Preparation method for titanium alloy material

Abstract

A preparation method for a titanium alloy material, which preparation method relates to the field of powder injection molding. The preparation method comprises the following steps: S1, preparing a titanium alloy fine powder and a titanium alloy coarse powder, wherein the particle size of the titanium alloy fine powder is in the range of 1-20 μm, and the particle size of the titanium alloy coarse powder is in the range of 50-100 μm; mixing the titanium alloy fine powder and the titanium alloy coarse powder to form a titanium alloy mixed powder, wherein the proportion of the titanium alloy coarse powder in the titanium alloy mixed powder is 50% or above; S2, mixing the titanium alloy mixed powder and a binder to prepare a feed; S3, placing the feed in an injection molding machine, and subjecting the feed to injection molding by means of a mold to form an injection blank; S4, degreasing the injection blank to obtain a degreased blank; and S5, subjecting the degreased blank to high-vacuum sintering to obtain a sintered blank. By mixing the 50-100 μm titanium alloy coarse powder and the 1-20 μm titanium alloy fine powder according to different proportions, part of the titanium alloy coarse powder is used for replacing the titanium alloy fine powder, to reduce the amount of the titanium alloy fine powder, thereby reducing the cost of the titanium alloy powder for metal injection molding.

Description

A method for preparing titanium alloy material Technical Field

[0001] The invention relates to the field of powder injection molding, and in particular to a method for preparing a titanium alloy material. Background Art

[0002] Titanium alloys, due to their excellent comprehensive properties, including high specific strength, corrosion resistance, high and low temperature resistance, non-magnetic properties, weldability, and excellent biocompatibility, are finding important applications in a wide range of fields, including aerospace, nuclear industry, weapons, marine, petroleum, chemical industry, medical treatment, and daily life, and are gaining increasing acceptance. However, the high cost of titanium alloys, due to the complex and lengthy preparation processes, has limited their application. Reducing costs has become a key issue that must be addressed in the development of titanium alloys.

[0003] Titanium alloy powder (1-20μm) used in metal injection molding has a low yield, resulting in high powder costs. Research on the application range of titanium alloy powders found that 20-50μm titanium alloy powders are mainly used in the 3D printing industry. Powders in the 50-100μm range are too large to be of practical value, are inexpensive, and are usually recycled.

[0004] When it comes to coarse / fine powder blends of titanium alloy powder, adding more coarse powder isn't necessarily better. Multiple factors need to be considered, including the tap density of the mixed powder, powder filling efficiency, and sintering performance. First, the tap density of coarse / fine powder blends varies depending on their ratio, and the design of the titanium alloy feedstock loading for metal injection molding is influenced by the tap density of the powders. A higher tap density increases the titanium alloy feedstock loading. Excessive loading can affect the flowability of the titanium alloy feedstock and increase injection risks. Furthermore, only a specific coarse / fine powder blend ratio can ensure that the fine powder fully fills the gaps between the coarse powder particles. Excessive coarse powder content may result in some gaps between the coarse powder particles being left unfilled, thus compromising the sintering density of the titanium alloy. Finally, while considering reducing raw material costs for titanium alloy injection molding through coarse / fine powder blends, the stability of the sintering performance should also be considered. If the sintering performance of the coarse / fine powder blend is too poor, the titanium alloy loses its usefulness.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a titanium alloy material, which reduces the amount of titanium alloy fine powder used by mixing 50-100 μm titanium alloy coarse powder and 1-20 μm titanium alloy fine powder in different proportions, and uses part of the titanium alloy coarse powder to replace the titanium alloy fine powder, thereby reducing the cost of titanium alloy powder used for metal injection molding.

[0007] The technical solution for achieving the purpose of the present invention is: the present invention comprises the following steps:

[0008] S1. Preparing titanium alloy fine powder and titanium alloy coarse powder, wherein the particle size of the titanium alloy fine powder is in the range of 1 to 20 μm, and the particle size of the titanium alloy coarse powder is in the range of 50 to 100 μm; mixing the titanium alloy fine powder and the titanium alloy coarse powder to form a titanium alloy mixed powder; the titanium alloy coarse powder accounts for 50% to 80% of the titanium alloy mixed powder;

[0009] S2, mixing the titanium alloy mixed powder and the binder to form a feed;

[0010] S3, placing the feed in an injection molding machine and forming it into an injection blank through a mold;

[0011] S4, degreasing the injection blank to obtain a degreased blank;

[0012] S5. Perform high vacuum sintering on the degreased blank to obtain a sintered blank.

[0013] Furthermore, the D50 of the titanium alloy fine powder is 10 to 13 μm; and the D50 of the titanium alloy coarse powder is 70 to 80 μm.

[0014] Furthermore, the ratio of the titanium alloy mixed powder to the binder in the above feed is 0.8≤V1 / V2≤1.9, wherein V1 is the volume of the titanium alloy mixed powder and V2 is the volume of the binder.

[0015] Theoretical powder loading = tap density (ρr) / theoretical density (ρ). During normal feeding preparation, the powder loading can be lower than the theoretical loading, but not higher (higher than the theoretical loading will result in the binder not fully coating all the powder, resulting in uneven feeding and affecting feeding fluidity). Our conclusion from the verification of different loading amounts of titanium alloy mixed powder is that the feeding fluidity is optimal when the ratio of alloy powder to polymer binder is within the range of 0.8-1.9.

[0016] Furthermore, the volume proportion of the titanium alloy mixed powder in the feed is 58% to 66%, and the rest is a polymer binder; the components of the polymer binder include 60% to 70% of polyoxymethylene, 12% to 15% of polyethylene, 15% to 20% of polypropylene and 3% to 5% of stearic acid in terms of mass percentage; the loading range of the feed is 53%-73%.

[0017] As an optimal design, the ratio of the titanium alloy mixed powder to the binder in the feed is 1:1; and the loading range of the feed is 58% to 66%.

[0018] Calculation of the optimal loading capacity shows that the loading range for coarse and fine powder mixtures of varying proportions is 53%-73%. A 1:1 mixture of coarse and fine powders has the highest tap density and, in theory, the best sintering densification effect. However, the theoretical loading capacity for a 1:1 mixture is 73%. Excessively high loading can affect feed fluidity. To ensure feed fluidity, the loading capacity for a 1:1 mixture is set at 58%-66%. Powder loading can be lower than the theoretical loading capacity, but not higher (a higher loading capacity will prevent the binder from fully coating all the powder, resulting in uneven feeding and impacting feed fluidity).

[0019] Furthermore, the technical parameters of the injection molding in the above step S3 are: mold temperature of 80-120° C., feed heating temperature of 160-220° C., injection pressure of 80-120 MPa; and holding time of 1-2.5 s.

[0020] Due to the high loading of titanium alloy mixed powder, the injection pressure needs to be low (high injection pressure will cause some fine powder to flow to the surface of the injection blank, which will not fill the gaps between the coarse powder particles). A certain holding time is to ensure that the injection blank is full and defect-free.

[0021] Furthermore, the technical parameters of the degreasing in the above step S4 are: catalytic degreasing is performed using oxalic acid as a medium, and the degreasing time is t≥(60+60*h)min, where h is the maximum thickness of the injection blank, in mm.

[0022] Furthermore, the technical parameters for sintering in the above step S5 are: high vacuum sintering is performed in a metal cavity sintering furnace, the pressure in the furnace is ≤1.0×10-3Pa, and the sintering temperature T satisfies 0.65TL≤T≤0.85TL.

[0023] Since the sintering kinetic energy of coarse powder is higher than that of fine powder, more sintering energy is required to form a sintering neck and perform densification sintering. Therefore, the sintering temperature T of the coarse and fine powder mixture is closer to 0.85TL.

[0024] A certain amount of fine powder is added on the basis of the low price and low content of impurity elements of coarse powder. During the mixing process, the fine powder can be effectively filled between the coarse powder particles, increasing the tap density of the coarse powder and avoiding the shortcomings of the coarse powder such as poor sintering density and poor mechanical properties. In addition, the feeding load can be fine-tuned by adjusting the ratio of coarse and fine powders, and the precise fine-tuning of the size of the sintered part can be achieved without affecting the mechanical properties of the sintered part (the loading amount is fine-tuned by adjusting the ratio of titanium alloy coarse powder and titanium alloy fine powder, thereby affecting the dimensional shrinkage of the sintered part). However, since the sintering densification temperature of the coarse powder is higher than that of the fine powder, the sintering temperature of the coarse / fine powder mixture should be based on the densification temperature of the coarse powder sintering, so as to ensure that a complete sintering neck can be formed between the coarse powder particles during the sintering process.

[0025] Due to its high activity, titanium alloys easily react with carbon and oxygen in the air to form carbides and oxides, which seriously affect the sintering performance of titanium alloys. Therefore, titanium alloy sintering must be carried out in a high vacuum sintering environment (principle: iron-based alloys, stainless steel, cobalt alloys, nickel-based alloys, copper alloys and other alloy materials are less active than hydrogen and carbon. If sintering is carried out in a hydrogen / carbon / high vacuum environment, the oxygen content in the alloy will be quickly replaced, resulting in rapid densification during the sintering process, and the goal of achieving high porosity through high oxygen content cannot be achieved. Because titanium alloys are extremely active, they must be sintered in a high vacuum environment (with stronger reducing properties than hydrogen and carbon atmospheres) to achieve partial reduction of titanium oxide and form sintering necks between powder particles.)

[0026] The present invention has positive effects: (1) The present invention reduces the amount of titanium alloy fine powder used by mixing 50-100 μm titanium alloy coarse powder and 1-20 μm titanium alloy fine powder in different proportions, and uses part of the titanium alloy coarse powder to replace the titanium alloy fine powder, thereby reducing the cost of titanium alloy powder used for metal injection molding.

[0027] (2) The present invention designs the mixing ratio of titanium alloy coarse powder and titanium alloy fine powder so that the titanium alloy fine powder can completely fill the gaps in the titanium alloy coarse powder, thereby solving the problem of the titanium alloy coarse powder not being sintered densely.

[0028] (3) The oxygen content of the titanium alloy coarse powder in the present invention is lower than that of the titanium alloy fine powder. Therefore, the titanium alloy mixed powder can effectively reduce the oxygen content of the product, which is beneficial to sintering densification. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments and in conjunction with the accompanying drawings, wherein

[0030] FIG1 is a metallographic microstructure of a sintered blank in Example 1 of the present invention;

[0031] FIG2 is a metallographic microstructure of a sintered blank in Example 2 of the present invention;

[0032] FIG3 is a metallographic microstructure of a sintered blank in a comparative example of the present invention. DETAILED DESCRIPTION

[0033] (Example 1)

[0034] The present invention comprises the following steps:

[0035] S1. Preparing titanium alloy fine powder and titanium alloy coarse powder, wherein the particle size of the titanium alloy fine powder is in the range of 1 to 20 μm (D50: 10 to 13 μm), and the particle size of the titanium alloy coarse powder is in the range of 50 to 100 μm (D50: 70 to 80 μm); mixing the titanium alloy fine powder and the titanium alloy coarse powder to form a titanium alloy mixed powder; the ratio of the titanium alloy coarse powder to the titanium alloy fine powder in the titanium alloy mixed powder is 1:1;

[0036] S2. Mixing a titanium alloy mixed powder and a binder to form a feed; wherein the ratio of the titanium alloy mixed powder to the binder is 1.6; the titanium alloy mixed powder accounts for 66% by volume of the feed, and the remainder is a polymer binder; the components of the polymer binder include, by mass percentage, 60% to 70% of polyoxymethylene, 12% to 15% of polyethylene, 15% to 20% of polypropylene, and 3% to 5% of stearic acid;

[0037] S3. Place the feed material in an injection molding machine and inject it into an injection blank through a mold; the injection parameters are: mold temperature of 80-120°C, feed material heating temperature of 160-220°C, injection pressure of 80-120 MPa; holding time of 1-2.5 s;

[0038] S4. Degreasing the injection blank to obtain a degreased blank; the specific technical parameters of the degreasing are: degreasing is performed by catalytic degreasing using an oxalic acid medium, and the degreasing time is t≥(60+60*h)min, where h is the maximum thickness of the injection blank, in mm;

[0039] S5. High-vacuum sintering is performed on the debinded blank to obtain a sintered blank. Specific technical parameters for sintering are: high-vacuum sintering in a metal cavity sintering furnace, furnace pressure ≤ 1.0 × 10⁻³ Pa, and sintering temperature T satisfying 0.65TL ≤ T ≤ 0.85TL. Because the sintering kinetic energy of coarse powder is higher than that of fine powder, more sintering energy is required to form a sintering neck and achieve densification. Therefore, the sintering temperature T of the coarse and fine powder mixture is closer to 0.85TL.

[0040] The density of the sintered part is 4.36 g / cm3, the yield strength reaches 870 MPa, and the elongation is about 5% (ISO22068-TC4 index: yield strength ≥ 600 MPa, elongation ≥ 3%, density ≥ 4.2 g / cm3). Figure 1 shows the metallographic microstructure of the sintered blank in this embodiment.

[0041] (Example 2)

[0042] The present invention comprises the following steps:

[0043] S1. Preparing titanium alloy fine powder and titanium alloy coarse powder, wherein the particle size of the titanium alloy fine powder is in the range of 1 to 20 μm (D50: 10 to 13 μm), and the particle size of the titanium alloy coarse powder is in the range of 50 to 100 μm (D50: 70 to 80 μm); mixing the titanium alloy fine powder and the titanium alloy coarse powder to form a titanium alloy mixed powder; the ratio of the titanium alloy coarse powder to the titanium alloy fine powder in the titanium alloy mixed powder is 3:2;

[0044] S2. Mixing the titanium alloy mixed powder and the binder to form a feedstock; wherein the ratio of the titanium alloy mixed powder to the binder is 1.6; the titanium alloy powder accounts for 64% by volume of the feedstock, and the remainder is a polymer binder. The polymer binder comprises, by mass percentage, 60% to 70% polyoxymethylene, 12% to 15% polyethylene, 15% to 20% polypropylene, and 3% to 5% stearic acid;

[0045] S3. Place the feed material in an injection molding machine and inject it into an injection blank through a mold; the injection parameters are: mold temperature of 80-120°C, feed material heating temperature of 160-220°C, injection pressure of 80-120 MPa; holding time of 1-2.5 s;

[0046] S4. Degreasing the injection blank to obtain a degreased blank; the specific technical parameters of the degreasing are: degreasing is performed by catalytic degreasing using an oxalic acid medium, and the degreasing time is t≥(60+60*h)min, where h is the maximum thickness of the injection blank, in mm;

[0047] S5. High-vacuum sintering is performed on the degreased blank to obtain a sintered blank. The specific technical parameters for sintering are: high-vacuum sintering in a metal cavity sintering furnace, furnace pressure ≤ 1.0 × 10-3 Pa, and sintering temperature T satisfying 0.65TL ≤ T ≤ 0.85TL. Since the sintering kinetic energy of coarse powder is higher than that of fine powder, more sintering energy is required to form a sintering neck and perform densification sintering. Therefore, the sintering temperature T of the coarse and fine powder mixture is closer to 0.85TL.

[0048] The density of the sintered part is 4.35 g / cm3, the yield strength reaches 875 MPa, and the elongation is about 5% (ISO22068-TC4 index: yield strength ≥ 600 MPa, elongation ≥ 3%, density ≥ 4.2 g / cm3). Figure 2 shows the metallographic microstructure of the sintered blank in this embodiment.

[0049] (Comparative Example)

[0050] The present invention comprises the following steps:

[0051] S1. Preparing titanium alloy fine powder and titanium alloy coarse powder, wherein the particle size of the titanium alloy fine powder is in the range of 1 to 20 μm (D50: 10 to 13 μm), and the particle size of the titanium alloy coarse powder is in the range of 50 to 100 μm (D50: 70 to 80 μm); mixing the titanium alloy fine powder and the titanium alloy coarse powder to form a titanium alloy mixed powder; the ratio of the titanium alloy coarse powder to the titanium alloy fine powder in the titanium alloy mixed powder is 4:1;

[0052] S2. Mixing the titanium alloy mixed powder and the binder to form a feedstock; wherein the ratio of the titanium alloy mixed powder to the binder is 1.3; the titanium alloy powder accounts for 58% by volume of the feedstock, and the remainder is a polymer binder. The polymer binder comprises, by mass percentage, 60% to 70% polyoxymethylene, 12% to 15% polyethylene, 15% to 20% polypropylene, and 3% to 5% stearic acid;

[0053] S3. Place the feed material in an injection molding machine and inject it into an injection blank through a mold; the injection parameters are: mold temperature of 80-120°C, feed material heating temperature of 160-220°C, injection pressure of 80-120 MPa; holding time of 1-2.5 s;

[0054] S4. Degreasing the injection blank to obtain a degreased blank; the specific technical parameters of the degreasing are: degreasing is performed by catalytic degreasing using an oxalic acid medium, and the degreasing time is t≥(60+60*h)min, where h is the maximum thickness of the injection blank, in mm;

[0055] S5. High-vacuum sintering is performed on the degreased blank to obtain a sintered blank. The specific technical parameters for sintering are: high-vacuum sintering in a metal cavity sintering furnace, a furnace pressure ≤1.0×10-3Pa, and a sintering temperature T satisfying 0.65TL≤T≤0.85TL. Because the sintering kinetic energy of coarse powder is higher than that of fine powder, more sintering energy is required to form a sintering neck and perform densification sintering. Therefore, the sintering temperature T of the coarse and fine powder mixture is closer to 0.85TL.

[0056] The density of the sintered part is 4.18 g / cm3, the yield strength reaches 490 MPa, and the elongation is about 2% (ISO22068-TC4 index: yield strength ≥ 600 MPa, elongation ≥ 3%, density ≥ 4.2 g / cm3). Figure 3 shows the metallographic microstructure of the sintered blank in this embodiment.

[0057] As can be seen from Examples 1 and 2, and the Comparative Examples, the ratio of coarse to fine titanium alloy powder in the titanium alloy mixed powder significantly influences the density, yield strength, and elongation of the sintered parts. A higher proportion of fine titanium alloy powder does not necessarily translate into higher product performance. Only by maintaining a reasonable mixing ratio within the range specified by the present invention can a titanium alloy material with excellent performance be achieved. The overall differences in the metallographic microstructures shown in Figures 1 through 3 can also be seen.

[0058] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a titanium alloy material, characterized in that The following steps are involved: S1. Prepare titanium alloy fine powder and titanium alloy coarse powder, wherein the particle size of the titanium alloy fine powder is in the range of 1 to 20 μm, and the particle size of the titanium alloy coarse powder is in the range of 50 to 100 μm; mix the titanium alloy fine powder and the titanium alloy coarse powder to form a titanium alloy mixed powder; the titanium alloy coarse powder accounts for 50% to 80% of the titanium alloy mixed powder; S2, mixing the titanium alloy mixed powder and the binder to form a feed material; S3, placing the feed material in an injection molding machine, and forming the feed material into an injection blank through a mold; S4, degreasing the injection blank to obtain a degreased blank; S5. Perform high vacuum sintering on the degreased blank to obtain a sintered blank.

2. The method for preparing a titanium alloy material according to claim 1, characterized in that: The D50 of the titanium alloy fine powder is 10 to 13 μm; the D50 of the titanium alloy coarse powder is 70 to 80 μm.

3. The method for preparing a titanium alloy material according to claim 1, characterized in that: The ratio of the titanium alloy mixed powder to the binder in the feed is 0.8≤V1 / V2≤1.9, wherein V1 is the volume of the titanium alloy mixed powder and V2 is the volume of the binder.

4. The method for preparing a titanium alloy material according to claim 1, characterized in that: The volume proportion of titanium alloy mixed powder in the feed is 58% to 66%, and the rest is polymer binder; the components of the polymer binder include 60% to 70% polyoxymethylene, 12% to 15% polyethylene, 15% to 20% polypropylene and 3% to 5% stearic acid in terms of mass percentage; the loading range of the feed is 53%-73%.

5. The method for preparing a titanium alloy material according to claim 1, characterized in that: The ratio of the titanium alloy mixed powder to the binder in the feed is 1:1; and the loading range of the feed is 58% to 66%.

6. The method for preparing a titanium alloy material according to claim 1, characterized in that: The technical parameters of the injection molding in step S3 are: mold temperature of 80-120° C., feed heating temperature of 160-220° C., injection pressure of 80-120 MPa, and holding time of 1-2.5 s.

7. The method for preparing a titanium alloy material according to claim 1, characterized in that: The technical parameters of degreasing in step S4 are: catalytic degreasing is performed using oxalic acid as a medium, and the degreasing time is degreasing time t≥(60+60*h)min, where h is the maximum thickness of the injection blank, in mm.

8. The method for preparing a titanium alloy material according to claim 1, characterized in that: The technical parameters for sintering in step S5 are: high vacuum sintering is performed in a metal cavity sintering furnace, the pressure in the furnace is ≤1.0×10-3Pa, and the sintering temperature T satisfies 0.65TL≤T≤0.85TL.

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