Powder particle size grading method and titanium and titanium alloy complex thin-walled parts and preparation methods thereof

Abstract

A powder particle size grading method and titanium and titanium alloy complex thin-walled parts and preparation methods thereof, the powder particle size grading method comprising respectively preparing titanium and titanium alloy coarse powder and titanium and titanium alloy fine powder as raw material powders; mixing the titanium and titanium alloy fine powder in the raw material powder with organic stearic acid according to a set ratio to obtain the titanium and titanium alloy fine powder after dry powder coating and modification; and calculating coarse and fine particle grading parameters, uniformly mixing the obtained coated and modified titanium and titanium alloy fine powder with the titanium and titanium alloy coarse powder of the raw material powder according to the coarse and fine particle grading parameters to obtain titanium and titanium alloy premixed powder. The present invention also discloses a method for preparing titanium and titanium alloy complex thin-walled parts and products thereof, wherein the titanium and titanium alloy premixed powder prepared by the above-mentioned powder particle size grading method is mixed with a highly conformal polyformaldehyde-based binder according to a set ratio, and then injection molded, degreased and sintered.

Description

Technical Field

[0001] The invention relates to powder metallurgy technology, and in particular to a particle size grading method for powder with high solid content and an injection molding preparation method for high-precision titanium and titanium alloy complex thin-walled parts and products. Background Art

[0002] Titanium and titanium alloys have excellent properties such as high specific strength, heat resistance, corrosion resistance, and good biocompatibility. They are widely used in aerospace, petrochemical, biomedical, marine and other fields. Titanium is a high melting point and highly active metal. It is difficult to prepare complex structures using traditional casting machine processing methods. The cost of parts is high and resources are wasted seriously, which seriously restricts the development of titanium alloys. Powder injection molding technology combines injection molding with powder metallurgy technology. It can directly prepare three-dimensional complex-shaped parts. The material utilization rate is close to 100%, which is easy to achieve mass production and has low manufacturing costs. It is an ideal titanium alloy manufacturing process.

[0003] Precisely controlling the dimensional accuracy of products is the core problem that powder injection molding technology needs to solve, especially for complex thin-walled parts made of titanium. Due to its complex structure, thin wall and low green strength, it collapses and deforms extremely during degreasing and sintering, and it is difficult to control the dimensional accuracy. During the thermal degreasing process, the high molecular polymer (high-density polyethylene, ethylene-vinyl acetate) that plays the role of skeleton will break the CC bond and decompose completely at around 500°C, while the pre-sintering temperature of titanium powder particles is relatively high (over 800°C). Therefore, in the range of 500-800°C, titanium powder particles only rely on weak van der Waals forces to maintain the shape of the degreased blank, and complex thin-walled parts are very prone to degreasing deformation and even collapse in this temperature range. In addition, during the sintering process, the lower solid content of powder in conventional feed (58-60 vol.%) will cause a larger shrinkage rate (15-20%) of the injection molded parts, increasing the difficulty of controlling the dimensional accuracy of titanium parts. Therefore, how to increase the solid content of powder and maintain shape retention after thermal degreasing is an urgent problem to be solved in this field in order to achieve dimensional accuracy control of complex thin-walled parts made of titanium materials. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for grading the particle size of a powder with a high solid content and a high-precision titanium and titanium alloy complex thin-walled part and a preparation method thereof in view of the above-mentioned defects of the prior art.

[0005] In order to achieve the above object, the present invention provides a method for particle size distribution of powder with high solid content, which comprises the following steps:

[0006] S100, preparing titanium and titanium alloy coarse powder and titanium and titanium alloy fine powder as raw material powders respectively;

[0007] S200, mixing the titanium and titanium alloy fine powder in the raw material powder with the organic stearic acid according to a set ratio by dry coating to obtain the titanium and titanium alloy fine powder after dry coating modification; and

[0008] S300, calculating coarse and fine particle gradation parameters, and uniformly mixing the titanium and titanium alloy fine powder obtained in step S200 with the titanium and titanium alloy coarse powder of the raw material powder in step S100 according to the coarse and fine particle gradation parameters to obtain titanium and titanium alloy premixed powder.

[0009] The above-mentioned method for particle size distribution of powder with high solid content, wherein in step S100, the titanium and titanium alloy coarse powder is spherical pure titanium, Ti-6Al-4V, Ti-6.5Al-2Zr-1Mo-1V and / or Ti-5Al-5Mo-5V-1Cr-1Fe powder, wherein the powder D 10 =10~15μm, D 50 =20~27μm, D 90 =38~45μm; the titanium and titanium alloy fine powder is spherical pure titanium, Ti-6Al-4V, Ti-6.5Al-2Zr-1Mo-1V and / or Ti-5Al-5Mo-5V-1Cr-1Fe powder, wherein the powder D 10 =0.5~2μm, D 50 =3~5μm, D 90 =6~8μm.

[0010] In the above-mentioned method for particle size distribution of powder with high solid content, in step S200, the mixing and coating temperature of the powder dry coating mixing is 90-120° C., the rotation speed is 10-30 r / min, and the time is 0.5-1.5 h.

[0011] In the above-mentioned method for particle size grading of powder with high solid content, in step S200, the content of stearic acid in the organic matter is 1 to 3 wt.%.

[0012] In the above-mentioned particle size distribution method for powder with high solid content, in step S300, the coarse and fine particle stacking ratio of the titanium and titanium alloy premixed powder is:

[0013]

[0014] Among them, λ mix is the stacking rate of the mixed system, λ c is the packing rate of coarse particles, λ f is the accumulation rate of fine particles, is the volume fraction of fine particles, ξ c is the inverse of the packing rate of coarse and fine particles, R is the particle size ratio of coarse particles to fine particles, and e is a natural constant, whose value is about 2.718.

[0015] In the above-mentioned particle size grading method for powder with high solid content, when the volume fraction of the titanium and titanium alloy fine powder is 0.1-0.4 vol.%, and the rest is the titanium and titanium alloy coarse powder, the coarse and fine particle stacking rate of the titanium and titanium alloy premixed powder is the highest.

[0016] In the above-mentioned method for particle size grading of powder with high solid content, in step S300, the mixing speed of mixing the titanium and titanium alloy fine powder with the titanium and titanium alloy coarse powder is 200-300 r / min, and the mixing time is 12-24 hours.

[0017] In order to better achieve the above-mentioned purpose, the present invention also provides a titanium and titanium alloy premixed powder prepared by the above-mentioned powder high solid content particle size grading method.

[0018] In order to better achieve the above-mentioned purpose, the present invention also provides a method for preparing complex thin-walled parts of titanium and titanium alloys, which comprises the following steps:

[0019] S10, mixing the titanium and titanium alloy premixed powder and the high-shape-retaining polyoxymethylene-based binder according to a set ratio, and then crushing them into granular feed;

[0020] S20, forming the granular feed on an injection molding machine to obtain a titanium or titanium alloy complex thin-walled blank;

[0021] S30, performing a degreasing process on the titanium and titanium alloy complex thin-walled blank, wherein the degreasing process includes a catalytic degreasing process and a thermal degreasing process; and

[0022] S40, sintering the titanium and titanium alloy complex thin-walled blank after degreasing treatment, and cooling it with the furnace to obtain a titanium and titanium alloy complex thin-walled finished product.

[0023] The above-mentioned method for preparing complex thin-walled parts of titanium and titanium alloys, wherein the polyoxymethylene-based adhesive includes the following components in percentage by mass: polyoxymethylene 75-82%, high-density polyethylene 3-7%, ethylene-vinyl acetate 2-5%, stearic acid 5-9% and carborane 5-10%.

[0024] In the above-mentioned method for preparing complex thin-walled parts of titanium and titanium alloys, the content of the polyoxymethylene-based binder is 64-70 vol.%.

[0025] In the above-mentioned method for preparing complex thin-walled parts of titanium and titanium alloys, in step S10, the mixing temperature is 165-190°C, the rotation speed is 10-40r / min, and the time is 1-2h; after the mixing is completed, it is cut into the granular feed by a crusher.

[0026] The above-mentioned method for preparing complex thin-walled parts of titanium and titanium alloys, wherein, in step S20, when forming on the injection molding machine, the granular feed is heated to 160-185°C, the injection pressure is 45-80MPa, the holding pressure is 40-100MPa, the holding time is 5-25s, the mold temperature is 50-100°C, and the injection speed is 50-80% of the maximum injection speed of the injection molding machine.

[0027] The above-mentioned method for preparing titanium and titanium alloy complex thin-walled parts, wherein the catalytic degreasing process uses nitric acid as the catalytic medium, the acid feed rate is 2-5 g / min, the degreasing temperature is 110-140°C, and the nitrogen flow rate is 3-6 m 3 / h, degreasing time is 4 to 8h.

[0028] The above-mentioned preparation method of titanium and titanium alloy complex thin-walled parts, wherein the thermal degreasing process is carried out under the protection of argon atmosphere, and the thermal degreasing process is to heat up from room temperature to 250-300°C at 0.5-1.5°C / min, and keep warm for 0.5-1.5h for the first stage of thermal degreasing; heat up to 350-400°C at 0.5-1.5°C / min, and keep warm for 0.5-1.5h for the second stage of thermal degreasing; heat up to 450-500°C at 0.5-1.5°C / min, and keep warm for 0.5-1.5h for the third stage of thermal degreasing; finally, heat up to 700-800°C at 0.5-2°C / min, and keep warm for 0.5-2h for the fourth stage of thermal degreasing.

[0029] In the above-mentioned method for preparing titanium and titanium alloy complex thin-walled parts, in step S40, the sintering treatment is carried out under argon gas protection or vacuum conditions, wherein the vacuum degree is 10 -2 ~10 -4 Pa; raising the temperature from the end temperature of the fourth stage thermal degreasing to 1000-1300°C at 2-5°C / min, keeping the temperature for 1-3h; then cooling to 700-800°C at 2-5°C / min; and finally cooling with the furnace.

[0030] In order to better achieve the above-mentioned purpose, the present invention also provides a high-precision titanium and titanium alloy complex thin-walled part produced by the above-mentioned method for producing titanium and titanium alloy complex thin-walled parts.

[0031] The above-mentioned titanium and titanium alloy complex thin-walled parts, wherein the titanium and titanium alloy complex thin-walled parts have a network-distributed TiB and TiC mixed reinforced equiaxial structure; the grain size of the TiB and TiC is 70-120μm; the TiB particles are short rod-shaped, 4-40μm long and 4-7μm wide; the TiC particles are spherical, with a diameter of 4-8μm; the volume percentage of the TiB particles is 10%-20%, and the volume percentage of the TiC particles is 5%-10%.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1) The use of a new polyoxymethylene-based binder suitable for complex thin-walled parts improves the shape retention of the blank and the dimensional accuracy of the final part;

[0034] 2) The fine titanium powder coated with stearic acid is graded with the coarse titanium powder to increase the solid content of the powder, reduce the sintering shrinkage, and improve the density and geometric size accuracy of the final product;

[0035] 3) The prepared high-precision titanium and titanium alloy complex thin-walled parts have a specific network distribution of TiB and TiC mixed reinforcement structure, and their room temperature mechanical properties are excellent.

[0036] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments, but is not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a scanning electron microscope morphology image of the coarse and fine Ti-6Al-4V alloy powders after premixing in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] The structural principle and working principle of the present invention are described in detail below in conjunction with the accompanying drawings:

[0039] The binder, high-precision titanium and titanium alloy complex thin-walled parts injection molding preparation method of the present invention firstly organically mixes coarse particles and stearic acid-coated fine particles of titanium powder through powder size grading, and adds them to a polyoxymethylene-based binder with a high decomposition temperature skeleton agent carborane component to prepare a new type of titanium feed with high powder solid content and high conformality, which gives the complex thin-walled titanium parts a strong conformality of the degreased blank, while reducing the sintering shrinkage rate and improving the dimensional accuracy control of the complex thin-walled titanium parts. In addition, carborane, as a ceramic precursor, can react with the titanium matrix in situ at above 700°C to generate TiC and TiB ceramic phase particles, significantly improving the mechanical properties of titanium parts.

[0040] The method for preparing titanium and titanium alloy complex thin-walled parts of the present invention comprises the following steps:

[0041] Step S10, preparing feed: mixing titanium and titanium alloy premixed powder and a high-conformity polyformaldehyde-based binder according to a set ratio, and then crushing to form granular feed; wherein the polyformaldehyde-based binder includes components in mass percentage: polyformaldehyde 75-82%, high-density polyethylene 3-7%, ethylene-vinyl acetate 2-5%, stearic acid 5-9% and carborane 5-10%; the polyformaldehyde-based binder content is preferably 64-70 vol.%; the mixing temperature is preferably 165-190°C, the rotation speed is preferably 10-40r / min, and the time is preferably 1-2h; after mixing, the granular feed can be cut into the granular feed by a crusher;

[0042] Step S20, injection molding: the granular feed is molded on an injection molding machine to obtain a complex thin-walled blank of titanium and titanium alloy; when molding on the injection molding machine, the granular feed is heated to 160-185°C, the injection pressure is preferably 45-80MPa, the holding pressure is preferably 40-100MPa, the holding time is preferably 5-25s, the mold temperature is preferably 50-100°C, and the injection speed is preferably 50-80% of the maximum injection speed of the injection molding machine

[0043] Step S30, degreasing: Degreasing the titanium and titanium alloy complex thin-walled blank, wherein the degreasing treatment includes a catalytic degreasing process and a thermal degreasing process; wherein the catalytic degreasing process uses nitric acid as a catalytic medium, the acid feed rate is preferably 2-5 g / min, the degreasing temperature is preferably 110-140°C, and the nitrogen flow rate is preferably 3-6 m 3 / h, the degreasing time is preferably 4 to 8h; the thermal degreasing process is carried out under the protection of an argon atmosphere, wherein the thermal degreasing process is carried out by heating from room temperature to 250 to 300°C at a rate of 0.5 to 1.5°C / min, and keeping the temperature for 0.5 to 1.5h for the first stage of thermal degreasing; heating to 350 to 400°C at a rate of 0.5 to 1.5°C / min, and keeping the temperature for 0.5 to 1.5h for the second stage of thermal degreasing; heating to 450 to 500°C at a rate of 0.5 to 1.5°C / min, and keeping the temperature for 0.5 to 1.5h for the third stage of thermal degreasing; and finally heating to 700 to 800°C at a rate of 0.5 to 2°C / min, and keeping the temperature for 0.5 to 2h for the fourth stage of thermal degreasing; and

[0044] Step S40, sintering: sintering the titanium and titanium alloy complex thin-walled blank after degreasing treatment, and cooling it with the furnace to obtain a titanium and titanium alloy complex thin-walled finished product; wherein the sintering treatment is carried out under argon gas protection or vacuum conditions, wherein the vacuum degree is preferably 10 -2 ~10 -4 Pa; raising the temperature from the end temperature of the fourth stage thermal degreasing to 1000-1300°C at 2-5°C / min, keeping the temperature for 1-3h; then cooling to 700-800°C at 2-5°C / min; and finally cooling with the furnace.

[0045] The high-precision titanium and titanium alloy complex thin-walled parts prepared by the preparation method of the present invention have a mesh-distributed TiB and TiC mixed reinforcement phase equiaxial structure; the grain size of the TiB and TiC is 70-120μm; the TiB particles are short rod-shaped, 4-40μm long and 4-7μm wide; the TiC particles are spherical, with a diameter of 4-8μm; the volume percentage of the TiB particles is 10%-20%, and the volume percentage of the TiC particles is 5%-10%.

[0046] In the above preparation method, the titanium and titanium alloy premixed powder used in step S10 is obtained by the following powder high solid content particle size distribution method, which includes the following steps:

[0047] Step S100, raw material preparation: prepare titanium and titanium alloy coarse powder and titanium and titanium alloy fine powder as raw material powders respectively; wherein the titanium and titanium alloy coarse powder is spherical pure titanium, Ti-6Al-4V, Ti-6.5Al-2Zr-1Mo-1V and / or Ti-5Al-5Mo-5V-1Cr-1Fe powder, wherein powder D 10 =10~15μm, D 50 =20~27μm, D 90 =38~45μm; the titanium and titanium alloy fine powder is spherical pure titanium, Ti-6Al-4V, Ti-6.5Al-2Zr-1Mo-1V and / or Ti-5Al-5Mo-5V-1Cr-1Fe powder, wherein the powder D 10 =0.5~2μm, D 50 =3~5μm, D 90 =6~8μm;

[0048] Step S200, coating: mixing the titanium and titanium alloy fine powder in the raw material powder with the organic stearic acid according to a set ratio by powder dry coating to obtain the titanium and titanium alloy fine powder after powder dry coating modification; wherein the mixing coating temperature for powder dry coating mixing is preferably 90-120°C, the rotation speed is preferably 10-30r / min, and the time is preferably 0.5-1.5h; the content of the organic stearic acid is preferably 1-3wt.%; and

[0049] Step S300, setting powder grading parameters and mixing: calculating the coarse and fine particle grading parameters, and uniformly mixing the titanium and titanium alloy fine powder obtained in step S200 with the titanium and titanium alloy coarse powder of the raw material powder in step S100 according to the coarse and fine particle grading parameters to obtain titanium and titanium alloy premixed powder; wherein, the mixing speed for mixing the titanium and titanium alloy fine powder with the titanium and titanium alloy coarse powder is preferably 200-300 r / min, and the mixing time is preferably 12-24 h.

[0050] Wherein, in step S300, the coarse and fine particle accumulation rate of the titanium and titanium alloy premixed powder is:

[0051]

[0052] In the formula, λ mix is the stacking rate of the mixed system, λ c is the packing rate of coarse particles, λ f is the accumulation rate of fine particles, is the volume fraction of fine particles, ξ c is the inverse of the coarse and fine particle stacking rate, R is the particle size ratio of coarse particles to fine particles, and e is a natural constant, whose value is about 2.718. When the volume fraction of the titanium and titanium alloy fine powder is 0.1-0.4 vol.%, and the rest is the titanium and titanium alloy coarse powder, the coarse and fine particle stacking rate of the titanium and titanium alloy premixed powder is the highest.

[0053] The present invention adds carborane, a skeleton component with a low melting point and a high decomposition temperature, to a polyoxymethylene-based binder, thereby enhancing the shape-keeping ability of complex thin-walled parts and solving the problem of deformation and collapse during the thermal degreasing process. 4 C will react with the titanium matrix in situ to generate fine dispersed TiB and TiC ceramic reinforcement phase particles, effectively improving the mechanical properties of complex thin-walled parts. The addition amount of carborane is 5-10%. If the addition amount is too low, it is difficult to effectively play the role of skeleton agent and maintain the shape of the green body. If the addition amount is too high, the generated TiB and TiC ceramic particles will be mixed with too many reinforcement phases and agglomerate, which will deteriorate the performance of the material.

[0054] In the polyoxymethylene-based binder, the thermal analysis results show that the decomposition temperatures of the skeleton agents high-density polyethylene and ethylene-vinyl acetate are both less than 500°C, while the sintering neck formation temperature of titanium powder exceeds 800°C. During the thermal debinding process, if the high-density polyethylene and ethylene-vinyl acetate that play the role of skeleton agent are completely removed, the force between the powder particles is mainly weak van der Waals force because the debinding temperature in the third stage has not reached the sintering neck formation and growth temperature. It is difficult to maintain the shape of the complex thin-walled green body to the pre-sintering stage, resulting in deformation or even collapse. However, carborane with a closed icosahedral cage structure redistributes electrons during the formation process, shortens the adjacent bond length, and forms a very stable covalent bond, so it has the characteristics of high temperature decomposition resistance. The introduction of carborane with low melting point and high decomposition temperature can not only meet the uniform mixing of various binder components during the mixing process, but also can rearrange its molecular configuration in the first three stages of the thermal debinding stage to obtain the most stable para-carborane, which continues to play the role of skeleton agent to maintain the shape of the green body, effectively improving the shape stability of complex thin-walled parts during the thermal debinding process. In addition, the melting point of carborane is 300-330℃, and the decomposition temperature is 700-800℃. Carborane will produce B during the high temperature decomposition process. 4 C, a hybrid reinforcement phase of TiB and TiC ceramic particles with a network distribution is generated in situ with the titanium matrix, which significantly improves the mechanical properties of the material.

[0055] In addition, due to the large specific surface energy of fine powder, powder particles are prone to agglomeration due to electrostatic forces and van der Waals forces, which increases the contact friction between powder particles and is not conducive to the effective filling of fine powder into the gaps between coarse particles during the powder size grading process. The organic stearic acid contains a polar group -COOH, which can be coated on the powder surface through Lewis acid-base reaction, reducing particle agglomeration and allowing fine particles to have the opportunity to enter the gaps between coarse particles, thereby increasing the powder tap density. The grading models derived from the existing powder discontinuous grading theory only consider the influence of the geometric factors of the powder on the packing rate, and do not consider the interactions between the electrostatic forces and van der Waals forces between the powders. Therefore, the model cannot be used ideally to predict the packing rate after coarse and fine particle grading, and the existing model often needs to be modified. For the existing mixed system model of two-size particles:

[0056]

[0057] Where: mix The stacking ratio of the mixed system, λ c is the packing rate of coarse particles, λ f is the accumulation rate of fine particles, is the volume fraction of fine particles, ξc is the inverse of the packing rate of coarse and fine particles, R is the particle size ratio of coarse particles to fine particles, and e is a natural constant with a value of approximately 2.718.

[0058] In order to more accurately describe the change of the stacking rate of the premixed powder of stearic acid surface coated fine powder, the present invention modifies some of its parameters. The modified discontinuous gradation theoretical model is:

[0059]

[0060] The calculated values ​​of the revised model fit the experimental values ​​better, and the accuracy is significantly improved compared with the uncorrected model, which is conducive to obtaining a high powder stacking rate to increase the feed loading, reduce the linear shrinkage during the sintering process, and help control the geometric accuracy of injection molded parts. However, due to the limited gap space between coarse particles and the fact that the size of fine particles is only 20% to 40% of the size of coarse particles, the fluidity of the feed will not be greatly reduced. In addition, the filling of fine particles also increases the contact points between coarse and fine particles, which is conducive to reducing the consumption of diffusion and mass transfer energy during the sintering process and promoting sintering densification.

[0061] The invention has been verified by experiments to be able to obtain complex thin-walled titanium parts with high precision, uniform internal structure, high density and excellent mechanical properties. The preparation method of the invention will be described in detail below through specific examples.

[0062] Example 1

[0063] Step S10, preparing feed:

[0064] Prepare premixed powder using steps S100-S300: Figure 1 , Figure 1 This is a scanning electron microscope morphology of the coarse and fine Ti-6Al-4V alloy powders premixed in Example 1 of the present invention. First, the coarse Ti-6Al-4V powder D is selected. 10 =11μm, D 50 =22μm, D 90 =40μm, fine Ti-6Al-4V powder D 10 =1μm, D 50 =4μm, D 90 =7μm; then the fine powder is surface coated with 3wt.% stearic acid, wherein the mixing and coating temperature is 120°C, the rotation speed is 15r / min, and the time is 1h; then the crude titanium alloy powder and the coated fine powder are evenly mixed, wherein the volume fraction of the added fine powder particles is 0.3vol.%, the rotation speed is 250r / min, and the time is 15h;

[0065] Selecting a binder: Selecting a solid powder loading of 70%, weighing 80% of polyoxymethylene, 5% of high-density polyethylene, 4% of ethylene-vinyl acetate, 5% of stearic acid, and 6% of carborane in a mass ratio to form a binder system;

[0066] Finally, the prepared premixed powder is kneaded with the binder at a temperature of 185°C, a rotation speed of 30 r / min, and a time of 1 hour. After the kneading is completed and cooled to room temperature, the feed is taken out and then a granular feed is obtained by a crusher.

[0067] Step S20: injection molding:

[0068] The feed is placed in an injection molding machine and heated to 185°C before injection. The injection pressure is 60MPa, the holding pressure is 70MPa, the holding time is 15s, the mold temperature is 65°C, and the injection speed is 50% of the maximum injection speed of the injection molding machine to prepare a complex thin-walled blank of titanium material.

[0069] Step S30, degreasing:

[0070] The above blanks were placed in a nitric acid environment for catalytic degreasing, with an acid feed rate of 3 g / min, a degreasing temperature of 120 °C, and a nitrogen flow rate of 3 m 3 / h, the degreasing time is 5h; then thermal degreasing is carried out under the protection of argon atmosphere, the thermal degreasing process is to increase the temperature from room temperature to 300℃ at 0.5℃ / min, and keep it warm for 1h for the first stage of thermal degreasing; then increase the temperature to 350℃ at 1℃ / min, and keep it warm for 0.5-1.5h for the second stage of thermal degreasing; finally, increase the temperature to 500℃ at 1℃ / min, and keep it warm for 1h for the third stage of thermal degreasing; increase the temperature to 700℃ at 2℃ / min, and keep it warm for 1h for the fourth stage of thermal degreasing.

[0071] Step S40, sintering:

[0072] The degreased blank is placed in a vacuum furnace for sintering at a vacuum degree of 10 -3 Pa; from the fourth stage hot debinding end temperature, the temperature is raised to 1250°C at 5°C / min and kept at that temperature for 2h; then the temperature is lowered to 800°C at 5°C / min; finally, the furnace is cooled.

[0073] Example 2

[0074] Step S10, preparing feed:

[0075] Preparation of premixed powder: First, select the coarse Ti-6Al-4V powder D 10 =11μm, D 50 =22μm, D 90 =40μm, fine Ti-6Al-4V powder D 10 =1μm, D 50 =4μm, D 90=7μm; then the fine powder is surface coated with 1wt.% stearic acid, wherein the mixing and coating temperature is 115°C, the rotation speed is 15r / min, and the time is 1h; then the crude titanium alloy powder and the coated fine powder are evenly mixed, wherein the volume fraction of the added fine powder particles is 0.1vol.%, the rotation speed is 280r / min, and the time is 15h;

[0076] Selecting a binder: Then selecting a solid powder loading of 64%, weighing 80% of polyoxymethylene, 5% of high-density polyethylene, 3% of ethylene-vinyl acetate, 5% of stearic acid, and 9% of carborane in a mass ratio to form a binder system;

[0077] Then the prepared premixed powder is mixed with the binder at a mixing temperature of 185°C, a rotation speed of 30 r / min, and a time of 1 hour. After the mixing is completed and cooled to room temperature, the feed is taken out and then a granular feed is obtained by a crusher.

[0078] Step S20: injection molding:

[0079] The feed is placed in an injection molding machine and heated to 180°C before injection. The injection pressure is 65MPa, the holding pressure is 70MPa, the holding time is 15s, the mold temperature is 65°C, and the injection speed is 50% of the maximum injection speed of the injection molding machine to prepare a complex thin-walled blank of titanium material.

[0080] Step S30, degreasing:

[0081] The above blanks were placed in a nitric acid environment for catalytic degreasing, with an acid feed rate of 3 g / min, a degreasing temperature of 125 °C, and a nitrogen flow rate of 3 m 3 / h, the degreasing time is 5h; then thermal degreasing is carried out under the protection of argon atmosphere, and the thermal degreasing process is to increase the temperature from room temperature to 300℃ at 0.5℃ / min, and keep it warm for 1h for the first stage of thermal degreasing; then increase the temperature to 350℃ at 1℃ / min, and keep it warm for 0.5-1.5h for the second stage of thermal degreasing; finally, increase the temperature to 500℃ at 1℃ / min, and keep it warm for 1h for the third stage of thermal degreasing; increase the temperature to 800℃ at 2℃ / min, and keep it warm for 1h for the fourth stage of thermal degreasing.

[0082] Step S40, sintering:

[0083] The degreased blank is placed in a vacuum furnace for sintering at a vacuum degree of 10 -3 Pa; from the fourth stage hot debinding end temperature, the temperature is raised to 1250°C at 5°C / min and kept at that temperature for 2h; then the temperature is lowered to 800°C at 5°C / min; finally, the furnace is cooled.

[0084] Example 3

[0085] Step S10, preparing feed:

[0086] Preparation of premixed powder: First, select coarse pure titanium powder D 10 =11μm, D 50 =22μm, D 90 =40μm, fine titanium alloy powder D 10 =1μm, D 50 =4μm, D 90 =7μm; then the fine pure titanium powder is surface coated with 2wt.% stearic acid, wherein the mixing and coating temperature is 115°C, the rotation speed is 15r / min, and the time is 1h; then the crude titanium alloy powder and the coated fine powder are evenly mixed, wherein the volume fraction of the added fine powder particles is 0.2vol.%, the rotation speed is 250r / min, and the time is 16h;

[0087] Selecting a binder: Selecting a solid powder loading of 67%, weighing 80% of polyoxymethylene, 5% of high-density polyethylene, 3% of ethylene-vinyl acetate, 5% of stearic acid, and 7% of carborane in a mass ratio to form a binder system;

[0088] Then the prepared premixed powder is mixed with the binder at a mixing temperature of 185°C, a rotation speed of 30 r / min, and a time of 1 hour. After the mixing is completed and cooled to room temperature, the feed is taken out and then a granular feed is obtained by a crusher.

[0089] Step S20: injection molding:

[0090] The feed is placed in an injection molding machine and heated to 180°C before injection. The injection pressure is 65MPa, the holding pressure is 70MPa, the holding time is 15s, the mold temperature is 65°C, and the injection speed is 50% of the maximum injection speed of the injection molding machine to prepare a complex thin-walled blank of titanium material.

[0091] Step S30, degreasing:

[0092] The above blanks were placed in a nitric acid environment for catalytic degreasing, with an acid feed rate of 3 g / min, a degreasing temperature of 125 °C, and a nitrogen flow rate of 3 m 3 / h, the degreasing time is 5h; then thermal degreasing is carried out under the protection of argon atmosphere, the thermal degreasing process is to increase the temperature from room temperature to 300℃ at 0.5℃ / min, and keep it for 1h for the first stage of thermal degreasing; then increase the temperature to 350℃ at 1℃ / min, and keep it for 1h for the second stage of thermal degreasing; finally, increase the temperature to 500℃ at 1℃ / min, and keep it for 1h for the third stage of thermal degreasing; increase the temperature to 770℃ at 2℃ / min, and keep it for 1h for the fourth stage of thermal degreasing.

[0093] Step S40, sintering:

[0094] The degreased blank is placed in a vacuum furnace for sintering at a vacuum degree of 10 -3 Pa; from the fourth stage hot debinding end temperature, the temperature is raised to 1250°C at 5°C / min and kept at that temperature for 2h; then the temperature is lowered to 800°C at 5°C / min; finally, the furnace is cooled.

[0095] Example 4

[0096] Step S10, preparing feed:

[0097] Preparation of premixed powder: First, select coarse pure titanium powder D 10 =15μm, D 50 =27μm, D 90 =45μm, fine pure titanium powder D 10 =0.5μm, D 50 =3μm, D 90 =6μm; then the fine powder is surface coated with 3wt.% stearic acid, wherein the mixing and coating temperature is 100°C, the rotation speed is 15r / min, and the time is 1h; then the crude titanium alloy powder and the coated fine powder are evenly mixed, wherein the volume fraction of the added fine powder particles is 0.3vol.%, the rotation speed is 280r / min, and the time is 15h;

[0098] Select a binder; then select a solid powder loading of 70%, and weigh 80% of polyoxymethylene, 5% of high-density polyethylene, 3% of ethylene-vinyl acetate, 5% of stearic acid, and 6% of carborane in a mass ratio to form a binder system;

[0099] Then the prepared premixed powder is mixed with the binder at a mixing temperature of 185°C, a rotation speed of 30 r / min, and a time of 1 hour. After the mixing is completed and cooled to room temperature, the feed is taken out and then a granular feed is obtained by a crusher.

[0100] Step S20: injection molding:

[0101] The feed is placed in an injection molding machine and heated to 175°C before injection. The injection pressure is 65MPa, the holding pressure is 70MPa, the holding time is 15s, the mold temperature is 65°C, and the injection speed is 50% of the maximum injection speed of the injection molding machine to prepare a complex thin-walled blank of titanium material.

[0102] Step S30, degreasing:

[0103] The above blanks were placed in a nitric acid environment for catalytic degreasing, with an acid feed rate of 3 g / min, a degreasing temperature of 125 °C, and a nitrogen flow rate of 3 m 3 / h, the degreasing time is 5h; then thermal degreasing is carried out under the protection of argon atmosphere, the thermal degreasing process is to increase the temperature from room temperature to 300℃ at 0.5℃ / min, and keep it warm for 1h for the first stage of thermal degreasing; then increase the temperature to 350℃ at 1℃ / min, and keep it warm for 1h for the second stage of thermal degreasing; finally, increase the temperature to 500℃ at 1℃ / min, and keep it warm for 1h for the third stage of thermal degreasing; increase the temperature to 700℃ at 2℃ / min, and keep it warm for 1h for the fourth stage of thermal degreasing.

[0104] Step S40, sintering:

[0105] The degreased blank is placed in a vacuum furnace for sintering at a vacuum degree of 10 -3 Pa; from the fourth stage hot debinding end temperature, the temperature is raised to 1300°C at 5°C / min and kept at this temperature for 2h; then the temperature is lowered to 800°C at 5°C / min; finally, the furnace is cooled.

[0106] Example 5

[0107] Step S10, preparing feed:

[0108] Preparation of premixed powder: First, select coarse pure titanium powder D 10 =10μm, D 50 =20μm, D 90 =38μm, fine pure titanium powder D 10 =2μm, D 50 =5μm, D 90 =8μm; then the fine powder is surface coated with 3wt.% stearic acid, wherein the mixing and coating temperature is 120°C, the rotation speed is 15r / min, and the time is 1h; then the crude titanium alloy powder and the coated fine powder are evenly mixed, wherein the volume fraction of the added fine powder particles is 0.1vol.%, the rotation speed is 280r / min, and the time is 15h;

[0109] Select a binder; then select a solid powder loading of 65%, and weigh 78% of polyoxymethylene, 5% of high-density polyethylene, 2% of ethylene-vinyl acetate, 5% of stearic acid, and 10% of carborane in a mass ratio to form a binder system;

[0110] Then the prepared premixed powder is mixed with the binder at a mixing temperature of 185°C, a rotation speed of 30 r / min, and a time of 1 hour. After the mixing is completed and cooled to room temperature, the feed is taken out and then a granular feed is obtained by a crusher.

[0111] Step S20: injection molding:

[0112] The feed is placed in an injection molding machine and heated to 180°C before injection. The injection pressure is 65MPa, the holding pressure is 70MPa, the holding time is 15s, the mold temperature is 65°C, and the injection speed is 50% of the maximum injection speed of the injection molding machine to prepare a complex thin-walled blank of titanium material.

[0113] Step S30, degreasing:

[0114] The above blanks were placed in a nitric acid environment for catalytic degreasing, with an acid feed rate of 3 g / min, a degreasing temperature of 125 °C, and a nitrogen flow rate of 3 m 3 / h, the degreasing time is 5h; then thermal degreasing is carried out under the protection of argon atmosphere, and the thermal degreasing process is to increase the temperature from room temperature to 300℃ at 1℃ / min, and keep it warm for 1h for the first stage of thermal degreasing; then increase the temperature to 350℃ at 1℃ / min, and keep it warm for 1h for the second stage of thermal degreasing; finally, increase the temperature to 500℃ at 1℃ / min, and keep it warm for 1h for the third stage of thermal degreasing; increase the temperature to 800℃ at 2℃ / min, and keep it warm for 1h for the fourth stage of thermal degreasing.

[0115] Step S40, sintering:

[0116] The degreased blank is placed in a vacuum furnace for sintering at a vacuum degree of 10 -3 Pa; from the fourth stage hot debinding end temperature, the temperature is raised to 1200°C at 5°C / min and kept at that temperature for 2h; then the temperature is lowered to 800°C at 5°C / min; finally, the furnace is cooled.

[0117] The following is a performance comparison experiment between the complex thin-walled parts produced by the preparation methods in Examples 1 to 5 and the complex thin-walled parts produced by the traditional process.

[0118] 1. Experimental Phenomenon

[0119] The complex thin-walled parts prepared in Examples 1 to 5 and the complex thin-walled parts prepared in Comparative Examples 1 to 5, wherein:

[0120] Comparative Example 1

[0121] Coarse and fine titanium powders with the same particle size composition and ingredients as in Example 1 were used, and then 70% of the solid powder loading was selected, and 80% of polyoxymethylene, 6% of high-density polyethylene, 7% of ethylene-vinyl acetate, and 7% of stearic acid were weighed in a mass ratio to form a binder system.

[0122] Then the feed preparation, injection molding, debinding and sintering are carried out in sequence, wherein the thermal debinding process is to heat up from room temperature to 300℃ at 1℃ / min and keep it for 1h for the first stage of thermal debinding; then heat up to 350℃ at 1℃ / min and keep it for 1h for the second stage of thermal debinding; finally, heat up to 500℃ at 1℃ / min and keep it for 1h for the third stage of thermal debinding; then heat up to 1200℃ at 5℃ / min and keep it for 2h; then cool down to 800℃ at 5℃ / min; finally, cool with the furnace.

[0123] It was found that in Comparative Example 1, during the third stage of thermal debinding to pre-sintering, the complex thin-walled parts collapsed and deformed and could not maintain their shape.

[0124] Comparative Example 2

[0125] Complex thin-walled parts are prepared by the same preparation process as in Example 1, except that the content of the binder components is different, especially the content of carborane is lower. Specifically, 81% of polyoxymethylene, 6% of high-density polyethylene, 5% of ethylene-vinyl acetate, 7% of stearic acid, and 2% of carborane are weighed in a mass ratio to form a binder system.

[0126] After testing, in Comparative Example 2, in the fourth stage of thermal debinding to pre-sintering, there were a large number of cracks in the complex thin-walled parts, which did not meet the use requirements.

[0127] Comparative Example 3

[0128] The same preparation process as in Example 1 is adopted to prepare complex thin-walled parts, except that the contents of the components of the binder system are different, especially the content of carborane is higher. Specifically, 75% of polyoxymethylene, 3% of high-density polyethylene, 2% of ethylene-vinyl acetate, 5% of stearic acid, and 15% of carborane are weighed in a mass ratio to form the binder system.

[0129] Comparative Example 4

[0130] The complex thin-walled parts were prepared by the same preparation process as in Example 1, except that stearic acid was not used to pre-coat the fine particle powder.

[0131] Comparative Example 5

[0132] The complex thin-walled product was prepared by the same preparation process as in Example 1, except that the content of stearic acid in the coating process was 8%.

[0133] 2. Experimental Methods

[0134] The performance of the complex thin-walled parts prepared in Examples 1 to 5 and Comparative Examples 1 to 5 was measured using conventional inspection methods in the prior art.

[0135] Performance Testing

[0136] (1) Relative density test: The relative density of Examples 1 to 5 and Comparative Examples 1 to 5 was measured.

[0137] (2) Mechanical property test: The room temperature tensile strength and elongation of Examples 1 to 5 and Comparative Examples 1 to 5 were measured.

[0138] (3) Powder property test: The loose density and tap density of Examples 1 to 5 and Comparative Examples 1 to 5 were measured.

[0139] 3. Experimental Results

[0140] After testing, the titanium material complex thin-walled parts prepared by the preparation method in Examples 1 to 5 have excellent conformality, high dimensional accuracy and excellent mechanical properties. In terms of microstructure, the prepared complex thin-walled parts have fine grains, uniform organization, and an equiaxed organizational structure with mixed reinforcement of TiB and TiC network distribution; wherein the grain size is 70 to 120 μm; the TiB particles are short rod-shaped, 4 to 40 μm long, 4 to 7 μm wide, and the TiC particles are spherical, with a size of about 4 to 8 μm; the volume percentage of the TiB particles is 10% to 20%, and the volume fraction of the TiC particles is 5% to 10%.

[0141] The experimental results of Examples 1 to 5 and Comparative Examples 1 to 5 are summarized below, as shown in Table 1.

[0142] Table 1 Comparison of the performance of complex thin-walled parts prepared in Examples 1 to 5 and Comparative Examples 1 to 5

[0143]

[0144] Through data comparison, in the third stage of thermal debinding to pre-sintering, the comparative example experienced collapse deformation of the complex thin-walled parts and could not maintain their shape; while in Examples 1 to 5 of the present invention, by introducing a carborane framework agent with a high heat-resistant temperature, the stability of complex thin-walled parts of titanium materials during thermal debinding was effectively improved, ensuring the injection molding process for preparing thin-walled parts of titanium materials with complex shapes. At the same time, an equiaxed structure with a mixed and enhanced network distribution of TiB and TiC was prepared, so that the complex thin-walled parts have excellent comprehensive mechanical properties. In addition, the use of organic stearic acid to coat the surface of the fine powder can reduce the interaction between the electrostatic force and van der Waals force between the fine powder particles, reduce the friction between the powder particles, and increase the loose and tap density of the powder, thereby increasing the solid phase loading of the powder.

[0145] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A particle size distribution method for powder with high solid content, It is characterized in that The steps include: S100, preparing titanium and titanium alloy coarse powder and titanium and titanium alloy fine powder as raw material powders respectively; S200, mixing the titanium and titanium alloy fine powder in the raw material powder with the organic stearic acid according to a set ratio by dry coating to obtain the titanium and titanium alloy fine powder after dry coating modification, wherein the content of the organic stearic acid is 1 to 3 wt.%; and S300, calculating the coarse and fine particle gradation parameters, and uniformly mixing the titanium and titanium alloy fine powder obtained in step S200 with the titanium and titanium alloy coarse powder of the raw material powder in step S100 according to the coarse and fine particle gradation parameters to obtain titanium and titanium alloy premixed powder, wherein the titanium and titanium alloy coarse powder is spherical pure titanium, Ti-6Al-4V, Ti-6.5Al-2Zr-1Mo-1V and / or Ti-5Al-5Mo-5V-1Cr-1Fe powder, wherein the powder D 10 =10~15μm, D 50 =20~27μm, D 90 =38~45μm; the titanium and titanium alloy fine powder is spherical pure titanium, Ti-6Al-4V, Ti-6.5Al-2Zr-1Mo-1V and / or Ti-5Al-5Mo-5V-1Cr-1Fe powder, wherein the powder D 10 =0.5~2μm, D 50 =3~5μm, D 90 =6~8μm; In step S200, the powder dry coating mixing is performed at a mixing temperature of 90 to 120°C, a rotation speed of 10 to 30 r / min, and a time of 0.5 to 1.5 h; In step S300, the coarse and fine particle accumulation rate of the titanium and titanium alloy premixed powder is: Among them, λ mix is the stacking rate of the mixed system, λ c is the packing rate of coarse particles, λ f is the accumulation rate of fine particles, is the volume fraction of fine particles, ξ c is the inverse of the coarse and fine particle stacking rate, R is the particle size ratio of coarse particles to fine particles, e is a natural constant, and its value is 2.718; and when the volume fraction of the titanium and titanium alloy fine powder is 0.1~0.4vol.%, and the rest is the titanium and titanium alloy coarse powder, the coarse and fine particle stacking rate of the titanium and titanium alloy premixed powder is the highest.

2. The method for particle size distribution of powder with high solid content as claimed in claim 1, It is characterized in that In step S300, the titanium and titanium alloy fine powder obtained in step S200 is mixed with the titanium and titanium alloy coarse powder of the raw material powder in step S100 at a mixing speed of 200 to 300 r / min for 12 to 24 hours.

3. A titanium and titanium alloy premixed powder prepared by the particle size grading method with high solid content of powder according to claim 1 or 2.

4. A method for preparing complex thin-walled parts of titanium and titanium alloys, It is characterized in that The steps include: S10, mixing the titanium and titanium alloy premixed powder according to claim 3 with a high-conformity polyoxymethylene-based binder according to a set ratio, and then crushing it into granular feed, wherein the content of the polyoxymethylene-based binder is 64-70 vol.%; the polyoxymethylene-based binder includes the following components in mass percentage: polyoxymethylene 75-82%, high-density polyethylene 3-7%, ethylene-vinyl acetate 2-5%, stearic acid 5-9% and carborane 5-10%; the carborane reacts in situ with the titanium matrix at above 700°C to generate TiC and TiB ceramic phase particles; S20, forming the granular feed on an injection molding machine to obtain a titanium or titanium alloy complex thin-walled blank; S30, degreasing the titanium and titanium alloy complex thin-walled blanks, the degreasing treatment includes a catalytic degreasing process and a thermal degreasing process; the catalytic degreasing process uses nitric acid as a catalytic medium, the acid feed rate is 2-5 g / min, the degreasing temperature is 110-140°C, and the nitrogen flow rate is 3-6 m 3 / h, the degreasing time is 4 to 8h; the thermal degreasing process is carried out under the protection of argon atmosphere, the thermal degreasing process is to heat up from room temperature to 250 to 300°C at 0.5 to 1.5°C / min, and keep warm for 0.5 to 1.5h for the first stage of thermal degreasing; to heat up to 350 to 400°C at 0.5 to 1.5°C / min, and keep warm for 0.5 to 1.5h for the second stage of thermal degreasing; to heat up to 450 to 500°C at 0.5 to 1.5°C / min, and keep warm for 0.5 to 1.5h for the third stage of thermal degreasing; finally, to heat up to 700 to 800°C at 0.5 to 2°C / min, and keep warm for 0.5 to 2h for the fourth stage of thermal degreasing; and S40, sintering the titanium and titanium alloy complex thin-walled blank after degreasing treatment, and cooling it with the furnace to obtain a titanium and titanium alloy complex thin-walled finished product; In step S40, the sintering process is carried out under argon gas protection or vacuum conditions, wherein the vacuum degree is 10 -2 ~10 -4 Pa; raising the temperature from the end temperature of the fourth stage thermal degreasing to 1000-1300°C at 2-5°C / min, keeping the temperature for 1-3h; then cooling to 700-800°C at 2-5°C / min; and finally cooling with the furnace.

5. The method for preparing titanium and titanium alloy complex thin-walled parts according to claim 4, It is characterized in that In step S10, the mixing temperature is 165-190° C., the rotation speed is 10-40 r / min, and the time is 1-2 h; after the mixing is completed, the material is cut into the granular feed by a crusher.

6. The method for preparing complex thin-walled parts of titanium and titanium alloys according to claim 4, It is characterized in that In step S20, when forming on the injection molding machine, the granular feed is heated to 160-185°C, the injection pressure is 45-80MPa, the holding pressure is 40-100MPa, the holding time is 5-25s, the mold temperature is 50-100°C, and the injection speed is 50-80% of the maximum injection speed of the injection molding machine.

7. A high-precision titanium and titanium alloy complex thin-walled part made by the method for making titanium and titanium alloy complex thin-walled parts according to any one of claims 4 to 6.

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