Low-cost heterogeneous organization TC4 titanium alloy and preparation method thereof

Abstract

The application discloses a low-cost heterogeneous structure TC4 titanium alloy and a preparation method thereof. The TC4 titanium alloy blank is obtained by the following steps: mixing TC4 titanium alloy fine powder and TC4 titanium alloy coarse powder, loading the mixture into a stainless steel sheath, performing vibration, vacuumizing, sealing and hot isostatic pressing treatment, and then performing heat preservation treatment and hot rolling on the TC4 titanium alloy blank together with the sheath. The process parameters of the hot isostatic pressing treatment and the hot rolling are controlled, and the principle of partial recrystallization is combined, so that the ratio of coarse grains and fine grains in the heterogeneous structure TC4 titanium alloy can be controlled, the low-cost and simple process flow characteristics are achieved, and the application is suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The application relates to a titanium alloy and a preparation method thereof, in particular to a low-cost heterostructure TC4 titanium alloy and a preparation method thereof, and belongs to the technical field of metal material processing. TECHNICAL BACKGROUND

[0002] Additive manufacturing as a rapid prototyping technology has been applied in many fields. Titanium alloy, as one of the most commonly used metal materials in additive manufacturing technology, is widely used in the fields of aerospace, industry, national defense, medical treatment, automobile and electronics due to its excellent performance.

[0003] At present, the most important method for titanium alloy additive manufacturing is laser selective melting technology and electron beam selective melting technology. However, both of the two technologies have strict requirements on the particle size of the powder, such as the laser selective melting technology requires the powder particle size to be 10-53 mu m, and the electron beam selective melting technology requires the powder particle size to be 40-100 mu m. However, the particle size distribution range of the powder obtained by the commonly used powdering method is far greater than the requirement of additive manufacturing on the powder. For example, the particle size of the powder prepared by gas atomization method is less than 300 mu m, and the powder with a particle size of less than 100 mu m accounts for about 70%; the particle size distribution of the titanium alloy powder prepared by the rotating electrode method is 50-300 mu m, and the powder with a particle size of less than 100 mu m accounts for about 20%. Therefore, the powder obtained by the current powdering technology needs to be strictly sieved before being used for additive manufacturing, and the fine powder (less than 10 mu m) and the coarse powder (greater than 100 mu m) that cannot be used after sieving accounts for at least more than 50%. When these fine powder and coarse powder are sold as by-products, the price is even lower than that of the raw material, especially the price of the coarse powder is even less than 60% of the price of the raw material, which causes great waste.

[0004] Heterostructure material is a new type of material developed based on the mechanism of heterogeneous deformation induced strengthening and heterogeneous deformation induced work hardening, and has excellent mechanical or physical properties that cannot be realized by traditional homogeneous materials. For example, the heterostructure sheet layer titanium has the high strength of nano-structured titanium and the good ductility of coarse-grained titanium. The main characteristics of this kind of material are that the alloy structure is composed of heterogeneous regions with different mechanical or physical properties, such as equiaxed crystals and fiber crystals, micron crystals and nanocrystals (fine crystals and coarse crystals), and the combination of non-precipitation strengthening grains and precipitation strengthening grains.

[0005] There are various methods for preparing heterogeneous structure alloys, such as accumulative roll-bonding, plastic deformation combined with recrystallization annealing, additive manufacturing, etc. Patent CN202211601065.2 discloses a method for preparing a high-performance ultra-fine-grained heterogeneous metastable β titanium alloy. The method obtains a recrystallized ultra-fine-grained and non-recrystallized deformed grain structure through multi-pass room temperature rolling and partial recrystallization annealing process. Patent CN202010818263.9 prepares a double-heterogeneous titanium-based composite material by generating titanium carbide and titanium boride reinforcing phases in situ in a titanium or titanium alloy substrate. The material not only has a heterogeneous structure of fine and coarse grains, but also has a gradient heterogeneous characteristic of the reinforcing phase in the fine grain area. Patent CN202310440915.3 prepares a heterogeneous equiaxed structure titanium alloy forging by high-temperature-cryogenic combined forging method.

[0006] Although most of the above methods for preparing heterogeneous structure alloys can be realized on existing equipment, the process control is often strict, and the process is relatively long, resulting in increased manufacturing cost, and the controllability of the heterogeneous structure cannot be realized.

[0007] Therefore, it is of great economic and social significance to invent a low-cost preparation method of heterogeneous structure TC4 titanium alloy, especially to realize the preparation of new materials by using industrial by-products or waste products. SUMMARY

[0008] In view of the deficiencies in the prior art for preparing heterogeneous structure TC4 titanium alloy, the first object of the present application is to provide a low-cost preparation method of heterogeneous structure TC4 titanium alloy. The method can use recycled titanium alloy powder that cannot be used in the field of additive manufacturing as raw material. According to the fine powder wrapped around the coarse powder formed after the cooperation of the recycled ultra-coarse and ultra-fine particle size TC4 titanium alloy powder, and combined with the principle of partial recrystallization in the hot rolling process, the process parameters of hot isostatic pressing and hot rolling are controlled to realize the accurate control of the ratio of coarse and fine grains in the heterogeneous structure TC4 titanium alloy.

[0009] The second object of the present application is to provide a low-cost heterogeneous structure TC4 titanium alloy with a relatively optimal combination of strength and plasticity.

[0010] To achieve the above technical purpose, the present application provides a low-cost preparation method of heterogeneous structure TC4 titanium alloy. The method is to mix TC4 titanium alloy fine powder and TC4 titanium alloy coarse powder, then load them into a stainless steel jacket, and then perform vibration, air extraction, sealing and hot isostatic pressing to obtain TC4 titanium alloy billet. The TC4 titanium alloy billet is subjected to heat treatment and hot rolling together with the jacket to obtain the TC4 titanium alloy. The TC4 titanium alloy fine powder and the TC4 titanium alloy coarse powder are both titanium alloy powder discarded in the field of additive manufacturing.

[0011] As a preferred scheme, the hot isostatic pressing treatment is under the condition of 750-850 DEG C, 150-180 MPa, and 2-4 hours.

[0012] As a preferred scheme, the hot rolling is under the condition of 850-860 DEG C, 30-40 m / min, 8-10%, and 40-50%.

[0013] In the process of preparing the heterogeneous structure TC4 titanium alloy, there are two kinds of titanium alloy powder, fine powder and coarse powder, and the particle size difference is significant. In the powder mixing process, the fine powder will be coated on the surface of the coarse powder by electrostatic adsorption, forming the form of fine powder wrapping coarse powder. After subsequent hot isostatic pressing treatment, the fine powder will form fine grains, and the coarse powder will form coarse grains, and still show the structure of fine grains surrounding coarse grains, meet the characteristics of heterogeneous structure, and form a dense material. In addition, the hot isostatic pressing blank is further hot rolled, and by controlling the total deformation, the interface position of coarse grains and fine grains can be preferentially recrystallized, forming new fine grains, so as to realize the regulation of the proportion of coarse and fine grains in the alloy, and ensure the optimal mechanical properties. In addition, the canning is not removed after hot isostatic pressing, and the hot rolling is directly carried out after heating and holding, which can reduce the oxidation of titanium alloy. Compared with conventional titanium alloy hot rolling, the anti-oxidation treatment before rolling is not needed, and the process is simplified. And under the rolling temperature condition provided in the application, the stainless steel canning is not easy to diffuse with titanium alloy, so the stainless steel canning is easy to remove after rolling.

[0014] The hot isostatic pressing temperature of the application is lower than the alpha to beta phase transition temperature of TC4 titanium alloy, which can avoid the phase transition during hot isostatic pressing and affect the proportion of coarse and fine grains. If the hot isostatic pressing temperature is too low, the sintered blank will have too low density and too many pores, and cracking will easily occur during subsequent hot rolling; and if the hot isostatic pressing temperature is too high, the phase transition will occur during sintering, the alloy after rolling will not have the heterogeneous structure characteristics of coarse and fine grains, and the mechanical properties of the alloy cannot realize the optimal matching of strength and plasticity. Higher pressure is selected than conventional TC4 titanium alloy hot isostatic pressing, on the one hand, due to the lower hot isostatic pressing temperature of the application, higher pressure is needed to realize densification of sintering; on the other hand, the intermediate particle size powder is missing in the raw material of the application, compared with conventional powder sintering, the tap density of the original powder is lower, and higher pressure is needed to make the sintering more dense.

[0015] The temperature of the hot rolling treatment is also lower than the phase transition temperature of the TC4 titanium alloy, and no phase transition from alpha to beta occurs, avoiding the uncontrollable grain size caused by the phase transition, and also avoiding the diffusion between the titanium alloy base and the can, so that the can is easily removed after rolling. Because the rolling temperature is relatively low, the deformation amount of each pass needs to be controlled to be small, so as to avoid excessive rolling force and rolling cracking. However, in order to achieve a larger strain rate, a larger rolling speed needs to be selected. A larger rolling strain rate can make it easier for twins to appear in the alloy, and then dynamic recrystallization occurs, forming fine grains, which makes up for the lack of a high content of coarse grains in the billet after hot isostatic pressing due to the high proportion of coarse powder in the raw material. In addition, the inventors have found that when the total deformation amount of rolling is 40-50%, the proportion of fine grains in the alloy after recrystallization can reach 70-80%, and the alloy has the best strength and plasticity combination. When the total deformation amount is small, the proportion of coarse grains that recrystallize is low, and a large amount of coarse grains remains after rolling, although the plasticity of the alloy is good, the strength of the alloy is low; when the total deformation amount is large, the recrystallization degree increases, and a large amount of coarse grains are converted into fine grains, or even all of the coarse grains are converted into fine grains, and the alloy does not have the characteristics of heterogeneous organization, and the alloy has high strength but low plasticity.

[0016] The fine powder and the coarse powder described in the application are inevitable products of the gas atomization, rotating electrode atomization or plasma atomization powder preparation process, and the mass percentage of the fine powder and the coarse powder is more than 50% of the total powder. Such powder cannot meet the requirements of powder particle size for manufacturing titanium alloy parts by laser selective melting and electron beam selective melting. The source of the coarse powder and the fine powder is not limited in industrial production, and the preparation method is also not limited. Generally, the powder that cannot meet the requirements of additive manufacturing after screening is used, but the coarse powder and the fine powder need to be packaged separately. The price of such powder is usually very low, especially the price of the coarse powder is usually less than 60% of the price of sponge titanium.

[0017] As a preferred scheme, the particle size of the TC4 titanium alloy fine powder is less than 10 μm; and the particle size of the TC4 titanium alloy coarse powder is greater than 100 μm. The particle size difference between the fine powder and the coarse powder in the application is large, which is beneficial to the formation of the form of fine powder wrapping coarse powder.

[0018] As a preferred scheme, the mass percentage of the TC4 titanium alloy fine powder is 20-30%, and the mass percentage of the TC4 titanium alloy coarse powder is 70-80%. In the application, the proportion of the coarse powder is much higher than that of the fine powder, which greatly reduces the cost of the alloy from the raw material end. Secondly, according to the proportion of the fine powder and the coarse powder and the preparation process, the heterogeneous organization of the prepared TC4 titanium alloy can be controlled, so that a product with excellent comprehensive performance is obtained. In the heterogeneous TC4 titanium alloy, when the proportion of fine grains is 70%-80% (the proportion of coarse grains is 20%-30%), the best strength and plasticity matching can be achieved. Therefore, the process design needs to be carried out around this goal.

[0019] When the proportion of fine powder in the raw material is less than 20% (the proportion of coarse powder is more than 80%), it is necessary to control a larger total deformation in the rolling process to ensure that more coarse grains occur dynamic recrystallization, so as to finally meet the proportion of fine grains in the heterogeneous structure of 70-80%. However, when the proportion of coarse powder is greater than 80%, the pores between the coarse powders lack enough fine powder to fill in the hot isostatic pressing ingot, which will lead to the porosity of the hot isostatic pressing ingot being too high, and the plastic deformation capacity of the high porosity ingot is poor, and the hot rolling process is prone to cracking, and the total deformation greater than 40-50% cannot be realized. Therefore, under the premise of requiring a larger total deformation to meet the fine grain proportion, the hot isostatic pressing ingot itself does not have the ability of large deformation, and the preparation process cannot be implemented.

[0020] When the proportion of fine powder in the raw material is 30-70% (the proportion of coarse powder is 30-70%), it is necessary to control the number of coarse grains to occur dynamic recrystallization, therefore, the total deformation controlled in the rolling process is less than 40-50%, but when the total deformation is less than 40-50%, the deformation energy provided by hot rolling is not enough to start dynamic recrystallization, that is, the deformation is small, dynamic recrystallization cannot be realized, and the requirement of the final fine grain proportion of 70-80% cannot be met.

[0021] When the proportion of fine powder in the raw material is 70-80%, the proportion of fine grains after hot isostatic pressing can meet the requirement of 70-80%, but under the premise of not performing plastic deformation, the strength of the hot isostatic pressing alloy is low, in addition, when the proportion of fine powder in the original mixed powder is high, the oxygen content in the alloy is high, which will reduce the plasticity of the alloy.

[0022] When the proportion of fine powder in the raw material is greater than 80%, no matter how to process, the proportion of fine grains in the final alloy is always greater than 80%, which cannot meet the optimal matching of the fine grain proportion of 70-80% in the heterogeneous structure, and also does not have cost advantage.

[0023] The stainless steel sleeve used in the application is in the shape of a cuboid, and the width and height are both more than 3 times the thickness; the wall thickness of the sleeve is 2-3 mm. It is further preferred that the width and height of the sleeve are more than 5 times the thickness, and the wall thickness of the sleeve is 2 mm.

[0024] As a preferred scheme, the process of the vacuumizing treatment is: first vacuumizing at room temperature to a vacuum degree of 1x10 -3 -5x10 -3 Pa, and then vacuumizing in a holding furnace at 450-480℃ to 1x10 -4 -5x10 -4Pa. The two-step vacuumizing is to reduce the oxygen content in the package as much as possible to avoid the oxidation of the titanium alloy powder during the hot isostatic pressing. If only vacuumizing at room temperature, the limit vacuum degree of the common mechanical vacuum pump cannot reach the requirement. The vacuum pump needs to be upgraded, and the secondary vacuumizing is carried out in a heated environment. The high vacuum state can be reached by the air exhaust of the common mechanical vacuum pump.

[0025] As a preferred solution, the blank obtained by the hot isostatic pressing does not need to remove the package and is directly heated and rolled with the package. Without removing the package, on the one hand, the production process is simplified; on the other hand, the existence of the package can avoid the oxidation of the titanium alloy during the heating and hot rolling, and no anti-oxidation treatment before rolling is needed compared with the conventional titanium alloy rolling.

[0026] As a preferred solution, the conditions of the heat preservation treatment are that the temperature is 850-860℃, and the time is 2-3 hours.

[0027] The application further provides a low-cost heterogeneous structure TC4 titanium alloy obtained by the above preparation method. The heterogeneous structure TC4 titanium alloy has better strength and plasticity.

[0028] As a preferred solution, the proportion of the fine crystal in the heterogeneous structure TC4 titanium alloy is 70-80%, and the proportion of the coarse crystal is 20-30%.

[0029] Compared with the prior art, the application has the following beneficial effects:

[0030] 1) The application uses the abandoned TC4 titanium alloy powder in the field of additive manufacturing as the raw material, which is also a byproduct in the field of powder manufacturing, significantly reduces the manufacturing cost, realizes the utilization of industrial byproducts, and has obvious economic and social value.

[0031] 2) The application uses the coarse powder and the fine powder to perform the hot isostatic pressing treatment below the α to β phase transition temperature of the TC4 titanium alloy, avoids the phase transition during the hot isostatic pressing, and can form coarse crystals and fine crystals respectively. Combined with the influence of the controlled hot rolling process parameters on the recrystallization degree, the proportion of the coarse and fine crystals in the final heterogeneous structure is accurately controlled, the alloy has the optimal combination of strength and plasticity, and has the characteristics of high controllability in the production process.

[0032] 3) The hot rolling is directly performed by using the package after the hot isostatic pressing, and no anti-oxidation treatment in the conventional process is needed, so that the production process is simplified. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 EBSD microstructure of the heterogeneous structure TC4 titanium alloy obtained in Example 2 of the application. DETAILED DESCRIPTION

[0034] The following are preferred embodiments of the present application, rather than all embodiments. Any equivalent process transformation made using the content of the present application specification, or direct or indirect application in other related technical fields, without departing from the principles of the present process innovation, is considered within the scope of patent protection of the present application.

[0035] Example 1

[0036] The -1340 mesh (less than 10 μm) and +150 mesh (greater than 100 μm) waste TC4 titanium alloy powder screened out in the field of additive manufacturing was selected as the raw material.

[0037] 7 kg of TC4 titanium alloy coarse powder and 3 kg of TC4 titanium alloy fine powder were weighed into a V-type mixer and mixed for 12 hours. The mixed powder was loaded into a stainless steel jacket with a width × height × thickness of 250 mm × 250 mm × 50 mm and a wall thickness of 2 mm, vibrated and vacuum treated; first vacuumed to 1 × 10 -3 Pa at room temperature, then placed in a 480℃ holding furnace and vacuumed to 1 × 10 - 4 Pa, then welded the vacuum pipe; then heat isostatic pressing was performed, the temperature was set to 850℃, the pressure was 150 MPa, the time was 4 hours, and the cooling method was furnace cooling. Subsequently, the heat isostatic pressing billet with the jacket was placed in an 850℃ resistance furnace for 3 hours, then directly hot rolled, the rolling speed was controlled at 30 m / min, the pass deformation was 10%, and the rolling was stopped when the total deformation was 50%. After removing the surface and side jacket of the rolled billet, a TC4 titanium alloy with heterogeneous structure was obtained.

[0038] The volume percentage of fine crystals in the TC4 titanium alloy prepared in this example was 75%, the tensile strength of the alloy was 963 MPa, the yield strength was 852 MPa, and the elongation after fracture was 13.8%.

[0039] Example 2

[0040] The -1340 mesh (less than 10 μm) and +150 mesh (greater than 100 μm) waste TC4 titanium alloy powder screened out in the field of additive manufacturing was selected as the raw material.

[0041] 8 kg of TC4 titanium alloy coarse powder and 2 kg of TC4 titanium alloy fine powder were weighed into a V-type mixer and mixed for 12 hours. The mixed powder was loaded into a stainless steel jacket with a width × height × thickness of 250 mm × 250 mm × 50 mm and a wall thickness of 2 mm, vibrated and vacuum treated; first vacuumed to 3 × 10 -3 Pa at room temperature, then placed in a 450℃ holding furnace and vacuumed to 5 × 10 - 4After Pa, the extraction pipe is welded together; then hot isostatic pressing is performed at a temperature of 800℃, a pressure of 170MPa, and a time of 3 hours, with furnace cooling. Subsequently, the hot isostatically pressed billet with a cladding is placed in an 860℃ resistance furnace and held for 2 hours before being directly hot rolled. The rolling speed is controlled at 35m / min, and the deformation per pass is 9%. Rolling is stopped when the total deformation reaches 45%. After removing the cladding from the surface and sides of the rolled billet, TC4 titanium alloy with a heterogeneous structure is obtained.

[0042] The TC4 titanium alloy prepared in this embodiment has a fine grain volume percentage of 70%, a tensile strength of 955 MPa, a yield strength of 843 MPa, and an elongation after fracture of 14.5%.

[0043] Example 3

[0044] Waste TC4 titanium alloy powder of -1340 mesh (less than 10μm) and +150 mesh (greater than 100μm) separated from additive manufacturing was selected as raw material.

[0045] Weigh 7.5 kg of coarse TC4 titanium alloy powder and 2.5 kg of fine TC4 titanium alloy powder and load them into a V-type mixer, mixing thoroughly for 12 hours. Pack the mixed powder into a stainless steel sleeve with dimensions of 250 mm x 250 mm x 50 mm and a wall thickness of 2 mm, vibrate to compact, and then vacuum. First, vacuum to 5 × 10⁻⁵ at room temperature. -3 Pa, then placed in a 480℃ holding furnace and evacuated to 4×10 -4 After Pa, the extraction pipe is welded together; then hot isostatic pressing is performed at a temperature of 750℃, a pressure of 180MPa, and a time of 4 hours, with furnace cooling. Subsequently, the hot isostatically pressed billet with a cladding is placed in an 860℃ resistance furnace and held for 3 hours before being directly hot rolled. The rolling speed is controlled at 30m / min, and the deformation per pass is 10%. Rolling is stopped when the total deformation reaches 40%. After removing the cladding from the surface and sides of the rolled billet, TC4 titanium alloy with a heterogeneous structure is obtained.

[0046] The TC4 titanium alloy prepared in this embodiment has a fine grain volume percentage of 78%, a tensile strength of 968 MPa, a yield strength of 855 MPa, and an elongation after fracture of 13.2%.

[0047] Example 4

[0048] Waste TC4 titanium alloy powder of -1340 mesh (less than 10μm) and +150 mesh (greater than 100μm) separated from additive manufacturing was selected as raw material.

[0049] 7 kg of TC4 titanium alloy coarse powder and 3 kg of TC4 titanium alloy fine powder were weighed into a V-type mixer and mixed for 12 hours. The mixed powder was loaded into a stainless steel jacket with a width of 250 mm, a height of 250 mm, and a thickness of 50 mm, and a wall thickness of 2 mm, and was vibrated and compacted, and vacuumized, first vacuumized to 2 x 10 -3 Pa at room temperature, and then placed in a 460°C holding furnace and vacuumized to 5 x 10 - 4 Pa, and then the vacuum pipe was welded; then hot isostatic pressing was performed, with a temperature of 850°C, a pressure of 180 MPa, a time of 3 hours, and a cooling method of furnace cooling. Subsequently, the hot isostatic pressing blank with the jacket was placed in an 850°C resistance furnace for 3 hours, and then directly hot rolled, with a rolling speed of 40 m / min and a pass deformation of 10%, and the rolling was stopped when the total deformation was 50%. After removing the jacket on the surface and sides of the rolled blank, a TC4 titanium alloy with heterogeneous microstructure was obtained.

[0050] The volume percentage of fine grains in the TC4 titanium alloy prepared in this example was 80%, the tensile strength of the alloy was 975 MPa, the yield strength was 862 MPa, and the elongation after fracture was 12.5%.

[0051] Comparative Example 1

[0052] The other processes and steps were the same as in Example 4, except that the hot isostatic pressing temperature was set to 700°C. Due to the excessively low hot isostatic pressing temperature, the sintered blank had excessively low density and many pores, and after removing the jacket after rolling, it was found that the material had serious cracking.

[0053] Comparative Example 2

[0054] The other processes and steps were the same as in Example 4, except that the hot isostatic pressing temperature was set to 900°C. Due to the hot isostatic pressing temperature exceeding the phase transition temperature of the alloy, the alloy had a phase transition during sintering, and after rolling, the alloy did not have the heterogeneous microstructure characteristics of coarse and fine grains, and the alloy was entirely coarse-grained, with a tensile strength of 875 MPa, a yield strength of 803 MPa, and an elongation after fracture of 11.6%. Compared with Example 4, the tensile strength and yield strength of the alloy were greatly reduced, and the plasticity was also reduced to a certain extent.

[0055] Comparative Example 3

[0056] The other processes and steps are the same as those of Example 4, except that the total deformation amount of hot rolling is controlled to be 80%, and due to the serious dynamic recrystallization during rolling, all coarse grains formed after hot isostatic pressing are converted into fine recrystallized grains, the alloy does not have the characteristic heterogeneous structure, the tensile strength of the alloy is 1027 MPa, the yield strength is 908 MPa, and the elongation after fracture is 5.7%. Compared with Example 4, although the tensile strength and yield strength of the alloy in the present example are improved to some extent, the plasticity is greatly reduced.

[0057] Comparative Example 4

[0058] The other processes and steps are the same as those of Example 4, except that the total deformation amount of rolling is controlled to be 20%, and due to the small rolling deformation amount, the degree of dynamic recrystallization during rolling is very low, resulting in a large number of coarse grains still existing in the final blank, and the volume percentage of fine grains is only 38%, which is slightly higher than that of fine powder in the original powder, the tensile strength of the alloy is 643 MPa, the yield strength is 635 MPa, and the elongation after fracture is 16.4%.

[0059] Since the ratio of fine grains and coarse grains in the alloy is 38:62, which does not meet the ideal coarse-fine grain ratio of the heterogeneous structure alloy, although the plasticity of the alloy is good, the strength is low.

[0060] Comparative Example 5

[0061] The other processes and steps are the same as those of Example 4, except that the rolling speed is controlled to be 10 m / min, and due to the small rolling speed, i.e. the strain rate of the alloy is reduced, the degree of dynamic recrystallization during rolling is higher, resulting in the volume percentage of fine grains in the final blank reaching 92%, which is much higher than the ideal ratio of 70-80%, and at the same time, the low strain rate and low dislocation density of the alloy also result in low strength. The tensile strength of the alloy is 952 MPa, the yield strength is 826 MPa, and the elongation after fracture is 10.8%. Compared with Example 4, the strength and plasticity of the alloy are reduced to some extent.

[0062] The coarse-fine grain ratio and tensile mechanical properties of the heterogeneous TC4 titanium alloy prepared in Examples 1-4 and Comparative Examples 1-5 are shown in Table 1.

[0063] Table 1 Coarse-fine grain ratio and tensile mechanical properties of the heterogeneous TC4 titanium alloy obtained in Examples and Comparative Examples

[0064]

Claims

1. A method for preparing low-cost heterogeneously structured TC4 titanium alloy, characterized in that: TC4 titanium alloy fine powder and TC4 titanium alloy coarse powder are mixed and loaded into a stainless steel sheath, and then vibration, air extraction, sealing and hot isostatic pressing are carried out to obtain a TC4 titanium alloy blank; the TC4 titanium alloy blank is first subjected to heat preservation treatment, and then hot rolling is carried out, and thus the TC4 titanium alloy blank is obtained; The TC4 titanium alloy fine powder and the TC4 titanium alloy coarse powder are both titanium alloy powders abandoned in the field of additive manufacturing; The hot isostatic pressing treatment is carried out at a temperature of 750-850 DEG C, a pressure of 150-180 MPa and a time of 2-4 hours; The hot rolling is carried out at a rolling temperature of 850-860 DEG C, a rolling speed of 30-40 m / min, a pass deformation of 8-10% and a total deformation of 40-50%. The TC4 titanium alloy fine powder has a particle size of less than 10 μm, and the TC4 titanium alloy coarse powder has a particle size of more than 100 μm.

2. The method according to claim 1, wherein the method is characterized by: The mass percentage of the TC4 titanium alloy fine powder is 20-30%, and the mass percentage of the TC4 titanium alloy coarse powder is 70-80%.

3. The method according to claim 1 or 2, characterized in that: After the sealing, vacuumizing is carried out: first, vacuumizing is carried out at room temperature to a vacuum degree of 1×10 -3 ~5×10 -3 Pa, and then vacuumizing is carried out in a 450~480℃ holding furnace to 1×10 -4 ~5×10 -4 Pa.

4. The method according to claim 3, wherein the method comprises the following steps: The heat preservation treatment is carried out at a temperature of 850-860 DEG C and a time of 2-3 hours. ​ 5. A low-cost heterogeneously structured TC4 titanium alloy, characterized in that: The preparation method of any one of claims 1-4.

6. The low-cost heterogeneously structured TC4 titanium alloy according to claim 5, characterized in that: The TC4 titanium alloy has a fine crystal ratio of 70-80% and a coarse crystal ratio of 20-30%.

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