Metallographic corrosion liquid and metallographic corrosion method for titanium-based composite material

Abstract

The invention relates to the technical field of titanium-based composite material metallographic corrosion, in particular to a titanium-based composite material metallographic corrosion liquid and a metallographic corrosion method. The metallographic etchant comprises hydrofluoric acid, sulfuric acid, nitric acid and distilled water in a volume ratio of (3.5-4.5): (1.5-2.5): (5.5-6.5): 100. The corrosion method comprises the following steps: manufacturing a metallographic specimen of the titanium-based composite material; sequentially carrying out grinding treatment and polishing treatment on the metallographic specimen; dropwise adding the metallographic etchant onto the polished surface of the metallographic sample, and carrying out corrosion treatment; the metallographic specimen subjected to corrosion treatment is subjected to washing and blow-drying treatment; and carrying out metallographic detection on the washed and blow-dried metallographic sample. After the titanium-based composite material is corroded, a high-quality metallographic structure which is clear in grain boundary, complete in grain and uniform in corrosion can be presented.

Description

Technical Field

[0001] The invention relates to the technical field of metallographic corrosion of titanium-based composite materials, and in particular to a metallographic corrosion liquid and a metallographic corrosion method for titanium-based composite materials. Background Art

[0002] With the increasing demand for high-performance materials in aerospace, automotive, and biomedical fields, titanium-based composites have emerged. Compared with traditional titanium alloys, titanium-based composites not only have higher specific strength and modulus, better high temperature resistance, better wear resistance and corrosion resistance, but also have stronger designability. Titanium-based composites can be precisely controlled according to specific application requirements by selecting different reinforcement types, contents, distribution methods, and titanium matrix materials to meet various complex working conditions and special requirements.

[0003] Due to the introduction of reinforcement phase into titanium-based composite materials, the microstructure complexity is significantly higher than that of ordinary titanium alloys. Traditional corrosive agents are not selective enough to corrode the multiphase interface in titanium-based composite materials, making it difficult to clearly present the interface morphology between the titanium matrix and the reinforcement phase.

[0004] In summary, it is necessary to develop a titanium-based composite material metallographic etching solution and a metallographic etching method to solve the problem that the interface morphology between the titanium matrix and the reinforcement phase is difficult to clearly present due to insufficient corrosion ability of traditional corrosive agents. Summary of the invention

[0005] The present invention aims to provide a titanium-based composite material metallographic etching solution and a metallographic etching method, and the specific technical scheme is as follows:

[0006] In a first aspect, the present invention provides a metallographic etching solution for a titanium-based composite material, wherein the titanium-based composite material comprises a titanium matrix and a reinforcement phase; the metallographic etching solution comprises hydrofluoric acid, sulfuric acid, nitric acid and distilled water in a volume ratio of 3.5-4.5:1.5-2.5:5.5-6.5:100.

[0007] Optionally, the molar content of the reinforcing phase in the titanium-based composite material does not exceed 20%; and the reinforcing phase includes at least one of TiB and TiN.

[0008] In a second aspect, the present invention provides a method for etching using the titanium-based composite material metallographic etching solution, comprising:

[0009] Step S1, preparing a metallographic sample of a titanium-based composite material;

[0010] Step S2, grinding and polishing the metallographic sample in sequence;

[0011] Step S3, dripping the metallographic etching liquid onto the polished surface of the metallographic sample to perform etching treatment;

[0012] Step S4, rinsing and drying the metallographic sample after the corrosion treatment;

[0013] Step S5, performing metallographic testing on the metallographic sample after the rinsing and drying treatment.

[0014] Optionally, the metallographic etching liquid is added dropwise until the polishing surface is completely covered.

[0015] Optionally, the corrosion time used in the corrosion treatment is 40 to 80 seconds.

[0016] Optionally, a metallographic cutting machine is used to cut the titanium-based composite material to obtain a primary sample, and the primary sample is placed in a mold sleeve and an embedding agent is added to obtain a metallographic sample; the embedding agent includes phenolic resin.

[0017] Optionally, the polishing process includes polishing the metallographic sample using sandpaper with mesh sizes of 180#, 600#, 1200# and 2000# in sequence until the surface of the metallographic sample is smooth and flat.

[0018] Optionally, the polishing process uses a grinding and polishing machine to polish the metallographic sample, and the polishing speed is controlled to be 500-600 rpm.

[0019] Optionally, the rinsing and drying treatment includes rinsing the metallographic sample with distilled water, dripping anhydrous ethanol after rinsing, and then drying the metallographic sample.

[0020] Optionally, the metallographic detection is performed using a metallographic microscope.

[0021] The application of the technical solution of the present invention has at least the following beneficial effects:

[0022] (1) The present invention provides a titanium-based composite material metallographic etching liquid and a metallographic etching method, which can present a high-quality metallographic structure with clear grain boundaries, complete grains and uniform etching after etching the titanium-based composite material. Specifically, the present invention uses a specific volume ratio of hydrofluoric acid, sulfuric acid, nitric acid and distilled water to mix and obtain a metallographic etching liquid, wherein the hydrofluoric acid sequentially dissolves the titanium oxide layer and the titanium matrix on the surface of the metallographic sample to generate Ti 4+ ; Nitric acid has strong oxidizing properties and can promote the formation of TiO2 passivation film on the surface of titanium substrate, inhibiting excessive corrosion of titanium substrate by hydrofluoric acid; sulfuric acid is used to increase the H + Concentration, H + Penetrating into the passive film accelerates the protonation reaction of the reinforcement phase and promotes the corrosion of the reinforcement phase. SO4 2- Can react with Ti in corrosion products 4+Forming stable complexes (such as [Ti(SO4)3] 2- ), prevent titanium salt deposition from blocking the corrosion interface, maintain the continuity of the corrosion reaction, and ensure that the corrosion presents a high-quality metallographic structure with clear grain boundaries, complete grains and uniform corrosion.

[0023] (2) The present invention uses a metallographic etching liquid to etch the metallographic sample for a time of 40 to 80 seconds, which can achieve controllable metallographic sample products. On the one hand, it ensures that the corrosion presents a high-quality metallographic structure with clear grain boundaries, complete grains and uniform corrosion. On the other hand, it can improve the observation efficiency of the metallographic structure.

[0024] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0026] Figure 1 This is a microstructure diagram of the metallographic sample after corrosion at 100 times in Example 1;

[0027] Figure 2 This is a microstructure diagram of the metallographic sample after corrosion at 200 times in Example 1;

[0028] Figure 3 This is a microstructure diagram of the metallographic sample after corrosion at 100 times in Comparative Example 1;

[0029] Figure 4 This is a microstructure diagram of the metallographic sample after corrosion at 200 times in Comparative Example 1;

[0030] Figure 5 This is a microstructure diagram of the metallographic sample after corrosion at 100 times in Comparative Example 2;

[0031] Figure 6 This is a microstructure diagram of the metallographic sample after corrosion at 200 times in Comparative Example 2;

[0032] Figure 7 This is a microstructure diagram of the metallographic sample after corrosion at 100 times in Comparative Example 3;

[0033] Figure 8 This is a microstructure diagram of the metallographic sample in Example 3 after corrosion at 200 times. DETAILED DESCRIPTION

[0034] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0035] Embodiment 1:

[0036] See also Figure 1 , a titanium-based composite material metallographic etching solution, the titanium-based composite material includes a titanium matrix and a reinforcement phase; the metallographic etching solution is obtained by mixing hydrofluoric acid, sulfuric acid, nitric acid and distilled water in a volume ratio of 4:2:6:100. Specifically, hydrofluoric acid (grade of analytical grade) is 4 mL, sulfuric acid (grade of analytical grade) is 2 mL, nitric acid (grade of analytical grade) is 6 mL, and distilled water is 100 mL.

[0037] The molar content of the reinforcing phase in the titanium-based composite material is 20%; the reinforcing phase is TiB and TiN; wherein the molar content of the reinforcing phase TiB in the titanium-based composite material is 10%, and the molar content of the reinforcing phase TiN in the titanium-based composite material is 10%.

[0038] A method for etching the titanium-based composite material metallographic etching solution comprises:

[0039] Step S1, preparing a metallographic sample of a titanium-based composite material;

[0040] Step S2, grinding and polishing the metallographic sample in sequence;

[0041] Step S3, adding the metallographic etching liquid dropwise until it completely covers the polished surface of the metallographic sample, and performing etching treatment; the etching time used in the etching treatment is 60s;

[0042] Step S4, rinsing and drying the metallographic sample after the corrosion treatment;

[0043] Step S5: Perform metallographic testing on the metallographic sample after the washing and drying process, specifically using a metallographic microscope to complete the metallographic testing. Figure 1 and Figure 2 .

[0044] A primary sample with a size of 10mm×10mm×10mm is prepared by cutting the titanium-based composite material with a metallographic cutting machine, and the primary sample is placed in a mold sleeve and an embedding agent is added to obtain a metallographic sample; the embedding agent includes phenolic resin.

[0045] The grinding process uses sandpaper with mesh numbers of 180#, 600#, 1200# and 2000# to grind the metallographic sample in sequence until the surface of the metallographic sample is smooth and flat. The equipment used for grinding is an AP-2 double-disc single-control grinding and polishing machine.

[0046] The polishing process uses a grinding and polishing machine and a polishing cloth to polish the metallographic sample, and the polishing speed is controlled to be 600 rpm.

[0047] The rinsing and drying process includes rinsing the metallographic sample with distilled water, dripping anhydrous ethanol on the sample after rinsing, and then drying the metallographic sample.

[0048] Comparative Example 1:

[0049] The difference from Example 1 is that the amount of sulfuric acid is zero. Figure 3 and Figure 4 .

[0050] Comparative Example 2:

[0051] The difference from Example 1 is that the amount of nitric acid used is reduced to 4 mL. Figure 5 and Figure 6 .

[0052] Comparative Example 3:

[0053] The difference from Example 1 is that the corrosion time is increased to 90s. Figure 7 and Figure 8 .

[0054] Depend on Figure 1-2 It is known that the metallographic test results of Example 1 can present a high-quality metallographic structure with clear grain boundaries, complete grains and uniform corrosion. This is because Example 1 uses a specific volume ratio of hydrofluoric acid, sulfuric acid, nitric acid and distilled water to mix and obtain a metallographic etching solution, wherein the hydrofluoric acid sequentially dissolves the titanium oxide layer and the titanium matrix on the surface of the metallographic sample to generate Ti 4+ ; Nitric acid has strong oxidizing properties and can promote the formation of TiO2 passivation film on the surface of titanium substrate, inhibiting excessive corrosion of titanium substrate by hydrofluoric acid; sulfuric acid is used to increase the H + Concentration, H + Penetrating into the passive film accelerates the protonation reaction of the reinforcement phase and promotes the corrosion of the reinforcement phase. SO4 2- Can react with Ti in corrosion products 4+ Forming stable complexes (such as [Ti(SO4)3] 2- ), prevent titanium salt deposition from blocking the corrosion interface, maintain the continuity of the corrosion reaction, and ensure that the corrosion presents a high-quality metallographic structure with clear grain boundaries, complete grains and uniform corrosion.

[0055] Depend on Figure 3-4 It is known that the metallographic test results of comparative example 1 have significant height differences at the interface, and the accumulation of corrosion products affects microscopic observation. This is because comparative example 1 does not use sulfuric acid, which causes nitric acid to cause the titanium substrate surface to form an overly thick and dense TiO2 passivation film. An overly thick passivation film will produce internal stress due to lattice mismatch; when the internal stress exceeds the bonding strength of the passivation film layer, microcrack defects or hole defects will form on the surface of the passivation film, which will become a channel for the corrosion liquid to penetrate. The concentrated corrosion at the defects causes its corrosion rate to be much higher than the average corrosion rate at the non-defective parts; an overly thick passivation film will cover the surface of the reinforcement phase, hindering the corrosion liquid from fully contacting the reinforcement phase, resulting in insufficient corrosion exposure of the reinforcement phase, and because sulfuric acid is not used, the H in the metallographic etching solution cannot be increased. + The concentration of hydrofluoric acid slows down the corrosion rate of the reinforcement phase, which eventually leads to the formation of a step-like interface between the titanium matrix and the reinforcement phase that is not fully corroded, that is, there is a significant height difference at the interface. 4+ , because no sulfuric acid is used, no SO4 2- Ti in corrosion products 4+ Forming stable complexes (such as [Ti(SO4)3] 2- ), which causes the corrosion products to accumulate on the corrosion interface and affects the microscopic observation.

[0056] Depend on Figure 5-6 It is known that the metallographic detection result of Comparative Example 2 shows that the coverage rate of black corrosion products is greater than 40%, which seriously interferes with the metallographic structure analysis. This is because the amount of nitric acid used in Comparative Example 2 is too low, so that the TiO2 passivation film formed by nitric acid on the surface of the titanium substrate is too thin, which is easily invalidated under the action of hydrofluoric acid and sulfuric acid, and then the hydrofluoric acid excessively corrodes the titanium oxide layer and the titanium substrate, that is, the coverage rate of black corrosion products is greater than 40%, which seriously interferes with the metallographic structure analysis.

[0057] Depend on Figure 7-8 It is known that the metallographic test results of Comparative Example 3 show the coexistence of yellow-brown titanium salt deposition and local pitting, which affects the metallographic structure observation. This is because the corrosion time used in Comparative Example 3 is too long, and hydrofluoric acid excessively corrodes the titanium oxide layer and the titanium matrix, resulting in excessive Ti corrosion. 4+ , SO4 2- With too much Ti 4+ Form a large number of complexes (such as [Ti(SO4)3] 2- ), it is easy to complex yellow-brown titanium salts and deposit on the corrosion interface, affecting the metallographic structure observation. In addition, excessive corrosion of the titanium oxide layer and the titanium matrix by hydrofluoric acid can easily lead to local pitting of the titanium matrix.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A titanium-based composite material metallographic etching solution, wherein the titanium-based composite material comprises a titanium matrix and a reinforcement phase; characterized in that: The metallographic etching solution comprises hydrofluoric acid, sulfuric acid, nitric acid and distilled water in a volume ratio of 3.5-4.5:1.5-2.5:5.5-6.5:

100.

2. The titanium-based composite material metallographic etching solution according to claim 1, characterized in that: The molar content of the reinforcing phase in the titanium-based composite material does not exceed 20%; the reinforcing phase includes at least one of TiB and TiN.

3. A method for etching the titanium-based composite material metallographic etching solution according to claim 2, characterized in that: include: Step S1, preparing a metallographic sample of a titanium-based composite material; Step S2, grinding and polishing the metallographic sample in sequence; Step S3, dripping the metallographic etching liquid onto the polished surface of the metallographic sample to perform etching treatment; Step S4, rinsing and drying the metallographic sample after the corrosion treatment; Step S5, performing metallographic testing on the metallographic sample after the rinsing and drying treatment.

4. The etching method of titanium-based composite material metallographic etching liquid according to claim 3, characterized in that: The metallographic etching liquid is added dropwise until the polishing surface is completely covered.

5. The etching method of titanium-based composite material metallographic etching liquid according to claim 3, characterized in that: The corrosion time used in the corrosion treatment is 40 to 80 seconds.

6. The etching method of titanium-based composite material metallographic etching liquid according to claim 3, characterized in that: A metallographic cutting machine is used to cut the titanium-based composite material to obtain a primary sample, and the primary sample is placed in a mold sleeve and an embedding agent is added to obtain a metallographic sample; the embedding agent includes phenolic resin.

7. The etching method of titanium-based composite material metallographic etching liquid according to claim 3, characterized in that: The polishing treatment includes polishing the metallographic sample with sandpaper of mesh numbers 180#, 600#, 1200# and 2000# in sequence until the surface of the metallographic sample is smooth and flat.

8. The etching method of titanium-based composite material metallographic etching liquid according to claim 3, characterized in that: The polishing process uses a grinding and polishing machine to polish the metallographic sample, and the polishing speed is controlled to be 500-600rpm.

9. The etching method of titanium-based composite material metallographic etching liquid according to claim 3, characterized in that: The rinsing and drying process includes rinsing the metallographic sample with distilled water, dripping anhydrous ethanol on the sample after rinsing, and then drying the metallographic sample.

10. The etching method of the titanium-based composite material metallographic etching solution according to any one of claims 3 to 9, characterized in that: The metallographic detection is performed using a metallographic microscope.

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