CN112048691B

CN112048691B - Method for preparing face-centered cubic phase in high-purity titanium thin strip

Info

Publication number: CN112048691B
Application number: CN202010989118.7A
Authority: CN
Inventors: 周红伟; 白凤梅; 宋孟; 孙雅馨; 刘相华
Original assignee: Anhui University of Technology AHUT
Current assignee: Anhui University of Technology AHUT
Priority date: 2020-09-18
Filing date: 2020-09-18
Publication date: 2021-12-21
Anticipated expiration: 2040-09-18
Also published as: CN112048691A

Abstract

The invention discloses a method for preparing a face-centered cubic phase in a high-purity titanium thin strip, and belongs to the technical field of titanium and titanium alloy rolling and heat treatment. The method comprises the steps of rolling high-purity titanium with a hexagonal close-packed (hcp) crystal structure in multiple steps, wherein the total reduction is more than or equal to 85%, obtaining a rolled high-purity titanium ribbon, and annealing the rolled ribbon at 450-600 ℃ for 0.5-8 h to obtain a large amount of face-centered cubic (fcc) phases in a hcp phase matrix. When the annealing time is 0.5-3 h, the formed fcc phase presents a needle-shaped and lath-shaped structure, and the average width of the structure is 0.2-0.3 μm. When the annealing time exceeds 3h, the fcc phase mainly takes on a lath-like and granular structure. The Fcc phase content increases with increasing annealing time, up to a maximum Fcc phase volume content of 22%.

Description

Method for preparing face-centered cubic phase in high-purity titanium thin strip

Technical Field

The invention relates to the technical field of titanium and titanium alloy rolling and heat treatment, in particular to a method for preparing a face-centered cubic phase in a high-purity titanium thin strip.

Background

Titanium and titanium alloy have excellent properties, such as corrosion resistance, oxidation resistance, good biocompatibility and the like, and have wide application in the fields of aerospace, ocean engineering, biomedicine, sports goods and the like. Titanium and titanium alloys commonly have two phases in the phase diagram, namely a hexagonal crystal structure (hcp), referred to as the alpha phase, and a body centered cubic structure (bcc), referred to as the beta phase. Pure titanium has a close-packed hexagonal crystal structure (hcp), referred to as the alpha phase, at room temperature. When the temperature is raised to a certain temperature (882 ℃), the alpha phase will be transformed into a body centered cubic structure (bcc), which is referred to as beta phase for short. The beta phase can be formed at room temperature by adding the beta phase forming element to the alpha phase. Titanium alloys can be classified into alpha titanium alloys, near-alpha titanium alloys, two-phase titanium alloys, beta titanium alloys, and the like according to the contents of alpha phase and beta phase. Different types of titanium alloys are obtained by alloying and the structure of the alpha/beta phase and the properties of the titanium alloy are controlled by heat treatment.

In recent years, it has been found that a face centered cubic crystal structure (fcc) phase is also present in pure titanium and titanium alloys. There are generally two methods to obtain the fcc phase in pure titanium. One is to obtain the fcc phase by pure titanium deformation including compression, rolling and drawing. In another method, the fcc phase is obtained by heat-treating pure titanium. These preparation methods have been documented in a large number of documents. However, the method prepared in the literature has low fcc phase content, and fcc phases are in needle-like or flake-like shapes. The width of the platelets is distributed from a few nanometers to 100 nanometers. Researches find that the deformability of high-purity Ti can be obviously improved by rolling, compression and other stress-induced fcc phase transformation. Hcp to fcc phase transition is considered to be an important deformation mechanism beyond dislocation slip and twinning.

As is well known, titanium and titanium alloy have poor deformability and are difficult to machine and form. Under deformation, the fcc crystal structure has more openable slip systems than the hcp and bcc phases. Therefore, fcc phase transformation coordination is stronger than hcp and bcc phases. Therefore, if a large amount of fcc phase is formed in pure Ti or titanium alloy, the deformability and processability of pure titanium and titanium alloy must be significantly improved. However, the existing method for preparing the fcc phase comprises attraction induced phase transformation and heat treatment induced phase transformation, the obtained fcc phase has small size in nanometer, the content is low, the deformation of the fcc phase has little influence on the performance of pure titanium and titanium alloy, and the advantage of the fcc phase is difficult to exert. At present, no papers and patents are found for preparing high-content, micron-sized fcc phases in high-purity titanium or titanium alloys.

Patent application No. 201710603363.8, filed for 22.7.7.2017, invented and created name: a preparation method of face-centered cubic structure titanium; the application firstly polishes a pure titanium substrate, then polishes the pure titanium substrate, and finally carries out ultrasonic cleaning; then sticking the black adhesive tape on the surface of the pure titanium matrix cleaned by ultrasonic wave, then carrying out laser shock twice by using a pulse laser, and removing the residue of the black adhesive tape; coating black paint on the surface of the pure titanium matrix from which the black adhesive tape residue is removed, performing primary laser impact on the surface of the pure titanium matrix by using a pulse laser, and obtaining the face-centered cubic structure titanium on the impact surface of the pure titanium matrix after the laser impact. The application prepares the face-centered cubic structure titanium by laser shock induction for the first time, but the application firstly has higher realization cost and secondly has relatively complicated realization process, thereby being inconvenient for industrialized popularization and application.

Disclosure of Invention

1. Technical problem to be solved by the invention

To overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for preparing a face centered cubic phase in a high purity titanium thin strip. In the high-purity titanium prepared by large plastic deformation rolling and subsequent recrystallization annealing, the fcc phase size is distributed between hundreds of nanometers and a few microns, the size is large, and the highest fcc phase content can reach 22 percent and the content is high.

2. Technical scheme

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

the invention relates to a method for preparing a face-centered cubic phase in a high-purity titanium thin strip, which comprises the following steps of:

1. surface treatment of high-purity titanium raw material

High-purity titanium cast ingots (the titanium content is 99.999 percent by mass) prepared by an electron beam melting method are used as raw materials. The use of cast ingots for roll compaction or pack rolling requires cutting the raw material into blocks. And according to the requirements of rolling equipment, obtaining the titanium block with a proper size by adopting wire cutting. Before rolling, the surface of the titanium block is polished by abrasive paper, and a heat affected area during linear cutting is removed. And then, placing the titanium block into alcohol for cleaning for about 10min at normal temperature by using an ultrasonic cleaning machine so as to prevent foreign matters on the surface from pressing into the sample in the rolling process and ensure the purity of the material.

2. Rolling deformation

The high-purity titanium plate is deformed under the multi-step rolling process, and after 15-25 times, the total reduction rate of the high-purity titanium (HP-Ti) raw material plate is more than or equal to 85 percent (the original thickness of the plate-the thickness after deformation/the original thickness of the plate) is multiplied by 100 percent). The deformation of multiple passes ensures the uniform compression deformation and the stable size of the thin strip. The deformation process is similar to the multi-step rolling process by other deformation processes such as dynamic compression deformation and cumulative pack rolling.

3. Recrystallization annealing process

Through tests, the recrystallization temperature of the high-purity thin strip with the total reduction rate of more than or equal to 85 percent is about 350-400 ℃, and the deformed high-purity titanium thin strip (with the total reduction rate of more than or equal to 85 percent) is annealed above the recrystallization temperature. And (3) putting the deformed high-purity thin strip into a vacuum furnace for annealing treatment, firstly, extracting vacuum, raising the vacuum degree to be less than or equal to 1Pa, then raising the temperature to 400-600 ℃, keeping the temperature for 0.5-8 h after the target temperature is reached, and then cooling the high-purity thin strip to the room temperature along with the furnace.

The annealing process mainly comprises two parameters of annealing temperature and annealing holding time, wherein the parameter of the annealing holding time is particularly important.

(1) Annealing heat preservation time

And after the target temperature is reached, the heat preservation time is 0.5-8 h, the fcc phase content is increased along with the extension of the heat preservation time, and the maximum fcc content can reach 22% after annealing for 8 h. The morphology of the fcc phase changes along with the prolonging of the heat preservation time, and when the heat preservation time is 0.5-3 h, the morphology of the fcc phase is needle-shaped and lath-shaped, the average width of the lath is more than or equal to 0.2 mu m, and the average length of the lath is more than or equal to 6 mu m. When the heat preservation temperature exceeds 3h, the fcc morphology is in two forms of lath and particle, and when the heat preservation time exceeds 5h, the fcc morphology is mainly in particle form, and the average particle size of the particles is 2.5 mu m.

(2) Annealing temperature

The annealing temperature range was 400-600 ℃, and the formation rate of the fcc phase increased with increasing temperature.

3. Advantageous effects

Compared with the prior art, the technical scheme provided by the invention has the following remarkable effects:

(1) compared with the conventional method for obtaining the fcc phase in the pure titanium through rolling deformation and heat treatment processes, the invention provides the method for preparing the high-purity titanium thin strip containing the face-centered cubic phase, the invention prepares the high-purity titanium through large plastic deformation rolling and subsequent recrystallization annealing, the fcc phase size is distributed between hundreds of nanometers and a few microns, the average size is large, and the highest content of the fcc phase can reach 22 percent and the content is high;

(2) according to the method for preparing the high-purity titanium thin strip containing the face-centered cubic phase, the high-purity titanium with high fcc phase content is obtained only through two steps of large plastic deformation rolling and recrystallization annealing, and the content, size and morphology of the fcc phase can be adjusted by controlling the annealing temperature and the annealing heat preservation time; the preparation process is simple and has strong feasibility; is beneficial to industrialized production.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) structure photograph of a 1mm thin strip in a rolled state in example 1 of the present invention.

FIG. 2 is a Transmission Electron Microscope (TEM) structure photograph of a 1mm thin strip in a rolled state in example 1 of the present invention.

FIG. 3 is a scanning electron micrograph of a 1mm thin strip in a rolled state after annealing at 500 ℃ for 1 hour in example 1 of the present invention.

FIG. 4 is a transmission electron micrograph of a 1mm thin strip in a rolled state after annealing at 500 ℃ for 1 hour in example 1 of the present invention.

FIG. 5 is a selected area diffraction photograph of fcc phase after annealing at 500 ℃ for 1 hour for a 1mm ribbon in cold rolled state in example 1 of the present invention.

FIG. 6 shows the SEM structure of a 1mm thin strip in a rolled state after annealing at 500 ℃ for 5 hours in example 2 of the present invention.

FIG. 7 shows TEM structures of 1mm thin strips in the rolled state after annealing at 500 ℃ for 5h in example 2 of the present invention.

FIG. 8 is an Electron Back Scattering Diffraction (EBSD) photograph of a 1mm thin strip in a rolled state after annealing at 500 ℃ for 5 hours in example 2 of the present invention.

FIG. 9 shows the metallographic structure of a 1mm thin strip in a rolled state, which is annealed at 500 ℃ for 5 hours in example 2 of the present invention.

Detailed Description

For a further understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings and examples.

Example 1

High-purity titanium (titanium content 99.999 percent by mass) prepared by an electron beam melting method is selected as a raw material, the original structure is coarse, and the average grain size is 2.5 mm.

The specific steps of this example are as follows:

(1) A12X 30X 50 mm-sized plate sample was obtained from a high purity titanium material by wire cutting, and was rolled in 20 passes with a total rolling reduction of 91.7% to prepare a thin strip having a thickness of 1 mm.

(2) And (3) putting the deformed high-purity thin strip into a vacuum furnace for annealing treatment, firstly, extracting vacuum with the vacuum degree of 0.8Pa, then heating to 500 ℃, keeping the temperature for 1h after the target temperature is reached, and then cooling to room temperature along with the furnace.

(3) Samples were distributed and sampled from the high purity titanium thin strip after rolling morphologys and annealing treatment by wire cutting, and the samples were subjected to Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) studies. The sample size for SEM observation was 10 mm. times.10 mm. times.1 mm. Firstly, a 0.3mm thin slice is cut out from a transmission sample, the sample with the diameter of 3mm and the thickness of 50 mu m is selected through mechanical polishing, and a TEM sample is prepared through electrolysis and double spraying. A FEI NANO SEM 430 model SEM thermal field emission high resolution SEM, a JEM1200 model SEM.

(4) The rolled deformation state high-purity titanium sample is ground, polished and corroded, the structure observed by a Scanning Electron Microscope (SEM) is shown in figure 1, and the rolled deformation state sample is uniform in structure and fuzzy in grain boundary. As shown in FIG. 2, the TEM photograph of the rolling deformation sample shows that an ultrafine grain structure is obtained after rolling deformation, and the median dislocation density of the structure is high.

(5) The annealed high-purity titanium thin strip sample is polished and corroded, and the structure observed by SEM is shown in FIG. 3. As can be seen from FIG. 3, recrystallization occurred after the annealing treatment, uniform hcp-phase equiaxial grains were formed, the average size of the hcp-phase grains was 7.5 μm, and a large amount of band structures were visible inside the hcp-phase grains.

(6) TEM and selective area electron diffraction analysis are carried out on the band tissue observed by SEM in the step (5), and the band tissue is determined to be an fcc phase. TEM photographs of the annealed high-purity titanium ribbon samples are shown in FIG. 4, and diffraction photographs of selected regions of the fcc phase band structure are shown in FIG. 5, and it is found that a large number of band structures are fcc phase by the calibration of the diffraction pattern, and the fcc phase and the hcp phase satisfy the crystallographic orientation relationship: [0001]_hcp//[001]_fcc，

(7) As can be seen from the foregoing steps (5) and (6), by the rolling deformation + annealing treatment, a large number of fcc phases in the form of stripes can be obtained in a high purity titanium thin strip, the average width of the stripes is 0.2 μm and the maximum width is 0.55 μm, the average length of the stripe is 5.6 μm, and the fcc phase is about 10%. Much higher than the width and content of the lamellar fcc phase prepared in known literature reports.

Example 2

The specific steps of this example are as follows:

(1) A12X 30X 50 mm-sized plate sample was obtained from a high purity titanium raw material by wire cutting, and subjected to 20 passes of rolling with a total rolling reduction of 91.7% to prepare a thin strip having a thickness of 1 mm.

(2) And (3) putting the deformed high-purity thin strip into a vacuum furnace for annealing treatment, firstly, extracting vacuum with the vacuum degree of 0.8Pa, then heating to 500 ℃, keeping the temperature for 5 hours after the target temperature is reached, and then cooling to room temperature along with the furnace.

(3) And sampling the rolled morphotropic and annealed high-purity titanium thin strip in a distributed manner by cutting through a wire, and performing Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) research on the sample. The sample size for SEM observation was 10 mm. times.10 mm. times.1 mm. Firstly, a 0.3mm thin slice is cut out from a transmission sample, the sample with the diameter of 3mm and the thickness of 50 mu m is selected through mechanical polishing, and a TEM sample is prepared through electrolysis and double spraying. A FEI NANO SEM 430 model SEM thermal field emission high resolution SEM, a JEM1200 model SEM.

(4) Grinding, polishing and corroding the high-purity titanium sample in the rolling deformation state, wherein the structure observed by a Scanning Electron Microscope (SEM) and a TEM is similar to that shown in figures 1 and 2, and an ultrafine crystal structure is obtained in the high-purity titanium thin strip after rolling deformation.

(5) The annealed high-purity titanium thin strip sample was polished and corroded, and the structure observed by SEM is shown in FIG. 6. As can be seen from FIG. 6, recrystallization occurred after the annealing treatment to form uniform hcp-phase equiaxial grains having an average hcp-phase grain size of 12.5 μm, and a large amount of granular texture was visible inside the hcp-phase grains, which are indicated by dotted circles and arrows in FIG. 6, and have an average grain size of 2 μm.

(6) TEM and selective area electron diffraction analysis were performed on the granular tissue observed by SEM in step (5), and the granular tissue was determined to be the fcc phase. A TEM photograph of the annealed high purity titanium ribbon sample is shown in FIG. 7, and a diffraction photograph of the selected region of the fcc phase in the annealed sample is shown in FIG. 8, and it is found that the granular structure is the fcc phase by the calibration of the diffraction pattern.

(7) As can be seen from the foregoing steps (5) and (6), a large amount of fcc phase grains are obtained in the hcp phase grains by the cold rolling + annealing method, and the average grain size is 2 μm and the fcc phase grain content is about 18% as measured by statistical analysis of the fcc phase grain size and content by the Electron Back Scattering Diffraction (EBSD) test method, as shown in FIG. 8, the light-colored grains in the figure are the fcc phase, and the dark-colored grains on the back are the hcp phase. Example 2 differed from the experimental parameters in example 1 only by the annealing time, and compared to example 1, the fcc phase size and content were significantly increased from those in example 1.

Example 3

The specific steps of this example are as follows:

(1) a 12 x 30 x 50mm gauge plate sample was obtained from a high purity titanium raw material by wire cutting, and subjected to 20 passes of rolling with a total reduction of 91.7% to prepare a thin strip having a thickness of 1mm, as shown in fig. 1.

(2) And (3) putting the deformed high-purity thin strip into a vacuum furnace for annealing treatment, firstly, extracting vacuum with the vacuum degree of 0.8Pa, then heating to 500 ℃, keeping the temperature for 8 hours after the target temperature is reached, and then cooling to room temperature along with the furnace.

(3) After annealing, the high purity ribbon recrystallized to form uniform hcp phase equiaxial grains having an average hcp phase grain size of 16.8 μm and a large number of fcc phase grains formed within the hcp phase grains, the grains having an average grain size of 2.7 μm and a volume content of about 22%.

Example 4

The specific steps of this example are as follows:

(1) A10X 20X 50 mm-sized plate sample was obtained from a high purity titanium material by wire cutting, and subjected to 18 passes of rolling at a total rolling reduction of 85% to prepare a thin strip having a thickness of 1.5 mm.

(2) And (3) putting the deformed high-purity thin strip into a vacuum furnace for annealing treatment, firstly, extracting vacuum with the vacuum degree of 0.8Pa, then heating to 450 ℃, keeping the temperature for 2 hours after the target temperature is reached, and then cooling to room temperature along with the furnace.

(3) After annealing, the high purity ribbon recrystallized to form uniform hcp-phase equiaxial crystallites having an average hcp phase grain size of 6 μm and a large number of fcc phase band structures within the hcp phase grains, with an average width of about 0.18 μm and a volume content of about 6.5%.

Example 5

The specific steps of this example are as follows:

(1) A15X 20X 50mm gauge plate sample was obtained from a high purity titanium starting material by wire cutting, and rolled in 25 passes at a total rolling reduction of 88% to prepare a thin strip having a thickness of 1.8 mm.

(2) And (3) putting the deformed high-purity thin strip into a vacuum furnace for annealing treatment, firstly, extracting vacuum with the vacuum degree of 0.8Pa, then heating to 600 ℃, keeping the temperature for 2 hours after the target temperature is reached, and then cooling to room temperature along with the furnace.

(3) After annealing, the high purity ribbon recrystallized to form uniform hcp phase equiaxial crystallites, the hcp phase crystallites had an average size of 6 μm and formed a large number of fcc phase grains and a band structure within the hcp phase crystallites, the average width of the bands was about 0.25 μm, the average grain size of the fcc phase grains was 2.2 μm, and the volume content was about 12.5%.

The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.

Claims

1. A method for preparing a face-centered cubic phase in a high-purity titanium thin strip is characterized by comprising the following steps: rolling or compressing and deforming a high-purity titanium raw material plate at room temperature, and then putting the deformed high-purity titanium thin strip into a vacuum furnace for annealing treatment, wherein the annealing temperature of the deformed high-purity titanium thin strip is higher than the recrystallization temperature of the deformed high-purity titanium thin strip, namely, fcc phase structure is obtained in hcp phase grains of the high-purity titanium; the morphology of the fcc phase structure obtained is changed by controlling the heat preservation time, and the method specifically comprises the following steps: controlling the heat preservation time to be more than or equal to 0.5h and less than 3h to obtain fcc phases with acicular and lath-shaped tissue morphologies; controlling the heat preservation time to be 3-5 h to obtain fcc phase with lath and granular tissue morphology; controlling the heat preservation time to be more than 5h and less than or equal to 8h, and obtaining the fcc phase with the tissue morphology mainly taking the granular shape.

2. The method of claim 1, wherein the method comprises the following steps: carrying out multi-pass rolling, accumulative pack rolling or dynamic compression deformation on the high-purity titanium raw material plate to obtain a deformed high-purity titanium thin strip with the total reduction rate of more than or equal to 85%; the multiple passes are 15-25 passes.

3. The method of claim 2, wherein the method comprises the following steps: and (3) putting the deformed high-purity titanium thin strip into a vacuum furnace for annealing treatment, firstly, vacuumizing until the vacuum degree is not more than 1Pa, then, heating to 400-600 ℃, keeping the temperature for 0.5-8 h after the target temperature is reached, and then, cooling to the room temperature along with the furnace.

4. The method for preparing the face centered cubic phase in the high purity titanium thin strip according to any one of claims 1 to 3, characterized in that: the raw material plate is high-purity titanium with the titanium content of 99.999 percent by mass, the surface of the raw material plate needs to be polished before rolling, and the raw material plate is placed in alcohol for cleaning for 10min at normal temperature by using an ultrasonic cleaning machine.

5. The method of claim 4, wherein the method comprises the following steps: the holding time is controlled to be prolonged, the fcc phase content is increased, and the maximum fcc content can reach 22 percent after 8 hours of annealing.

6. The method of claim 5, wherein the method comprises the following steps: the incubation temperature was controlled to increase and the rate of formation of the fcc phase increased.