously form on its surface in an oxidizing environment to resist subsequent oxidative corrosion. Therefore, the molybdenum metal etchant can clearly etch the metallographic structure of the molybdenum metal matrix without any corrosion to the steel matrix. By controlling the steel etchant to be composed of cupric chloride, analytically pure hydrochloric acid, analytically pure sulfuric acid and ethanol, the iron with a low reduction potential (E°≈-0.44Vvs.SHE) in the steel matrix is ​​exposed in an acidic environment containing Cl - The steel corrosive agent is oxidized to Fe 2+ or Fe 3+ , and copper chloride acts as an oxidant and reacts with Fe 2+ or Fe 3+ The generation of soluble products accelerates corrosion, thereby exposing the microstructure in the steel matrix. The standard reduction potential of molybdenum in the molybdenum metal matrix (E°≈-0.15Vvs.SHE) is significantly higher than that of iron, and it is not easily oxidized in the same corrosive agent, i.e., the steel corrosive agent. Therefore, the steel corrosive agent can clearly corrode the metallographic structure of the steel matrix without corrosive effects on the molybdenum metal matrix.

[0008] The above-mentioned metallographic etchant for molybdenum / steel composite materials is characterized in that the ratio of the mass of the cupric chloride to the volume of analytically pure hydrochloric acid, analytically pure sulfuric acid, and ethanol is 5:80:20:100, the mass unit is g, and the volume unit is mL.

[0009] At the same time, the present invention also discloses a corrosion method using the metallographic corrosive agent for the molybdenum / steel composite material, which is characterized in that the surface of the molybdenum / steel composite material is firstly subjected to wiping corrosion by using a molybdenum metal corrosive agent, and then the surface of the molybdenum / steel composite material is subjected to wiping corrosion by using a steel corrosive agent.

[0010] The above-mentioned corrosion method is characterized in that the wiping corrosion time of the molybdenum metal corrosive agent is 10s.

[0011] The above-mentioned corrosion method is characterized in that the wiping corrosion time of the steel metal corrosive agent is 10s to 15s.

[0012] In addition, the present invention also discloses a corrosion method using the metallographic corrosive agent for the molybdenum / steel composite material, which is characterized in that the surface of the molybdenum / steel composite material is firstly subjected to wiping corrosion by using a steel corrosive agent, and then the surface of the molybdenum / steel composite material is subjected to wiping corrosion by using a molybdenum metal corrosive agent.

[0013] The above-mentioned corrosion method is characterized in that the wiping corrosion time of the steel metal corrosive agent is 10s to 15s.

[0014] The above-mentioned corrosion method is characterized in that the wiping corrosion time of the molybdenum metal corrosive agent is 10s.

[0015] The present invention adopts a step-by-step corrosion method, firstly, a molybdenum metal corrosive agent or a steel corrosive agent in a metallographic corrosive agent is used to wipe and corrode the surface of the molybdenum / steel composite material, and then another corrosive agent is used to wipe and corrode the surface of the molybdenum / steel composite material, so that the connection interface of the dissimilar materials and the metallographic structure of the matrix are clearly displayed, and the corrosive agent used first does not corrode the surrounding uncorroded materials, and the corrosive agent used later does not corrode the corroded materials, that is, when the molybdenum side is corroded first, the steel does not corrode, or when the steel side is corroded first, the molybdenum side does not corrode. The corrosion process is stable and easy to operate, so there is no requirement for the use order of different corrosive agents, and the interface and matrix structure of the molybdenum / steel composite material can be clearly visible.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The metallographic etchant of the present invention comprises a molybdenum metal etchant and a steel etchant. By controlling the composition ratio of the two etchants, the molybdenum metal etchant and the steel etchant both have good corrosion effects on the corresponding side substrates, and have no corrosion effects on the other side substrates, thereby avoiding the corrosion of steel by the molybdenum metal etchant and the interference of the steel etchant on the corrosion of the molybdenum metal, so that the connection interface and the substrate metallographic structure of the molybdenum / steel composite material are clearly displayed.

[0018] 2. The present invention adopts a step-by-step etching method, firstly using any one of the metallographic etching agents to wipe-etch the substrate on the corresponding side of the surface of the molybdenum / steel composite material, and then using another etching agent to wipe-etch the substrate on the other side of the surface of the molybdenum / steel composite material. There is no requirement for the order of using different etching agents, and the interface and matrix structure of the molybdenum / steel composite material can be clearly seen.

[0019] 3. The present invention develops molybdenum metal etchant and steel etchant for molybdenum / steel composite materials, and adopts a step-by-step corrosion method to quickly realize the metallographic corrosion of the interface between molybdenum and steel and the metallographic corrosion on both sides. The corrosion process is stable and easy to operate, avoiding the adverse effects of different etchants on different substrates in the step-by-step method.

[0020] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the interface microstructure diagram of the molybdenum / steel composite material after being wiped and corroded by a molybdenum metal corrosive agent in Example 1 of the present invention.

[0022] Figure 2 This is the interface microstructure diagram of the molybdenum / steel composite material after being rubbed and corroded by a molybdenum metal corrosive agent and a steel corrosive agent in Example 1 of the present invention.

[0023] Figure 3 This is the interface microstructure diagram of the molybdenum / steel composite material after being rubbed and corroded by a steel corrosive agent in Example 2 of the present invention.

[0024] Figure 4 This is an interface microstructure diagram of the molybdenum / steel composite material after being rubbed and corroded by a steel corrosive agent and a molybdenum metal corrosive agent in Example 2 of the present invention. DETAILED DESCRIPTION

[0025] Example 1

[0026] The metallographic etchant for the molybdenum / steel composite material of the present embodiment comprises a molybdenum metal etchant and a steel etchant, wherein the molybdenum metal etchant is composed of 50 mL of a 10% by mass aqueous solution of ferrocyanide and 50 mL of a 10% by mass aqueous solution of sodium hydroxide, and the steel etchant is composed of 5 g of cupric chloride, 80 mL of analytically pure hydrochloric acid, 10 mL of analytically pure sulfuric acid and 100 mL of ethanol, wherein the mass fraction of the analytically pure hydrochloric acid is 36% to 38%, and the mass fraction of the analytically pure sulfuric acid is 95% to 98%.

[0027] The etching method of the molybdenum / steel composite material using a metallographic etchant of the present embodiment comprises the following steps:

[0028] Step 1: Cutting, grinding (including rough grinding and fine grinding), and mechanical polishing the molybdenum / steel composite material in sequence; the sandpaper brands used in the grinding are 120#, 800#, 1200#, and 2000#, respectively; and the mechanical polishing uses a silicon dioxide polishing liquid with a particle size of 1 μm;

[0029] Step 2: Use a cotton ball to dip in a molybdenum metal corrosive agent to wipe the surface of the molybdenum / steel composite material that has been mechanically polished in step 1, and corrode the molybdenum substrate for 10 seconds;

[0030] Step 3: Rinse the surface of the molybdenum / steel composite material after wiping and corroding in step 2 with clean water until the residual molybdenum metal corrosive agent is completely removed, then soak the surface of the molybdenum / steel composite material with anhydrous ethanol and immediately dry it with a hair dryer. Figure 1 As shown, the molybdenum matrix of the molybdenum / steel composite material corrodes, while the steel matrix is ​​not corroded and is not affected;

[0031] Step 4: Use a cotton ball dipped in a steel corrosive agent to wipe the surface of the molybdenum / steel composite material dried in step 3, and corrode the steel substrate for 10 seconds;

[0032] Step 5: Rinse the surface of the molybdenum / steel composite material after wiping and corroding in step 4 with clean water until the residual steel corrosive agent is completely removed, then soak the surface of the molybdenum / steel composite material with anhydrous ethanol and immediately dry it with a hair dryer to obtain the corroded molybdenum / steel composite material for metallographic observation.

[0033] Figure 2 The interface microstructure diagram of the molybdenum / steel composite material after being rubbed and corroded by the molybdenum metal corrosive agent and the steel corrosive agent in Example 1 of the present invention is shown in FIG. Figure 2 It can be seen that the structures on both sides of the molybdenum / steel composite material are clearly visible, and there is no shallow corrosion or over-corrosion.

[0034] Example 2

[0035] The metallographic etchant for the molybdenum / steel composite material of the present embodiment comprises a molybdenum metal etchant and a steel etchant, wherein the molybdenum metal etchant is composed of 50 mL of a 10% by mass aqueous solution of ferrocyanide and 50 mL of a 10% by mass aqueous solution of sodium hydroxide, and the steel etchant is composed of 5 g of cupric chloride, 80 mL of analytically pure hydrochloric acid, 10 mL of analytically pure sulfuric acid and 100 mL of ethanol, wherein the mass fraction of the analytically pure hydrochloric acid is 36% to 38%, and the mass fraction of the analytically pure sulfuric acid is 95% to 98%.

[0036] The etching method of the molybdenum / steel composite material using a metallographic etchant of the present embodiment comprises the following steps:

[0037] Step 1: Cutting, grinding (including rough grinding and fine grinding), and mechanical polishing the molybdenum / steel composite material in sequence; the sandpaper brands used in the grinding are 120#, 800#, 1200#, and 2000#, respectively; and the mechanical polishing uses a silicon dioxide polishing liquid with a particle size of 1 μm;

[0038] Step 2: Use a cotton ball to dip into a steel corrosive agent to wipe the surface of the molybdenum / steel composite material that has been mechanically polished in step 1, and corrode the steel substrate for 10 seconds;

[0039] Step 3: Rinse the surface of the molybdenum / steel composite material after wiping and corroding in step 2 with clean water until the residual steel corrosive agent is completely removed, then soak the surface of the molybdenum / steel composite material with anhydrous ethanol and immediately dry it with a hair dryer. Figure 3 As shown, the steel matrix of the molybdenum / steel composite material corrodes, while the molybdenum matrix is ​​not corroded and is not affected;

[0040] Step 4: Use a cotton ball dipped in a molybdenum metal corrosive agent to wipe the surface of the molybdenum / steel composite material dried in step 3, and corrode the molybdenum substrate for 10 seconds;

[0041] Step 5: Rinse the surface of the molybdenum / steel composite material after wiping and corroding in step 4 with clean water until the residual steel corrosive agent is completely removed, then soak the surface of the molybdenum / steel composite material with anhydrous ethanol and immediately dry it with a hair dryer to obtain the corroded molybdenum / steel composite material for metallographic observation.

[0042] Figure 4 The interface microstructure diagram of the molybdenum / steel composite material after being rubbed and corroded by the steel corrosive agent and the molybdenum metal corrosive agent in Example 1 of the present invention is shown in FIG. Figure 4 It can be seen that the structures on both sides of the molybdenum / steel composite material are clearly visible, and there is no shallow corrosion or over-corrosion.

[0043] Example 3

[0044] The metallographic etchant for the molybdenum / steel composite material of the present embodiment comprises a molybdenum metal etchant and a steel etchant, wherein the molybdenum metal etchant is composed of 50 mL of a 10% by mass aqueous solution of ferrocyanide and 50 mL of a 10% by mass aqueous solution of sodium hydroxide, and the steel etchant is composed of 5 g of cupric chloride, 80 mL of analytically pure hydrochloric acid, 20 mL of analytically pure sulfuric acid and 100 mL of ethanol, wherein the mass fraction of the analytically pure hydrochloric acid is 36% to 38%, and the mass fraction of the analytically pure sulfuric acid is 95% to 98%.

[0045] The etching method of the molybdenum / steel composite material using a metallographic etchant of the present embodiment comprises the following steps:

[0046] Step 1: Cutting, grinding (including rough grinding and fine grinding), and mechanical polishing the molybdenum / steel composite material in sequence; the sandpaper brands used in the grinding are 120#, 800#, 1200#, and 2000#, respectively; and the mechanical polishing uses a silicon dioxide polishing liquid with a particle size of 1 μm;

[0047] Step 2: Use a cotton ball to dip in a molybdenum metal corrosive agent to wipe the surface of the molybdenum / steel composite material that has been mechanically polished in step 1, and corrode the molybdenum substrate for 10 seconds;

[0048] Step 3: Rinse the surface of the molybdenum / steel composite material after wiping and corroding in step 2 with clean water until the residual molybdenum metal corrosive agent is completely removed, then soak the surface of the molybdenum / steel composite material with anhydrous ethanol and immediately blow dry with a hair dryer;

[0049] Step 4: Use a cotton ball dipped in a steel corrosive agent to wipe the surface of the molybdenum / steel composite material dried in step 3, and corrode the steel substrate for 10 seconds;

[0050] Step 5: Rinse the surface of the molybdenum / steel composite material after wiping and corroding in step 4 with clean water until the residual steel corrosive agent is completely removed, then soak the surface of the molybdenum / steel composite material with anhydrous ethanol and immediately dry it with a hair dryer to obtain the corroded molybdenum / steel composite material for metallographic observation.

[0051] Metallographic observation shows that the structures on both sides of the molybdenum / steel composite material after wiping and corrosion by the molybdenum metal corrosive agent and the steel corrosive agent in this embodiment are all clearly visible, the interface is slightly blackened, and there is no shallow corrosion or over-corrosion.

[0052] Example 4

[0053] The metallographic etchant for the molybdenum / steel composite material of the present embodiment comprises a molybdenum metal etchant and a steel etchant, wherein the molybdenum metal etchant is composed of 50 mL of a 10% by mass aqueous solution of ferrocyanide and 50 mL of a 10% by mass aqueous solution of sodium hydroxide, and the steel etchant is composed of 5 g of cupric chloride, 80 mL of analytically pure hydrochloric acid, 10 mL of analytically pure sulfuric acid and 100 mL of ethanol, wherein the mass fraction of the analytically pure hydrochloric acid is 36% to 38%, and the mass fraction of the analytically pure sulfuric acid is 95% to 98%.

[0054] The etching method of the molybdenum / steel composite material using a metallographic etchant of the present embodiment comprises the following steps:

[0055] Step 1: Cutting, grinding (including rough grinding and fine grinding), and mechanical polishing the molybdenum / steel composite material in sequence; the sandpaper brands used in the grinding are 120#, 800#, 1200#, and 2000#, respectively; and the mechanical polishing uses a silicon dioxide polishing liquid with a particle size of 1 μm;

[0056] Step 2: Use a cotton ball to dip in a molybdenum metal corrosive agent to wipe the surface of the molybdenum / steel composite material that has been mechanically polished in step 1, and corrode the molybdenum substrate for 10 seconds;

[0057] Step 3: Rinse the surface of the molybdenum / steel composite material after wiping and corroding in step 2 with clean water until the residual molybdenum metal corrosive agent is completely removed, then soak the surface of the molybdenum / steel composite material with anhydrous ethanol and immediately blow dry with a hair dryer;

[0058] Step 4: Use a cotton ball dipped in a steel corrosive agent to wipe the surface of the molybdenum / steel composite material dried in step 3, and corrode the steel substrate for 15 seconds;

[0059] Step 5: Rinse the surface of the molybdenum / steel composite material after wiping and corroding in step 4 with clean water until the residual steel corrosive agent is completely removed, then soak the surface of the molybdenum / steel composite material with anhydrous ethanol and immediately dry it with a hair dryer to obtain the corroded molybdenum / steel composite material for metallographic observation.

[0060] Metallographic observation shows that the structures on both sides of the molybdenum / steel composite material after wiping and corrosion by molybdenum metal corrosive agent and steel corrosive agent in this embodiment are all clearly visible, the grain boundary on the steel side is darker in color, and there is no shallow corrosion or over-corrosion.

[0061] In summary, the metallographic etchant for the molybdenum / steel composite material of the present invention realizes the metallographic structure corrosion of the interface between molybdenum and steel and both sides in steps and quickly, and when corroding molybdenum, the steel side is not corroded, or when corroding steel, the molybdenum side is not corroded, and there is no order in which the etchants are used.

[0062] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A metallographic etchant for molybdenum / steel composite materials, characterized in that: The invention comprises a molybdenum metal corrosive agent and a steel corrosive agent, wherein the molybdenum metal corrosive agent is composed of a ferrocyanide aqueous solution with a mass concentration of 10% and a sodium hydroxide aqueous solution with a mass concentration of 10% in a volume ratio of 1:1, and the steel corrosive agent is composed of cupric chloride, analytically pure hydrochloric acid, analytically pure sulfuric acid and ethanol, and the mass ratio of the cupric chloride to the volumes of the analytically pure hydrochloric acid, analytically pure sulfuric acid and ethanol is 5:80:10-20:100, the mass unit is g, and the volume unit is mL, wherein the mass fraction of the analytically pure hydrochloric acid is 36%-38%, and the mass fraction of the analytically pure sulfuric acid is 95%-98%.

2. The metallographic etching agent for molybdenum / steel composite material according to claim 1, characterized in that: The ratio of the mass of the cupric chloride to the volumes of analytically pure hydrochloric acid, analytically pure sulfuric acid and ethanol is 5:80:20:100, with the mass unit being g and the volume unit being mL.

3. A method for etching the molybdenum / steel composite material using the metallographic etchant for the molybdenum / steel composite material as claimed in claim 1 or 2, characterized in that: Firstly, a molybdenum metal corrosive agent is used to wipe and corrode the surface of the molybdenum / steel composite material, and then a steel corrosive agent is used to wipe and corrode the surface of the molybdenum / steel composite material.

4. The etching method according to claim 3, characterized in that: The wiping corrosion time of the molybdenum metal corrosive agent is 10s.

5. The etching method according to claim 3, characterized in that: The wiping corrosion time of the steel metal corrosive agent is 10s to 15s.

6. A method for etching the molybdenum / steel composite material using the metallographic etchant for the molybdenum / steel composite material as claimed in claim 1 or 2, characterized in that: Firstly, a steel corrosive agent is used to wipe and corrode the surface of the molybdenum / steel composite material, and then a molybdenum metal corrosive agent is used to wipe and corrode the surface of the molybdenum / steel composite material.

7. The etching method according to claim 6, characterized in that: The wiping corrosion time of the steel metal corrosive agent is 10s to 15s.

8. The etching method according to claim 6, characterized in that: The wiping corrosion time of the molybdenum metal corrosive agent is 10s.

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