Metallographic structure display method for 3D printing of tantalum and tantalum alloy

Abstract

The application discloses a metallographic structure display method for 3D printing tantalum and tantalum alloy, which comprises sample grinding, sample polishing, preparation of an etchant, metallographic etching and metallographic observation, wherein the etchant used creatively introduces hydrogen peroxide and uses the same as a main component to construct an etchant system mainly composed of hydrogen peroxide and supplemented by a strong acid composition, so that the technical problem that a traditional strong acid etchant cannot effectively etch the 3D printing formed tantalum / tantalum alloy is solved, and the safety of the preparation process is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallographic sample preparation, and particularly relates to a method for displaying the metallographic structure of 3D printed tantalum and tantalum alloy. BACKGROUND

[0002] Metal tantalum gradually becomes the basic material of new medical implants due to its unique physical and chemical properties and excellent biological inertness and biocompatibility, and is also widely used in the aerospace industry, such as tantalum-tungsten alloy which has high high-temperature tensile strength and anti-creep deformation ability, and tantalum-zirconium alloy which has strong corrosion resistance. However, in the medical and aerospace fields, the product shapes are relatively complex due to the particularity of the product use scene, and it is difficult to achieve by traditional processing methods, but the emergence of 3D printing technology makes it possible.

[0003] In the process of 3D printing forming products, metallographic analysis is an indispensable step. Metallographic analysis is to display the metallographic structure of metal materials, and then observe the metallographic structure of metal materials by using a metallographic microscope. Generally, the method is to make it appear by using etchant corrosion. Through metallographic analysis, the metallurgical quality of raw materials such as segregation and non-metallic inclusion distribution type and level can be checked. At the same time, metallographic analysis can provide the basis for adjusting the process and modifying the process parameters, and guide the production, such as whether the quenching heating temperature, holding time and cooling speed are appropriate or not. However, metal tantalum and tantalum alloy have good corrosion resistance, and traditional etchants cannot achieve good corrosion effect. Only by using a combination of strong acids such as hydrofluoric acid and sulfuric acid can it be used with difficulty. For example, page 62 of the Metallographic Etching Manual discloses a corrosion method for tantalum, which is immersed in a hydrofluoric acid solution for ten seconds. The invention patent with application number 202111446198.2 discloses a method for displaying the metallographic structure of a tantalum target, which uses an etchant with a ratio of HF:H2SO4:HNO3=4:1:2 for corrosion. The invention patent with application number 2019101565685 also uses an etchant with a ratio of HF:H2SO4:HNO3=3:1:1. However, the applicant found in use that tantalum or tantalum alloy processed by 3D printing is more fine, and traditional etchants often cannot achieve good corrosion effect. SUMMARY

[0004] The purpose of the present application is to provide a method for displaying the metallographic structure of 3D printed tantalum and tantalum alloy, which overcomes the problem that traditional etchant systems cannot effectively treat 3D printed tantalum and tantalum alloy. A new etchant system is used to etch 3D printed tantalum and tantalum alloy, and the metallographic structure can be clearly and completely displayed.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A method for displaying the metallographic structure of tantalum and tantalum alloys by 3D printing, comprising:

[0007] S1: Sample grinding, wherein the sample is tantalum or tantalum alloy;

[0008] S2: Sample polishing; The sample is ground and polished on a metallographic grinding and polishing machine to form a polished surface on the sample;

[0009] S3: Preparation of corrosive agent;

[0010] S4: Metallographic Etching: The etchant is applied to the polished surface of the sample by means of immersion, dripping, or wiping.

[0011] S5: Metallographic observation;

[0012] The characteristic feature is that the corrosive agent is a mixture of hydrogen peroxide and a strong acid, wherein the content of hydrogen peroxide can be increased or decreased appropriately according to the corrosion effect.

[0013] Furthermore, the strong acid composition comprises HF, H2SO4, and HNO3, prepared in a volume ratio of 2:5:1.

[0014] Furthermore, the sample is a solid cube specimen formed from tantalum metal powder using 3D printing technology.

[0015] Furthermore, in the sample polishing step, water is used as a wetting agent, and metallographic wet sandpaper is used to polish the sample in multiple passes.

[0016] Furthermore, the sample polishing step involves six grinding passes, with each pass using metallographic wet sandpaper of grits of 180, 400, 800, 1600, 2500, and 5000.

[0017] This invention creatively introduces hydrogen peroxide as the main component, constructing a corrosion agent system with hydrogen peroxide as the primary component and a strong acid composition as a secondary component. This overcomes the technical problem that traditional strong acid corrosion agents cannot effectively corrode 3D-printed tantalum / tantalum alloys. Simultaneously, hydrogen peroxide can reduce splashing of the strong acid composition during preparation, improving the safety of the preparation process. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0019] In the attached image:

[0020] Figure 1The metallographic structures of the final samples a1 and a2 of Example 1 are shown schematically.

[0021] Figure 2 The metallographic structure of the final sample b in Comparative Example 1 is shown schematically.

[0022] Figure 3 The metallographic structure of the final sample c in Comparative Example 1 is shown schematically.

[0023] Figure 4 The metallographic structure of the final sample d in Comparative Example 1 is shown schematically.

[0024] Figure 5 The metallographic structure of the final sample e in Comparative Example 1 is shown schematically.

[0025] Figure 6 The metallographic structure of the final sample f in Comparative Example 1 is shown schematically.

[0026] Figure 7 The metallographic structure of the final sample g in Comparative Example 2 is shown schematically. Detailed Implementation

[0027] Example

[0028] 3D printing differs from traditional processing methods not only in its forming conditions but also in the microstructure of the resulting products. Traditionally processed tantalum metal exhibits equiaxed crystals, while 3D-printed tantalum / tantalum alloys are columnar or dendritic crystals with finer grains. While finer grains often result in better mechanical properties, they also enhance corrosion resistance, increasing the difficulty of etching. Therefore, this embodiment modifies the etchant formulation by creatively introducing hydrogen peroxide, forming an etchant system primarily composed of hydrogen peroxide and supplemented by a strong acid composition. This system, combined with the following method, effectively etches the 3D-printed tantalum / tantalum alloys.

[0029] Specifically, it includes the following steps:

[0030] S1: Sample grinding:

[0031] Prepare one set of samples. On a metallographic polishing machine, using water as a wetting agent, use metallographic wet sandpaper to polish the samples in multiple passes. When the polished surface is flat, the polishing marks are in the same direction, and the polishing marks from the previous pass are completely eliminated, the polishing pass is finished. Change to sandpaper with a larger grit and continue polishing. Before changing each sandpaper, rinse the sample and polishing disc with water to prevent the sandpaper particles from the previous pass from affecting the quality of subsequent sample preparation. Also, during each polishing pass, the direction of the polishing marks should be perpendicular to the direction of the polishing marks from the previous pass until a flat polished surface is formed.

[0032] In this embodiment, six grinding passes are used, with the metallographic wet sandpaper used in each pass being 180 mesh, 400 mesh, 800 mesh, 1600 mesh, 2500 mesh, and 5000 mesh, respectively.

[0033] It should be noted that the sample can be made of tantalum or tantalum alloy. In this embodiment, a solid cube sample is formed by tantalum metal powder through the SLM process in 3D printing technology. The purity of the tantalum powder is ≥99.9% and the sphericity is ≥98%.

[0034] S2: Sample polishing;

[0035] The smooth surface of the sample is mechanically polished on a metallographic polishing machine using a polishing pad and diamond suspension polishing solution until the smooth surface of the sample is free of scratches and has a mirror finish. The polished surface is then rinsed with anhydrous ethanol and dried for later use.

[0036] S3: Preparation of corrosive agent;

[0037] S31: Slowly pour nitric acid into a container containing hydrogen peroxide while stirring continuously;

[0038] S32: After the solution is cooled to room temperature, nitric acid is added while stirring continuously. After cooling to room temperature, concentrated sulfuric acid is added.

[0039] The etchant used in this embodiment is prepared by mixing H2O2, HF, H2SO4, and HNO3 in a volume ratio of 25:2:5:1.

[0040] S4: Metallographic corrosion;

[0041] The etchant was applied to the polished surfaces of different samples by immersion, dripping, or wiping for 10–30 seconds. The samples were then rinsed with anhydrous ethanol and the polished surfaces were dried.

[0042] S5: Metallographic observation;

[0043] The polished surfaces of two samples etched with different etchants were observed using a metallographic microscope. The above steps were repeated to obtain two samples, a1 and a2.

[0044] like Figure 1 As shown, a1 and a2 have clear and complete crystalline phase structures with distinct grains and clear grain boundary lines without coarsening or overlap. The combination of etchant and processing method in this embodiment can obviously solve the problem of metallographic structure display of tantalum and tantalum alloys in 3D printing.

[0045] Compare with Example 1

[0046] This comparative example includes the following steps:

[0047] S1: Sample grinding:

[0048] Prepare 5 sets of samples. On a metallographic polishing machine, using water as a wetting agent, use metallographic wet sandpaper to polish the samples in multiple passes. When the polished surface is flat, the polishing marks are in the same direction, and the polishing marks from the previous pass are completely eliminated, the polishing pass is finished. Then, replace the sandpaper with a larger grit and continue polishing. Before changing the sandpaper, rinse the sample and the polishing disc with water to prevent the sandpaper particles from the previous pass from affecting the quality of subsequent sample preparation. During each pass, the polishing marks are perpendicular to the polishing marks from the previous pass until a flat polished surface is formed. In this example, 6 passes of polishing are used, with the metallographic wet sandpaper grits used in each pass being 180 grit, 400 grit, 800 grit, 1600 grit, 2500 grit, and 5000 grit, respectively.

[0049] It should be noted that the sample can be tantalum or tantalum alloy. The comparative example used here is a solid cube sample formed by SLM process of tantalum metal powder. The purity of tantalum powder is ≥99.9% and the sphericity is ≥98%.

[0050] S2: Sample polishing;

[0051] The smooth surface of the sample is mechanically polished on a metallographic polishing machine using a polishing pad and diamond suspension polishing solution until the smooth surface of the sample is free of scratches and has a mirror finish. The polished surface is then rinsed with anhydrous ethanol and dried for later use.

[0052] S3: Preparation of corrosive agent;

[0053] S31: Slowly pour nitric acid into a container containing hydrofluoric acid while stirring continuously;

[0054] S32: After the solution is cooled to room temperature, concentrated sulfuric acid is added continuously with constant stirring, and then cooled to room temperature; it is then ready for use after cooling to room temperature.

[0055] The different corrosives in this comparative example were prepared according to the proportions shown in the table below by volume.

[0056] Table 1 - Corrosion agent ratio table for Comparative Example 1

[0057] Sample No. Component Ratio (volume ratio) b HF: H2SO4: HNO3 4：1：2 c HF: H2SO4: HNO3 3：1：1 d HF: H2SO4: HNO3 2：1：2 e HF: H2SO4: HNO3 2：3：2 f HF: H2SO4: HNO3 2：5：1

[0058] S4: Metallographic corrosion;

[0059] The etchant was applied to the polished surfaces of different samples by immersion, dripping, or wiping for 10–30 seconds. The samples were then rinsed with anhydrous ethanol and the polished surfaces were dried.

[0060] S5: Metallographic observation;

[0061] The polished surfaces of two samples etched with different etchants were observed using a metallographic microscope, and the resulting metallographic structures are as follows: Figures 2 to 6As shown.

[0062] In this comparative example, the components of the etchant are the same, and the raw materials and polishing methods of the samples are also the same. The difference lies in the ratio of each component in the etchant. The etchant used in samples b and c is a strong acidic composition mainly composed of hydrofluoric acid. The etchant used in sample b is the etchant formula for the metallographic structure of tantalum target material disclosed in the invention patent application number 202111446 198.2, and the etchant used in sample c is the etchant formula for the metallographic structure display method of tantalum and niobium alloy disclosed in the invention patent application number 201910156568.5. According to the published documents, it can be found that both of the above etchants can etch the polished surface of tantalum and tantalum alloy formed by conventional processes and obtain qualified, clear and complete metallographic structures. Therefore, in this comparative example, the ratios disclosed in the above two patent documents are used to verify whether the traditional etchant components can effectively etch tantalum / tantalum alloy formed by 3D printing. Figure 2 As shown, the metallographic image reveals numerous pitting corrosion pits, with no obvious grain boundaries. Figure 3 In the image, the grain boundaries are incomplete, wide, and blurry, with numerous pitting corrosion pits appearing in the middle. Obviously, the two metallographic images mentioned above cannot be used for metallographic observation, indicating that 3D-printed tantalum and tantalum alloys are different from traditionally processed products. The etchants used in traditional metallographic treatments cannot be directly applied to 3D-printed tantalum and tantalum alloys.

[0063] Furthermore, without changing the components, the ratio between the components was adjusted and experiments were conducted to obtain samples d, e, and f. Although the ratio between the three components was changed, such as... Figures 4 to 6 As shown, the problems of incomplete grain boundary manifestation and numerous pits still exist, indicating that changing the ratio alone, without altering the composition, has not yielded better technical results.

[0064] Compare with Example 2

[0065] S1: Sample grinding:

[0066] Prepare one set of samples. On a metallographic polishing machine, using water as a wetting agent, grind the samples multiple times with metallographic wet sandpaper. When the ground surface is flat, the grinding marks are in the same direction, and the grinding marks from the previous pass are completely eliminated, the grinding pass is finished. Replace with sandpaper of a larger grit and continue grinding. Before each change of sandpaper, rinse the sample and grinding disc with water to prevent the sandpaper particles from the previous pass from affecting the quality of subsequent sample preparation. During each grinding pass, the grinding mark direction is perpendicular to the grinding mark direction of the previous pass until a flat ground surface is formed. In this embodiment, 6 grinding passes are used, and the metallographic wet sandpaper grits used in each pass are 180 grit, 400 grit, 800 grit, 1600 grit, 2500 grit, and 5000 grit.

[0067] It should be noted that the sample can be tantalum or tantalum alloy. The comparative example used here is a solid cube sample formed by SLM process of tantalum metal powder. The purity of tantalum powder is ≥99.9% and the sphericity is ≥98%.

[0068] S2: Sample polishing;

[0069] The smooth surface of the sample is mechanically polished on a metallographic polishing machine using a polishing pad and diamond suspension polishing solution until the smooth surface of the sample is free of scratches and has a mirror finish. The polished surface is then rinsed with anhydrous ethanol and dried for later use.

[0070] S3: Preparation of corrosive agent;

[0071] S31: Slowly pour nitric acid into a container containing hydrofluoric acid while stirring continuously;

[0072] S32: After the solution is cooled to room temperature, concentrated sulfuric acid is added continuously with constant stirring, and then cooled to room temperature; it is then ready for use after cooling to room temperature.

[0073] The corrosive agent used in this comparative example was prepared by mixing H2O2, HF, H2SO4, and HNO3 in a volume ratio of 2:5:1:25.

[0074] S4: Metallographic corrosion;

[0075] The etchant was applied to the polished surfaces of different samples by immersion, dripping, or wiping for 10–30 seconds. The samples were then rinsed with anhydrous ethanol and dried to obtain sample g.

[0076] S5: Metallographic observation;

[0077] The polished surface of sample g was observed using a metallographic microscope, and the resulting metallographic structure is as follows: Figure 7 As shown.

[0078] contrast Figure 1 , Figure 7 It is obvious that Figure 1 It can etch distinct grain boundaries, and the interfaces are clear and unambiguous. Figure 7 In the case of the medium, almost no grain boundaries were formed by corrosion, which is obviously insufficient. According to common knowledge, water does not react with the acid mentioned above and only plays a diluting role. The large amount of water added significantly diluted the acidic composition with sulfuric acid as the main component, resulting in a low corrosion capacity of the entire corrosive system, and thus it was unable to form obvious grain boundaries.

[0079] In contrast, the corrosive agent in the examples also used the same proportions, the difference being that hydrogen peroxide, rather than water, constituted the largest proportion. Figure 1As shown, the etchant with added hydrogen peroxide can corrode clear grain boundaries, indicating that the combination of hydrogen peroxide and strong acid produces a synergistic effect, achieving effective corrosion of the difficult-to-corrode 3D-printed tantalum / tantalum alloy.

[0080] In addition, the etchant in the examples is a etchant system with hydrogen peroxide as the main component. The content of hydrogen peroxide is much higher than that of other components. In the sample preparation, a strong acid composition is added to the hydrogen peroxide, making the mixing process safer, generating less heat, and more convenient for actual use.

[0081] It should be noted that the reagents used in the above examples and control examples are all analytical grade reagents.

[0082] Finally, it should be noted that the embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for displaying the metallographic structure of tantalum and tantalum alloys by 3D printing, comprising: S1: Sample grinding, wherein the sample is tantalum or tantalum alloy; S2: Sample polishing; The sample is ground and polished on a metallographic grinding and polishing machine to form a polished surface on the sample; S3: Preparation of corrosive agent; S4: Metallographic Etching: The etchant is applied to the polished surface of the sample by means of immersion, dripping, or wiping. S5: Metallographic observation; The feature is that the sample is a solid cube specimen formed by tantalum or tantalum alloy metal powder through 3D printing technology, and the etchant is a mixture of hydrogen peroxide and a strong acid composition, wherein the content of hydrogen peroxide is 3 to 8 times the content of the strong acid composition. The strong acid composition includes: HF, H 2 SO 4 HNO3 was prepared in a volume ratio of 2:5:

1.

2. The method for metallographic display of tantalum and tantalum alloys by 3D printing according to claim 1, characterized in that: In the sample polishing step, water is used as a wetting agent, and metallographic wet sandpaper is used to polish the sample in multiple passes.

3. The method for metallographic display of tantalum and tantalum alloys by 3D printing according to claim 2, characterized in that: The sample polishing process involves six grinding passes, with each pass using metallographic wet sandpaper of grits of 180, 400, 800, 1600, 2500, and 5000.

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