Method for preparing high-gloss titanium alloy

Abstract

The invention discloses a method for preparing a high-gloss titanium alloy, and belongs to the field of powder metallurgy. The preparation method comprises the following steps: firstly, taking Ti-6Al-4V and Ti-6Al-4V-0.5 Fe powder as raw materials, and carrying out pressing or injection molding to obtain a green body; then, the green body sample is subjected to degreasing and pressureless vacuum sintering to obtain a titanium alloy sintered sample, and the sintered sample is subjected to surface nitriding modification and precise polishing treatment; finally, the surface glossiness of the titanium alloy nitrided for 1 hour reaches 607 + / -5 Gu, the microhardness reaches 705 + / -88 HV1.0, and the roughness is lower than 0.041 [mu] m. By adding a trace amount of Fe element (0.5 wt.%) and liquid phase sintering to refine grains and reduce pores, nitriding treatment is performed after sintering to form an extremely thin and compact titanium nitride layer, and then multi-stage precision polishing is matched, so that the surface hardness is improved, the roughness is remarkably reduced, the glossiness is improved, and the method has the characteristics of simple process, economy, high efficiency, suitability for large scale and the like.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, and particularly relates to a method for preparing high-gloss titanium alloys. Background Technology

[0002] Ti-6Al-4V (TC4 titanium alloy) possesses advantages such as high specific strength, good biocompatibility, excellent corrosion resistance, and comprehensive mechanical properties, making it widely used in aerospace, biomedicine, marine chemical, and 3C product fields. However, due to the high deformation resistance, poor room-temperature plasticity, and high high-temperature activity of TC4 titanium alloy, it is difficult to process. Traditional forming methods (casting, forging, machining, etc.) suffer from low efficiency, high cost, and material waste when processing it. Powder metallurgy near-net-shape forming technologies such as metal powder injection molding and compression molding can directly form complex-shaped titanium alloys, featuring low cost, short process, and environmental friendliness, enabling low-cost preparation of titanium alloys. Polishing is the final process applied to powder metallurgy titanium alloy exterior parts (such as 3C products), and the microstructure of the titanium alloy surface determines the final gloss and mirror effect. However, when TC4 titanium alloy is prepared using powder near-net-shape forming technology (such as injection molding), its microstructure is usually a lath Widmanstätten structure. During the polishing process, residual stress caused by dislocation accumulation is easily generated at the lath interface, which aggravates the interference effect and diffuse scattering of light of a specific wavelength, ultimately leading to a reduction in the gloss of the titanium alloy, making it unsuitable for use in consumer electronics exterior parts and other components.

[0003] Traditional powder metallurgy-prepared Ti-6Al-4V titanium alloys, due to their lath Widmanstätten microstructure, are prone to residual stress at the lath interfaces during polishing, resulting in severe light scattering and low gloss, making it difficult to meet the high gloss requirements of consumer electronics and other surface-mount components. Although some existing technologies (such as nitriding and polishing) are used to improve surface properties, they have not systematically solved the problem of synergistically improving the surface gloss and hardness of powder metallurgy titanium alloys.

[0004] Therefore, there is an urgent need to develop a method that takes into account the microstructure, surface quality, and hardness of titanium alloy surfaces, thereby improving the surface gloss after polishing. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing high-gloss titanium alloys. This invention uses injection molding or compression molding to prepare high-gloss titanium alloys, resulting in a microstructure suitable for polishing, significantly improving surface quality and hardness. This method is simple, economical, efficient, and suitable for large-scale production.

[0006] This invention provides a method for preparing high-gloss titanium alloys, characterized by the following steps: Step 1a: The raw material powder is pressed into shape to obtain a pressed green body; Step 1b: Mix the raw material powder with the binder, knead and then extrude to obtain granular feed, and perform injection molding on the granular feed to obtain injection green body; The nominal composition of the titanium alloy is mainly Ti-6Al-4V and Ti-6Al-4V-0.5Fe, and the raw material powder is hydrogenated dehydrogenated powder; The Ti-6Al-4V powder has a particle size of 15–53 μm and an oxygen content of less than 1600 ppm; Step 2: Catalytically degrease the pressed or injected green body to obtain a degreased green body; Step 3: Sinter the degreased blank; Step 4: Perform atmospheric nitriding modification and surface precision polishing on the sintered sample.

[0007] Furthermore, when pressing and forming the powder using a hydraulic press in step 1a, the powder needs to be compacted and spread throughout the mold cavity. The hydraulic press pressure should be maintained at 450-500 MPa, and the holding time should be maintained at 12-13 seconds.

[0008] Further, in step 1b, the premixing is carried out in a V-type mixer for 4-8 hours at a speed of 140-160 r / min; the internal mixing temperature is 180-190℃ for 1-3 hours; the binder is selected from at least one of polyoxymethylene, polyethylene, stearic acid, and ethylene-vinyl acetate copolymer; the titanium alloy powder accounts for 58 vol.%-64 vol.% of the total volume; the injection temperature is 180-190℃, the injection pressure is 180-195 bar, the injection speed is 60-80%, the injection mold is a stretching strip mold, and the circulating oil temperature is 120-130℃.

[0009] Furthermore, the catalytic degreasing is oxalic acid catalytic degreasing, at a temperature of 100–150°C, for a time of 8–12 hours.

[0010] Further, the sintering in step 3 involves: heating to 200–250°C, 400–500°C, and 550–600°C at a rate of 1.5–3°C / min, holding at these temperatures for 0.5–1.5 h; heating to 1250–1350°C at a rate of 3–10°C / min, holding at these temperatures for 1–3 h; and maintaining a vacuum of 0.01 Pa during the vacuum pressureless sintering process, followed by furnace cooling to room temperature.

[0011] Furthermore, the atmosphere nitriding modification process is as follows: the sintered product is heated to 900-1000℃ in a tube furnace at a rate of 5-10℃ / min and held for 1-3 hours; high-purity nitrogen (>99.99%) is circulated throughout the heating process; during the cooling process, high-purity argon (>99.99%) is switched to cool the furnace to room temperature at a flow rate of 1.0 L / min.

[0012] Furthermore, the surface precision polishing process includes three steps: roughing, intermediate polishing, and fine polishing. Roughing: using sandpaper or sanding belt to efficiently remove rough skin, cutting marks, and burrs from the surface. Intermediate polishing: using a sisal wheel to remove the processing texture formed by roughing. Fine polishing: using a buffing wheel and polishing wax to completely eliminate the fine scratches left by intermediate polishing, so that the surface achieves a mirror or high-gloss effect.

[0013] In a preferred embodiment, the particle size of the raw material powder is 15–53 μm, preferably 28.4 μm; Preferably, the Fe raw material powder is high-purity iron powder with a purity ≥99.9%.

[0014] In a preferred embodiment, in step 2, the catalytic degreasing is oxalic acid-catalyzed degreasing; In the technical solution of the present invention, polyoxymethylene can be fully removed by catalytic degreasing.

[0015] The key technical point of this invention is: 1. By adding trace amounts of Fe (0.5 wt.%), the grains are refined and the porosity is reduced by utilizing the liquid phase sintering mechanism, providing a more uniform and dense matrix for subsequent nitriding and polishing.

[0016] 2. After sintering, nitriding is performed to form an extremely thin and dense titanium nitride layer (which improves the problems caused by the lath Widmanstätten structure). Combined with multi-stage precision polishing, not only is the surface hardness improved, but the roughness is also significantly reduced and the gloss is improved.

[0017] 3. The data from the examples show that the effect is significant: after nitriding for 1 hour, the surface gloss of the titanium alloy reached 607±5 Gu (an improvement of about 30% compared to 462 Gu), the microhardness reached 705±88 HV (an improvement of about 60% compared to 448±59 HV), and the roughness was less than 0.041 μm (an improvement of about 20% compared to 0.051 μm).

[0018] Therefore, this invention possesses outstanding substantive features and technological advancements in terms of process combination, material design, and performance synergy. The method of this invention is not only applicable to Ti-6Al-4V and Ti-6Al-4V-0.5Fe alloys, but those skilled in the art can also select titanium alloy raw materials with different compositions according to actual needs. By changing technical parameters such as injection temperature, injection pressure, and sintering temperature, different sintered products can be produced. Subsequently, the sintered products undergo surface nitriding modification. The modified products, combined with subsequent precision polishing, can also synergistically improve surface quality and surface hardness.

[0019] The present invention has the following beneficial effects: 1. By doping with Fe and sintering powder under pressureless vacuum, the liquid phase sintering mechanism is utilized to significantly refine the grains, reduce porosity, and improve the matrix structure.

[0020] 2. A synergistic process of "surface nitriding + precision polishing" is employed to achieve high surface hardness, high gloss, and low roughness. Specifically, after nitriding for 1 hour, the surface gloss reaches 607±5 Gu, and the microhardness reaches 705±88 HV. 1.0 Roughness is less than 0.041 μm.

[0021] 3. The titanium alloy prepared by this invention can achieve a near-mirror finish after polishing. It features simple processing, low cost, and mass production capability, and can be applied on a large scale in fields such as 3C consumer electronics. Attached Figure Description

[0022] Figure 1 These are scanning electron microscope images and particle size distribution diagrams of Ti-6Al-4V powder in Example 1 of this invention.

[0023] Figure 2 This is a scanning electron microscope image of the metallographic structure of the sample sintered at 1300℃ for 2 hours in Example 1 of this invention.

[0024] Figure 3 This is a scanning electron microscope image of the polished surface morphology of the sample sintered at 1300℃ for 2 hours in Example 1 of this invention.

[0025] Figure 4 This is a color change diagram of the un-nitrided and nitrided (1h-3h) processes in this invention. Detailed Implementation

[0026] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0028] Example 1

[0029] The preparation method of this embodiment includes the following steps: Step 1: Prepare 2 kg of Ti-6Al-4V raw material powder, the specific composition of which, by mass percentage, includes: Al: 5.94 wt.%, V: 3.90 wt.%, with the balance being Ti; premix the above-mentioned raw material powder with high-purity iron powder in a V-type mixer for 5 h at 150 r / min to obtain Ti-6Al-4V-0.5Fe raw material powder; the Ti-6Al-4V-0.5Fe raw material powder, by mass percentage, includes: Al: 5.94 wt.%, V: 3.90 wt.%, Fe: 0.5 wt.%, with the balance being Ti; in this embodiment, the particle size of the raw material powder is 28.4 μm, and the oxygen content is less than 1600 ppm; the Ti-6Al-4V raw material powder is all hydrogenated dehydrogenated powder.

[0030] Step 2: Ti-6Al-4V raw material powder and Ti-6Al-4V-0.5Fe raw material powder are pressed into compacted green bodies using a hydraulic press. During pressing, the raw material powder is vibrated to fill the mold cavity. The pressing pressure is 500 MPa, and the holding time is 12–13 s. Ti-6Al-4V raw material powder and binder (polyoxymethylene) are premixed in a V-type mixer for 30 min, with Ti-6Al-4V raw material powder accounting for 58 vol.%–64 vol.% of the total volume of Ti-6Al-4V raw material powder and binder. The mixed powder is then kneaded in an internal mixer for 2 h, followed by extrusion granulation to obtain feedstock with a particle size of 2–4 mm. The mixing temperature is 185℃. The resulting feedstock is then injection molded using an injection molding machine and a stretching strip injection mold: the injection temperature is 185℃, the injection pressure is 190 bar, the injection speed is 70%, and the circulating oil temperature is 130℃.

[0031] Step 3: Place the pressed green billet and the stretched green billet into the oxalic acid degreasing furnace for degreasing. The temperature of the oxalic acid degreasing furnace is 135℃ and the degreasing time is 9 hours to fully remove the binder.

[0032] Step 4: Sinter the degreased products separately: Place the degreased blanks into a high vacuum sintering furnace for vacuum pressureless degreasing sintering to obtain sintered samples. The sintering process is as follows: heat at a rate of 2.5℃ / min, hold at three plateaus of 250℃, 450℃, and 550℃ for 1 h each; finally, heat to 1300℃ at a rate of 5℃ / min and hold for 2 h; the vacuum degree of sintering is 0.01Pa; finally, cool to room temperature with the furnace to obtain titanium alloy samples.

[0033] Step 5: Perform precision surface polishing on the sintered sample, including roughing (using sandpaper to efficiently remove rough skin, cutting marks and burrs from the surface), medium polishing (using a sisal wheel to remove the processing texture formed by roughing), and fine polishing (using a buffing wheel and polishing wax to completely eliminate the fine scratches left by medium polishing).

[0034] The surface gloss of the titanium alloy sample from step five was tested using a YH4372-T micro-orifice gloss meter and a Taylor Hobson roughness tester, respectively. The hardness was also tested using a VTD 512 micro Vickers hardness tester. The load test force was 1000g, and the holding time was 15s. The surface gloss of the pressed Ti-6Al-4V titanium alloy was 462 Gu, and the microhardness reached 448±59 HV. 1.0 The surface roughness is 0.050 μm. The surface gloss of the pressed Ti-6Al-4V-0.5Fe titanium alloy is 479 Gu, and the microhardness reaches 465±60 HV. 1.0 The surface roughness is 0.048 μm. The surface gloss of the injection-molded Ti-6Al-4V titanium alloy is 453 Gu, and the microhardness reaches 512±59 HV. 1.0 Roughness 0.055 μm.

[0035] The sample from step five was sanded from coarse to fine using 240 to 3000 grit sandpaper, and then polished using a PG-1A polishing machine. Finally, the sample was rubbed and etched for 30 to 60 seconds using Kroll reagent (hydrofluoric acid: concentrated nitric acid: water volume ratio of 1:3:15 to 30).

[0036] Figure 1 The image shows the Ti-6Al-4V powder used in this embodiment; in the figure, (a) is a scanning electron microscope image; and (b) is a particle size distribution diagram.

[0037] Figure 2The images shown are scanning electron microscope (SEM) images of the metallographic structure of the sample sintered at 1300℃ for 2 hours in this embodiment. In the images, (a) shows pressed Ti-6Al-4V; (b) shows pressed Ti-6Al-4V-0.5Fe; and (c) shows injection-molded Ti-6Al-4V. It can be seen that the pressed Ti-6Al-4V and Ti-6Al-4V-0.5Fe, through the introduction of Fe, reduce their porosity and refine their grain size. Compared to pressed Ti-6Al-4V, injection-molded Ti-6Al-4V... Wider and nascent Larger grain size.

[0038] Figure 3 The images shown are scanning electron microscope (SEM) images of the polished surface morphology of the samples sintered at 1300℃ for 2 hours in this embodiment. In the images, (a) shows the pressed Ti-6Al-4V sample; (b) shows the pressed Ti-6Al-4V-0.5Fe sample; and (c) shows the injection-molded Ti-6Al-4V sample. It can be seen that the surface of the pressed Ti-6Al-4V-0.5Fe sample with added Fe is smoother than the other two Ti-6Al-4V samples. Furthermore, the surface roughness of the pressed Ti-6Al-4V sample after direct polishing is lower than that of the injection-molded Ti-6Al-4V sample.

[0039] Example 2

[0040] The preparation method in this embodiment is the same as in Example 1, except that a nitriding modification treatment is performed after sintering in step four. The process is as follows: The sintered product was heated to 950°C in a tube furnace at a rate of 5°C / min and held for 1 hour. High-purity nitrogen (>99.99%) was purged throughout the heating process. During the cooling process, high-purity argon (>99.99%) was purged to room temperature at a flow rate of 1.0 L / min.

[0041] Tests showed that the pressed Ti-6Al-4V titanium alloy had a surface gloss of 606 Gu and a microhardness of 733±66 HV. 1.0 The surface roughness is 0.039 μm. The surface gloss of the pressed Ti-6Al-4V-0.5Fe titanium alloy is 613 Gu, and the microhardness reaches 549±34 HV. 1.0 The surface roughness is 0.038 μm. The surface gloss of the injection-molded Ti-6Al-4V titanium alloy is 602 Gu, and the microhardness reaches 629±76 HV. 1.0 Roughness 0.041 μm.

[0042] Example 3

[0043] The preparation method in this embodiment is the same as in Example 2, except that the heat preservation time in the nitriding modification treatment is 2 h.

[0044] Tests showed that the pressed Ti-6Al-4V titanium alloy had a surface gloss of 561 Gu and a microhardness of 930±87 HV. 1.0 The surface roughness is 0.048 μm. The surface gloss of the pressed Ti-6Al-4V-0.5Fe titanium alloy is 572 Gu, and the microhardness reaches 894±67 HV. 1.0 The surface roughness is 0.044 μm. The surface gloss of the injection-molded Ti-6Al-4V titanium alloy is 557 Gu, and the microhardness reaches 850±121 HV. 1.0 Roughness 0.052 μm.

[0045] Example 4

[0046] The preparation method in this embodiment is the same as in embodiment 2, except that the heat preservation time in the modification treatment is 3 h.

[0047] Tests showed that the pressed Ti-6Al-4V titanium alloy had a surface gloss of 544 Gu and a microhardness of 949±71 HV. 1.0 The surface roughness is 0.051 μm. The surface gloss of the pressed Ti-6Al-4V-0.5Fe titanium alloy is 551 Gu, and the microhardness reaches 905±70 HV. 1.0 The surface roughness is 0.049 μm. The surface gloss of the injection-molded Ti-6Al-4V titanium alloy is 542 Gu, and the microhardness reaches 962±71 HV. 1.0 Roughness 0.056 μm.

[0048] In Examples 1-4, the test results show that for Ti-6Al-4V-0.5Fe titanium alloy, both nitrided and unnitrided alloys exhibit higher surface gloss and microhardness compared to Ti-6Al-4V titanium alloy, while showing significantly lower surface roughness. This indicates that adding trace amounts of Fe (0.5 wt.%) and utilizing a liquid-phase sintering mechanism to refine grains and reduce porosity effectively improves the surface gloss and microhardness, and reduces surface roughness. Furthermore, subsequent nitriding and polishing of the sintered titanium alloy further enhances its surface gloss and microhardness, while reducing surface roughness. Comparatively, Examples 2-4 demonstrate that the nitriding time significantly impacts the surface gloss and microhardness, as well as the reduction of surface roughness. A nitriding time of 1 hour yields the best results; further increases in nitriding time lead to excessively high surface hardness, negatively affecting subsequent polishing.

[0049] Color change diagram of Ti-6Al-4V after nitriding for 1-3 h in compression molding is shown below. Figure 4 As can be seen from the figure: the unnitrided sample appears silvery-white with a metallic luster; after nitriding for 1 hour, a very thin and dense layer of titanium nitride is formed, turning golden yellow; after nitriding for 2 hours, the compound layer on the surface thickens and turns brown again; after nitriding for 3 hours, the compound layer on the surface continues to thicken and finally turns gray.

[0050] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-gloss titanium alloy, characterized in that, The specific steps are as follows: Step 1a: The raw material powder is pressed into shape to obtain a pressed green body; Step 1b: Mix the raw material powder with the binder, knead and then extrude to obtain granular feed, and perform injection molding on the granular feed to obtain injection green body; The nominal composition of the titanium alloy is mainly Ti-6Al-4V and Ti-6Al-4V-0.5Fe, and the raw material powder is hydrogenated dehydrogenated powder; The Ti-6Al-4V powder has a particle size of 15–53 μm and an oxygen content of less than 1600 ppm; Step 2: Catalytically degrease the pressed or injected green body to obtain a degreased green body; Step 3: Sinter the degreased blank; Step 4: Perform atmospheric nitriding modification and surface precision polishing on the sintered sample.

2. The method for preparing a high-gloss titanium alloy according to claim 1, characterized in that, When pressing and forming the powder using a hydraulic press in step 1a, the powder needs to be compacted and spread throughout the mold cavity. The hydraulic press pressure should be maintained at 450-500 MPa, and the holding time should be maintained at 12-13 seconds.

3. The method for preparing a high-gloss titanium alloy according to claim 1, characterized in that, In step 1b, the premixing is carried out in a V-type mixer for 4-8 hours at a speed of 140-160 r / min; the internal mixing temperature is 180-190℃ for 1-3 hours; the binder is selected from at least one of polyoxymethylene, polyethylene, stearic acid, and ethylene-vinyl acetate copolymer; the titanium alloy powder accounts for 58 vol.%-64 vol.% of the total volume; the injection temperature is 180-190℃, the injection pressure is 180-195 bar, the injection speed is 60-80%, the injection mold is a stretching strip mold, and the circulating oil temperature is 120-130℃.

4. The method for preparing a high-gloss titanium alloy according to claim 1, characterized in that, The catalytic degreasing in step 2 is oxalic acid catalytic degreasing, at a temperature of 100-150℃ for 8-12 hours.

5. The method for preparing a high-gloss titanium alloy according to claim 1, characterized in that, The sintering process described in step 3 involves heating at 1.5–3 °C / min to 200–250 °C, 400–500 °C, and 550–600 °C, and holding at these temperatures for 0.5–1.5 h; heating at 3–10 °C / min to 1250–1350 °C and holding at these temperatures for 1–3 h; the vacuum degree during the vacuum pressureless sintering process is 0.01 Pa, and the furnace is cooled to room temperature.

6. The method for preparing a high-gloss titanium alloy according to claim 1, characterized in that, The atmosphere nitriding modification process is as follows: the sintered product is heated to 900-1000℃ in a tube furnace at a rate of 5-10℃ / min and held for 1-3 hours; high-purity nitrogen (>99.99%) is circulated throughout the heating process; during the cooling process, high-purity argon (>99.99%) is switched to cool the furnace to room temperature at a flow rate of 1.0 L / min.

7. The method for preparing a high-gloss titanium alloy according to claim 1, characterized in that, The surface precision polishing process includes three steps: roughing, intermediate polishing, and fine polishing. Roughing: Use sandpaper or sanding belt to efficiently remove rough skin, cutting marks and burrs from the surface; Medium polishing: Use a burr wheel to remove the processing texture formed by roughing; Fine polishing: Use a buff wheel and polishing wax to completely eliminate the fine scratches left by medium polishing, so that the surface achieves a mirror or high gloss effect.

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