A metallographic corrosion method suitable for additive manufacturing of high-strength and tough Ti-5321 alloy

Abstract

The present invention discloses a metallographic etching method for additively manufactured high-strength and tough Ti-5321 alloys, and the specific process is: firstly, the high-strength and tough Ti-5321 alloys obtained by additive manufacturing are coarsely ground and finely ground, and after polishing, a metallographic etching agent prepared by hydrofluoric acid solution, nitric acid solution, hydrogen peroxide solution and deionized water is used to etch until the polished surface changes color, and then anhydrous ethanol is used to clean and blow dry to obtain a metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy. The present invention controls the composition of the metallographic etching agent to ensure that it has a suitable corrosion rate, so that the microstructure of the metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy is clearly displayed, which can clearly display the characteristics of the inhomogeneity of the additively manufactured organization at low magnification, and can clearly and completely present the fine phases such as the ultrafine α phase in the Ti-5321 alloy after heat treatment at high magnification, so as to meet the microstructure observation under different observation magnifications.

Description

Technical Field

[0001] The invention belongs to the technical field of metallographic preparation of metal materials, and in particular relates to a metallographic corrosion method suitable for additive manufacturing of high-strength and tough Ti-5321 alloy. Background Art

[0002] Additive manufacturing technology is a technology that uses materials to add layers of materials to manufacture parts. It has the advantages of high forming efficiency, complex formed parts, small thermal deformation, a wide range of forming materials, and high cost performance. The high-strength and toughness Ti-5321 (Ti-5Al-3Mo-3V-2Zr-2Cr-1Nb-1Fe) titanium alloy prepared by additive manufacturing (laser cladding forming) technology not only has good surface morphology, but also excellent mechanical properties. It can be widely used in aerospace, military and other fields.

[0003] Since the laser cladding forming technology has the process characteristics of complex thermal cycle characteristics, fast solidification and cooling speed, the formed Ti-5321 titanium alloy microstructure has a certain degree of inhomogeneity, the edge cooling rate is fast, the structure is fine, while the center cooling rate is slow, the structure is coarse and grows along the thermal deposition direction. After heat treatment, the Ti-5321 titanium alloy will also have an ultrafine α phase with an average width of only 0.1μm. Therefore, when the alloy is observed at a lower magnification after corrosion using traditional reagents (hydrofluoric acid: nitric acid: water = 1:3:7), its microstructure will show that the corrosion degree of the center part of the sample and the edge part of the structure are inconsistent. The edge part of the structure is often over-corroded and the grain boundary and phase boundary cannot be distinguished, making it difficult to observe the complete microscopic morphology of the sample; and after heat treatment of the Ti-5321 titanium alloy, it is difficult to clearly observe the ultrafine α phase at a higher magnification. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a metallographic corrosion method suitable for additive manufacturing of high-strength and toughness Ti-5321 alloy in view of the deficiencies of the above-mentioned prior art. The metallographic etching agent used in the method has a suitable corrosion rate for additive manufacturing of high-strength and toughness Ti-5321 alloy, which can clearly show the characteristics of the inhomogeneity of the structure of additive manufacturing at low magnification, avoid the problem of unclear grain boundaries and phase boundaries caused by uneven corrosion, and make the ultrafine α phase and other fine phases in the Ti-5321 alloy after heat treatment at high magnification clearly and completely present, effectively solving the problem that the structure contrast of the additive manufacturing high-strength and toughness Ti-5321 titanium alloy is low and it is difficult to distinguish fine phases.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a metallographic corrosion method suitable for additive manufacturing of high-strength and tough Ti-5321 alloy, characterized in that the specific process of the method is: firstly, the high-strength and tough Ti-5321 alloy obtained by additive manufacturing is coarsely ground and finely ground by water-abrasive sandpaper, and after polishing, it is corroded by a metallographic corrosive agent until the polished surface changes color, and then it is cleaned and dried by anhydrous ethanol to obtain a metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy; the metallographic corrosive agent is prepared by hydrofluoric acid solution, nitric acid solution, hydrogen peroxide solution and deionized water.

[0006] The commonly used high-strength and tough titanium alloy etchant is composed of hydrofluoric acid solution, nitric acid solution and deionized water. This etchant is highly corrosive and will cause excessive corrosion or uneven corrosion to samples with uneven structures, especially alloy samples manufactured by additive manufacturing. The use of this etchant is not conducive to the complete observation of the high-strength and tough Ti-5321 alloy with uneven structure characteristics of additive manufacturing, and it is also impossible to observe the ultra-fine precipitated α phase in the high-strength and tough Ti-5321 alloy after heat treatment.

[0007] The metallographic etching agent of the present invention is prepared by hydrofluoric acid solution, nitric acid solution, hydrogen peroxide solution and deionized water. By retaining high concentrations of hydrofluoric acid and nitric acid components in the metallographic etching agent, the corrosion effect on the surface of the high-strength and tough Ti-5321 alloy for additive manufacturing is ensured, so that the microstructure is revealed; at the same time, by adding hydrogen peroxide components in the metallographic etching agent, on the one hand, the corrosion rate is controlled to avoid excessive corrosion acid concentration causing excessively fast corrosion rate, and on the other hand, although the oxidizing property of hydrogen peroxide is not enough to corrode the alloy surface, it can be used as a catalyst to promote the corrosion effect of hydrofluoric acid and nitric acid, avoiding the difficulty in distinguishing fine phases due to excessively fast or too slow corrosion rate. In addition, hydrogen peroxide also has a certain cleaning effect, can effectively remove oil stains and other stains on the alloy surface, play a role in cleaning the alloy surface, and avoid the adverse interference of stains on the microstructure observation in the alloy.

[0008] The above-mentioned metallographic etching method suitable for additive manufacturing of high-strength and tough Ti-5321 alloy is characterized in that the metallographic etching agent is prepared by hydrofluoric acid solution, nitric acid solution, hydrogen peroxide solution and deionized water in a volume ratio of 0.5-1:2-2.5:0.5-1:6-7.

[0009] The above-mentioned metallographic corrosion method suitable for additive manufacturing of high-strength and tough Ti-5321 alloy is characterized in that the mass concentration of the hydrofluoric acid solution is 35% to 40%, the mass concentration of the nitric acid solution is 65% to 70%, and the mass concentration of the hydrogen peroxide solution is 25% to 30%.

[0010] The above-mentioned metallographic corrosion method suitable for additive manufacturing of high-strength and toughness Ti-5321 alloy is characterized in that the time for corrosion until the polished surface changes color is 5s to 7s.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] 1. The method of the present invention controls the composition of the metallographic etchant to ensure that it has a suitable corrosion rate for the additively manufactured high-strength and tough Ti-5321 alloy, so that the metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy has a clear microstructure, avoids insufficient corrosion that causes the microstructure to be unable to be fully displayed, and excessive corrosion that causes fine phases to be difficult to distinguish, especially avoids the problem of uneven corrosion caused by the uneven organization of the Ti-5321 alloy formed by additive manufacturing. It can make the characteristics of the additive manufacturing organization inhomogeneity clearly appear at low magnifications, avoid the problem of unclear grain boundaries and phase boundaries caused by uneven corrosion, and make the ultrafine α phase and other fine phases in the Ti-5321 alloy after heat treatment at high magnifications clearly and completely present, meeting the microstructure observation under different observation magnifications.

[0013] 2. The corrosion process of the present invention is relatively simple and easy to implement, easier to operate and regulate, suitable for experimental exploration and industrial production, and has good production application prospects.

[0014] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a metallographic microstructure diagram of the metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy obtained in Example 1 of the present invention at a low magnification.

[0016] Figure 2 This is a metallographic microstructure diagram of the metallographic sample of the additively manufactured high-strength and toughness Ti-5321 alloy obtained in Example 1 of the present invention at a high magnification.

[0017] Figure 3 This is a metallographic microstructure diagram of the metallographic sample of the additively manufactured high-strength and toughness Ti-5321 alloy obtained in Comparative Example 1 of the present invention at a high magnification. DETAILED DESCRIPTION

[0018] Example 1

[0019] The specific process of this embodiment is: first, the high-strength and toughness Ti-5321 alloy obtained by additive manufacturing is coarsely ground and finely ground with water-abrasive sandpaper, and after polishing, it is corroded with a metallographic etchant for 5s until the polished surface changes color, and then it is cleaned and blown dry with anhydrous ethanol to obtain a metallographic sample of the high-strength and toughness Ti-5321 alloy manufactured by additive manufacturing; the metallographic etchant is prepared by a hydrofluoric acid solution with a mass concentration of 35% to 40%, a nitric acid solution with a mass concentration of 65% to 70%, a hydrogen peroxide solution with a mass concentration of 25% to 30%, and deionized water in a volume ratio of 1:2:1:6.

[0020] Figure 1 The metallographic microstructure of the metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy obtained in this embodiment at a low magnification. Figure 1 It can be seen that the uneven characteristics of the additively manufactured microstructure in the high-strength and toughness Ti-5321 alloy manufactured at low magnifications are very obvious, and the grains and grain boundaries are clear and obvious.

[0021] Figure 2 The metallographic microstructure of the metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy obtained in this embodiment at a high magnification is shown in FIG. Figure 2 It can be seen that in the microstructure of the additively manufactured high-strength and tough Ti-5321 alloy at high magnification, the ultrafine α phase with a width of only 0.1 μm is black and in the shape of tiny needles, with obvious contrast and clearly visible.

[0022] Comparative Example 1

[0023] The specific process of this comparative example is: first, the high-strength and toughness Ti-5321 alloy obtained by additive manufacturing is coarsely ground and finely ground with water-abrasive sandpaper, and after polishing, it is corroded with a metallographic corrosive agent for 7 seconds until the polished surface changes color, and then it is cleaned and blown dry with anhydrous ethanol to obtain a metallographic sample of the high-strength and toughness Ti-5321 alloy manufactured by additive manufacturing; the metallographic corrosive agent is prepared by a hydrofluoric acid solution with a mass concentration of 35%, a nitric acid solution with a mass concentration of 65%, and deionized water in a volume ratio of 1:3:7.

[0024] Figure 3 The metallographic microstructure of the metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy obtained in this comparative example at a high magnification. Figure 3 It can be seen that the microstructure of the additively manufactured high-strength and tough Ti-5321 alloy after corrosion by conventional corrosive agents at high magnifications is not obvious, and the morphology and characteristics of the ultrafine α phase cannot be clearly observed.

[0025] Will Figure 2 and Figure 3By comparison, it can be seen that the microstructure contrast and clarity of the metallographic sample of the additively manufactured Ti-5321 alloy prepared by the metallographic etching agent and etching method of the present invention are significantly better than the microstructure of the metallographic sample prepared by the traditional conventional etching agent in Comparative Example 1, indicating that the etching effect of the metallographic etching agent of the present invention is better.

[0026] Example 2

[0027] The specific process of this embodiment is: first, the high-strength and toughness Ti-5321 alloy obtained by additive manufacturing is coarsely ground and finely ground with water-abrasive sandpaper, and after polishing, it is corroded with a metallographic etchant for 6 seconds until the polished surface changes color, and then it is cleaned and blown dry with anhydrous ethanol to obtain a metallographic sample of the high-strength and toughness Ti-5321 alloy manufactured by additive manufacturing; the metallographic etchant is prepared by a hydrofluoric acid solution with a mass concentration of 35%, a nitric acid solution with a mass concentration of 65%, a hydrogen peroxide solution with a mass concentration of 25%, and deionized water in a volume ratio of 0.5:2:1:7.

[0028] After testing, the metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy obtained in this embodiment has obvious grain boundaries in the low-magnification structure, and the ultrafine α phase is clearly visible in the high-magnification structure with obvious contrast.

[0029] Example 3

[0030] The specific process of this embodiment is: first, the high-strength and toughness Ti-5321 alloy obtained by additive manufacturing is coarsely ground and finely ground with water-abrasive sandpaper, and after polishing, it is corroded with a metallographic etchant for 7 seconds until the polished surface changes color, and then it is cleaned and blown dry with anhydrous ethanol to obtain a metallographic sample of the high-strength and toughness Ti-5321 alloy manufactured by additive manufacturing; the metallographic etchant is prepared by a hydrofluoric acid solution with a mass concentration of 35%, a nitric acid solution with a mass concentration of 65%, a hydrogen peroxide solution with a mass concentration of 25%, and deionized water in a volume ratio of 1:2.5:0.5:6.

[0031] After testing, the metallographic sample of the additively manufactured high-strength and tough Ti-5321 alloy obtained in this embodiment has obvious grain boundaries in the low-magnification structure, and the ultrafine α phase is clearly visible in the high-magnification structure with obvious contrast.

[0032] 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 corrosion method suitable for additive manufacturing of high-strength and tough Ti-5321 alloy, It is characterized in that The specific process of the method is: firstly, the high-strength and toughness Ti-5321 alloy obtained by additive manufacturing is coarsely ground and finely ground by using water-abrasive sandpaper, and after polishing, it is corroded by using a metallographic corrosive agent until the polished surface changes color, and then it is cleaned and blown dry by using anhydrous ethanol to obtain a metallographic sample of the high-strength and toughness Ti-5321 alloy manufactured by additive manufacturing; the metallographic corrosive agent is prepared by hydrofluoric acid solution, nitric acid solution, hydrogen peroxide solution and deionized water according to a volume ratio of 0.5-1:2-2.5:0.5-1:6-7, the mass concentration of the hydrofluoric acid solution is 35%-40%, the mass concentration of the nitric acid solution is 65%-70%, and the mass concentration of the hydrogen peroxide solution is 25%-30%; the time for corroding until the polished surface changes color is 5s-7s.

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