High-fluidity Ti-6Al-4V alloy particle feed and preparation method thereof

Abstract

The invention belongs to the technical field of metal material preparation, and discloses a high-fluidity Ti-6Al-4V alloy particle feed and a preparation method thereof. The feed is formed by compounding 85%-92% vol of spherical Ti-6Al-4V alloy powder and 8%-15% vol of a multi-component binder containing a platinum-titanium dioxide catalyst, and low-temperature catalytic degreasing, gradient thermal degreasing and presintering are completed in a single continuous period in cooperation with a catalysis-gradient integrated heat treatment process. Through systematic innovation of feeding component design, catalyst integration and a heat treatment system, an efficient, clean and low-deformation Ti-6Al-4V metal injection molding technical path is constructed, and the inherent contradiction between degreasing thoroughness and material purity in the prior art is fundamentally solved; and technical support is provided for large-scale and high-reliability manufacturing of high-end titanium alloy precision parts.

Description

Technical Field

[0001] This invention belongs to the field of metal material preparation technology, and relates to the feeding of high-flowability Ti-6Al-4V alloy particles and its preparation method. Background Technology

[0002] Metal injection molding (MIM) technology has been widely used in the automotive, aerospace, and high-end electronics industries due to its ability to produce high-performance metal parts with complex geometries near-net-shapes. Especially for difficult-to-machine materials like titanium alloys, MIM demonstrates significant advantages in achieving lightweighting and structural integration. Among these, Ti-6Al-4V alloy, as the most widely used α+β type titanium alloy, is widely used in manufacturing critical structural components with extremely stringent reliability and service life requirements, such as gears, bearing housings, and electronic control unit housings in transmission systems, thanks to its excellent specific strength, corrosion resistance, and good biocompatibility. However, the successful application of Ti-6Al-4V alloy in MIM still faces a series of deep-seated technical bottlenecks, particularly the increasingly prominent contradictions in the material's intrinsic properties during debinding and high-temperature processing.

[0003] Traditional metal injection molding processes typically employ thermal debinding or solvent debinding to remove the organic binder system from the feedstock. While thermal debinding is a mature technology, it relies on high temperatures to melt, diffuse, and ultimately decompose the binder, resulting in a lengthy process that often takes tens of hours or even days. During this process, defects such as blistering, cracking, or dimensional distortion can easily occur inside the preform due to uneven binder flow or differences in volatilization rates. More critically, Ti-6Al-4V alloys exhibit extremely high chemical reactivity at high temperatures, readily reacting with trace amounts of carbon, oxygen, and other impurities in the environment to form a brittle surface layer or internal inclusions, significantly reducing the material's ductility and fatigue performance.

[0004] Even under an inert atmosphere, such contamination is difficult to completely avoid if there are local temperature fluctuations or insufficient atmosphere purity during the degreasing stage. While solvent degreasing can be carried out at lower temperatures, it is often difficult to completely remove the internal binder due to limitations in the solubility of the binder system and the depth of solvent penetration. The residue may also introduce carbon contamination during subsequent sintering, which also affects the mechanical integrity of the final product.

[0005] As high-end manufacturing demands greater consistency in component performance, structural complexity, and production efficiency, the inherent flaws in traditional degreasing methods have gradually become the core contradiction hindering the development of Ti-6Al-4V metal injection molding technology. The degreasing process essentially seeks a balance between thoroughly removing organic matter and avoiding material contamination and deformation, but current technologies struggle to achieve both simultaneously.

[0006] Increasing the debinding temperature to shorten the cycle exacerbates the reaction tendency between titanium alloys and impurity elements; conversely, lowering the temperature or extending the debinding time to suppress the reaction is not only inefficient, but also makes the binder, which remains in a semi-molten state for an extended period, more prone to causing billet collapse or pore structure deterioration. Furthermore, debinding and sintering are usually performed as two independent processes, and the intermediate transfer process inevitably introduces environmental exposure risks. Even when operating in a high-purity atmosphere, the cumulative effect of trace oxygen partial pressure can be amplified during the high-temperature sintering stage, leading to grain boundary embrittlement. Summary of the Invention

[0007] To achieve the above-mentioned objectives, this invention provides a high-flowability Ti-6Al-4V alloy particle feedstock and its preparation method. The feedstock is composed of spherical Ti-6Al-4V alloy powder with a specific particle size distribution and a multi-component binder system in a precise ratio. It is combined with a catalytic-gradient integrated heat treatment process to ensure the flowability of injection molding while achieving a seamless connection between debinding and pre-sintering. This effectively suppresses the deformation of the green body, avoids carbon and oxygen contamination, and significantly improves the density and mechanical property consistency of the final sintered body.

[0008] The high-flowability Ti-6Al-4V alloy particle feedstock of this invention is composed of the following components by volume percentage: 85%-92% spherical Ti-6Al-4V alloy powder and 8%-15% binder system. The spherical Ti-6Al-4V alloy powder has a particle size distribution satisfying D10≥8μm, D50=15±2μm, D90≤28μm, and a sphericity higher than 0.92, an oxygen content ≤800ppm, and a carbon content ≤200ppm. This particle size distribution design ensures high packing density and low internal friction resistance during injection molding, thereby endowing the feedstock with excellent shear-thinning properties and mold-filling ability.

[0009] The binder system comprises the following components by mass percentage: 55%-65% polyoxymethylene (POM), 15%-25% polypropylene, 8%-12% ethylene-vinyl acetate copolymer, 3%-6% stearic acid, and 2%-4% nano-sized titanium dioxide catalyst carrier particles. POM, as the main binder, has a molecular weight of 80,000-120,000 g / mol and a melting point of 165-175℃; the polypropylene has a melt flow rate of 25-35 g / 10 min; the ethylene-vinyl acetate copolymer contains 28%-32% vinyl acetate (mass fraction); the stearic acid has a purity ≥99.5%; and the nano-sized titanium dioxide catalyst carrier particles have an average particle size of 20-50 nm and a specific surface area of ​​80-120 m². 2 / g, its surface is loaded with 0.5%-1.5% (mass fraction) of platinum nanoparticles, and the average particle size of the platinum particles is 3-8nm.

[0010] The preparation method of the feed includes the following steps: First, the spherical Ti-6Al-4V alloy powder is dried in a vacuum drying oven at 120°C for 4 hours to remove surface adsorbed moisture; then, the dried powder and the components of the binder system are added to a twin-screw mixer in the above proportions, and the mixture is mixed in a nitrogen protective atmosphere at a temperature range of 180-190°C, with a screw speed of 60-80 rpm and a mixing time of 30-45 min, until a uniform, non-agglomerated mixture is obtained; finally, the obtained mixture is extruded through a single-screw extruder, water-cooled, and pelletized to obtain cylindrical feed particles with a particle size of ø3mm×2mm.

[0011] The core of this invention lies in the synergistic effect of the feed and a catalytic-gradient integrated heat treatment process. This process completes three stages—catalytic degreasing, gradient thermal degreasing, and pre-sintering—within a single continuous heat treatment cycle. The specific steps are as follows: The first stage is the catalytic debinding stage: The injection-molded green body is placed in a tube furnace, and high-purity nitrogen (purity ≥99.999%) is introduced as a protective atmosphere at a flow rate of 2-5 L / min. The furnace temperature is increased from room temperature to 110°C at a rate of 1°C / min and held for 30 minutes to remove physically adsorbed water. Subsequently, the temperature is increased to 135°C at a rate of 1°C / min, and formaldehyde gas at a concentration of 500-2000 ppm is introduced at this temperature as a depolymerization initiator, while simultaneously activating the catalyst. Under the catalysis of the platinum-titanium dioxide catalyst, the polyoxymethylene (POM) backbone undergoes end-group depolymerization to generate gaseous formaldehyde monomers. This reaction continues for 2 to 4 hours within the temperature range of 135-145°C, removing more than 85% of the POM component from the binder system. The temperature in this stage is far below the melting point of POM, and the green body maintains a solid structure with no risk of flow deformation.

[0012] The second stage is the gradient thermal degreasing stage: After catalytic degreasing, the formaldehyde gas supply is stopped, a high-purity nitrogen atmosphere is maintained, and ultra-high-purity argon (purity ≥99.9999%, oxygen content ≤1ppm, hydrocarbon content ≤0.1ppm) is switched as the subsequent protective atmosphere, with the gas flow rate adjusted to 1-3L / min. The furnace temperature is increased from 145℃ to 350℃ at an extremely slow heating rate of 0.5℃ / min. During this process, the residual polypropylene, ethylene-vinyl acetate copolymer, and stearic acid are gradually pyrolyzed in the inert atmosphere into low-molecular-weight gaseous products (mainly C1-C4 hydrocarbons, CO2, and H2O), which are carried out of the furnace by a continuous gas flow. This gradient heating strategy ensures that the binder decomposition rate matches the gas diffusion rate, avoiding internal pressure buildup that could lead to bubbling or cracking.

[0013] The third stage is the pre-sintering stage: after the furnace temperature reaches 350℃, it continues to rise to 650℃ at a heating rate of 0.3℃ / min, and is held at 650℃ for 1 hour. At this temperature, atomic diffusion begins to occur on the surface of the Ti-6Al-4V alloy powder particles, forming preliminary necking, significantly increasing the contact area between particles, and giving the billet sufficient mechanical strength to resist gravitational deformation during subsequent high-temperature sintering. Simultaneously, since organic matter has been largely removed at this point, and the entire process is under ultra-high purity argon protection, no oxidation or carburization occurs on the powder surface, providing clean interface conditions for subsequent high-temperature sintering.

[0014] After the above integrated heat treatment, the green billet can be directly transferred to a high-temperature sintering furnace and held at 1280-1320℃ for 2 to 4 hours to finally obtain a Ti-6Al-4V alloy sintered body with a relative density ≥99.2%, oxygen content ≤1200ppm, and carbon content ≤300ppm. Its room temperature tensile strength ≥950MPa, elongation ≥12%, and fatigue limit (10... 7 (After one cycle) ≥520MPa, the performance indicators are significantly better than those of similar products prepared by the traditional stepwise debinding-sintering process.

[0015] In a preferred embodiment of the present invention, the nano-sized titanium dioxide catalyst support particles are pre-treated with surface silanization before feed preparation. Specifically, titanium dioxide nanoparticles are dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane is added at 2% of the mass of titanium dioxide. The mixture is stirred at 60°C for 4 hours, and after centrifugation, washing, and drying, a surface-amino-functionalized catalyst support is obtained. This treatment enhances the interfacial compatibility between the catalyst particles and the organic binder matrix, prevents agglomeration during mixing, and ensures uniform distribution of catalytic active sites in the feed, thereby improving the uniformity and efficiency of catalytic degreasing.

[0016] In another preferred embodiment of the present invention, the heating program of the gradient thermal degreasing stage adopts a segmented temperature control strategy: the heating rate is 0.3℃ / min in the 145-200℃ range; 0.6℃ / min in the 200-300℃ range; and 0.4℃ / min in the 300-350℃ range. This strategy is optimized based on the pyrolysis kinetics of different binder components, so that the decomposition peaks of polypropylene (main pyrolysis range 250℃-350℃) and ethylene-vinyl acetate copolymer (main pyrolysis range 300℃-400℃) are staggered, avoiding concentrated release of gaseous products and further reducing the internal stress of the green body.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention, through systematic innovation in feed component design, catalyst integration, and heat treatment process, constructs a highly efficient, clean, and low-deformation Ti-6Al-4V metal injection molding technology path. It fundamentally solves the inherent contradiction between thorough degreasing and material purity in existing technologies, providing technical support for the large-scale and high-reliability manufacturing of high-end titanium alloy precision parts. Detailed Implementation

[0018] This invention provides a high-flowability Ti-6Al-4V alloy particle feedstock and its preparation method, aiming to solve technical problems in traditional metal injection molding processes such as long debinding cycles, easy deformation of the billet, and the susceptibility of Ti-6Al-4V alloy to carbon and oxygen contamination during high-temperature treatment, leading to deterioration of mechanical properties. By precisely controlling the particle size distribution of spherical Ti-6Al-4V alloy powder, constructing a multi-component synergistic binder system, and integrating a nano-scale platinum-titanium dioxide catalyst, combined with a catalytic-gradient integrated heat treatment process, this invention achieves the completion of three key stages—catalytic debinding, gradient thermal debinding, and pre-sintering—within a single continuous heat treatment cycle. This significantly improves the density, purity, and mechanical property consistency of the final sintered body while ensuring high feedstock flowability.

[0019] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0020] Example 1: Preparation steps: Spherical Ti-6Al-4V alloy powder (D10=8μm, D50=15μm, D90=26μm, sphericity 0.93, oxygen content 750ppm, carbon content 180ppm) was mixed with a binder at a volume ratio of 90:10; the binder contained, by mass ratio, 60% polyoxymethylene, 20% polypropylene, 10% ethylene-vinyl acetate copolymer, 5% stearic acid, and 5% platinum-titanium dioxide catalyst (platinum loading 1.0%, titanium dioxide particle size 30nm); 120 Vacuum drying at ℃ for 4 hours; twin-screw compounding at 185℃ under nitrogen protection (70 rpm, 35 minutes); extrusion pelleting into ø3mm×2mm feedstock; catalytic-gradient integrated heat treatment: catalytic degreasing at 140℃ with 1000ppm formaldehyde gas for 3 hours, gradient heating under ultra-high purity argon protection (145-200℃ 0.3℃ / min, 200-300℃ 0.6℃ / min, 300-350℃ 0.4℃ / min), pre-sintering at 650℃ for 1 hour; high-temperature sintering at 1300℃ for 3 hours.

[0021] Example 2: Preparation steps: Spherical Ti-6Al-4V alloy powder and binder were mixed at a volume ratio of 92:8; the binder contained 65% polyoxymethylene, 18% polypropylene, 8% ethylene-vinyl acetate copolymer, 4% stearic acid, and 5% platinum-titanium dioxide catalyst by mass ratio; the mixing temperature was 190℃ (80 rpm, 40 minutes); the remaining preparation and heat treatment steps were the same as in Example 1.

[0022] Example 3: Preparation steps: Spherical Ti-6Al-4V alloy powder and binder were mixed at a volume ratio of 85:15; the binder contained 55% polyoxymethylene, 25% polypropylene, 12% ethylene-vinyl acetate copolymer, 6% stearic acid, and 2% platinum-titanium dioxide catalyst by mass ratio; the mixing temperature was 180℃ (60 rpm, 30 minutes); the remaining preparation and heat treatment steps were the same as in Example 1.

[0023] Example 4: Preparation steps: The platinum-titanium dioxide catalyst was surface-treated with 3-aminopropyltriethoxysilane (silane addition amount was 2% of the titanium dioxide mass); the binder contained 60% polyoxymethylene, 20% polypropylene, 10% ethylene-vinyl acetate copolymer, 5% stearic acid, and 5% of the treated catalyst by mass ratio; the remaining preparation and heat treatment steps were the same as in Example 1.

[0024] Example 5: Preparation steps: The platinum loading in the platinum-titanium dioxide catalyst is 1.5%; the binder contains 60% polyoxymethylene, 20% polypropylene, 10% ethylene-vinyl acetate copolymer, 5% stearic acid, and 5% of the catalyst by mass ratio; the formaldehyde gas concentration in the catalytic degreasing stage is 2000ppm, and the time is 2 hours; the remaining steps are the same as in Example 1.

[0025] Example 6: Preparation steps: The platinum loading in the platinum-titanium dioxide catalyst is 0.5%; the binder contains 60% polyoxymethylene, 20% polypropylene, 10% ethylene-vinyl acetate copolymer, 5% stearic acid, and 5% of the catalyst by mass ratio; the formaldehyde gas concentration in the catalytic degreasing stage is 500 ppm, and the time is 4 hours; the remaining steps are the same as in Example 1.

[0026] Example 7: Preparation steps: The gradient thermal degreasing stage uses a uniform heating rate of 0.5℃ / min (without segmented temperature control); the remaining preparation and heat treatment steps are the same as in Example 1.

[0027] Comparative Example 1: Preparation steps: The binder is a platinum-free titanium dioxide catalyst containing 65% polyoxymethylene, 20% polypropylene, 10% ethylene-vinyl acetate copolymer, and 5% stearic acid by mass ratio; conventional thermal degreasing is used (heating at 180-350℃ at 1℃ / min, without catalytic stage); the remaining powder parameters, preparation and sintering steps are the same as in Example 1.

[0028] Comparative Example 2: Preparation steps: Irregularly shaped Ti-6Al-4V alloy powder (sphericity 0.75, particle size distribution D10=8μm, D50=15μm, D90=28μm) was used; the remaining binder formulation, preparation and heat treatment steps were the same as in Example 1.

[0029] Comparative Example 3: Preparation steps: Catalytic-gradient integrated heat treatment omits the pre-sintering stage (direct sintering at 1300℃ after degreasing); the remaining preparation and heat treatment steps are the same as in Example 1.

[0030] The sintered bodies of Examples 1-7 exhibited significantly higher densities (99.2%-99.7%), tensile strengths (950-980 MPa), and elongations (12.5%-13.5%) than those of Comparative Examples 1-3, and lower oxygen (1050-1150 ppm) and carbon (270-290 ppm) contents. This demonstrates that the feed formulation (containing platinum-titanium dioxide catalyst) and the integrated catalytic-gradient heat treatment process of this invention can effectively solve the problems of degreasing deformation and carbon and oxygen contamination. Among them, Example 2, with the highest powder content (92 vol%), showed the best sintered density and strength; Example 4, due to the catalyst silanization treatment, exhibited improved dispersion uniformity and elongation superior to the untreated group.

[0031] Comparative Example 1, without a catalyst and using traditional hot debinding, had a sintered body density of only 97.5% and a tensile strength of 880 MPa (90 MPa lower than Example 1), and the green body exhibited bubbling. This demonstrates that the platinum-titanium dioxide catalyst can reduce the debinding temperature, prevent binder melting and deformation, and reduce carbon and oxygen adsorption. Example 5, with its high platinum loading, shortened the debinding time, while Example 6, with its low loading, extended the cycle but still met the performance requirements, indicating that the catalyst loading is effective in the range of 0.5%-1.5%.

[0032] Comparative Example 2 used non-spherical powder, and the feed viscosity increased sharply (180℃ / 100s). -1 The density of the green body was 98.0% (2.5% lower than that of Example 1) due to the low packing density and poor flowability of the non-spherical powder, which affected the feeding, forming and sintering densification. Comparative Example 3 did not undergo pre-sintering, and the green body did not have initial necking. It underwent high-temperature sintering deformation, with a density of 98.5% and an elongation of 10% (3% lower than that of Example 1), proving that pre-sintering can enhance the strength of the green body and ensure sintering stability.

[0033] Example 7 uses a uniform gradient degreasing rate, and the elongation is slightly lower than that of Example 1 (12.7% vs 13%), indicating that segmented temperature control (matching the pyrolysis characteristics of different binders) can further optimize the degreasing uniformity. Example 3 has the best feed flowability with low powder content (viscosity 160 Pa·s), which is suitable for complex thin-walled parts, and the elongation reaches 13.5%, reflecting the flexibility of the formulation.

[0034] The performance indicators of Comparative Examples 1-3 did not meet the requirements of high-end applications, while the sample of the Example could meet the mechanical and purity requirements of Ti-6Al-4V alloy precision parts in aerospace, high-end electronics and other fields, highlighting the industrialization value of the technical solution of this invention.

[0035] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-flowability Ti-6Al-4V alloy particle feedstock, characterized in that, It is composed of spherical Ti-6Al-4V alloy powder and a binder system in a volume percentage, wherein the spherical Ti-6Al-4V alloy powder accounts for 85%-92% and the binder system accounts for 8%-15%. The binder system comprises, by weight percentage: 55%-65% polyoxymethylene, 15%-25% polypropylene, 8%-12% ethylene-vinyl acetate copolymer, 3%-6% stearic acid, and 2%-4% nano-sized titanium dioxide catalyst carrier particles.

2. The high-flowability Ti-6Al-4V alloy particle feed according to claim 1, characterized in that, The mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer is 28%-32%.

3. The high-flowability Ti-6Al-4V alloy particle feed according to claim 1, characterized in that, The nanoscale titanium dioxide catalyst has 0.5%-1.5% by mass of platinum nanoparticles loaded on its surface.

4. The high-flowability Ti-6Al-4V alloy particle feed according to claim 3, characterized in that, The nano-sized titanium dioxide catalyst support particles are surface-silanized, with 3-aminopropyltriethoxysilane grafted onto their surface. The amount of silane added is 2% of the mass of titanium dioxide.

5. A method for preparing high-flowability Ti-6Al-4V alloy particles as described in any one of claims 1 to 4, characterized in that, Includes the following steps: The spherical Ti-6Al-4V alloy powder was vacuum dried at 120°C for 4 hours; the dried powder and the components of the binder system were then mixed in a twin-screw extruder at 180-190°C under nitrogen protection, with a screw speed of 60-80 rpm and a mixing time of 30-45 min. The uniformly mixed mixture is extruded by a single screw, water-cooled, and pelletized to obtain cylindrical feed pellets with a size of ø3mm×2mm.

6. The preparation method according to claim 5, characterized in that, Before mixing, the nano-sized titanium dioxide catalyst carrier particles are dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane is added for surface silanization treatment. After centrifugation, washing, and drying, they are premixed with other binder components to form a premixed binder.

7. A catalytic-gradient integrated heat treatment process using high-flowability Ti-6Al-4V alloy particles as described in any one of claims 1 to 4 as feedstock, characterized in that, Includes the following consecutive stages: The first stage is the catalytic degreasing stage, in which 500-2000 ppm of formaldehyde gas is introduced at 135-145℃, and under the action of platinum-titanium dioxide catalyst, polyoxymethylene is depolymerized into gaseous formaldehyde for 2-4 hours. The second stage is the gradient thermal degreasing stage, in which the temperature is increased from 145℃ to 350℃ at a rate of 0.5℃ / min under the protection of ultra-high purity argon gas, so that the residual binder components are pyrolyzed and discharged. The third stage is the pre-sintering stage, in which the temperature is increased to 650℃ at a rate of 0.3℃ / min and held for 1 hour to form a preliminary necking structure between Ti-6Al-4V alloy powder particles.

8. The catalytic-gradient integrated heat treatment process according to claim 7, characterized in that, The gradient thermal degreasing stage employs a segmented temperature control strategy: Within the temperature range of 145-200℃, the heating rate is 0.3℃ / min; In the temperature range of 200-300℃, the heating rate is 0.6℃ / min; In the 300-350℃ range, the heating rate is 0.4℃ / min.

9. The catalytic-gradient integrated heat treatment process according to claim 7, characterized in that, The catalytic degreasing stage is carried out under a high-purity nitrogen atmosphere at a gas flow rate of 2-5 L / min. The gradient thermal degreasing and pre-sintering stage switches to ultra-high purity argon gas with a gas flow rate of 1-3 L / min. The oxygen content of the ultra-high purity argon gas is ≤1 ppm and the hydrocarbon content is ≤0.1 ppm.

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