A high-efficiency, low-cost hcp-fcc two-phase coexisting nanocrystalline extremely thin titanium strip and a preparation method thereof

Abstract

The application discloses a kind of high-efficiency, low-cost hcp-fcc two-phase coexistence nanocrystalline extremely thin titanium strip and its preparation method, including the following process: by the method of asynchronous rolling titanium strip material is rolled to target size, so that the titanium close-packed hexagonal matrix in titanium strip material is formed face-centered cubic phase;When titanium strip material is rolled to target size by the method of asynchronous rolling, the parameters to be controlled include rolling speed, front tension, back tension and pre-pressing force, and multiple-pass rolling is carried out to obtain titanium strip material of target size.The method of the application can realize the continuous production of high-efficiency, low-cost hcp-fcc two-phase coexistence ultrafine-grained extremely thin titanium strip, and does not need intermediate annealing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium rolling, and particularly relates to a high-efficiency, low-cost nanocrystalline extremely thin titanium strip with coexistence of hcp-fcc two phases and a preparation method thereof. BACKGROUND

[0002] Titanium and titanium alloy are an important strategic resource, and have a large number of applications in the industrial and life fields due to high strength, good plasticity and toughness, excellent impact resistance and good corrosion resistance, such as manufacturing various containers, heat exchangers, pipelines, filter cartridges of water purification devices and the like. Titanium and titanium alloy have product structure simplification, volume miniaturization and function diversification for micro electro mechanical systems (MEMS), and have numerous applications in the fields of biological medicine, avionics, precision instruments, computers, microelectronics and the like. The advantages of ultra-fine-grained metal materials and extremely thin strips have great commercial potential, but the conventional ultra-fine-grained metal material preparation method is difficult to realize continuous and low-cost production, which limits the research and application thereof.

[0003] In the prior art, the preparation of extremely thin titanium strips usually adopts a synchronous rolling process, that is, the upper and lower rollers deform the titanium strip at the same speed. Although this method can achieve the thinning of the titanium strip, it has obvious shortcomings in the preparation of nanocrystalline extremely thin titanium strips. First, since the stress on the titanium strip in the synchronous rolling process is mainly uniform compressive stress, the deformation strain mode is single, thereby limiting the proportion of the hcp→fcc phase transition, resulting in a low content of the FCC phase and the inability to stably form an hcp-fcc two-phase coexistence structure, which is crucial to improving the comprehensive mechanical properties of titanium materials. Second, the grain refinement effect is limited, making it difficult to balance the strength and plasticity of the titanium strip, and failing to meet the requirements of high strength and high plasticity. Finally, under the condition of large deformation, synchronous rolling is prone to produce defects such as wrinkling, edge cracking and strip breaking, affecting the forming quality, reducing the production efficiency and causing high production cost. Therefore, the traditional synchronous rolling process cannot meet the demand of efficiently and low-cost preparing hcp-fcc two-phase coexistence nanocrystalline extremely thin titanium strips. In order to solve the above problems, the present application provides an innovative asynchronous rolling method. Compared with ordinary rolling, in asynchronous rolling, the surface linear velocities of the two working rollers are not equal, so that there is an additional "rubbing zone" in the rolling deformation zone. The metal in the "rubbing zone" is not only subjected to the action of rolling pressure, but also subjected to the action of shear force. Asynchronous rolling can reduce the rolling pressure, reduce the rolling passes and realize large reduction under the combined action of tensile stress, compressive stress and shear stress, compared with the traditional rolling process, the heat treatment process of intermediate annealing is reduced, and the implementation process is relatively simple, which is convenient for industrialization and application. In recent years, people have obtained fcc phase in the process of large plastic deformation, but the fcc phase needs a large amount of deformation and stress, and the content of the fcc phase is not easy to control. Asynchronous rolling can realize large reduction, so it can reduce the rolling passes and save cost compared with the traditional method, and the content of the fcc phase can be controlled by rolling parameters. Related researches have found that the fcc phase can improve the plasticity and the dislocation density in the fcc phase is high, which can improve the strength, so that the prepared material has good performance in matching the strength and plasticity. SUMMARY

[0004] To solve the above problems of the prior art, the present application provides a high-efficiency and low-cost hcp-fcc two-phase coexistence nanocrystalline extremely thin titanium strip and a preparation method thereof. The pure titanium strip is rolled by asynchronous rolling, and the upper and lower working rollers are alternated in speed online to fully refine the grains and obtain fcc phase ultra-fine grain pure titanium extremely thin strip with different contents.

[0005] To achieve the above purpose, the present application adopts the following technical solutions:

[0006] A preparation method of a high-efficiency and low-cost hcp-fcc two-phase coexistence nanocrystalline extremely thin titanium strip, comprising the following processes:

[0007] The titanium strip is rolled to a target size by an asynchronous rolling method, so that a face-centered cubic phase is formed in a close-packed hexagonal matrix in the titanium strip;

[0008] When the titanium strip is rolled to the target size by the asynchronous rolling method, the controlled parameters include rolling speed, front tension, back tension and pre-pressing force, and multi-pass rolling is carried out to obtain the titanium strip of the target size.

[0009] Preferably, the raw material of the titanium strip is a cold-rolled and annealed titanium strip.

[0010] Preferably, the rolling speed is 34% to 50% of the maximum rolling speed of the rolling mill, and the asynchronous speed ratio is 1.2 to 1.4.

[0011] Preferably, the front tension is 200 to 250 MPa, and the back tension is 100 to 150 MPa.

[0012] Preferably, the pre-pressing force is 80% to 90% of the maximum rolling force of the rolling mill.

[0013] Preferably, when the titanium strip is rolled to the target size by the asynchronous rolling method, the cumulative reduction coefficient is 12.5 to 50.

[0014] Preferably, the total deformation of the titanium strip is 20% to 80%, and the pass deformation gradually decreases as the deformation increases.

[0015] Preferably, the target thickness of the titanium strip is 20 to 80 microns.

[0016] Preferably, the rolling speed is 45 to 55 mm / s.

[0017] The application also provides a high-efficiency and low-cost nanocrystalline ultra-thin titanium strip with coexisting hcp-fcc phases, which is prepared by the preparation method described above, has a grain size of 0.1 to 1 micron, and has a face-centered cubic phase content of 0.64% to 5.23%.

[0018] Compared with the prior art, the application has the following technical effects:

[0019] The application adopts asynchronous rolling and tension combination forming technology for rolling, can use fewer rolling passes to obtain ultra-fine grain pure titanium ultra-thin strips of different thicknesses, has great advantages in process, can greatly refine the grain, and obtains ultra-fine grains. In the rolling process, the rolling speed, front and back tension and pre-pressing force set by the control system can control the content of the fcc phase (face-centered cubic phase), and prepare pure titanium ultra-thin strips with different fcc phase contents, so as to improve the strength and plasticity of the material, and improve the forming quality of micro parts. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a TEM photograph of the hcp-fcc two-phase coexisting ultrafine-grained pure titanium extremely thin strip prepared in Example 1 of the present application.

[0021] Figure 2 is a TEM photograph of the hcp matrix in Example 1 of the present application.

[0022] Figure 3 is a TEM selected area diffraction pattern photograph of the hcp-fcc two-phase in Example 1 of the present application.

[0023] Figure 4 is an EBSD photograph of the fcc phase content in Example 1 of the present application.

[0024] Figure 5 is an EBSD photograph of the fcc phase content in Example 2 of the present application.

[0025] Figure 6 is an EBSD photograph of the fcc phase content in Example 3 of the present application.

[0026] Figure 7 is an EBSD photograph of the fcc phase content in Example 4 of the present application.

[0027] Figure 8 is a TEM photograph of the hcp-fcc two-phase coexisting ultrafine-grained extremely thin titanium strip in Example 4 of the present application. DETAILED DESCRIPTION

[0028] For further understanding of the present application, the present application is described in detail with reference to the accompanying drawings and examples.

[0029] The preparation method of the high-efficiency and low-cost hcp-fcc two-phase coexisting nanocrystalline extremely thin titanium strip of the present application comprises the following steps:

[0030] Step 1, the raw material is an industrial pure titanium strip, and the surface of the raw material is cleaned before rolling;

[0031] Step 2, the cold-rolled and annealed titanium strip is subjected to multi-pass rolling by using a four-roll 3M rolling mill, and the rolling process does not need intermediate annealing treatment.

[0032] Step 3, the rolling speed, front and rear tension and pre-pressing force of the asynchronous extremely thin strip rolling mill are set, and the asynchronous and tension cold rolling is performed to obtain pure titanium extremely thin strips with different thicknesses;

[0033] Step 4, first, large deformation rolling is performed, and the rolling speed, front and rear tension and pre-pressing force are adjusted on line during rolling, and multi-pass rolling is performed, and the rolling process does not need intermediate annealing treatment;

[0034] Step 5, the thickness of the rolled piece is measured, and the rolling speed, front and rear tension and pre-pressing force are reset for small reduction rolling;

[0035] Step 6, repeat to step 5, roll the pure titanium strip to the target thickness, complete the rolling;

[0036] In the finished product rolled, fcc phase is generated in the hcp matrix.

[0037] In the above steps 4 and 5, the rolling speed is set to 34%~50% of the maximum rolling speed of the rolling mill, and the speed ratio is 1.3.

[0038] In the above steps 4 and 5, the front and rear tension stress and the pre-pressing force are set to 80%~90% of the maximum rolling force of the rolling mill.

[0039] In the above steps 4 and 5, when the speed ratio is 1.2~1.4, the working roll with faster rolling speed in the asynchronous thin strip rolling mill is the fast working roll, and the working roll with slower rolling speed is the slow working roll, and the speed of the fast working roll is always faster than that of the slow working roll.

[0040] The above rolling mill sets the rolling speed and speed ratio through the control system, and the control system includes a main control computer, a PLC and an operation table. The grain size of the titanium strip product is 0.1~1μm.

[0041] The titanium strip raw material used in the following embodiments of the application is an industrial pure titanium strip with a grade of TA1 and an initial thickness of 0.1mm. Its chemical composition (wt%) is 0.18 (O), 0.015 (H), 0.03 (N), 0.08 (C), 0.2 (Fe), and the tensile strength of the original titanium strip is 320MPa.

[0042] Example 1:

[0043] The specific steps of the preparation method of the high-efficiency and low-cost hcp-fcc two-phase coexisting nanocrystalline ultra-thin titanium strip of the embodiment are as follows:

[0044] Step (1), an asynchronous rolling mill is used, and the rolling speed, front and rear tension stress and pre-pressing force of the asynchronous thin strip rolling mill are set, wherein the rolling speed is 55mm / s, the front and rear tension stress is 250MPa and 150MPa respectively, the pre-pressing force is 400kN, which is 80% of the maximum rolling force of the rolling mill, and the speed ratio of the rolling mill is set to 1.4.

[0045] Step (2), start the rolling mill to roll the pure titanium strip in one pass, and adjust the front and rear tension stress online during rolling, and the adjustment range is 60~250MPa; during rolling, the upper working roll is the fast working roll, and the lower working roll is the slow working roll.

[0046] Step (3): After one rolling pass, the thickness of the pure titanium strip is measured to be 70 μm. The front and rear tensions and pre-clamping force are readjusted. The rolling speed is 55 mm / s, the speed ratio is 1.4, the front and rear tensions are 230 MPa and 130 MPa respectively, and the pre-clamping force is 450 kN, which is 90% of the maximum rolling force of the mill.

[0047] Step (4): Start the rolling mill to perform a second pass of rolling on the pure titanium strip. During rolling, adjust the front and rear tensions online, with an adjustment range of 60~250MPa. During rolling, the lower work roll is the fast work roll, and the upper work roll is the slow work roll. After the two passes, roll the pure titanium strip to 80μm to complete the rolling process; the cumulative reduction coefficient is 12.5.

[0048] The finished product image of the rolled titanium strip in this embodiment is shown below. Figure 1 As shown, its surface quality is good. Samples were taken from an 80 μm thick pure titanium foil and observed using transmission electron microscopy (TEM). Figure 2 The image shows a TEM image of the matrix, which reveals lamellar structures within the matrix, as indicated by the arrows. After... Figure 3 Selected electron diffraction (SAED) patterns revealed that the lamellar structure was an FCC phase. EBSD was used to statistically analyze the FCC phase content, as shown below. Figure 4 As shown, the face-centered cubic phase content in the titanium strip obtained in this embodiment is 0.64%.

[0049] Example 2

[0050] The specific steps of the high-efficiency, low-cost preparation method of the nanocrystalline ultrathin titanium strip with HCP-FCC coexistence in this embodiment are as follows:

[0051] Step (1): Using an asynchronous rolling mill, set the rolling speed, front and rear tensions and pre-clamping force of the asynchronous ultra-thin strip rolling mill. The rolling speed is 55 mm / s, the front and rear tensions are 230 MPa and 130 MPa respectively, the pre-clamping force is 450 kN, which is 90% of the maximum rolling force of the rolling mill, and the speed ratio of the rolling mill is set to 1.3.

[0052] Step (2): Start the rolling mill to roll the pure titanium strip in one pass. During rolling, adjust the front and rear tensions online. The adjustment range is 60~250MPa. During rolling, the upper work roll is the fast work roll and the lower work roll is the slow work roll.

[0053] Step (3): After one rolling pass, the thickness of the pure titanium strip is measured to be 70 μm; then repeat steps (1) to (2) to roll the pure titanium strip to 60 μm.

[0054] Step (4), re-adjust the front and back tension and pre-pressing force, the rolling speed is 55 mm / s, the allometric ratio is 1.3, the front and back tension is 230 MPa and 120 MPa respectively, and the pre-pressing force is 450 kN, which is 90% of the maximum rolling force of the rolling mill;

[0055] Step (5), start the rolling mill to roll the pure titanium strip in the next pass, and adjust the front and back tension on line during rolling, the adjustment range is 60-250 MPa; during rolling, the lower work roll is the fast work roll and the upper work roll is the slow work roll.

[0056] Step (6), repeat steps (4) to (5), roll the pure titanium strip into 60 μm in 4 passes, the reduction in each pass is the same, and the rolling is completed; the cumulative reduction coefficient is 16.7;

[0057] TEM observation is performed on the sample taken from the 60 μm thick pure titanium foil, and EBSD is used to count the fcc phase content, as shown in Figure 5 The face-centered cubic phase content of the titanium strip obtained in this embodiment is 1.32%.

[0058] Example 3

[0059] The specific steps of the preparation method of the high-efficiency and low-cost hcp-fcc two-phase coexisting nanocrystalline ultra-thin titanium strip in this embodiment are as follows:

[0060] Step (1), an asynchronous rolling mill is used, and the rolling speed, front and back tension and pre-pressing force of the asynchronous ultra-thin strip rolling mill are set, wherein the rolling speed is 50 mm / s, the front and back tension is 220 MPa and 120 MPa respectively, the pre-pressing force is 450 kN, which is 90% of the maximum rolling force of the rolling mill, and the allometric ratio of the rolling mill is set to 1.3.

[0061] Step (2), start the rolling mill to roll the pure titanium strip in one pass, and adjust the front and back tension on line during rolling, the adjustment range is 60-250 MPa; during rolling, the upper work roll is the fast work roll and the lower work roll is the slow work roll.

[0062] Step (3), after one-pass rolling, the thickness of the pure titanium strip is measured to be 70 μm; then repeat steps (1) to (2) to roll the pure titanium strip to 60 μm;

[0063] Step (4), re-adjust the front and back tension and pre-pressing force, the rolling speed is 45 mm / s, the allometric ratio is 1.3, the front and back tension is 210 MPa and 110 MPa respectively, and the pre-pressing force is 450 kN, which is 90% of the maximum rolling force of the rolling mill;

[0064] Step (5), start the rolling mill to roll the pure titanium strip in the next pass, and adjust the front and rear tension stresses on line during rolling, and the adjustment range is 60-250 MPa; during rolling, the lower work roll is the fast work roll, and the upper work roll is the slow work roll.

[0065] Step (6), repeat steps (4) to (5) to roll the pure titanium strip into 60 μm in 4 passes, and the reduction in each pass is the same; then roll the 60 μm thick pure titanium strip into 40 μm in 3 passes, and the reduction in each pass is the same, to complete the rolling; the cumulative reduction coefficient is 25;

[0066] TEM observation is performed on the sample taken from the 40 μm thick pure titanium foil, and EBSD is used to statistically analyze the fcc phase content, as shown in FIG. 2, the fcc phase content in the titanium strip obtained in this embodiment is 2.82%. Figure 6

[0067] Embodiment 4

[0068] The specific steps of the preparation method of the high-efficiency and low-cost hcp-fcc two-phase coexisting nanocrystalline extremely thin titanium strip in this embodiment are as follows:

[0069] Step (1), an asynchronous rolling mill is used, and the rolling speed, front and rear tension stresses and pre-pressing force of the asynchronous extremely thin strip rolling mill are set, wherein the rolling speed is 45 mm / s, the front and rear tension stresses are 200 MPa and 100 MPa respectively, the pre-pressing force is 450 kN, which is 90% of the maximum rolling force of the rolling mill, and the asynchronous ratio of the rolling mill is set to 1.2.

[0070] Step (2), start the rolling mill to roll the pure titanium strip in one pass, and adjust the front and rear tension stresses on line during rolling, and the adjustment range is 60-250 MPa; during rolling, the upper work roll is the fast work roll, and the lower work roll is the slow work roll.

[0071] Step (3), after one-pass rolling, the thickness of the pure titanium strip is measured to be 70 μm; then repeat steps (1) to (2) to roll the pure titanium strip to 60 μm;

[0072] Step (4), adjust the front and rear tension stresses and the pre-pressing force again, the rolling speed is 45 mm / s, the asynchronous ratio is 1.2, the front and rear tension stresses are 160 MPa and 60 MPa respectively, and the pre-pressing force is 450 kN, which is 90% of the maximum rolling force of the rolling mill;

[0073] Step (5), start the rolling mill to roll the pure titanium strip in the next pass, and adjust the front and rear tension stresses on line during rolling, and the adjustment range is 60-250 MPa; during rolling, the lower work roll is the fast work roll, and the upper work roll is the slow work roll.

[0074] ​Step (6): Repeat steps (4) to (5) to roll the pure titanium strip to 60 μm in 4 passes, with the same reduction in each pass; then roll the 60 μm thick pure titanium strip to 40 μm in 3 passes, with the same reduction in each pass; then roll the 40 μm thick pure titanium strip to 20 μm in 4 passes, with the same reduction in each pass, to complete the rolling; the cumulative reduction coefficient is 50.

[0075] Samples were taken from 20 μm thick pure titanium foil, observed using transmission electron microscopy (TEM), and the fcc phase content was statistically analyzed using EBSD. Figure 7 As shown, the face-centered cubic phase content in the titanium strip obtained in this embodiment is 5.23%. From Figure 8 As can be seen, the grain size after rolling is approximately 200-300 nm. Figure 8 As can be seen from SAED, the diffraction spots exhibit curvature, indicating the formation of randomly oriented ultrafine crystals and subgrains during the rolling process. From... Figure 8 It can also be seen that the organization contains FCC phases, such as Figure 8 As shown by the arrow in the upper left corner, this indicates that an ultrafine-grained structure with HCP-FCC coexisting phases was obtained after 80% deformation.

[0076] As can be seen from the above-described scheme of this invention, the processing method of this invention can form a face-centered cubic (fcc) phase in a pure titanium hexagonal close-packed (hcp) matrix. Furthermore, the fcc phase content increases with increasing deformation, rising from 0.64% at 20% deformation to 5.23% at 80% deformation. The method of this invention enables efficient, low-cost, continuous production of ultrafine-grained, ultrathin titanium strips with coexisting hcp and fcc phases, without the need for intermediate annealing.

Claims

1. A method for preparing high-efficiency, low-cost, hcp-fcc two-phase coexisting nanocrystalline ultra-thin titanium strip, characterized in that, The process comprises the following steps: rolling the titanium strip to a target size by an asynchronous rolling method to form a face-centered cubic phase in a close-packed hexagonal matrix of titanium in the titanium strip; controlling parameters including rolling speed, front tension, back tension and pre-pressing force when rolling the titanium strip to a target size by an asynchronous rolling method, and performing multi-pass rolling to obtain the titanium strip of the target size; the rolling speed is 34%~50% of the maximum rolling speed of the rolling mill, and the asynchronous speed ratio ranges from 1.2 to 1.4; the front tension is 200~250MPa, and the back tension is 100~150MPa; the pre-pressing force is 80%~90% of the maximum rolling force of the rolling mill; the cumulative reduction coefficient is 12.5~50 when rolling the titanium strip to a target size by an asynchronous rolling method; the rolling speed is 45~55mm / s.

2. The method according to claim 1, wherein the method is characterized by, The raw material of the titanium strip is a cold-rolled annealed titanium strip.

3. The method according to claim 1, wherein the method is characterized by, The total deformation of the titanium strip is 20%~80%, and the pass deformation gradually decreases as the deformation increases.

4. The method according to claim 1, wherein the method is characterized by, The target thickness of the titanium strip is 20~80μm.

5. A high efficiency, low cost, hcp-fcc two phase coexisting nanocrystalline ultra-thin titanium ribbon, characterized in that, The titanium strip is prepared by the method of any one of claims 1-4, and the grain size of the titanium strip is 0.1~1μm, and the content of the face-centered cubic phase is 0.64%~5.23%.

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