Method for preparing high-gloss titanium alloy

Abstract

The invention discloses a method for preparing a high-gloss titanium alloy, and belongs to the technical field of powder metallurgy. The method comprises the steps that raw material powder of Ti-6Al-4V or Ti-6Al-4V-0.5 Fe is subjected to pressing forming, and a pressed green body is obtained; or mixing the raw material powder with a binder, banburying, and extruding to obtain particle feed; performing injection molding on the granular feed to obtain an injection green body; performing catalytic degreasing on the pressed green body or the injected green body to obtain a degreased green body; and sintering the degreased blank. The titanium alloy prepared through the method can achieve the effect similar to a mirror surface after being polished, has the characteristics of being simple in process, low in cost, capable of being produced in batches and the like, and can be applied to the fields of 3C consumer electronics and the like on a large scale.

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, its processing is difficult. 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] 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 gloss of their polished surfaces. Summary of the Invention

[0004] 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, which significantly improves surface quality and hardness. This method is simple, economical, efficient, and suitable for large-scale production.

[0005] This invention provides a method for preparing high-gloss titanium alloys, comprising the following steps:

[0006] Step 1a: The raw material powder is pressed into shape to obtain a pressed green body;

[0007] or,

[0008] Step 1b: Mix the raw material powder with the binder, knead and then extrude to obtain granular feed; perform injection molding on the granular feed to obtain injection preform;

[0009] The composition of the raw material powder is selected from any of the following by mass percentage:

[0010] ①Al: 5.50~6.75wt.%, V: 3.50~4.50wt.%, balance being Ti and unavoidable impurities;

[0011] ②Al: 5.50–6.75 wt.%, V: 3.50–4.50 wt.%, Fe: 0.45–0.55 wt.%, with the balance being Ti and unavoidable impurities;

[0012] Step 2: Catalytically degrease the pressed or injected green body to obtain a degreased green body;

[0013] Step 3: Sinter the degreased blank.

[0014] In the technical solution of the present invention, the nominal composition of the titanium alloy is Ti-6Al-4V or Ti-6Al-4V-0.5Fe; wherein, the raw material powder of Ti-6Al-4V-0.5Fe can be obtained by mixing the raw material powder of Ti-6Al-4V with iron powder; the mixing is carried out in a V-type mixer; the mixing time is 4 to 8 hours and the rotation speed is 140 to 160 r / min.

[0015] In a preferred embodiment, the particle size of the raw material powder is 15-53 μm, preferably 28.4 μm;

[0016] Preferably, the oxygen content of the raw material powder is less than 1600 ppm;

[0017] Preferably, the raw material powders of Ti, Al, and V are hydrogenated dehydrogenated powders;

[0018] Preferably, the Fe raw material powder is high-purity iron powder with a purity ≥ 99.9%.

[0019] In a preferred embodiment, in step 1a, the pressing pressure is 450-500 MPa, and the holding time is 12-13 s.

[0020] In a preferred embodiment, in step 1b, the mixing temperature is 180–190°C and the time is 1–3 hours.

[0021] In a preferred embodiment, in step 1b, the adhesive is selected from at least one of polyoxymethylene, polyethylene, stearic acid, and ethylene-vinyl acetate copolymer;

[0022] Preferably, the volume of the raw material powder is 58 vol.% to 64 vol.% of the total volume of the raw material powder and the binder.

[0023] In a preferred embodiment, in step 1b, the injection temperature is 180–190°C, the injection pressure is 180–195 bar, the injection speed is 60–80%, and the circulating oil temperature is 120–130°C.

[0024] In a preferred embodiment, in step 2, the catalytic degreasing is oxalic acid-catalyzed degreasing;

[0025] Preferably, the catalytic degreasing temperature is 100–150°C and the time is 8–12 hours;

[0026] In a preferred embodiment, step 3, the sintering process includes the following steps:

[0027] Stage ①: Heat to 200-250℃ and hold for 0.5-1 hour;

[0028] Stage ②: Heat to 400-500℃ and hold for 1-1.5 hours;

[0029] Stage ③: Heat to 550-600℃ and hold for 1-1.5 hours;

[0030] Stage 4: Raise the temperature to 1250-1350℃ and hold for 1-3 hours;

[0031] Preferably, the sintering is vacuum sintering;

[0032] Preferably, the heating rate of stages ① to ③ is 1.5 to 3 °C / min;

[0033] Preferably, the heating rate in stage ④ is 3–10 °C / min;

[0034] In some specific embodiments, the sintering is followed by furnace cooling to room temperature.

[0035] In a preferred embodiment, a nitriding modification treatment is further included; the nitriding modification treatment includes:

[0036] The sintered product is heat-treated in a nitrogen atmosphere.

[0037] Preferably, the temperature of the heat treatment is 900–1000°C;

[0038] Preferably, the heating rate of the heat treatment is 5–10 °C / min;

[0039] Preferably, the heat treatment holding time is 1 to 3 hours;

[0040] Preferably, the heat treatment includes cooling to room temperature in an inert atmosphere, wherein the inert atmosphere is nitrogen.

[0041] In a preferred embodiment, the method further includes a precision polishing operation on the sintered product or the product after nitriding modification.

[0042] The present invention has the following beneficial effects:

[0043] 1. This invention utilizes Fe element doping and pressureless vacuum sintering of powder to greatly promote material migration and porosity elimination, and significantly refines grain size by employing a liquid phase sintering mechanism.

[0044] 2. This invention further modifies the sintered product by surface nitriding. The modified product, combined with subsequent precision polishing, synergistically improves surface quality and surface hardness; 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.

[0045] 3. The titanium alloy prepared by this invention can achieve a near-mirror finish after polishing. It features simple process, low cost, and mass production capability, and can be applied on a large scale in fields such as 3C consumer electronics. Attached Figure Description

[0046] Figure 1 These are scanning electron microscope images and particle size distribution diagrams of Ti-6Al-4V powder in Example 1 of this invention.

[0047] 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.

[0048] 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.

[0049] Figure 4 This is a color change diagram of the un-nitrided and nitrided (1h-3h) processes in this invention. Detailed Implementation

[0050] 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.

[0051] 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.

[0052] Example 1

[0053] The preparation method of this embodiment includes the following steps:

[0054] 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 and unavoidable impurities; premix the above-mentioned raw material powder with high-purity iron powder in a V-type mixer for 5 hours 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 and unavoidable impurities; 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.

[0055] Step 2: Use a hydraulic press to press Ti-6Al-4V raw material powder and Ti-6Al-4V-0.5Fe raw material powder into pressed green blanks. During the pressing process, the raw material powder needs to be vibrated and spread to fill the mold cavity. The pressing pressure is 500MPa and the holding time is 12-13s.

[0056] Ti-6Al-4V raw material powder and binder (polyoxymethylene) were premixed in a V-type mixer for 30 min. The Ti-6Al-4V raw material powder accounted for 58 vol.% to 64 vol.% of the total volume of Ti-6Al-4V raw material powder and binder. The mixed powder was kneaded in an internal mixer for 2 h, and then extruded and granulated to obtain feedstock with a particle size of 2 to 4 mm. The mixing temperature was 185℃. The obtained feedstock was injection molded using an injection molding machine and a stretch strip injection mold to obtain stretch strip green body. The injection temperature was 185℃, the injection pressure was 190 bar, the injection speed was 70%, and the circulating oil temperature was 130℃.

[0057] 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.

[0058] Step four: 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: At a heating rate of 2.5℃ / min, hold at three plateaus of 250℃, 450℃, and 550℃ for 1 hour each; finally, heat to 1300℃ at 5℃ / min and hold for 2 hours; the vacuum degree of sintering is 0.01Pa; finally, cool to room temperature with the furnace to obtain titanium alloy samples.

[0059] 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).

[0060] 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 0.055μm.

[0061] 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.

[0062] The titanium alloy sample from step four was polished from coarse to fine using 240 to 3000 grit sandpaper, and then polished using a PG-1A polishing machine. Finally, the sample was etched with Kroll reagent (hydrofluoric acid: concentrated nitric acid: water volume ratio of 1:3:15-30) for 30-60 seconds, and the metallographic structure of the obtained sample surface was observed. Figure 2 These are scanning electron microscope (SEM) images of the metallographic structure of the samples 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, have reduced porosity and refined grain size. Compared with pressed Ti-6Al-4V, injection-molded Ti-6Al-4V has wider α laths and larger primary β grains.

[0063] Figure 3These are scanning electron microscope (SEM) images of the polished surface morphology of the samples obtained in step five of this embodiment. In the figures, (a) shows the pressed Ti-6Al-4V; (b) shows the pressed Ti-6Al-4V-0.5Fe; and (c) shows the injection-molded Ti-6Al-4V. It can be seen that the surface of the pressed Ti-6Al-4V-0.5Fe with added Fe is smoother than the other two Ti-6Al-4V samples. At the same time, the surface roughness of the pressed Ti-6Al-4V sample after direct polishing is lower than that of the injection-molded Ti-6Al-4V.

[0064] Example 2

[0065] 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:

[0066] 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.

[0067] 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 0.041μm.

[0068] Example 3

[0069] 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 hours.

[0070] 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 0.052μm.

[0071] Example 4

[0072] 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 hours.

[0073] 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 0.056μm.

[0074] The color change diagrams of unnitrided and nitrided Ti-6Al-4V pressed products for 1-3 hours in Examples 1-4 are 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.

[0075] 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, Includes the following steps: Step 1a: The raw material powder is pressed into shape to obtain a pressed green body; or, Step 1b: Mix the raw material powder with the binder, knead and then extrude to obtain granular feed; perform injection molding on the granular feed to obtain injection preform; The composition of the raw material powder is selected from any of the following by mass percentage: ①Al: 5.50~6.75wt.%, V: 3.50~4.50wt.%, balance being Ti and unavoidable impurities; ②Al: 5.50–6.75 wt.%, V: 3.50–4.50 wt.%, Fe: 0.45–0.55 wt.%, with the balance being Ti and unavoidable impurities; Step 2: Catalytically degrease the pressed or injected green body to obtain a degreased green body; Step 3: Sinter the degreased blank.

2. The method according to claim 1, characterized in that, The particle size of the raw material powder is 15-53 μm, preferably 28.4 μm; Preferably, the oxygen content of the raw material powder is less than 1600 ppm; Preferably, the raw material powders of Ti, Al, and V are hydrogenated dehydrogenated powders; Preferably, the Fe raw material powder is high-purity iron powder with a purity ≥ 99.9%.

3. The method according to claim 1, characterized in that, In step 1a, the pressing pressure is 450-500 MPa, and the holding time is 12-13 s.

4. The method according to claim 1, characterized in that, In step 1b, the mixing temperature is 180–190°C, and the time is 1–3 hours.

5. The method according to claim 1, characterized in that, In step 1b, the adhesive is selected from at least one of polyoxymethylene, polyethylene, stearic acid, and ethylene-vinyl acetate copolymer; Preferably, the volume of the raw material powder is 58 vol.% to 64 vol.% of the total volume of the raw material powder and the binder.

6. The method according to claim 1, characterized in that, In step 1b, the injection temperature is 180–190°C, the injection pressure is 180–195 bar, the injection speed is 60–80%, and the circulating oil temperature is 120–130°C.

7. The method according to claim 1, characterized in that, In step 2, the catalytic degreasing is oxalic acid-catalyzed degreasing; Preferably, the catalytic degreasing temperature is 100–150°C and the time is 8–12 hours.

8. The method according to claim 1, characterized in that, In step 3, the sintering process includes the following steps: Stage ①: Heat to 200-250℃ and hold for 0.5-1 hour; Stage ②: Heat to 400-500℃ and hold for 1-1.5 hours; Stage ③: Heat to 550-600℃ and hold for 1-1.5 hours; Stage 4: Raise the temperature to 1250-1350℃ and hold for 1-3 hours; Preferably, the sintering is vacuum sintering; Preferably, the heating rate of stages ① to ③ is 1.5 to 3 °C / min; Preferably, the heating rate in stage ④ is 3–10 °C / min.

9. The method according to claim 1, characterized in that, It also includes nitriding modification treatment; the nitriding modification treatment includes: The sintered product is heat-treated in a nitrogen atmosphere. Preferably, the temperature of the heat treatment is 900–1000°C; Preferably, the heating rate of the heat treatment is 5–10 °C / min; Preferably, the heat treatment holding time is 1 to 3 hours; Preferably, the heat treatment includes cooling to room temperature in an inert atmosphere, wherein the inert atmosphere is nitrogen.

10. The method according to any one of claims 1-9, characterized in that, It also includes precision polishing of sintered or nitrided products.

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