CN114669742B - High-performance titanium or titanium alloy workpiece and method for preparing same by adopting two-step sintering method - Google Patents
High-performance titanium or titanium alloy workpiece and method for preparing same by adopting two-step sintering method Download PDFInfo
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- 238000005245 sintering Methods 0.000 title claims abstract description 108
- 239000010936 titanium Substances 0.000 title claims abstract description 91
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 title claims abstract description 67
- 229910052719 titanium Inorganic materials 0.000 title claims abstract description 64
- 238000000034 method Methods 0.000 title claims abstract description 58
- 229910001069 Ti alloy Inorganic materials 0.000 title claims abstract description 45
- 239000000843 powder Substances 0.000 claims abstract description 45
- 238000004321 preservation Methods 0.000 claims abstract description 14
- 239000002994 raw material Substances 0.000 claims abstract description 10
- 239000011261 inert gas Substances 0.000 claims abstract description 7
- 239000012071 phase Substances 0.000 claims description 32
- 239000013078 crystal Substances 0.000 claims description 24
- 230000008569 process Effects 0.000 claims description 18
- 239000011159 matrix material Substances 0.000 claims description 17
- 238000001816 cooling Methods 0.000 claims description 13
- 238000003825 pressing Methods 0.000 claims description 13
- 238000009694 cold isostatic pressing Methods 0.000 claims description 9
- 238000001746 injection moulding Methods 0.000 claims description 8
- 238000004519 manufacturing process Methods 0.000 claims description 8
- 229910052751 metal Inorganic materials 0.000 claims description 8
- 239000002184 metal Substances 0.000 claims description 8
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 6
- 230000002457 bidirectional effect Effects 0.000 claims description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 5
- 239000001301 oxygen Substances 0.000 claims description 5
- 229910052760 oxygen Inorganic materials 0.000 claims description 5
- 239000002245 particle Substances 0.000 claims description 5
- 229910052786 argon Inorganic materials 0.000 claims description 3
- 238000009423 ventilation Methods 0.000 claims description 3
- 239000008384 inner phase Substances 0.000 claims description 2
- 238000002360 preparation method Methods 0.000 abstract description 16
- 238000000280 densification Methods 0.000 abstract description 14
- 230000008878 coupling Effects 0.000 abstract 1
- 238000010168 coupling process Methods 0.000 abstract 1
- 238000005859 coupling reaction Methods 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 26
- 239000000463 material Substances 0.000 description 13
- 230000005012 migration Effects 0.000 description 13
- 238000013508 migration Methods 0.000 description 13
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- 229910000883 Ti6Al4V Inorganic materials 0.000 description 11
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
- B22F3/1003—Use of special medium during sintering, e.g. sintering aid
- B22F3/1007—Atmosphere
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
- B22F3/1017—Multiple heating or additional steps
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/045—Alloys based on refractory metals
- C22C1/0458—Alloys based on titanium, zirconium or hafnium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C14/00—Alloys based on titanium
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
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Abstract
The invention provides a high-performance titanium or titanium alloy workpiece and a method for preparing the same by adopting a two-step sintering method, wherein the preparation method comprises the following steps: preparing a raw blank by taking titanium-based powder as a raw material; carrying out pressureless two-step sintering under the protection of vacuum or inert gas to obtain titanium or titanium alloy products; wherein the sintering temperature in the first step is 1130-1220 ℃, and the heat preservation time is 0-1 h; the sintering temperature in the second step is 1050-1120 ℃, and the heat preservation time is 5-20 h. The preparation method realizes the coupling between the high densification of the product and the grain refinement through pressureless two-step sintering, further improves the comprehensive mechanical property of the product, and simultaneously effectively reduces the sintering temperature and the energy and equipment loss.
Description
Technical Field
The invention relates to the technical field of powder metallurgy, in particular to a high-performance titanium or titanium alloy workpiece and a method for preparing the same by adopting a two-step sintering method.
Background
Titanium and titanium alloy have the excellent characteristics of high specific strength, high temperature resistance, corrosion resistance and the like, are widely applied to various fields of aerospace, national defense and military industry, petrochemical industry, biomedical treatment and the like, and are one of important strategic materials for dual purposes of military and civil use in China. However, titanium and titanium alloy have the problems of high activity, high melting point, low heat conductivity and the like, the traditional casting and machining method is difficult to prepare complex structures, the material utilization rate is less than 10%, the defects of component segregation, shrinkage cavity, air holes, inclusion residues and the like are easy to occur, and the performance advantages of the material are difficult to fully develop. The powder metallurgy process comprises a plurality of advanced manufacturing technologies such as additive manufacturing, powder injection molding and the like, so that the near-end molding of titanium and titanium alloy products can be realized, the material utilization rate can be greatly improved, the preparation cost can be effectively reduced, and meanwhile, the uniform fine crystal structure can be obtained, and the product has excellent comprehensive performance, so that the powder metallurgy process becomes one of the most effective technical means for preparing high-performance titanium and titanium alloy products.
However, titanium-based powder has a low self-diffusion coefficient, poor sintering activity, and difficulty in densification by pressureless sintering. To increase the degree of densification of the powder by sintering, high temperature or pressure sintering methods are often employed. However, the high-temperature sintering is easy to cause coarse grain structure, so that the mechanical property of the product is seriously reduced; and the pressure sintering methods such as spark plasma sintering, hot pressing, hot isostatic pressing and the like also have the problems that the product shape is single, the complex product is difficult to prepare, the preparation cost is high and the like.
Therefore, how to realize pressureless sintering densification of titanium-based powders is a core problem in preparing high-performance titanium and titanium alloy products.
Disclosure of Invention
In order to solve the problems in the prior art, the main purpose of the invention is to provide a high-performance titanium or titanium alloy workpiece and a method for preparing the same by adopting a two-step sintering method.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a method for producing a high-performance titanium or titanium alloy article by a two-step sintering method.
The method for preparing the high-performance titanium or titanium alloy workpiece by adopting the two-step sintering method comprises the following steps:
preparing a raw blank by taking titanium-based powder as a raw material;
carrying out pressureless two-step sintering under the protection of vacuum or inert gas to obtain titanium or titanium alloy products; wherein,,
the sintering temperature in the first step is 1130-1220 ℃, and the heat preservation time is 0-1 h;
the sintering temperature in the second step is 1050-1120 ℃, and the heat preservation time is 5-20 h.
Further, the heat preservation time of the first sintering step is 0-0.5 h.
Further, the heat preservation time of the second sintering is 6-14 h.
Further, the cooling rate of the first step sintering temperature to the second step sintering temperature is 5-10 ℃/min.
Further, in the first sintering step, the temperature rising rate is 5-10 ℃/min.
Further, the powder granularity of the titanium-based powder is less than or equal to 45 mu m;
preferably, the oxygen content is less than or equal to 2000ppm.
Further, the green body material is prepared by any one of mechanical unidirectional pressing, mechanical bidirectional pressing, cold isostatic pressing or metal injection molding;
preferably, the green stock has a relative density of 55 to 85%.
Further, the pressure of the mechanical unidirectional pressing and the mechanical bidirectional pressing is 30-80 MPa, and the pressure maintaining time is 2-8 min;
the pressure of the cold isostatic pressing is 200-300 MPa, and the pressure maintaining time is 3-10 min;
the pressure of the metal injection molding is 100-200 MPa, the pressure maintaining time is 0.25-2 min, and the temperature is 160-200 ℃.
Further, the inert gas is argon, and the ventilation flow is 0.1-0.6L/min; or the vacuum degree is less than or equal to 10 - 2 Pa。
In order to achieve the above object, according to a second aspect of the present invention, there is provided a high-performance titanium or titanium alloy article.
The high-performance titanium or titanium alloy product prepared by the method has a structure of a matrix phase and a grain boundary phase distributed among the matrix phases; or a matrix phase, a grain boundary phase distributed among the matrix phases, and a crystal inner phase distributed in the matrix phase; wherein,,
the matrix phase is alpha-Ti and is in equiaxial shape;
the grain boundary phase is beta-Ti;
the intra-crystal phase is alpha-Ti+beta-Ti and is in a lath shape;
the total content of beta-Ti in the tissue is 4.5-5.8%, and the rest is alpha-Ti.
Further, the structure of the titanium article includes equiaxed and near equiaxed alpha-Ti phases; the average size of the alpha-Ti phase is 9-23 mu m.
Further, the density of the titanium workpiece and the titanium alloy workpiece is more than or equal to 98.5%, and the grain size is less than or equal to 21.2 mu m; the tensile strength of the titanium alloy part is 998-1023 MPa, the yield strength is 916-938 MPa, and the elongation is 10.8-11.6%;
the tensile strength of the titanium product is 655-698 MPa, the yield strength is 568-607 MPa, and the elongation is 14.6-18.8%.
The two-step sintering method utilizes the index change rule between the crystal boundary migration activation energy, the crystal boundary diffusion activation energy and the sintering temperature, and establishes an adaptive powder sintering system by reasonably regulating and controlling the sintering temperature interval and the heating rate, thereby relieving the coupling effect between sintering densification and grain growth, realizing densification and grain refinement of metal parts and providing a new thought for manufacturing high-performance titanium and titanium alloy products.
The density is a key factor influencing the mechanical properties of titanium workpieces. The lower the density is, the more the quantity of residual pores is, and in the material service process, the residual pores are extremely easy to form crack sources, so that the strength and the plasticity of the material are rapidly reduced. Because titanium-based powder has low sintering activity and difficult densification, sintering densification is usually promoted by increasing the sintering temperature, but this method tends to cause coarse grains. According to the Hall-Petch criterion (as in equation 1), coarse grains cause a decrease in the yield strength of the material, while fine grains increase the yield strength of the material. And the finer the crystal grains, the more the crystal grains are in equal area or equal volume, the plastic deformation is performed in a plurality of crystal grains at the same time, so that the stress concentration is effectively avoided, and the plastic lifting of the material is facilitated. Therefore, how to realize grain refinement on the premise of ensuring high density is an important way for preparing high-performance titanium and titanium alloy products.
In sigma s Is the yield limit of the material; sigma (sigma) 0 K are constants; d is the average grain size.
Macroscopically, powder sintering is the process of pore shrinkage and elimination. In the early stage of sintering, the powder can be bonded to form a sintering neck, and the density is obviously improved. The process mainly uses the surface free energy as driving force, and the height of the surface free energy depends on the relative surface area of the powder. The finer the powder particles, the greater the relative surface area, the higher the surface free energy, which contributes to the greater length of the sintering neck. As the sintering neck grows up gradually, the free energy of the powder surface is depleted, and a large number of tiny holes and closed holes are formed in the inner part of the product. The crystal boundary is used as a vacancy 'trap', and the internal atomic arrangement is loose and scattered, so that the crystal boundary is a rapid channel for mass transfer in the later stage of sintering. During sintering, both grain boundary migration and diffusion play an important role in densification of the green body. However, grain boundary migration tends to cause rapid grain growth, which is controlled primarily by grain boundary migration activation energy. The smaller the activation energy, the more easily the grains grow. The grain size and the grain boundary migration diffusion coefficient accord with a Hillert sintering model, and the relation is shown in a formula (2). The grain boundary migration coefficient and grain boundary migration activation satisfy the Arrhenius equation (formula (3)). The diffusion of the grain boundary can diffuse or absorb excessive vacancies in the pores through the adjacent grain boundary, and the grain growth can not be caused, and the excessive vacancies are mainly controlled by the activation energy of the diffusion of the grain boundary. The smaller the activation energy, the lower the energy barrier for the transition required for grain boundary diffusion, the easier the pores are eliminated to achieve densification. The relationship between the grain size and the grain boundary diffusion coefficient accords with a Johnson sintering model and is shown in a formula (4). Under the condition that the crystal grains grow normally, the crystal boundary diffusion coefficient and the crystal boundary diffusion activation can meet the Arrhenius equation (formula 5). Therefore, it is a key to solve the above problems to suppress the migration of grain boundaries and promote the diffusion of grain boundaries.
Wherein G is avg Is the average grain size; g 0 Is the initial grain size; t is sintering time; gamma is grain boundary energy; m is M b Is the grain boundary migration coefficient; m is M b,0 Is a pre-finger factor; q (Q) b Activation energy for grain boundary migration. k (k) B Is the boltzmann constant; t is absolute temperature.
Wherein L is 0 Is the initial sample size; Δl is the amount of change in sample size after sintering; ΔL/L 0 Is the linear shrinkage of the sample; omega is atomic volume; delta is the grain boundary thickness; d (D) GB Is the grain boundary diffusion coefficient; d (D) GB,0 Is a pre-finger factor; q (Q) GB The activation energy is for grain boundary diffusion.
At the traditional solid-phase sintering temperature, the migration and diffusion of the grain boundary are in active states, and the sintering densification and the growth of the crystal grains have coupling effects. Therefore, the coupling effect between the two materials is successfully relieved by the two-step sintering method. The first sintering step should be heated to a higher temperature, but the temperature is reduced by 100-300 ℃ compared with the traditional solid phase sintering temperature. After the heat preservation is carried out for a short time, the powder is bonded to form a sintering neck, and the density is 70-90% of the theoretical density. If the density exceeds 90%, the sintered body is mostly small circular closed pores, the pinning effect of the pores on the grain boundary is seriously weakened, and powerful conditions are provided for migration of the grain boundary. If the density is lower than 70%, the heat preservation time of the second step of sintering can be greatly prolonged, and more energy loss is caused. And then quickly cooling to the second sintering temperature for long-time heat preservation, wherein the activation energy of crystal boundary migration at the temperature is obviously increased, the activation energy of crystal boundary diffusion is maintained at a lower level, and the crystal boundary diffusion is kept in an active state all the time, so that the effect of eliminating residual closed pores to promote sintering densification is achieved, and meanwhile, fine grains are ensured not to coarsen.
Compared with the prior art, the invention has the following advantages:
1) The two-step sintering process is suitable for various titanium-based powder forming technologies such as mechanical unidirectional pressing, cold isostatic pressing, metal injection forming and the like, and has the advantages of simple preparation process, short flow, easy operation, low equipment requirement and great economic benefit.
2) The two-step sintering process can effectively inhibit the growth process of crystal grains in the later sintering period in the traditional sintering process of the titanium-based powder, promote sintering densification, and the prepared titanium product has high density, fine crystal grains and excellent mechanical properties.
3) Compared with the traditional sintering process, the two-step sintering process reduces the sintering temperature of the titanium-based powder by 100-300 ℃, and effectively reduces the energy and equipment loss. The method is not limited to titanium and titanium alloy, and provides a new idea for sintering other high-melting-point and high-activity metal materials.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to designate like parts throughout the figures. In the drawings:
FIG. 1 is a diagram of a metallographic structure of a Ti-6Al-4V alloy prepared by a cold isostatic pressing-two-step sintering method in example 1 provided by the invention;
FIG. 2 is a diagram showing a metallographic structure of a Ti-6Al-4V alloy prepared by an injection molding-two-step sintering method in example 2 provided by the invention.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
According to an embodiment of the present invention, there is provided a method for preparing a high performance titanium or titanium alloy article using a two-step sintering process.
The preparation method comprises the following steps:
s1: preparing powder raw materials: titanium-based powder is selected as a raw material.
Wherein the titanium-based powder is pure titanium powder or titanium alloy powder; the titanium alloy powder may be Ti-6Al-4V alloy powder. The particle size of the titanium-based powder is less than or equal to 45 mu m, and the powder is spherical, nearly spherical or irregularly shaped; the oxygen content of the titanium-based powder is less than or equal to 2000ppm.
S2: blank manufacturing: preparing titanium-based powder into a green blank.
Wherein, the green blank is prepared by any one of mechanical unidirectional pressing, mechanical bidirectional pressing, cold isostatic pressing or metal injection molding; the relative density of the green stock is 55-85%.
In the invention, the pressure of the mechanical unidirectional pressing is 30-80 MPa, and the dwell time is 2-8 min.
The pressure of mechanical bidirectional pressing is 30-80 MPa, and the pressure maintaining time is 2-8 min.
The pressure of the cold isostatic pressing is 200-300 MPa, and the pressure maintaining time is 3-10 min.
The pressure of the metal injection molding is 100-200 MPa, the pressure maintaining time is 0.25-2 min, and the temperature is 160-200 ℃.
S3: sintering: placing the green compact material into a sintering furnace, and vacuum-treating (vacuum degree is less than or equal to 10) -2 Pa) or under the protection of inert gas, carrying out pressureless two-step sintering, and cooling along with a furnace to obtain a titanium or titanium alloy workpiece; wherein,,
the sintering temperature in the first step is 1130-1220 ℃, the heat preservation time is 0-1 h, preferably 0-0.5 h, and the heating rate is 5-10 ℃/min;
the second sintering temperature is 1050-1120 ℃, the heat preservation time is 5-20 h, preferably 6-14 h, and the cooling rate of the first sintering temperature to the second sintering temperature is 5-10 ℃/min.
In the invention, the inert gas can be argon, the purity is 99.999 percent, and the ventilation flow is 0.1 to 0.6L/min.
The preparation method and the prepared product thereof in the present invention will be described in detail by specific examples.
Example 1:
taking Ti-6Al-4V alloy powder with granularity less than or equal to 20 mu m as a raw material, wherein the powder has spherical particle shape and oxygen content of 1400ppm, then carrying out cold isostatic pressing on the powder at room temperature to obtain a green body, wherein the pressure of the cold isostatic pressing is 250MPa, the pressure maintaining time is 5min, and finally, placing the obtained green body in an argon atmosphere protection sintering furnace for sintering treatment. The specific sintering process is as follows: rapidly heating to 1140 ℃ from room temperature at 5 ℃/min without heat preservation; then cooling to 1080 ℃ at 8 ℃/min, and preserving heat for 12 hours; and cooling to room temperature along with the furnace to obtain the Ti-6Al-4V alloy product.
Example 2:
taking Ti-6Al-4V alloy powder with granularity less than or equal to 45 mu m as a raw material, wherein the powder is approximately spherical in particle shape and 1300ppm in oxygen content, and firstly uniformly mixing the powder and a polyoxymethylene-based binder on an atmosphere internal mixer; then injection molding is carried out, the injection temperature is 185 ℃, the injection pressure is 120MPa, and the dwell time is 30s; then carrying out catalytic degreasing to obtain a green body; and finally, placing the obtained green body in an argon atmosphere protection sintering furnace for sintering treatment. The specific sintering process is as follows: rapidly heating to 1160 ℃ from room temperature at 8 ℃/min, and preserving heat for 0.25h; then cooling to 1100 ℃ at a speed of 5 ℃/min, and preserving heat for 9 hours; and cooling to room temperature along with the furnace to obtain the Ti-6Al-4V alloy product.
Examples 3 to 6 all use the same two-step sintering method as examples 1 and 2, except that the raw material powder parameters, the powder forming method, the sintering process parameters, and the like are summarized in examples 1 to 6, and the details of the raw material powder parameters, the powder forming method, the sintering process parameters, and the overall properties are shown in table 1.
Table 1 summary of the preparation process parameters in examples 1 to 6
The titanium-based articles prepared in examples 1 to 6 and comparative examples 1 to 8 were subjected to performance comparison experiments as follows.
1. Experimental objects
The titanium-based articles prepared in examples 1 to 6 and the titanium-based articles prepared in comparative examples 1 to 8, wherein:
comparative example 1:
the preparation process in comparative example 1 is described with reference to example 1, but differs from example 1 in that: the two-step sintering method is not adopted, the temperature is increased to 1300 ℃ from the room temperature at 5 ℃/min, and the temperature is kept for 2 hours.
Comparative example 2:
the preparation process in comparative example 2 is described with reference to example 1, but differs from example 1 in that: the sintering temperature of the first step is 1300 ℃, and the sintering temperature of the second step is 1200 ℃.
Comparative example 3:
the preparation process in comparative example 3 is described with reference to example 1, but differs from example 1 in that: and the second step is to cool at a rate of 2 ℃/min.
Comparative example 4:
the preparation process in comparative example 4 is described with reference to example 2, but differs from example 2 in that: the sintering temperature of the first step is 1060 ℃, and the sintering temperature of the second step is 1000 ℃.
Comparative example 5:
the preparation process in comparative example 5 is described with reference to example 4, but differs from example 4 in that: the two-step sintering method is not adopted, the temperature is increased to 1250 ℃ at 5 ℃/min, and the heat is preserved for 2 hours.
Comparative example 6:
the preparation process in comparative example 6 is described with reference to example 4, but differs from example 4 in that: the sintering temperature of the first step is 1250 ℃, and the sintering temperature of the second step is 1150 ℃.
Comparative example 7:
the preparation process in comparative example 7 is described with reference to example 4, but differs from example 4 in that: and the second step is carried out at a cooling rate of 1.5 ℃/min.
Comparative example 8:
the preparation process in comparative example 8 is described with reference to example 5, but differs from example 5 in that: the particle size of the raw material powder used is less than 150 μm.
2. Experimental method
The titanium-based articles prepared in examples 1 to 6 and comparative examples 1 to 8 were subjected to performance measurement by a conventional detection method in the prior art.
And (3) performance detection:
(1) Relative density testing: the relative densities of the articles prepared in examples 1 to 6 and comparative examples 1 to 8 were measured, respectively.
(2) Mechanical property test: the tensile strength at room temperature, yield strength and elongation were measured for the articles prepared in examples 1 to 6 and comparative examples 1 to 8, respectively.
3. Experimental results
The properties of the titanium and titanium alloy articles of examples 1-6 and comparative examples 1-8 are summarized in Table 2.
Table 2 summary of titanium and titanium alloy properties in examples 1 to 6 and comparative examples 1 to 8
As can be seen from Table 2, the product prepared in the embodiment of the invention has high density of 98.5-99.0%, fine crystal grains, grain size of 9.6-21.2 μm and excellent mechanical properties, wherein the titanium alloy product has warm tensile strength of 998-1023 MPa, yield strength of 916-938 MPa and elongation of 10.8-11.6%; the temperature tensile strength of the pure titanium product is 655-698 MPa, the yield strength is 568-607 MPa, and the elongation is 14.6-18.8%.
FIG. 1 shows a microstructure of a Ti-6Al-4V alloy article prepared in example 1, from which it can be seen that the Ti-6Al-4V alloy article consists essentially of an equiaxed alpha-Ti matrix phase and a grain boundary phase of beta-Ti distributed between the matrix phases, wherein the beta-Ti content is 5.6%, the balance being alpha-Ti; the average size of matrix phase grains was 9.6. Mu.m.
FIG. 2 shows a microstructure of the Ti-6Al-4V alloy product prepared in example 2, from which it can be seen that the Ti-6Al-4V alloy product consists essentially of an equiaxed alpha-Ti matrix phase, a grain boundary phase of beta-Ti, and a small amount of lath-like intragranular phase of alpha-Ti+beta-Ti, wherein the total content of beta-Ti in the structure is 5.3%, the balance being alpha-Ti; the average size of matrix phase grains was 21.2. Mu.m.
The comparative tests show that the sintering is carried out at the traditional solid-phase sintering temperature or the excessively high two-step sintering temperature, the density of the obtained product is reduced, the grain growth is obvious, the mechanical properties of titanium and titanium alloy products are reduced, the plasticity is obviously reduced or basically has no plasticity, and brittle fracture is easy to occur, such as comparative examples 1, 2, 5 and 6. The use of coarse raw powder or too low a two-step sintering temperature resulted in a dramatic decrease in densification, brittle fracture of the part, and substantial no plasticity, as in comparative examples 4 and 8. In the two-step sintering process, the cooling rate of the second step sintering is controlled, and once the cooling rate is too low, crystal grains grow up, so that the plasticity is reduced. Therefore, the titanium or titanium alloy blank is sintered in two steps under the proper sintering temperature range and cooling rate, and the titanium and titanium alloy product with high compactness, fine crystal grain and excellent mechanical property can be obtained.
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (9)
1. A method for preparing a high-performance titanium or titanium alloy workpiece by adopting a two-step sintering method, which is characterized by comprising the following steps:
preparing a raw blank by taking titanium-based powder as a raw material;
carrying out pressureless two-step sintering under the protection of vacuum or inert gas to obtain titanium or titanium alloy products; wherein,,
the sintering temperature in the first step is 1130-1220 ℃, the heating rate is 5-10 ℃/min, and the heat preservation time is 0-1 h;
the sintering temperature is 1050-1120 ℃ and the heat preservation time is 5-20 h; and the cooling rate of the first-step sintering temperature to the second-step sintering temperature is 5-10 ℃/min.
2. The method for producing a high-performance titanium or titanium alloy article by a two-step sintering method according to claim 1, wherein the powder particle size of the titanium-based powder is 45 μm or less.
3. The method for producing a high-performance titanium or titanium alloy article by a two-step sintering method according to claim 2, wherein the oxygen content of the titanium-based powder is 2000ppm or less.
4. The method for preparing a high-performance titanium or titanium alloy product by a two-step sintering method according to claim 1, wherein the green compact is prepared by any one of mechanical unidirectional pressing, mechanical bidirectional pressing, cold isostatic pressing or metal injection molding.
5. The method for producing a high-performance titanium or titanium alloy article by a two-step sintering process according to claim 4, wherein the green compact has a relative density of 55 to 85%.
6. The method for preparing a high-performance titanium or titanium alloy product by adopting a two-step sintering method according to claim 4, wherein the pressures of the mechanical unidirectional pressing and the mechanical bidirectional pressing are both 30-80 MPa, and the dwell time is 2-8 min;
the pressure of the cold isostatic pressing is 200-300 MPa, and the pressure maintaining time is 3-10 min;
the pressure of the metal injection molding is 100-200 MPa, the pressure maintaining time is 0.25-2 min, and the temperature is 160-200 ℃.
7. The method for preparing a high-performance titanium or titanium alloy product by adopting a two-step sintering method according to claim 1, wherein the inert gas is argon, and the ventilation flow is 0.1-0.6L/min; or the vacuum degree is less than or equal to 10 -2 Pa。
8. The high-performance titanium or titanium alloy product prepared by the method of any one of claims 1 to 7, wherein the structure of the titanium alloy product is a matrix phase and a grain boundary phase distributed among the matrix phases; or a matrix phase, a grain boundary phase distributed among the matrix phases, and a crystal inner phase distributed in the matrix phase; wherein,,
the matrix phase is alpha-Ti and is in equiaxial shape;
the grain boundary phase is beta-Ti;
the intra-crystal phase is alpha-Ti+beta-Ti and is in a lath shape;
the total content of beta-Ti in the tissue is 4.5-5.8%, and the balance is alpha-Ti;
the structure of the titanium part comprises an equiaxed and near-equiaxed alpha-Ti phase, and the average size of the alpha-Ti phase is 9-23 mu m.
9. The high performance titanium or titanium alloy article of claim 8, wherein the density of both the titanium article and the titanium alloy article is greater than or equal to 98.5%, and the grain size is less than or equal to 21.2 μm; the tensile strength of the titanium alloy part is 998-1023 MPa, the yield strength is 916-938 MPa, and the elongation is 10.8-11.6%;
the tensile strength of the titanium product is 655-698 MPa, the yield strength is 568-607 MPa, and the elongation is 14.6-18.8%.
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