CN111842488A - Process method for realizing uniform fine-grained structure of TiAl alloy based on cross-clad rolling - Google Patents

Abstract

The invention belongs to the field of sheet rolling and plastic forming, discloses a process method for realizing a uniform fine-grained structure of TiAl alloy based on cross wrapping rolling, and aims to solve the problem of current TiAl alloy rolling by combining wrapping and cross rolling. The problem of uneven organization of the plate. Including the homogenization or hot isostatic pressing of TiAl alloy ingots, the cross rolling process of RD1 and RD2 commutation at the temperature of 1250℃～1270℃, the pass deformation in the RD1 direction is less than 24%, and the rolling The rolling speed is less than 0.5m/s, the pass deformation in the RD2 direction is less than 18%, the rolling speed is less than 1.2m/s, the cumulative total deformation is 60% to 90%, and the sheath is removed to obtain a TiAl alloy plate. Compared with the traditional rolling method, in the present invention, the internal lamella structure of the cross-rolled TiAl alloy plate is fully broken and recrystallized, which reduces or weakens the anisotropy of the structure and improves the uniformity of the structure; meanwhile, ingot TiAl is used. Alloy direct cladding cross-rolling realizes low-cost TiAl alloy wide sheet, shortens the process flow, and promotes the industrial application of TiAl alloy rolled sheet.

Description

Process method for realizing uniform fine-grained structure of TiAl alloy based on cross-clad rolling

technical field

The invention belongs to the field of sheet rolling and plastic forming, and particularly relates to a process method for realizing uniform fine-grained structure of TiAl alloy based on cross-clad rolling.

Background technique

TiAl alloy is a new lightweight high temperature structural material with low density, high specific strength and high specific modulus, excellent high temperature creep resistance and oxidation resistance, which can be used for nozzle parts, internal structural parts, Protective plates, etc., the thermal protection plate structure of supersonic aircraft, precision-guided missile wings, rudders and other structures have great application prospects in the fields of aerospace and automobile engines. TiAl alloy has low room temperature plasticity, poor deformation ability at high temperature, serious local rheology of thermal deformation, and uneven microstructure, which seriously restricts the preparation of high-performance TiAl alloy sheet. So far, the problems existing in the preparation technology of TiAl alloy sheets have not been well solved.

The preparation technology of TiAl alloy rolled sheet mainly includes isothermal rolling and wrapping rolling. Among them, the wrapping rolling adopts wrapping to prevent destabilizing phenomena such as oxidation and cracking, and the preparation of difficult-to-deform metal plates can be realized on a traditional rolling mill, which is a low-cost and efficient plate preparation method. However, local rheology is prone to occur during the rolling process of TiAl alloys, the lamellae are not easily broken, and the sheet itself has a huge residual lamella structure, resulting in uneven structure, and the current wrapping rolling technology cannot completely eliminate the huge residual lamellae Organizing, solving the problem of uneven organization. In recent years, some scientific research institutes have used multi-directional forging technology to successfully prepare magnesium, aluminum and titanium-aluminum alloys with uniform structure and fine grains. preparation, and the cost is high.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies of the prior art and solve the problems of difficulty in preparing high-quality TiAl-based alloy plates and uneven structure, the present invention improves the traditional wrapping rolling and multi-directional forging technologies. The combined process is aimed at breaking the huge lamellar structure inside the plate, reducing the anisotropy of the plate structure, thereby improving the uniformity of the structure, and obtaining a high-quality wide-width TiAl alloy plate with a uniform fine-grained structure and low cost.

The specific technical scheme of the present invention is: a process method for realizing a uniform fine-grained structure of TiAl alloy based on cross-clad rolling, comprising the following steps:

Step 1, billet preparation: TiAl alloy ingot is used as the raw material, and then the ingot is subjected to homogenization treatment or hot isostatic pressing process; plate-shaped alloy billet is obtained after treatment with wire electric discharge and mechanical grinding;

Step 2, wrapping and rolling pretreatment: the wrapping material can be selected from a metal material with high resistance to high temperature deformation, which is processed and welded with the plate-shaped alloy blank obtained in step 1 to obtain a wrapping slab; To reduce the deformation resistance during the rolling process, it is necessary to preheat the sheathed slab and the roll. The sheathed slab is heated to 1250℃～1270℃ with the furnace, and the temperature is kept for 30～60min, and the roll is preheated to 200℃～300℃. ℃, start rolling;

Step 3, high temperature cross rolling: the rolling temperature is 1250℃～1270℃, the rolling speed is not more than 1.2m/s, and the strain rate per pass is 1.0～3.0s ⁻¹ ; firstly along the length direction of the sheathed slab , as the rolling direction RD1, rolling 1 to 3 passes, the deformation of each pass is less than 24%, the rolling speed is less than 0.5m/s, and the rolled sheet reaches the target length; then the sheathed slab is rotated horizontally by 90° , along the direction perpendicular to the length, as the rolling direction RD2, rolling 1 to 5 passes, the deformation of each pass is <18%, the rolling speed is <1.2m/s, and the cumulative total deformation is 60% to 90% , and cooled to room temperature with the furnace to complete the cross-rolling; when the temperature drops below 1100°C during the cross-rolling process, the slab needs to be returned to the furnace and heated to 1250°C to 1270°C, and kept for 4 to 6 minutes;

Step 4, removing the cover: the cover of the rolled sheet with the cover in step 3 is removed by turning or grinding, and a TiAl alloy wide sheet with uniform structure is obtained after mechanical orthosis.

Preferably, in the above step 2, the wrapping material is heat-resistant 2520 stainless steel (0Cr25Ni20) with high deformation resistance; the wrapping thickness is 30% to 50% of the slab thickness, and vacuum electron beam welding is used for sealing and welding. The low deformation resistance of the wrapping material easily leads to the cracking of the edge wrapping during the cross-rolling process, and its good ductility easily leads to a sharp increase in the width of the sheet, making the rolling process impossible.

Preferably, the rolling passes in the RD1 direction in the above step 3 are 1 to 3 passes, and the total rolling deformation control in the RD1 direction is determined according to the required sheet width, and the deformation is too large to ensure that the roll width can be rolled after the cross. At the same time, it affects the change of the layer thickness ratio of the sheathing material and the base material, which is not conducive to the stability of the sheathing structure, and easily leads to cracking and a decrease in the thermal protection effect.

Preferably, during the cross rolling in the above step 3, the deformation amount of the pass in the RD1 direction is 18% to 24%, and the rolling speed is controlled to be 0.3m/s to 0.5m/s.

Preferably, in the cross rolling process in the above step 3, the deformation amount of the first two passes in the RD2 direction is 10% to 16%, and the rolling speed is 0.6m/s to 0.8m/s; the deformation amount of the third to fifth passes is less than 10%. %, control the rolling speed to be 0.8m/s～1.0m/s. As the deformation of the sheathing sheet increases, it is necessary to increase the rolling speed and reduce the deformation amount to reduce the rolling force, prevent heat dissipation during the rolling process and maintain the stability of the sheathing structure.

The advantages and beneficial effects of the present invention are:

1. The present invention provides a process method for a high-quality TiAl alloy sheet. The combination of wrapping and cross rolling reduces the possibility of edge cracking of the sheet. At the same time, the huge residual lamella structure inside the TiAl alloy sheet is Under the action of bidirectional rolling and shearing force, it is fully broken and recrystallized, and the grains are finer, and the anisotropy of the structure is reduced or weakened, and the uniformity and equiaxiality of the plate structure are improved.

2. The present invention can be directly processed and formed in the as-cast state, shortens the technological process, has low equipment requirements, can directly obtain high-quality and low-cost TiAl alloy wide-width thin plates, improves the yield of TiAl plates, and promotes TiAl alloy rolling. Industrial applications of sheet metal.

Description of drawings

Fig. 1 is the schematic diagram of the process flow of the present invention.

Figure 2 (a) is a microstructure picture of the TiAl alloy sheet prepared in Example 1 of the present invention, and (b) is a microstructure picture of the TiAl alloy sheet prepared by a unidirectional rolling process.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the content.

Example 1:

In this embodiment, a process method for realizing uniform fine-grained structure of TiAl alloy by cross-clad rolling,

Its forming process is shown in Figure 1, and the specific steps are as follows:

The material of this example is a TiAl alloy whose nominal composition is Ti-44Al-5Nb-(Mo, V, B). The α/β transformation point temperature of the alloy measured by differential scanning calorimetry (DSC) is about 1160 °C .

Step 1, billet preparation: the raw material is a TiAl alloy ingot obtained by 3 times of remelting by vacuum consumable arc melting method, and then the ingot is homogenized. The homogenization process is as follows: temperature 1250℃～1270℃ , the time is 4h to 6h, and the furnace is cooled; the plate-shaped alloy blank with the surface roughness Ra6 is obtained after the wire EDM and mechanical grinding treatment, and the thickness of the slab is 10mm;

Step 2, wrapping and rolling pretreatment: The TiAl alloy slab is wrapped, and the wrapping material is heat-resistant stainless steel with high deformation resistance to prevent the wrapping plate from being too wide to cause cracking or failure of rolling. The thickness of the sheath is 3mm, and the vacuum electron beam welding method is used for sealing and welding to obtain the sheathed slab; before the sheathing, the surface of the slab and the sheathing needs to be cleaned; Preheat the sheathing slab and the roll, and heat the sheathing blank to 1250℃～1270℃ with the furnace, and keep the temperature for 30～40min; the roll is preheated to 200℃ and start rolling;

Step 3, cross rolling: the rolling temperature is 1250°C to 1270°C; firstly, three passes are rolled along the length direction of the sheathed slab (as rolling direction RD1), and the deformation amount of each pass is 20% to 22%, which is To prevent the cracking of the as-cast slab, choose a slower rolling speed of 0.3m/s to 0.5m/s, the cumulative deformation is about 72%, and the length of the rolled sheet is 400mm; then rotate the sheathed slab horizontally by 90° , 3 passes of rolling along the direction perpendicular to the length (as rolling direction RD2), the deformation of the first two passes is 10% to 12%, and the rolling speed is 0.6m/s to 0.8m/s; the deformation of the third pass The amount of rolling is 8% to 10%, and the rolling speed is controlled to be 0.8m/s to 1.0m/s to prevent cracking caused by excessive heat dissipation. The cumulative deformation is about 40%, and it is cooled to room temperature with the furnace to complete the cross-rolling; During the rolling process, when the temperature drops below 1100°C, the slab needs to be returned to the furnace and heated to 1250°C to 1270°C, and kept for 4 to 6 minutes;

Step 4, removing the covering: the covering of the rolled sheet with the covering in step 3 is removed by turning or grinding to obtain a TiAl alloy wide sheet with uniform structure.

Compared with the sheet structure obtained under the unidirectional rolling process (see Fig. 2b), the TiAl alloy sheet prepared in this example (see Fig. 2a) has a significant reduction in the number and size of lamellae compared with conventional rolling. With a certain recrystallized structure, the structure is more uniform, the grains are finer, the surface flatness is good, and there is no crack defect.

This embodiment can be directly processed in the as-cast state, shortens the process flow, requires low equipment, and can obtain high-quality, low-cost, wide TiAl alloy plates with dimensions of 400mm×240mm×2mm (length×width×thickness).

Example 2:

The difference from Example 1 is that: in step 3 of this example, rolling along the direction of RD1 for 2 passes, the deformation of each pass is 22% to 24%, and the rolling speed is 0.3m/s to 0.5m/s; 4 to 5 passes in the direction of rolling, the deformation of the first two passes is 12% to 14%, the rolling speed is 0.6m/s to 0.8m/s; the deformation of the third to fifth passes is 6% to 8% , the rolling speed is 0.8m/s～1.2m/s. Other processing steps and process parameters are the same as in Example 1. Compared with conventional rolling, the TiAl alloy wide-width sheet prepared in this example also has a significant reduction in the aggregate fraction of giant lamellae, a more uniform structure, finer grains, and no crack defects.

Example 3:

The difference from Example 1 is that: in this example, in step 3, rolling along the direction of RD1 for 1 pass, the deformation of each pass is 22% to 24%; rolling along RD2 for 2 to 3 passes, the deformation of each pass is 10%, and the rolling speed is controlled to be 0.8 m/s to 1.0 m/s. Other processing steps and process parameters are the same as in Example 1. The TiAl alloy wide-width sheet prepared in this example has a reduced group fraction, a relatively uniform structure, good surface flatness, and no crack defects.

Claims (5)

1. The process method for realizing the TiAl alloy uniform fine grain structure based on the cross sheath rolling is characterized by comprising the following steps of:

step 1, preparing a blank: adopting TiAl alloy ingot casting as a raw material, and then carrying out homogenization treatment or hot isostatic pressing process on the ingot casting; performing wire cut electrical discharge machining and mechanical polishing treatment to obtain a plate-shaped alloy blank;

step 2, pre-treatment of sheathing and rolling: the sheathing material is a metal material, and is processed with the plate-shaped alloy blank obtained in the step 1 to obtain a sheathing plate blank; preheating the sheathed plate blank and the roller, heating the sheathed plate blank to 1250-1270 ℃ along with a furnace, preserving heat for 30-60 min, preheating the roller to 200-300 ℃, and starting rolling;

Step 3, high-temperature cross rolling: the rolling temperature is 1250-1270 ℃, the rolling speed is not more than 1.2m/s, and the strain rate of each pass is 1.0-3.0 s^-1(ii) a Firstly, rolling for 1-3 times along the length direction of the sheathed plate blank as the rolling direction RD1, wherein the deformation of each time is<24% rolling speed<0.5m/s, the rolled plate reaches the target length; then horizontally rotating the wrapped plate blank by 90 degrees and rolling the wrapped plate blank by 1 to hot in the direction perpendicular to the length direction as the rolling direction RD25 passes, each pass has the deformation of<18% rolling speed<1.2m/s, the accumulated total deformation is 60-90%, and the steel is cooled to room temperature along with the furnace to finish cross rolling; when the temperature is reduced to below 1100 ℃ in the cross rolling process, returning the plate blank to the furnace and heating to 1250-1270 ℃, and preserving heat for 4-6 min;

step 4, removing the sheath: and (3) removing the sheath of the rolled plate with the sheath in the step (3) by adopting a turning or grinding method, and obtaining the TiAl alloy wide plate with uniform tissue after mechanical reshaping.

2. The process method for realizing the TiAl alloy uniform fine grain structure based on the cross-jacket rolling as claimed in claim 1, wherein the jacket material in the step 2 is heat-resistant 2520 stainless steel; the thickness of the sheath is 30% -50% of the thickness of the plate blank, and the vacuum electron beam welding method is adopted for sealing welding.

3. The process method for realizing the TiAl alloy uniform fine grain structure based on the cross-sheath rolling according to the claim 1 or 2, characterized in that the deformation of the RD1 direction pass in the step 3 cross rolling process is 18-24%, and the rolling speed is controlled to be 0.3-0.5 m/s.

4. The process method for realizing the TiAl alloy uniform fine grain structure based on the cross-sheath rolling according to the claim 1 or 2, characterized in that the deformation of the previous two passes in the direction of RD2 in the step 3 is 10-16%, and the rolling speed is 0.6-0.8 m/s; the deformation of the third to fifth passes is less than 10 percent, and the rolling speed is controlled to be 0.8-1.0 m/s.

5. The process method for realizing the TiAl alloy uniform fine grain structure based on the cross-sheath rolling according to the claim 1 or 2, characterized in that, the blank preparation in the step 1: the method comprises the following steps of remelting a TiAl alloy ingot obtained by a vacuum consumable arc melting method for 3 times by using an original material, and then carrying out homogenization treatment on the ingot, wherein the homogenization treatment process comprises the following steps: the temperature is 1250-1270 ℃, the time is 4-6 h, and the furnace is cooled; the alloy blank with the surface roughness Ra6 is obtained after wire cut electrical discharge machining and mechanical grinding treatment, and the thickness of the plate blank is 10 mm.

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