CN114643359B - Preparation method of high-strength powder metallurgy Ti-W alloy bar - Google Patents

Preparation method of high-strength powder metallurgy Ti-W alloy bar Download PDF

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CN114643359B
CN114643359B CN202210299502.3A CN202210299502A CN114643359B CN 114643359 B CN114643359 B CN 114643359B CN 202210299502 A CN202210299502 A CN 202210299502A CN 114643359 B CN114643359 B CN 114643359B
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alloy bar
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CN114643359A (en
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刘咏
李娜
曹远奎
刘彬
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Central South University
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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
    • B22F3/02—Compacting only
    • 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
    • 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
    • B22F3/24—After-treatment of workpieces or articles
    • 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
    • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
    • 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
    • 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
    • B22F3/24—After-treatment of workpieces or articles
    • B22F2003/248—Thermal after-treatment
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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Abstract

The invention discloses a preparation method of a high-strength powder metallurgy Ti-W alloy bar, which comprises the following steps: the preparation method comprises the steps of mixing Ti powder and W powder to obtain mixed powder, then carrying out compression molding, then carrying out sintering in a vacuum environment, and adopting a high sintering temperature to accelerate the diffusion speed between W particles and a Ti matrix, realizing control on incomplete diffusion of the W particles, enabling a sintered blank bar material alloy obtained by sintering to have a heterostructure consisting of a W-rich region and a Ti-rich region, then carrying out two-time thermal deformation treatment in a two-phase region and immediately carrying out air cooling, thus obtaining a typical gradient heterostructure, wherein compared with a uniformly distributed dual-phase structure titanium alloy, the gradient heterostructure consisting of a nano dual-phase region and a submicron dual-phase region can generate strain gradient during plastic deformation and is coordinated with each other to deform, so that the strength of the alloy reaches more than 1500MPa, and meanwhile, the 10% elongation is kept, and the preparation of the high-strength high-toughness titanium alloy is realized.

Description

Preparation method of high-strength powder metallurgy Ti-W alloy bar
Technical Field
The invention belongs to the field of titanium alloy materials, and particularly relates to a preparation method of a high-strength powder metallurgy Ti-W alloy bar.
Background
The titanium alloy has the characteristics of excellent high specific strength, high specific modulus, corrosion resistance, light weight and the like, and is widely applied to important fields of aerospace, ship industry, medical appliances, automobiles and the like at present. Particularly in the field of aerospace, the application of the titanium alloy can effectively reduce the weight of the airplane body and parts and greatly improve the energy efficiency. With the rapid development of the aerospace field, research and development of high-performance titanium alloy have received great attention in order to improve the service life of parts in a severe service environment. At present, the tensile strength of developed high-strength and high-toughness titanium alloys such as Ti5553, ti1300, TB10 and the like can reach 1300MPa, and the titanium alloys are successfully applied to key parts of airplanes. However, in the preparation process of these titanium alloys, a large amount of alloying elements need to be added to form a solid solution structure, and the cost of raw materials is high. In order to further improve the strength of titanium alloys, researchers have strengthened the materials by means of subsequent large deformation treatment and control of precipitation of fine secondary phases by complex heat treatment processes, but the plasticity of the materials is significantly reduced. For example, zhang jin Yu et al, 202011176639.7, discloses a high-strength metastable beta titanium alloy, which is improved to 1471MPa by adding a large amount of alloy elements and then hot rolling, solution treatment and aging treatment at the temperature of the titanium alloy dual-phase region, but the plasticity is remarkably reduced to 3%. In general, the existing high-strength and high-toughness titanium alloy has complex component proportion, complex preparation process and difficult simultaneous acquisition of high strength and high plasticity.
The refractory metal W has high hardness and good high-temperature resistance, and W is a beta-phase stable element of Ti which can be dissolved with Ti to form a Ti-W alloy. At present, researchers find that Ti-W alloy has higher strength and hardness and keeps good plasticity, but the existing preparation process is complex and has larger energy consumption. The preparation methods used for the traditional Ti-W alloy are mainly casting and powder metallurgy methods. Because W has a high melting point (3410 ℃), it is difficult to melt during melting, the energy consumption is high, and composition segregation and coarse grains are easy to occur in the ingot, which causes uneven structure. When the powder metallurgy method is adopted, in order to enable the W particles to be completely diffused at a certain temperature, the nano-scale W particles are used as raw materials, so that the preparation cost is greatly increased, and the nano-scale W particles are easy to agglomerate, so that the alloy components are not uniform. Therefore, a novel high-strength and high-toughness titanium alloy with simple components and fine and uniform structure is very urgent.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a preparation method of a high-strength powder metallurgy Ti-W alloy bar, which can improve the strength of a titanium alloy to be more than 1500MPa on the premise of ensuring good plasticity, and has the advantages of simple component proportion, fine and uniform structure and simple and convenient preparation process.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the invention relates to a preparation method of a high-strength powder metallurgy Ti-W alloy bar, which comprises the following steps:
mixing Ti powder and W powder to obtain mixed powder, pressing and forming the mixed powder to obtain a green blank bar, sintering the green blank bar in a vacuum environment to obtain a sintered blank bar, carrying out thermal deformation treatment on the sintered blank bar, and carrying out air cooling to obtain a high-strength Ti-W alloy bar;
the sintering temperature is 1350-1450 ℃, and the sintering time is 2-4 h.
The preparation method of the invention comprises the steps of obtaining mixed powder, pressing and molding, sintering in a vacuum environment, adopting higher sintering temperature to accelerate the diffusion speed between W particles and a Ti matrix, realizing the control of incomplete diffusion of the W particles, enabling the sintered blank bar material alloy to have a heterostructure consisting of a W-rich area and a Ti-rich area, then performing two times of thermal deformation treatment in a two-phase area and immediately performing air cooling, so that a submicron martensite alpha-Ti phase is separated out from the matrix in the Ti-rich area, and a nanoscale martensite alpha-Ti phase is separated out from the matrix in the W-rich area due to the slow diffusion speed, thereby obtaining a typical gradient heterostructure, wherein compared with the uniformly distributed two-phase structure titanium alloy, the gradient heterostructure consisting of the nanometer two-phase area and the submicron two-phase area can generate strain gradient during plastic deformation, the strain gradient and the deformation are coordinated with each other, so that the strength of the alloy reaches more than 1500MPa, meanwhile, the 10% elongation is kept, and the preparation of the high-toughness titanium alloy is realized.
Preferably, the mass fraction of Ti powder in the mixed powder is 60 to 95%, preferably 70 to 80%.
Preferably, the particle size of the Ti powder is less than or equal to 50 microns, and the particle size of the W powder is 1-10 microns.
More preferably, the particle size of the Ti powder is 10 to 50 μm, and the particle size of the W powder is 3 to 8 μm.
Preferably, the powder shapes of the Ti powder and the W powder are both irregular shapes. The inventor finds that the Ti powder and the W powder with the irregular particle sizes are mixed most uniformly, the sintering compactness is highest, and the final performance is optimal.
Preferably, the mixing is performed on a three-dimensional mixer, and the mixing time is 6 to 14 hours, and more preferably 8 to 12 hours.
In the actual operation process, titanium powder and tungsten powder are put into a mixing tank according to the proportion, and the mixing tank is repeatedly vacuumized and filled with argon for three times.
Preferably, the compression molding mode is cold isostatic pressing, the pressure of the compression molding is 200-300 MPa, and the pressure maintaining time is 20-500 s.
By controlling the pressure of the press forming within the above range, the density of the material after final sintering is highest.
Further preferably, the pressure of the cold isostatic pressing is 200 to 250MPa, and the pressure maintaining time is 60 to 300s. Preferred cold isostatic compaction pressures and dwell times allow sintering to form a dense microstructure.
In a preferred embodiment, the sintering procedure is as follows: firstly heating to 500-600 deg.C, holding the temp. for 0.5-2 hr, then heating to 700-800 deg.C, holding the temp. for 0.5-2 hr, then heating to 1350-1450 deg.C, holding the temp. for 2-4 hr, and when the described sintering process is implemented, the vacuum degree is less than 5X 10 -2 Pa。
The sintering of the invention preferably adopts three-stage vacuum sintering, firstly low-temperature sintering is carried out at 500-600 ℃ to remove impurities such as water vapor, grease and the like in a green body, then heat preservation is carried out at 700-800 ℃ to remove hydrogen adsorbed by titanium powder, hydrogen embrittlement is avoided, and finally high-temperature sintering is carried out at 1350-1450 ℃ to densify the structure and eliminate pores.
The inventor finds that the sintering procedure of the invention has a large influence on the final appearance, and each sintering step is indispensable, if low-temperature and medium-temperature sintering is not carried out, water vapor and hydrogen in the material can not be discharged, pores are left in the material, and the performance of the material is seriously influenced; meanwhile, if the low-temperature sintering and the medium-temperature sintering are not well controlled, the high-temperature sintering is also influenced, and for the high-temperature section sintering, W cannot be diffused due to too low sintering temperature and too short heat preservation time, and W can be completely diffused due to too high sintering time and too long heat preservation time, so that a homogeneous structure is formed. Therefore, if the sintering procedure is not well controlled, the morphology of the present invention cannot be obtained.
Preferably, the thermal deformation mode is two times of hot extrusion, the temperature of the first hot extrusion is 950-1050 ℃, and the section surface shrinkage is 50-90%; the temperature of the second hot extrusion is 850-900 ℃, and the shrinkage of the cross section surface is 50-90%.
In the invention, through two times of extrusion, the W-rich area and the Ti-rich area are elongated along the extrusion direction, the crystal grains are recrystallized, the structure is refined, air cooling is carried out immediately after the extrusion is finished, the submicron martensite alpha-Ti phase is separated out from the matrix in the Ti-rich area, and the nanometer martensite alpha-Ti phase is separated out from the matrix in the W-rich area due to the slow diffusion speed, so that a typical gradient heterostructure is obtained.
The inventor finds that the cooling mode after extrusion is important, the required morphology can be obtained only by immediate air cooling, and the morphology of the invention can not be obtained by furnace cooling, water cooling and the like.
Further preferably, the temperature of the first hot extrusion is 950 to 1000 ℃, the reduction rate of the cross section is 70 to 90 percent, and the preferred hot extrusion temperature and time can further eliminate residual pores.
Further preferably, the temperature of the second hot extrusion is 900-950 ℃, the reduction rate of the cross section surface is 70-90%, and the preferred hot extrusion temperature and time can refine the structure.
Preferably, the Ti-W alloy bar has a heterostructure with a microstructure composed of W-rich areas and Ti-rich areas, the W-rich areas are composed of a beta-Ti matrix and a nanoscale alpha-Ti phase dispersed in the beta-Ti matrix, and the Ti-rich areas are composed of the beta-Ti matrix and a submicron alpha-Ti phase dispersed in the beta-Ti matrix.
In the invention, the W-rich region is a gradient diffusion interface formed by mutual diffusion of a W element and a titanium matrix, W is dissolved into the titanium matrix to form W-rich beta-Ti in the W-rich region, and the Ti-rich region is a non-diffusion region, so that a heterostructure is formed.
Further preferably, the morphology of the submicron alpha-Ti phase is needle-like.
Preferably, in the Ti-W alloy bar, the mass fraction of Ti is 60-95%.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the preparation method of the high-strength powder metallurgy Ti-W alloy bar, incomplete diffusion of a W element is controlled by adjusting sintering temperature and heat preservation time in the preparation process, so that the prepared alloy has a heterostructure consisting of a W-rich area and a Ti-rich area. Meanwhile, two times of thermal deformation treatment are carried out in a two-phase area and air cooling is carried out immediately, so that submicron martensite phase is separated out from the matrix in a Ti-rich area, and nanoscale martensite phase is separated out from the matrix in a W-rich area due to the slow diffusion speed, and a typical gradient heterostructure is formed. Compared with the titanium alloy with the uniformly distributed dual-phase structure, the gradient heterostructure consisting of the nanometer dual-phase region and the submicron dual-phase region can generate strain gradient during plastic deformation and is deformed in a coordinated manner, so that the strength of the alloy reaches more than 1500MPa, the elongation of 10 percent is kept, and the preparation of the high-strength and high-toughness titanium alloy is realized.
(2) In addition, the process flow is simple and convenient, the time consumption is short, the high-strength and high-toughness titanium alloy can be rapidly prepared, and the industrial production requirement is met.
Drawings
FIG. 1 is a process flow diagram of the present invention.
FIG. 2 is an axial SEM photograph of a high-strength Ti-W alloy bar prepared in example 1 of the present invention.
FIG. 3 is an axial true stress-strain curve of a high strength Ti-W alloy bar prepared in example 1 of the present invention.
Detailed Description
In order to facilitate an understanding of the invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.
Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
Example 1
The Ti-W alloy bar comprises the following components by weight percent of Ti-20W and is prepared by the following steps:
(1) Weighing Ti powder (D) according to the nominal composition 50 =40 μm) and W powder (D) 50 =5 microns), placing the metal powder into a mixing tank, repeatedly vacuumizing and filling argon into the mixing tank for three times, and placing the mixing tank into a three-dimensional mixer to be uniformly mixed for 12 hours to obtain mixed composite powder.
(2) And (3) carrying out cold isostatic pressing on the mixed composite powder, and controlling the pressing pressure to be 220MPa and the pressing time to be 300s to obtain a pressed green blank bar.
(3) And performing three-stage vacuum sintering on the obtained green blank bar, wherein the three-stage vacuum sintering comprises low-temperature, medium-temperature and high-temperature sintering. The low-temperature sintering temperature is controlled to be 600 ℃, the heat preservation time is 2 hours, and the vacuum degree is lower than 1 multiplied by 10 -3 Pa; the medium-temperature sintering temperature is controlled to be 800 ℃, the heat preservation time is 2 hours, and the vacuum degree is lower than 1 multiplied by 10 -3 Pa; controlling the high-temperature sintering temperature to 1350 ℃, the heat preservation time to be 4h, and the vacuum degree to be lower than 1 multiplied by 10 -3 Pa. And cooling along with the furnace to obtain a sintered blank bar.
(4) And carrying out two times of hot extrusion on the obtained sintered blank rod material. The first hot extrusion temperature is 950 ℃, the heat preservation time is 30min, and the shrinkage of the cross section surface is 75 percent; the temperature of the second hot extrusion is 950 ℃, the heat preservation time is 30min, and the reduction rate of the cross section surface is 75 percent, so as to obtain the titanium alloy bar.
The axial microstructure of the prepared powder metallurgy Ti-W alloy bar is analyzed by a scanning electron microscope, an SEM image is shown in figure 2, the alloy bar is tightly combined without defects, the microstructure of the alloy bar is a heterostructure consisting of a W-rich area and a Ti-rich area, the W-rich area is a nano-scale dual-phase structure, and the Ti-rich area is a submicron-scale dual-phase structure. The true stress-strain curve of the titanium alloy bar is measured by a universal mechanical testing machine and is shown in figure 3, the tensile strength of the titanium alloy bar is 1523MPa, and the elongation is 10%. Compared with the existing titanium alloy material, the high-strength Ti-W alloy bar material obtained by the embodiment has better strong plastic bonding.
Example 2
The Ti-W alloy bar comprises the following components of Ti-20W, and the preparation process comprises the following steps:
(1) Weighing Ti powder (D) according to the nominal composition 50 =40 μm) and W powder (D) 50 =5 microns), placing the metal powder into a mixing tank, repeatedly vacuumizing and filling argon into the mixing tank for three times, and placing the mixing tank into a three-dimensional mixer to be uniformly mixed for 14 hours to obtain mixed composite powder.
(2) And (3) carrying out cold isostatic pressing on the mixed composite powder, and controlling the pressing pressure to be 250MPa and the pressing time to be 180s to obtain a pressed green blank bar.
(3) And (3) performing three-stage vacuum sintering on the obtained green blank bar stock, wherein the three-stage vacuum sintering is divided into low-temperature, medium-temperature and high-temperature sintering. The low-temperature sintering temperature is controlled to be 550 ℃, the heat preservation time is 2 hours, and the vacuum degree is lower than 1 multiplied by 10 -3 Pa; the medium-temperature sintering temperature is controlled to be 750 ℃, the heat preservation time is 2 hours, and the vacuum degree is lower than 1 multiplied by 10 -3 Pa; controlling the high-temperature sintering temperature to 1400 ℃, the heat preservation time to 3.5h, and the vacuum degree to be lower than 1 multiplied by 10 -3 Pa. And cooling along with the furnace to obtain a sintered blank bar.
(4) And carrying out two times of hot extrusion on the obtained sintered blank rod material. The first hot extrusion temperature is 1000 ℃, the heat preservation time is 30min, and the cross-sectional surface shrinkage is 85%; the temperature of the second hot extrusion is 900 ℃, the heat preservation time is 30min, and the reduction rate of the cross section surface is 80 percent, so as to obtain the titanium alloy bar.
The axial microstructure of the powder metallurgy Ti-W alloy bar is analyzed by a scanning electron microscope, the alloy bar is tightly combined without defects, the microstructure of the alloy bar is a heterostructure consisting of a W-rich area and a Ti-rich area, the W-rich area is of a nano-scale dual-phase structure, and the Ti-rich area is of a submicron-scale dual-phase structure. The tensile strength of the titanium alloy bar is 1558MPa and the elongation is 6 percent by adopting a universal mechanical testing machine. Compared with the existing titanium alloy material, the high-strength Ti-W alloy bar obtained by the embodiment has better strong plastic bonding.
Example 3
The Ti-W alloy bar comprises the following components of Ti-30W, and the preparation process comprises the following steps:
(1) Weighing Ti powder (D) according to the nominal components 50 =30 μm) and W powder (D) 50 =3 mu m), placing the metal powder into a mixing tank, repeatedly vacuumizing and filling argon into the mixing tank for three times, and placing the mixing tank into a three-dimensional mixer to be uniformly mixed for 10 hours to obtain mixed composite powder.
(2) And (3) carrying out cold isostatic pressing on the mixed composite powder, and controlling the pressing pressure to be 280MPa and the pressing time to be 100s to obtain a pressed green blank bar.
(3) And (3) performing three-stage vacuum sintering on the obtained green blank bar stock, wherein the three-stage vacuum sintering is divided into low-temperature, medium-temperature and high-temperature sintering. The low-temperature sintering temperature is controlled to be 500 ℃, the heat preservation time is 2 hours, and the vacuum degree is lower than 1 multiplied by 10 -3 Pa; the medium-temperature sintering temperature is controlled to be 700 ℃, the heat preservation time is 2 hours, and the vacuum degree is lower than 1 multiplied by 10 -3 Pa; controlling the high-temperature sintering temperature to 1450 ℃, the heat preservation time to 3 hours, and the vacuum degree to be lower than 1 multiplied by 10 -3 Pa. And cooling along with the furnace to obtain a sintered blank bar.
(4) And carrying out two times of hot extrusion on the obtained sintered blank rod material. The first hot extrusion temperature is 1050 ℃, the heat preservation time is 30min, and the cross-sectional surface shrinkage rate is 90%; the temperature of the second hot extrusion is 850 ℃, the heat preservation time is 30min, and the reduction rate of the cross section surface is 70 percent, so as to obtain the titanium alloy bar.
The axial microstructure of the powder metallurgy Ti-W alloy bar is analyzed by a scanning electron microscope, the alloy bar is tightly combined without defects, the microstructure of the alloy bar is a heterostructure consisting of a W-rich area and a Ti-rich area, the W-rich area is a nano-scale biphase structure, and the Ti-rich area is a submicron-scale biphase structure. The tensile strength of the titanium alloy bar is 1460MPa and the elongation is 7.5% measured by a universal mechanical testing machine. Compared with the existing titanium alloy material, the high-strength Ti-W alloy bar material obtained by the embodiment has better strong plastic bonding.
Example 4
The Ti-W alloy bar comprises the following components of Ti-30W, and the preparation process comprises the following steps:
(1) Weighing Ti powder (D) according to the nominal composition 50 =30 μm) and W powder (D) 50 =5 microns), placing the metal powder into a mixing tank, repeatedly vacuumizing and filling argon into the mixing tank for three times, and placing the mixing tank into a three-dimensional mixer to be uniformly mixed for 6 hours to obtain mixed composite powder.
(2) And (3) carrying out cold isostatic pressing on the mixed composite powder, and controlling the pressing pressure to be 200MPa and the pressing time to be 500s to obtain a pressed green blank bar.
(3) And performing three-stage vacuum sintering on the obtained green blank bar, wherein the three-stage vacuum sintering comprises low-temperature, medium-temperature and high-temperature sintering. The low-temperature sintering temperature is controlled to be 600 ℃, the heat preservation time is 2 hours, and the vacuum degree is lower than 1 multiplied by 10 -3 Pa; the medium-temperature sintering temperature is controlled to be 800 ℃, the heat preservation time is 2 hours, and the vacuum degree is lower than 1 multiplied by 10 -3 Pa; controlling the high-temperature sintering temperature to 1350 ℃, the heat preservation time to be 4h, and the vacuum degree to be lower than 1 multiplied by 10 -3 Pa. And cooling along with the furnace to obtain a sintered blank bar.
(4) And carrying out two times of hot extrusion on the obtained sintered blank rod material. The first hot extrusion temperature is 1050 ℃, the heat preservation time is 30min, and the shrinkage of the cross section surface is 70%; and the temperature of the second hot extrusion is 850 ℃, the heat preservation time is 30min, and the shrinkage of the cross section surface is 70 percent, so that the titanium alloy bar is obtained.
The axial microstructure of the powder metallurgy Ti-W alloy bar is analyzed by a scanning electron microscope, the alloy bar is tightly combined without defects, the microstructure of the alloy bar is a heterostructure consisting of a W-rich area and a Ti-rich area, the W-rich area is of a nano-scale dual-phase structure, and the Ti-rich area is of a submicron-scale dual-phase structure. The tensile strength of the titanium alloy bar is 1425MPa and the elongation is 8% by using a universal mechanical testing machine. Compared with the existing titanium alloy material, the high-strength Ti-W alloy bar material obtained by the embodiment has better strong plastic bonding.
Comparative example 1
Preparing a Ti-W alloy bar according to the parameters of the embodiment 1, executing the step 3, and directly sintering the obtained green bar at a high temperature, wherein the high-temperature sintering parameters are the same as those in the embodiment 1. Subsequently, two hot extrusion passes were carried out according to the parameters in example 1 to obtain a titanium alloy bar.
The axial microstructure of the powder metallurgy Ti-W alloy bar is analyzed by a scanning electron microscope, the microstructure of the alloy bar is a heterostructure consisting of a W-rich area and a Ti-rich area, the W-rich area is a nano-scale biphase structure, and the Ti-rich area is a submicron-scale biphase structure. But the alloy bar has poor compactness and residual pores. The tensile strength of the titanium alloy bar is 1384MPa and the elongation is less than 1 percent by adopting a universal mechanical testing machine.
The reason for the occurrence of premature fracture was analyzed as: because low-temperature and medium-temperature sintering is not carried out, water vapor, hydrogen and the like in the pressed green bar stock are not completely discharged to leave residual pores, and the residual pores become crack sources in the stretching process, so that the material has poor plasticity and can fail due to premature fracture.
Comparative example 2
Preparing a Ti-W alloy bar according to the parameters of the embodiment 1, executing the step 3, adjusting the high-temperature sintering temperature to 1200 ℃, the heat preservation time to 2h, and the vacuum degree to be lower than 1 multiplied by 10 -3 And Pa, cooling along with the furnace to obtain a titanium alloy sintered blank bar. Subsequently, two hot extrusion passes were carried out according to the parameters in example 1 to obtain a titanium alloy bar.
The W particles in the Ti-W alloy bar prepared by the comparative example do not diffuse in a large area, and still exist in a titanium matrix in a granular shape, and a microstructure consisting of a nanoscale double-phase area and a submicron double-phase area is not formed, so that the prepared titanium alloy bar is actually a Ti-W composite bar.
Comparative example 3
Preparing a Ti-W alloy bar according to the parameters of the embodiment 1, executing the step 3, adjusting the high-temperature sintering temperature to 1450 ℃, the heat preservation time to 6 hours, and the vacuum degree to be lower than 1 multiplied by 10 -3 And Pa, cooling along with the furnace to obtain a titanium alloy sintered blank bar. Then, two times of hot extrusion were performed according to the parameters in example 1, and the sample was broken during the first hot extrusion, failing to successfully produce a high-strength titanium alloy bar. The grain size of the sintered blank bar is analyzed by a metallographic microscope, and the grain size of the sintered blank bar reaches about 500 mu m, and the coarse grains reduce the work hardening capacity of the material, so that the material is cracked during extrusion.
Therefore, the selection of the sintering process is an important parameter of the invention, and the reasonable sintering process is the premise of controlling the diffusion degree of the alloy elements and is also the key for obtaining the high-strength titanium alloy.
Comparative example 4
Preparing a Ti-W alloy bar according to the parameters of the embodiment 1, executing the step 4, adjusting the temperature of the first hot extrusion to be 800 ℃, and crushing a sample during extrusion to fail to prepare the high-strength titanium alloy bar.
Therefore, when the titanium alloy is processed by the hot deformation process, the hot deformation temperature is strictly grasped.
Comparative example 5
The other conditions were the same as in example 1 except that the mixed composite powder was charged into a hot press sintering mold, and then placed into a vacuum hot press sintering furnace, and hot press sintered in a vacuum atmosphere. The axial microstructure of the prepared powder metallurgy Ti-W alloy bar is analyzed by a scanning electron microscope, and a plurality of pores exist in the alloy bar. The tensile strength of the titanium alloy bar is 1387MPa and the elongation is less than 3 percent by adopting a universal mechanical testing machine.
And (3) analyzing the generation of pores and hydrogen brittleness: in the hot-pressing sintering process, the pressure of the hot-pressing sintering is limited to a certain extent due to the graphite mold, so that pores exist in the combination of the non-spherical powder, and the pores are difficult to eliminate after the thermal deformation, so that the material is brittle. The cold isostatic pressing and three-stage sintering method can combine non-spherical powder without pores, and completely eliminate residual water vapor, hydrogen and the like in the powder, so that the material has good compactness.
Comparative example 6
The other conditions were the same as in example 1 except that after the two passes of extrusion, the sample was cooled by furnace cooling. The axial microstructure of the powder metallurgy Ti-W alloy bar is analyzed by a scanning electron microscope, the alloy bar is tightly combined without defects, the microstructure of the alloy bar is a heterostructure consisting of a W-rich area and a Ti-rich area, but the sizes of precipitated phases in the W-rich area and the Ti-rich area reach several micrometers to tens of micrometers, a biphase Widmanschner structure is formed, and a typical gradient heterostructure is not seen. The tensile strength of the titanium alloy bar is 1264MPa and the elongation is 6% by adopting a universal mechanical testing machine.
The reason for the decrease in both strength and plasticity was analyzed as follows: as the heat distortion temperature is carried out in a two-phase region, alpha-Ti can be separated out from a beta-Ti matrix, when the cooling speed is too slow, the separated second phase alpha-Ti can grow gradually to form a typical Widmannstatten structure with the beta-Ti matrix, the whole structure can not form the gradient structure described in the embodiment 1, and the synergistic strengthening and toughening effects brought by the gradient structure are also lost.

Claims (8)

1. A preparation method of a high-strength powder metallurgy Ti-W alloy bar is characterized by comprising the following steps: the method comprises the following steps: preparing Ti powder and W powder, mixing to obtain mixed powder, pressing and forming the mixed powder to obtain a green blank bar, sintering the green blank bar in a vacuum environment to obtain a sintered blank bar, thermally deforming the sintered blank bar, and air cooling to obtain a high-strength Ti-W alloy bar;
the sintering temperature is 1350-1450 ℃, and the sintering time is 2-4 h;
the thermal deformation mode is two times of hot extrusion, the temperature of the first hot extrusion is 950-1050 ℃, and the shrinkage of the cross section surface is 50-90%; the temperature of the second hot extrusion is 850-900 ℃, and the shrinkage of the cross section surface is 50-90%.
2. The method for preparing the high-strength powder metallurgy Ti-W alloy bar according to the claim 1, wherein the method comprises the following steps: in the mixed powder, the mass fraction of Ti powder is 60-95%.
3. The method for preparing the high-strength powder metallurgy Ti-W alloy bar according to the claim 1, characterized in that: the particle size of the Ti powder is less than or equal to 50 mu m, and the particle size of the W powder is 1-10 mu m; the powder shapes of the Ti powder and the W powder are irregular.
4. The method for preparing the high-strength powder metallurgy Ti-W alloy bar according to the claim 1, characterized in that: the mixing is carried out on a three-dimensional mixer, and the mixing time is 6-14 h.
5. The method for preparing the high-strength powder metallurgy Ti-W alloy bar according to the claim 1, characterized in that: the compression molding mode is cold isostatic pressing, the pressure of the compression molding is 200-300 MPa, and the pressure maintaining time is 20-500 s.
6. The method for preparing the high-strength powder metallurgy Ti-W alloy bar according to the claim 1, characterized in that: the sintering procedure is as follows: firstly heating to 500-600 deg.C, heat-insulating for 0.5-2 h, then heating to 700-800 deg.C, heat-insulating for 0.5-2 h, then heating to 1350-1450 deg.C, heat-insulating for 2-4 h, when sintering, the vacuum degree is less than 5X 10 -2 Pa。
7. The method for preparing the high-strength powder metallurgy Ti-W alloy bar according to the claim 1, characterized in that: the microstructure of the Ti-W alloy bar is a heterostructure consisting of a W-rich area and a Ti-rich area, the W-rich area consists of a beta-Ti matrix and a nano alpha-Ti phase dispersed in the beta-Ti matrix, and the Ti-rich area consists of the beta-Ti matrix and a submicron alpha-Ti phase dispersed in the beta-Ti matrix.
8. The method for preparing the high-strength powder metallurgy Ti-W alloy bar according to the claim 1, wherein the method comprises the following steps: in the Ti-W alloy bar, the mass fraction of Ti is 60-95%.
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US20080029186A1 (en) * 2006-02-14 2008-02-07 Stanley Abkowitz Homogeneous titanium tungsten alloys produced by powder metal technology
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