High-performance mim titanium alloy powder and hot isostatic pressing preparation method thereof

Abstract

The application discloses a kind of high-performance MIM titanium alloy powder and its hot isostatic pressing preparation method, belong to metal powder injection molding technical field.The application uses sponge titanium and Al-V intermediate alloy as raw material, electrode stick is prepared by vacuum self-consumption arc melting;Pre-alloyed powder is prepared by using vacuum inert gas atomization process;High-performance MIM titanium alloy powder is obtained by multistage screening, magnetic separation and air separation dust;The powder is mixed with binder to prepare feedstock, after injection molding, solvent degreasing and hot degreasing, hot isostatic pressing densification treatment is carried out, and high-performance MIM titanium alloy component is obtained by vacuum annealing.The application is prepared by pre-alloyed powder, multistage purification, MIM forming and hot isostatic pressing densification combined process, the relative density of the component is greater than or equal to 99.5%, the tensile strength is greater than or equal to 975MPa, the elongation is greater than or equal to 11.8%, and the component has high strength, high toughness and excellent fatigue resistance.

Description

Technical Field

[0001] This invention belongs to the field of metal powder injection molding technology, and more specifically, relates to a high-performance MIM titanium alloy powder and its hot isostatic pressing preparation method. Background Technology

[0002] Titanium alloys, due to their high specific strength, good corrosion resistance, and excellent biocompatibility, are used in aerospace, precision equipment, medical devices, and other fields. Metal powder injection molding technology, with its near-net-shape forming, ability to form complex structural parts in one step, high material utilization, and high production efficiency, is a process route for manufacturing small, complex titanium alloy structural parts.

[0003] Titanium alloy structural components used in aerospace and precision equipment must withstand alternating loads and temperature cycling shocks during service. When titanium alloy powder prepared by gas atomization is subjected to MIM (Metal Injection Molding) process, the following observations were made regarding the morphology, particle size distribution, and impurity content of the powder: some powder particles deviate from spherical shape, and satellite particles adhere to the surface; the oxygen content distribution range of the powder is relatively wide, and the oxygen content of some batches can exceed a certain threshold; the particle size distribution shows a broad distribution or multi-peak distribution characteristics.

[0004] In the MIM process, when using powders with the aforementioned morphological characteristics and particle size distribution, uneven distribution of the binder may occur during the feeding and mixing stage; underfilling and weld lines may appear at the end of the cavity filling stage during injection molding; and after debinding and sintering, the interior of the green body may exhibit porosity, micropores, and microstructure segregation. When testing the mechanical properties of the sintered body, the measured values ​​of its elongation after fracture and fatigue limit fluctuate. To address the residual porosity inside the green body, a process scheme employing atmospheric pressure sintering followed by hot isostatic pressing (HIP) has been developed.

[0005] While this process can increase the relative density of the sintered body, residual isolated pores can still be observed in the microstructure, and the dimensional shrinkage of the billet during densification exhibits anisotropy. Therefore, how to further eliminate residual isolated pores in MIM titanium alloy components and improve their dimensional accuracy during densification is a pressing technical problem that needs to be solved. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, the technical problem to be solved by the present invention is to provide a high-performance MIM titanium alloy powder and its preparation method, as well as a method for preparing components using the powder via hot isostatic pressing. The method involves preparing pre-alloyed powder through vacuum consumable arc melting and vacuum inert gas atomization, combined with a purification process of multi-stage sieving, magnetic separation for impurity removal, and air classification for dust removal, to obtain high-performance MIM titanium alloy powder with low oxygen content and narrow particle size distribution. This powder is then subjected to mixing, injection molding, gradient degreasing, and hot isostatic pressing for high-temperature and high-pressure densification, followed by vacuum annealing, to obtain MIM titanium alloy components that possess both high strength, high toughness, and excellent fatigue resistance.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing high-performance MIM titanium alloy powder includes the following steps:

[0009] 1) Titanium alloy electrode rods were prepared by vacuum arc melting using sponge titanium and Al-V master alloy as raw materials and according to the composition of Ti-6Al-4V alloy.

[0010] 2) Melt the titanium alloy electrode rod obtained in step 1) in a vacuum inert gas atomizing furnace, control the superheat of the melt to 80~120℃, use high-purity argon gas for atomization, and collect the pre-alloyed powder after cooling.

[0011] 3) The pre-alloyed powder obtained in step 2) is sieved to obtain powder with a particle size of 15~53μm, and then subjected to magnetic separation and air separation to obtain high-performance MIM titanium alloy powder.

[0012] Preferably, in step 1), the alloy composition, by mass percentage, is Al 5.8%~6%, V 4%~4.2%, and the balance is Ti.

[0013] Preferably, in step 1), the vacuum degree of the vacuum self-consuming arc melting is not higher than 3×10⁻⁶. -2 Pa, after two melting processes, the surface oxide layer is removed by turning.

[0014] Preferably, in step 2), the atomization pressure is 4~5MPa and the injection angle between the atomizing gas and the melt flow is 45°~55°.

[0015] The method described yields high-performance MIM titanium alloy powder.

[0016] A method for preparing components using the high-performance MIM titanium alloy powder via hot isostatic pressing includes the following steps:

[0017] S1. The high-performance MIM titanium alloy powder is mixed with a binder to prepare a feedstock, with a powder loading of 62-68 vol%, and then injection molded to obtain an injection preform.

[0018] S2. The injection preform obtained in step S1 is immersed in n-heptane at 40~60℃ for solvent degreasing, and then thermal degreasing is carried out under the protection of flowing argon to obtain a degreased preform;

[0019] S3. The degreased green body obtained in step S2 is first pre-sintered, and then hot isostatic pressing is performed at a temperature of 920~940℃ and a pressure of 135~150MPa to obtain a densified green body.

[0020] S4. The densified blank obtained in step S3 is annealed under vacuum conditions to obtain a high-performance MIM titanium alloy component.

[0021] Preferably, in step S1, the binder is a paraffin-based binder or a polyoxymethylene-based binder; the paraffin-based binder is composed of 55-65 parts by weight of paraffin wax, 25-35 parts by weight of high-density polyethylene, 3-8 parts by weight of stearic acid, and 3-8 parts by weight of microcrystalline wax; the polyoxymethylene-based binder is composed of 85-92 parts by weight of polyoxymethylene copolymer, 3-8 parts by weight of plasticizer, 2-5 parts by weight of stearic acid, and 1-2 parts by weight of 2,6-di-tert-butyl-4-methylphenol; the injection temperature of the injection molding is 170-180℃, the injection pressure is 85-95MPa, and the holding time is 10-15s.

[0022] Preferably, in step S2, the solvent degreasing time is 6-8 hours; the thermal degreasing is carried out under the protection of flowing argon gas, with a gradual heating rate of 0.8-2℃ / min to 220-300℃ and holding for 0.8-1 hours, and then with a heating rate of 1.5-2℃ / min to 600℃ and holding for 2 hours.

[0023] Preferably, in step S3, the pre-sintering is performed at a vacuum level better than 5 × 10⁻⁶. -3 The heat treatment is carried out at 1250~1280℃ for 3~3.5h; the pressure increase rate during hot isostatic pressing is 10MPa / min, the heat holding and pressure holding time is 2.5~3h, and after the heat treatment, the pressure is released at 8MPa / min and the temperature is reduced to room temperature at 3℃ / min.

[0024] In step S4, the annealing process is carried out under a vacuum degree better than 1×10⁻⁶. -2 Under Pa conditions, the temperature is increased to 780~800℃ at a rate of 5℃ / min and held for 1.5~2h, then cooled to room temperature in the furnace; or, the temperature is first held at 780~800℃ for 1.5~2h and then cooled to 500℃ in the furnace, and then increased to 700℃ and held for 1h for double annealing.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0026] 1) This invention combines vacuum self-consuming arc melting to prepare electrode rods with vacuum inert gas atomization powder preparation. The entire process is protected by an inert atmosphere, which effectively inhibits powder oxidation. The resulting pre-alloyed powder has an oxygen content of ≤0.12wt% and uniform composition.

[0027] 2) This invention uses multi-stage sieving to extract powder of the target particle size, combined with magnetic separation and air classification for dust removal, effectively removing satellite powder, ultrafine powder, and ferromagnetic impurities, achieving a bulk density ≥2.3 g / cm³. 3 This significantly improves the flowability and filling properties of the powder, making it suitable for the precision molding requirements of MIM.

[0028] 3) This invention employs a hot isostatic pressing (HIP) high-temperature and high-pressure densification process (920–940℃, 135–150 MPa). Utilizing the uniform pressure of isotropic pressing, residual porosity and loose defects within the billet are eliminated. The densified billet has a relative density ≥99.5% and a porosity ≤0.4%. After HIP densification, vacuum annealing is applied to eliminate internal stress and regulate the grain structure, resulting in MIM titanium alloy components with both high strength and high toughness. The tensile strength is ≥975 MPa, the yield strength is ≥878 MPa, the elongation is ≥11%, and the fatigue limit is (10… 7 It has a strength of ≥510MPa (secondary) and excellent comprehensive mechanical properties and good adaptability. Attached Figure Description

[0029] Figure 1 The chart shows a comparison of the loose packing density and tapped density of the MIM titanium alloy powders obtained in Examples 1-6 and Comparative Example 1.

[0030] Figure 2 Comparison of particle size distribution of MIM titanium alloy powders obtained in Examples 1-6 and Comparative Example 1;

[0031] Figure 3 Comparison of the tensile properties of MIM titanium alloy components obtained in Examples 1-6 and Comparative Examples 1-3;

[0032] Figure 4 The fatigue limit comparison diagram shows the MIM titanium alloy components obtained in Examples 1-6 and Comparative Examples 1-3. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is further described below with reference to specific embodiments. Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0034] The sponge titanium particles used in the following examples have a particle size of 0.83~12.7mm and are of industrial purity; the Al-V master alloy particles have a particle size of 6~20mm and are of AlV55 grade.

[0035] Example 1

[0036] This embodiment provides a method for preparing high-performance MIM titanium alloy powder and a hot isostatic pressing method using the powder, including the following steps:

[0037] 1) Preparation of titanium alloy electrode rods

[0038] According to the target composition of Ti-6Al-4V alloy, sponge titanium particles and Al-V master alloy particles were weighed to ensure that the mass percentage of Al in the alloy was 6.0 wt%, V was 4.0 wt%, and the balance was Ti. The raw materials were mixed and pressed into electrode blocks, which were then placed in a vacuum arc remelting furnace at a vacuum degree not exceeding 3 × 10⁻⁶. -2 The first melting is carried out under Pa conditions; after completion, the ingot is flipped for a second melting. After melting, the surface oxide layer is removed by turning to obtain a titanium alloy electrode rod with uniform composition.

[0039] 2) Preparation of pre-alloyed powder by gas atomization

[0040] Place the electrode rod obtained in step 1) in a vacuum inert gas atomizing furnace and evacuate it to a vacuum level not exceeding 8 × 10⁻⁶. -2 After Pa, high-purity argon gas is introduced, and medium-frequency induction heating is used for melting. The superheat of the melt is controlled at 100℃. The superheated melt is injected into the atomization chamber through a guide pipe and atomized with 4.5MPa high-purity argon gas using a circumferential slit tightly coupled nozzle. The spray angle between the atomizing gas and the melt flow is 50°. The melt droplets are cooled and solidified by argon gas circulation in the atomization tower and collected by a cyclone separator to obtain pre-alloyed powder.

[0041] 3) Powder sieving and purification

[0042] The pre-alloyed powder obtained in step 2) is sieved through a 53μm sieve and a 15μm sieve in sequence to extract powder with a particle size range of 15~53μm. Ferromagnetic impurities are removed by magnetic separation with a magnetic field strength of 1.5T. Finally, satellite powder and ultrafine powder are removed by air separation to obtain high-performance MIM titanium alloy powder.

[0043] 4) Preparation of MIM feedstock and injection molding

[0044] The high-performance MIM titanium alloy obtained in step 3) is mixed with a paraffin-based binder at a powder loading of 65 vol% in a mixer at 150°C and 30 rpm for 2 hours to obtain a uniform feedstock. The paraffin-based binder consists of 60 parts paraffin wax, 30 parts high-density polyethylene, 5 parts stearic acid, and 5 parts microcrystalline wax by weight. The feedstock is crushed and fed into a single-screw extruder granulator, where it is melt-extruded and granulated at 160-170°C to obtain granular feedstock. The granular feedstock is added to the barrel of an injection molding machine and injection molded at an injection temperature of 170°C, an injection pressure of 90 MPa, and a holding time of 12 s to obtain a titanium alloy injection preform.

[0045] 5) Degreasing treatment

[0046] The injection preform obtained in step 4) is first immersed in n-heptane at 50°C for solvent degreasing for 8 hours. After drying, it is placed in a hot degreasing furnace. Under the protection of flowing argon, the temperature is first increased to 300°C at 1°C / min and held for 1 hour, then increased to 600°C at 2°C / min and held for 2 hours. After cooling in the furnace, the degreased preform is obtained.

[0047] 6) Hot isostatic pressing densification

[0048] The degreased green body obtained in step 5) is placed in a high-vacuum sintering furnace, and sintered under a vacuum degree better than 5 × 10⁻⁶. -3 Under Pa conditions, the temperature was increased to 1280℃ at a rate of 5℃ / min and held for 3 hours for pre-sintering to obtain a pre-sintered gold-bonded billet. The pre-sintered gold-bonded billet was then transferred to a hot isostatic pressing furnace, evacuated, and filled with high-purity argon. The temperature was increased to 920℃ at a rate of 5℃ / min, and the pressure was simultaneously increased to 135MPa at a rate of 10MPa / min. The temperature and pressure were maintained at 920℃ and 135MPa for 3 hours. After the holding and pressure maintenance, the pressure was released at 8MPa / min and the temperature was reduced to room temperature at a rate of 3℃ / min to obtain a densified billet.

[0049] 7) Vacuum annealing treatment

[0050] The densified green body obtained in step 6) is placed in a vacuum annealing furnace, and subjected to a vacuum degree better than 1×10⁻⁶. -2 Under Pa conditions, the temperature was increased to 780℃ at a rate of 5℃ / min and held for 2 hours. After the holding period, the temperature was slowly cooled to room temperature in the furnace to obtain a high-performance MIM titanium alloy component.

[0051] Example 2

[0052] This embodiment provides a method for preparing high-performance MIM titanium alloy powder and a hot isostatic pressing method using the powder, including the following steps:

[0053] 1) Preparation of titanium alloy electrode rods

[0054] According to the target composition of the Ti-5.8Al-4.2V alloy, sponge titanium particles and Al-V master alloy particles were weighed to ensure that the mass percentage of Al in the alloy was 5.8wt%, V was 4.2wt%, and the balance was Ti. The raw materials were mixed and pressed into electrode blocks, which were then placed in a vacuum arc remelting furnace at a vacuum degree not exceeding 3×10⁻⁶. -2 The first melting is carried out under Pa conditions; after completion, the ingot is flipped for a second melting. After melting, the surface oxide layer is removed by turning to obtain a titanium alloy electrode rod with uniform composition.

[0055] 2) Preparation of pre-alloyed powder by gas atomization: Same as step 2) in Example 1;

[0056] 3) Powder sieving and purification: Same as step 3) in Example 1;

[0057] 4) Preparation of MIM feedstock and injection molding: Same as step 4) in Example 1;

[0058] 5) Degreasing treatment: Same as step 5) in Example 1;

[0059] 6) Hot isostatic pressing densification: Same as step 6) in Example 1;

[0060] 7) Vacuum annealing: Same as step 7) in Example 1, to obtain high-performance MIM titanium alloy components.

[0061] Example 3

[0062] This embodiment provides a method for preparing high-performance MIM titanium alloy powder and a hot isostatic pressing method using the powder, including the following steps:

[0063] 1) Preparation of titanium alloy electrode rod: Same as step 1) in Example 1;

[0064] 2) Preparation of pre-alloyed powder by gas atomization

[0065] Place the electrode rod obtained in step 1) in a vacuum inert gas atomizing furnace and evacuate it to a vacuum level not exceeding 8 × 10⁻⁶. -2 After Pa, high-purity argon gas is introduced, and medium-frequency induction heating is used for melting. The superheat of the melt is controlled at 120℃. The superheated melt is injected into the atomization chamber through the guide pipe and atomized with 5MPa high-purity argon gas using a ring-slit tightly coupled nozzle. The spray angle between the atomizing gas and the melt flow is 45°. The melt droplets are cooled and solidified by argon gas circulation in the atomization tower and collected by a cyclone separator to obtain pre-alloyed powder.

[0066] 3) Powder sieving and purification: Same as step 3) in Example 1;

[0067] 4) Preparation of MIM feedstock and injection molding

[0068] The high-performance MIM titanium alloy obtained in step 3) is mixed with a paraffin-based binder at a powder loading of 67 vol% in a mixer at 150°C and 30 rpm for 2 hours to obtain a uniform feedstock. The paraffin-based binder consists of 60 parts paraffin wax, 30 parts high-density polyethylene, 5 parts stearic acid, and 5 parts microcrystalline wax by weight. The feedstock is crushed and fed into a single-screw extruder granulator, where it is melt-extruded and granulated at 160-170°C to obtain granular feedstock. The granular feedstock is added to the barrel of an injection molding machine and injection molded at an injection temperature of 175°C, an injection pressure of 95 MPa, and a holding time of 10 s to obtain a titanium alloy injection preform.

[0069] 5) Degreasing treatment: Same as step 5) in Example 1;

[0070] 6) Hot isostatic pressing densification: Same as step 6) in Example 1;

[0071] 7) Vacuum annealing: Same as step 7) in Example 1, to obtain high-performance MIM titanium alloy components.

[0072] Example 4

[0073] This embodiment provides a method for preparing high-performance MIM titanium alloy powder and a hot isostatic pressing method using the powder, including the following steps:

[0074] 1) Preparation of titanium alloy electrode rod: Same as step 1) in Example 1;

[0075] 2) Preparation of pre-alloyed powder by gas atomization: Same as step 2) in Example 1;

[0076] 3) Powder sieving and purification

[0077] The pre-alloyed powder obtained in step 2) is sieved through a 53μm sieve and a 20μm sieve in sequence to extract powder with a particle size range of 20~53μm. Ferromagnetic impurities are removed by magnetic separation with a magnetic field strength of 1.5T. Finally, satellite powder and ultrafine powder are removed by air separation to obtain high-performance MIM titanium alloy powder.

[0078] 4) Preparation of MIM feedstock and injection molding

[0079] The high-performance MIM titanium alloy obtained in step 3) is mixed with a paraffin-based binder at a powder loading of 64 vol% in a mixer at 150°C and 30 rpm for 2 hours to obtain a uniform feedstock. The paraffin-based binder consists of 60 parts paraffin wax, 30 parts high-density polyethylene, 5 parts stearic acid, and 5 parts microcrystalline wax by weight. The feedstock is crushed and fed into a single-screw extruder granulator, where it is melt-extruded and granulated at 160-170°C to obtain granular feedstock. The granular feedstock is added to the barrel of an injection molding machine and injection molded at an injection temperature of 170°C, an injection pressure of 90 MPa, and a holding time of 12 s to obtain a titanium alloy injection preform.

[0080] 5) Degreasing treatment: Same as step 5) in Example 1;

[0081] 6) Hot isostatic pressing densification: Same as step 6) in Example 1;

[0082] 7) Vacuum annealing: Same as step 7) in Example 1, to obtain high-performance MIM titanium alloy components.

[0083] Example 5

[0084] This embodiment provides a method for preparing high-performance MIM titanium alloy powder and a hot isostatic pressing method using the powder, including the following steps:

[0085] 1) Preparation of titanium alloy electrode rod: Same as step 1) in Example 1;

[0086] 2) Preparation of pre-alloyed powder by gas atomization: Same as step 2) in Example 1;

[0087] 3) Powder sieving and purification: Same as step 3) in Example 1;

[0088] 4) Preparation of MIM feedstock and injection molding

[0089] The high-performance MIM titanium alloy obtained in step 3) is mixed with a polyoxymethylene-based binder at a powder loading of 62 vol% in a mixer at 160°C for 2 hours to obtain a uniform feedstock. The polyoxymethylene-based binder consists of 88 parts by weight of polyoxymethylene copolymer, 5 parts by weight of dioctyl phthalate, 3 parts by weight of stearic acid, and 2 parts by weight of 2,6-di-tert-butyl-4-methylphenol. The feedstock is crushed and fed into a single-screw extruder for melt extrusion granulation at 160~170°C to obtain granular feedstock. The granular feedstock is added to the barrel of an injection molding machine and injection molded at an injection temperature of 180°C, an injection pressure of 85 MPa, and a holding time of 15 s to obtain a titanium alloy injection preform.

[0090] 5) Degreasing treatment

[0091] The injection preform obtained in step 4) is first immersed in n-heptane at 50°C for solvent degreasing for 6 hours. After drying, it is placed in a hot degreasing furnace. Under the protection of flowing argon, the temperature is first raised to 220°C at 0.8°C / min and held for 1 hour, then raised to 600°C at 1.5°C / min and held for 2 hours. After cooling in the furnace, the degreased preform is obtained.

[0092] 6) Hot isostatic pressing densification: Same as step 6) in Example 1;

[0093] 7) Vacuum annealing: Same as step 7) in Example 1, to obtain high-performance MIM titanium alloy components.

[0094] Example 6

[0095] This embodiment provides a method for preparing high-performance MIM titanium alloy powder and a hot isostatic pressing method using the powder, including the following steps:

[0096] 1) Preparation of titanium alloy electrode rod: Same as step 1) in Example 1;

[0097] 2) Preparation of pre-alloyed powder by gas atomization: Same as step 2) in Example 1;

[0098] 3) Powder sieving and purification: Same as step 3) in Example 1;

[0099] 4) Preparation of MIM feedstock and injection molding: Same as step 4) in Example 1;

[0100] 5) Degreasing treatment: Same as step 5) in Example 1;

[0101] 6) Hot isostatic pressing densification

[0102] The degreased green body obtained in step 5) is placed in a high-vacuum sintering furnace, and sintered under a vacuum degree better than 5 × 10⁻⁶. -3 Under Pa conditions, the temperature was increased to 1250℃ at a rate of 5℃ / min and held for 3.5h for pre-sintering to obtain a pre-sintered bonded gold billet. Subsequently, the pre-sintered bonded gold billet was transferred to a hot isostatic pressing furnace, evacuated, and filled with high-purity argon. The temperature was increased to 940℃ at a rate of 5℃ / min, and the pressure was simultaneously increased to 150MPa at a rate of 10MPa / min. The temperature and pressure were maintained at 940℃ and 150MPa for 2.5h. After the holding and pressure maintenance, the pressure was released at 8MPa / min and the temperature was reduced to room temperature at a rate of 3℃ / min to obtain a densified billet.

[0103] 7) Vacuum annealing treatment

[0104] The densified green body obtained in step 6) is placed in a vacuum annealing furnace, and subjected to a vacuum degree better than 1×10⁻⁶. -2Under Pa conditions, the temperature is increased to 800℃ at a rate of 5℃ / min and held for 1.5h. After holding, the temperature is cooled to 500℃ in the furnace, and then increased to 700℃ at a rate of 5℃ / min and held for 1h for secondary annealing. After cooling to room temperature in the furnace, high-performance MIM titanium alloy components are obtained.

[0105] Comparative Example 1

[0106] This comparative example provides a method for preparing MIM titanium alloy powder and a method for preparing the powder using hot isostatic pressing, including the following steps:

[0107] 1) Preparation of titanium alloy electrode rod: Same as step 1) in Example 1;

[0108] 2) Preparation of pre-alloyed powder by gas atomization: Same as step 2) in Example 1;

[0109] 3) Powder sieving

[0110] The pre-alloyed powder obtained in step 2) is sieved through a 53μm sieve and a 15μm sieve in sequence to extract powder with a particle size range of 15~53μm. Without magnetic separation and air separation, MIM titanium alloy powder is directly obtained.

[0111] 4) Preparation of MIM feedstock and injection molding: Same as step 4) in Example 1;

[0112] 5) Degreasing treatment: Same as step 5) in Example 1;

[0113] 6) Hot isostatic pressing densification: Same as step 6) in Example 1;

[0114] 7) Vacuum annealing: Same as step 7) in Example 1, to obtain MIM titanium alloy components.

[0115] Comparative Example 2

[0116] This comparative example provides a method for preparing MIM titanium alloy powder and a method for preparing the powder using hot isostatic pressing, including the following steps:

[0117] 1) Preparation of titanium alloy electrode rod: Same as step 1) in Example 1;

[0118] 2) Preparation of pre-alloyed powder by gas atomization: Same as step 2) in Example 1;

[0119] 3) Powder sieving and purification: Same as step 3) in Example 1;

[0120] 4) Preparation of MIM feedstock and injection molding: Same as step 4) in Example 1;

[0121] 5) Degreasing treatment: Same as step 5) in Example 1;

[0122] 6) Atmospheric pressure sintering

[0123] The degreased green body obtained in step 5) is placed in a high-vacuum sintering furnace, and sintered under a vacuum degree better than 5 × 10⁻⁶. -3 Under normal pressure conditions, the temperature was increased to 1280℃ at a rate of 5℃ / min and sintered for 3 hours, followed by furnace cooling to obtain a densified green body.

[0124] 7) Vacuum annealing: Same as step 7) in Example 1, to obtain MIM titanium alloy components.

[0125] Comparative Example 3

[0126] This comparative example provides a method for preparing MIM titanium alloy powder and a method for preparing the powder using hot isostatic pressing, including the following steps:

[0127] 1) According to the target composition of Ti-6Al-4V alloy, weigh industrial pure titanium powder (particle size 15~53μm), aluminum powder (particle size 15~53μm) and vanadium powder (particle size 15~53μm), and mix them in a V-type mixer under argon protection for 4 hours to obtain mixed element powder;

[0128] 2) Preparation of MIM feedstock and injection molding

[0129] Take the mixed element powder obtained in step 1), mix it with the paraffin-based binder at a powder loading of 65 vol% in a mixer at 150°C and 30 rpm for 2 hours to obtain a uniform feed; wherein, the paraffin-based binder is composed of 60 parts paraffin, 30 parts high-density polyethylene, 5 parts stearic acid, and 5 parts microcrystalline wax by weight; after crushing, the feed is fed into a single-screw extruder granulator, and melt-extruded and granulated at 160~170°C to obtain granular feed; add the granular feed into the barrel of an injection molding machine, and injection mold at an injection temperature of 170°C, an injection pressure of 90 MPa, and a holding time of 12 s to obtain a titanium alloy injection preform;

[0130] 3) Degreasing treatment: Same as step 5) in Example 1;

[0131] 4) Atmospheric pressure sintering

[0132] The degreased green body obtained in step 3) is placed in a high-vacuum sintering furnace, and sintered at a vacuum level better than 5 × 10⁻⁶. -3 Under normal pressure conditions, the temperature was increased to 1280℃ at a rate of 5℃ / min and sintered for 3 hours, followed by furnace cooling to obtain a densified green body.

[0133] 5) Hot isostatic pressing densification: Same as step 6) in Example 1;

[0134] 6) Vacuum annealing: Same as step 7) in Example 1, to obtain MIM titanium alloy components.

[0135] The performance of MIM titanium alloy powders and their components prepared in Examples 1-6 and Comparative Examples 1-3 was tested. Oxygen content was determined according to GB / T 4698.7 "Chemical Analysis Methods for Sponge Titanium, Titanium and Titanium Alloys". Loose packing density was determined according to GB / T 1479.1 "Determination of Loose Packing Density of Metal Powders"; tap density was determined according to GB / T 5162 "Determination of Tap Density of Metal Powders". Particle size distribution was determined according to GB / T 19077 "Particle Size Analysis by Laser Diffraction", and the D10, D50, and D90 values ​​were recorded. Room temperature tensile properties were determined according to GB / T 228.1 "Tensive Testing of Metallic Materials": tensile strength, yield strength (specified plastic extension strength Rp0.2), and elongation after fracture were measured on an electronic universal testing machine using proportional specimens at a tensile rate of 2 mm / min. Each test group consisted of at least 5 specimens, and the results were the arithmetic mean. Fatigue limit was determined according to GB / T3075 "Method for controlling axial force in fatigue testing of metallic materials": a rotary bending fatigue testing machine was used, stress ratio R=-1, test frequency 50Hz, and number of cycles 1×10. 7 The fatigue limit was determined using the lifting method, with no fewer than 15 specimens per group. The test results are shown in Tables 1 and 2.

[0136] Table 1. Performance test results of MIM titanium alloy powder obtained in Examples 1-6 and Comparative Examples 1-3

[0137] Oxygen content / wt% <![CDATA[Bulk density / g·cm -3 > <![CDATA[Tap density / g·cm -3 > D10 / μm D50 / μm D90 / μm Example 1 0.10 2.5 2.8 12 25 48 Example 2 0.10 2.5 2.8 13 24 47 Example 3 0.08 2.6 2.9 8 18 35 Example 4 0.09 2.5 2.8 18 32 50 Example 5 0.10 2.5 2.8 12 25 48 Example 6 0.10 2.5 2.8 12 25 48 Comparative Example 1 0.18 1.8 2.1 5 30 62 Comparative Example 2 0.10 2.5 2.8 12 25 48 Comparative Example 3 0.25 — — — — —

[0138] Note: Comparative Example 3 uses an elemental mixing method to prepare powder, which is not a pre-alloyed powder. The loose packing density, tap density and particle size distribution of the powder are not suitable for direct comparison and are indicated by "—".

[0139] Table 2 Performance test results of MIM titanium alloy components obtained in Examples 1-6 and Comparative Examples 1-3

[0140] Relative density / % Tensile strength / MPa Yield strength / MPa Elongation / % <![CDATA[Fatigue limit (10 7 cycles) / MPa]]> Example 1 99.7 985 885 12.5 520 Example 2 99.6 992 890 13.1 525 Example 3 99.7 995 895 12.8 530 Example 4 99.5 975 878 11.8 510 Example 5 99.6 980 882 12.3 515 Example 6 99.7 988 888 13.0 528 Comparative Example 1 98.1 810 730 5.5 350 Comparative Example 2 96.5 850 760 8.5 320 Comparative Example 3 98.8 880 795 3.2 380

[0141] As shown in Tables 1 and 2, the oxygen content of the powders obtained in Examples 1-6 is no more than 0.1 wt%, the powder quality is excellent and the consistency between batches is good; the relative density of the components is no less than 99.5%, the tensile strength is no less than 975 MPa, the elongation is no less than 11.8%, the fatigue limit is no less than 510 MPa, and the comprehensive mechanical properties are excellent.

[0142] Depend on Figure 1 As can be seen, the embodiments of the present invention combine vacuum argon atomization pre-alloyed powder preparation with multi-stage sieving, magnetic separation for impurity removal, and air separation for dust removal and purification processes, resulting in powder particles with good flowability and filling properties.

[0143] Depend on Figure 2 It can be seen that the particle sizes D10, D50 and D90 of the MIM titanium alloy powders obtained in Examples 1-6 are all stably distributed within the target particle size range of 15 to 53 μm. The particle size distribution is narrow and controllable, which is beneficial to improving the mixing uniformity of MIM feed and the powder flowability during injection molding.

[0144] Depend on Figure 3 It can be seen that the MIM titanium alloy components obtained in Examples 1-6 exhibit a good match between high strength and high plasticity, and the performance fluctuations among the examples are small, with good process stability and reproducibility.

[0145] Depend on Figure 4 It can be seen that the MIM titanium alloy components obtained in Examples 1-6 have excellent fatigue resistance under alternating loads.

[0146] This invention utilizes vacuum argon atomization of pre-alloyed powder preparation, multi-stage sieving and purification, MIM molding, hot isostatic pressing densification, and vacuum annealing. Through the synergistic effect of these steps, high-quality MIM titanium alloy powder can be stably obtained, and MIM titanium alloy components with high strength, high toughness, and excellent fatigue resistance can be prepared.

[0147] 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-performance MIM titanium alloy powder, characterized in that, Includes the following steps: 1) Titanium alloy electrode rods were prepared by vacuum arc melting using sponge titanium and Al-V master alloy as raw materials and according to the composition of Ti-6Al-4V alloy. 2) Melt the titanium alloy electrode rod obtained in step 1) in a vacuum inert gas atomizing furnace, control the superheat of the melt to 80~120℃, use high-purity argon gas for atomization, and collect the pre-alloyed powder after cooling. 3) The pre-alloyed powder obtained in step 2) is sieved to obtain powder with a particle size of 15~53μm, and then subjected to magnetic separation and air separation to obtain high-performance MIM titanium alloy powder.

2. The method for preparing high-performance MIM titanium alloy powder according to claim 1, characterized in that, In step 1), the alloy composition, by mass percentage, is Al 5.8%~6%, V 4%~4.2%, and the balance is Ti.

3. The method for preparing high-performance MIM titanium alloy powder according to claim 1, characterized in that, In step 1), the vacuum degree of vacuum self-consuming arc melting is not higher than 3×10. -2 Pa, after two melting processes, the surface oxide layer is removed by turning.

4. The method for preparing high-performance MIM titanium alloy powder according to claim 1, characterized in that, In step 2), the atomization pressure is 4~5MPa, and the injection angle between the atomizing gas and the melt flow is 45°~55°.

5. The high-performance MIM titanium alloy powder prepared by the method according to any one of claims 1-4.

6. A method for preparing components using the high-performance MIM titanium alloy powder described in claim 5 via hot isostatic pressing, characterized in that, Includes the following steps: S1. The high-performance MIM titanium alloy powder is mixed with a binder to prepare a feedstock, with a powder loading of 62-68 vol%, and then injection molded to obtain an injection preform. S2. The injection preform obtained in step S1 is immersed in n-heptane at 40~60℃ for solvent degreasing, and then thermal degreasing is carried out under the protection of flowing argon to obtain a degreased preform; S3. The degreased green body obtained in step S2 is first pre-sintered, and then hot isostatic pressing is performed at a temperature of 920~940℃ and a pressure of 135~150MPa to obtain a densified green body. S4. The densified blank obtained in step S3 is annealed under vacuum conditions to obtain a high-performance MIM titanium alloy component.

7. The method for preparing components by hot isostatic pressing according to claim 6, characterized in that, In step S1, the binder is a paraffin-based binder or a polyoxymethylene-based binder. The paraffin-based binder consists of 55-65 parts paraffin wax, 25-35 parts high-density polyethylene, 3-8 parts stearic acid, and 3-8 parts microcrystalline wax by weight. The polyoxymethylene-based binder consists of 85-92 parts polyoxymethylene copolymer, 3-8 parts plasticizer, 2-5 parts stearic acid, and 1-2 parts 2,6-di-tert-butyl-4-methylphenol by weight. The injection molding temperature is 170-180℃, the injection pressure is 85-95 MPa, and the holding time is 10-15 s.

8. The method for preparing components by hot isostatic pressing according to claim 6, characterized in that, In step S2, the solvent degreasing time is 6-8 hours; the thermal degreasing is carried out under the protection of flowing argon gas, with a gradual heating rate of 0.8-2℃ / min to 220-300℃ and holding for 0.8-1 hours, and then with a heating rate of 1.5-2℃ / min to 600℃ and holding for 2 hours.

9. The method for preparing components by hot isostatic pressing according to claim 6, characterized in that, In step S3, the pre-sintering is carried out under a vacuum degree better than 5×10⁻⁶. -3 The heat treatment is carried out at 1250~1280℃ for 3~3.5h; the pressure increase rate during hot isostatic pressing is 10MPa / min, the heat holding and pressure holding time is 2.5~3h, and after the heat treatment, the pressure is released at 8MPa / min and the temperature is reduced to room temperature at 3℃ / min.

10. The method for preparing components by hot isostatic pressing according to claim 6, characterized in that, In step S4, the annealing process is carried out under a vacuum degree better than 1×10⁻⁶. -2 Under Pa conditions, the temperature is increased to 780~800℃ at a rate of 5℃ / min and held for 1.5~2h, then cooled to room temperature in the furnace; or, the temperature is first held at 780~800℃ for 1.5~2h and then cooled to 500℃ in the furnace, and then increased to 700℃ and held for 1h for double annealing.

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