CN115044847A - Method for preparing large-size titanium alloy fine-grain blank based on CVCE method - Google Patents

Abstract

The invention belongs to the technical field of metal plastic processing, and relates to a method for preparing a large-size titanium alloy fine-grain blank based on a CVCE method, which comprises the following steps: s1, calculating the size of the blank, and blanking to obtain a titanium alloy blank; s2, heating the titanium alloy blank to 850-900 ℃, and performing continuous variable-section circular extrusion deformation to obtain a titanium alloy cylinder; after the required total deformation circulation pass is completed, namely the required accumulated strain is reached, carrying out water cooling on the titanium alloy cylinder; s3, heating the water-cooled titanium alloy cylinder to 750-800 ℃, preserving heat for 2-3 hours, and performing air cooling for annealing heat treatment to obtain the titanium alloy fine-grained blank uniformly distributed along the radial structure. The problem of poor deformation permeability of large-size bars during grain refinement is solved.

Description

A method for preparing large-scale titanium alloy fine-grained billets based on CVCE method

technical field

The invention belongs to the technical field of metal plastic processing, in particular to a method for preparing a large-scale titanium alloy fine-grained blank based on a CVCE method.

Background technique

The application of high-performance titanium alloys in aerospace accounts for about 70% of the total output of titanium materials, and the amount and types of applications in aircraft have increased significantly with the improvement of aircraft performance. In order to meet the development and production of large-scale integral forgings for aircraft, it is necessary to use titanium alloy billets with high quality and increasing sizes.

For titanium alloys, the uniformity of grain size and microstructure distribution is one of the important evaluation indicators of high-quality titanium alloys. It is an important parameter affecting the mechanical properties of materials (such as fatigue, creep and yield strength), and titanium The formability of the alloy and the properties of the parts it processes are also closely related to the grain size and distribution of the billet used. In addition, the structure of titanium alloy forgings is hereditary. When the structure of the blank is coarse and uneven, it is difficult to eliminate such defects during subsequent die forging or heat treatment, and will eventually remain in the forgings and reduce the performance of the part. .

Research data shows that when a certain method can be used to obtain an equiaxed, fine and uniform titanium alloy structure, the plasticity of the material and the uniformity during forming can be significantly improved. Titanium alloy bar is a commonly used blank type in the processing of many parts on aircraft. Therefore, obtaining equiaxed, small, and uniform high-quality and large-sized titanium alloy bars is crucial for obtaining large-size, high-performance titanium alloy forgings. effect.

Large plastic deformation technology has strong grain refinement ability and has been recognized by the material science community as the most promising method for preparing ultrafine grained materials. At present, the refining technology of small-sized bars is relatively mature, including equal channel angular extrusion (ECAE), high pressure torsion (HPT), reciprocating extrusion (CEC), large ratio extrusion (extrusion ratio above 100), continuous extrusion Variable cross-section cyclic extrusion (continuous variable cross-section recycled extrusion, CVCE) and the like, especially the CVCE method, the small-sized bar blank prepared by it has better tissue uniformity along the radial direction. However, the refinement quality control of large-sized bars has always been a technical difficulty, which is mainly due to the inhomogeneity of the microstructure and properties along the radial direction due to the poor deformation permeability of the core of large-sized bars. For example, when the free forging process of repeated upsetting and elongation commonly used in industrial production is used to refine grains, due to the multiple upsetting involved in deformation, the process is more complicated and the efficiency of large deformation is low; ≤2.5～3, the height and volume of the prepared blank are small, and the refining efficiency is low; it is difficult for the deformation to penetrate into the core of the bar blank, which makes the central tissue thicker than other parts, resulting in the uniformity of its microstructure along the radial direction. poor sex, etc.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing large-sized titanium alloy fine-grained blanks based on the CVCE method, so as to solve the problem of poor deformation permeability of large-sized rods during grain refinement.

The present invention is achieved through the following technical solutions:

A method for preparing a large-scale titanium alloy fine-grained billet based on a CVCE method, comprising the following steps:

S1. Calculate the size of the billet, and perform blanking to obtain a titanium alloy billet;

S2, heating the titanium alloy billet to 850°C to 900°C, and performing continuous variable cross-section cyclic extrusion deformation to obtain a titanium alloy cylinder;

After the required total deformation cycle is completed, the titanium alloy cylinder is water-cooled;

S3, heating the water-cooled titanium alloy cylinder to 750-800° C., holding the temperature for 2-3 hours, and performing annealing heat treatment to obtain a titanium alloy fine-grained billet with uniform distribution along the radial direction.

Further, the titanium alloy billet has a height-diameter ratio of ≤3.5 and a bar with a diameter of ≥100 mm.

Further, in S2, the cyclic extrusion deformation of the continuously variable section specifically includes the following steps:

2.1. First, according to the diameter specification and height-diameter ratio of the titanium alloy billet, the deformation equipment and extrusion die are selected, and the heated bar billet is extruded into a circular truncated body with 6° to 9°;

2.2. Turn the small diameter end of the circular truncated body upward and the large diameter end downward, and continue to use the deformation equipment to upset the circular truncated body into a cylinder with the same diameter as the original blank;

2.3. Then rotate the upsetting cylinder by 180°, and then extrude it into a truncated truncated body with 6° to 9°; the taper of the truncated truncated body is the same as that of the truncated truncated body extruded in step 2.1;

2.4. Finally, turn the small diameter end of the circular truncated body downward and the large diameter end upward, and use the deformation equipment to upset it into a cylinder with the same diameter as the original blank; so far, one deformation cycle has been completed;

2.5. Repeat 2.1-2.4 until the required number of deformation cycles is reached, obtain the corresponding cumulative strain amount, and stop.

Further, in S2, the heating temperature of the titanium alloy billet is 100°C to 150°C in addition to the recrystallization temperature.

Further, between the deformation processes of continuous variable cross-section cyclic extrusion deformation, if the billet temperature is less than 700°C, it is placed in a heating furnace to be heated to 850-900°C and then kept for (D _{cylindrical billet} /4) min.

Further, in S1, according to the die angle, the height h and the radius r of the small diameter end of the continuously variable section body are determined:

According to the principle that the volume does not change during deformation, the volume of the extruded continuously variable cross-section body is V truncated _body = V _cylinder , that is, πh(R ² +Rr+r ² )/3=πR ² H, and the height of the cylinder is calculated. H, and control the height-diameter ratio of the continuously variable section body h/[(D+d)/2]≤3.5, where R and D are the radius of the cylinder and the diameter of the cylinder, respectively;

Then, according to the calculated height H, blank the titanium alloy billet of known diameter.

Further, the die angle is 6° to 9°.

Further, in S3, the method of the annealing heat treatment is air cooling.

Compared with the prior art, the present invention has the following beneficial technical effects:

The invention discloses a method for preparing a large-scale titanium alloy fine-grained billet based on a CVCE method. According to the plastic deformation process system of TC4 titanium alloy, the type of equipment, the operation method of continuous variable section cyclic extrusion deformation, etc., and by controlling the annealing temperature and Time, determine the continuous variable section cyclic extrusion process parameters and heat treatment process parameters with better grain refinement effect. When the continuous variable section cyclic extrusion method is used to refine the large-sized bar blank, in the extrusion process of the same deformation cycle, the edge of the blank is simultaneously subjected to the combined action of the extrusion force and the friction force between the blank and the edge of the die. Therefore, this part is a relatively large deformation area, but in the upsetting process, the center of the blank is a large deformation area, so that the deformation permeability of the blank in one deformation cycle is good, and the accumulated strain is large. Therefore, the microstructure of the blank along the radial direction is evenly distributed and the central microstructure is relatively finer, while the blank obtained by the conventional upsetting-elongation free forging process has poor deformation permeability and coarse microstructure in the center of the blank. In addition, since the deformation is selected in the temperature range of only 100 to 150°C above the recrystallization temperature of the alloy, and then annealing is performed above the recrystallization temperature near the recrystallization temperature (750 to 800°C), not only the plastically deformed metal can be deformed. Recrystallization takes place to present an equiaxed shape, and it will not grow and coarsen due to excessive temperature. In addition, the diameter specifications of the fine-grained materials prepared by CVCE are not limited, and larger-sized fine-grained rods can also be produced, which can be realized only by using larger tonnage deformation equipment and larger-sized molds. Therefore, the CVCE method has great advantages in the preparation of large-scale fine-grained rods, and meets the growing demand for large-scale, high-quality titanium alloy rods in aviation.

Further, the heating temperature of the titanium alloy billet is designed to be 100 ° C ~ 150 ° C on the basis of the recrystallization temperature, so that not only can the plastically deformed metal recrystallize and present an equiaxed shape, but also not because the temperature is too high. make it grow and thicken.

Description of drawings

Figure 1 shows the technological process of continuous variable cross-section cyclic extrusion;

合金原始坯料沿径向的显微组织分布：图2(a)为合金原始坯料边部的显微组织，图2(b)为合金原始坯料R/2处的显微组织，图2(c)为合金原始坯料中心的显微组织；Figure 2 is

The microstructure distribution of the alloy original billet along the radial direction: Fig. 2(a) is the microstructure of the edge of the alloy original billet, Fig. 2(b) is the microstructure of the alloy original billet at R/2, Fig. 2(c) ) is the microstructure of the center of the alloy original billet;

合金原始坯料经900℃，6循环，水冷(WC)后，沿径向的显微组织分布：图3(a)为合金边部的显微组织，图3(b)为合金坯料R/2处的显微组织，图3(c)为合金中心的显微组织；Figure 3 is

The microstructure distribution along the radial direction of the original alloy billet after 6 cycles at 900 °C and water cooling (WC): Figure 3(a) is the microstructure of the edge of the alloy, and Figure 3(b) is the alloy billet R/2 The microstructure at the center of the alloy is shown in Figure 3(c);

合金原始坯料经900℃，6循环，WC+750℃/2h，空冷(AC)后，沿径向的显微组织分布：图4(a)为合金边部的显微组织，图4(b)为合金R/2处的显微组织，图4(c)为合金中心的显微组织。Figure 4 is

The microstructure distribution along the radial direction of the alloy original billet after 900℃, 6 cycles, WC+750℃/2h, air cooling (AC): Figure 4(a) is the microstructure of the edge of the alloy, Figure 4(b) ) is the microstructure at the alloy R/2, and Fig. 4(c) is the microstructure at the center of the alloy.

Detailed ways

The invention discloses a method for preparing a large-scale titanium alloy fine-grained blank based on a CVCE method, comprising the following steps:

Firstly, according to the alloy type and diameter specification of the bar, select the appropriate deformation temperature, deformation speed and height-diameter ratio, and use appropriate deformation equipment and extrusion die to extrude the heated bar blank into a 6-9 ° circular truncated body;

Then, turn the small diameter end of the circular truncated body upward and the large diameter end downward, and continue to use deformation equipment to upset it into a cylinder with the same diameter as the original blank;

Then rotate the upsetting cylinder by 180° (turn), and then extrude it into a truncated cone with the same taper as the previous extrusion process;

Finally, turn the small diameter end of the circular truncated body upward and the large diameter end downward, and use a deformation device to upset it into a cylinder with the same diameter as the original billet. After this step is completed, one deformation cycle (including 4 deformation processes of extrusion-upsetting-extrusion-upsetting) is realized.

The above process is repeated until the required number of deformation cycles is reached, and the corresponding cumulative strain amount can be obtained.

Between the deformation processes of continuous variable cross-section cyclic extrusion deformation, if the billet temperature is less than 700 °C, it is placed in a heating furnace to be heated to 850-900 °C and then kept for (D _{cylindrical billet} /4) min.

During the deformation process, according to the temperature drop of the billet, appropriate annealing treatment can be given to eliminate work hardening and improve the plastic deformation ability of the material.

The high-diameter ratio H/D>3 of the large-sized fine-grained bar prepared by the invention has high refining efficiency; after the same cyclic deformation, the accumulated deformation is large and the refining effect is good; the microstructure is distributed along the radial direction It is more uniform, and the structure at the center of the bar is finer; the diameter specification of the prepared fine-grained alloy is not limited, and it can be realized only by increasing the tonnage of the deformation equipment and the size specification of the mold.

Relevant descriptions are given below with reference to specific embodiments.

When the present invention adopts continuous variable section cyclic extrusion deformation to prepare large-scale titanium alloy fine-grained blanks, the steps used are as follows:

1) Calculate the size of the blank and carry out blanking.

According to the die angle of 6°, determine the height h and the radius r of the small diameter end of the continuously variable section body (truncated cone):

According to the principle that the volume does not change during deformation, the volume of the extruded continuously variable cross-section body is V truncated _body = V _cylinder , that is, πh(R ² +Rr+r ² )/3=πR ² H, and the height of the cylinder is calculated. H, and control the height-diameter ratio of the continuously variable section body h/[(D+d)/2]≤3.5, where R and D are the radius of the cylinder and the diameter of the cylinder, respectively. Then, according to the calculated height H, blank the titanium alloy billet of known diameter.

2) Heating. The billet was heated to 900°C according to the recrystallization temperature of the TC4 titanium alloy.

3) Continuously changing section cyclic extrusion deformation. Plastic deformation is carried out using the procedure shown in Figure 1:

First, the TC4 alloy cylinder bar shown in Figure 1a is drawn (extruded) into a truncated cone with 6° as shown in Figure 1b by using an air hammer or hydraulic press with a suitable tonnage; Face up, with the large diameter end facing down, use a deformation device to upset it into a cylinder with the same diameter as the original billet as shown in Figure 1c; then, rotate the upsetting cylinder by 180° (steering) to extrude form a circular truncated body with a 6° die angle as shown in Figure 1d; finally, turn the small diameter end of the circular truncated body as shown in Figure 1d upward and the large diameter end downward, and use a deformation device to upset it into a circular truncated body as shown in Figure 1a and the original Cylinders with equal diameters of blanks. Repeat the above process until the desired amount of cumulative strain is reached. In the process of continuous variable section cyclic extrusion, due to extrusion deformation and upsetting deformation, the sample is a truncated cone with continuously variable section, and the degree of deformation of each layer along the axial direction is different, and the middle needs to be reversed extrusion. Four processes complete a deformation cycle, so that the billet can be deformed uniformly, so this process is called continuous variable section cyclic extrusion. This is repeated until the desired cumulative strain is reached.

If the temperature of the billet is relatively large (the billet temperature is less than 700°C) between the deformation processes, it needs to be placed in a heating furnace to be heated to the deformation temperature and then kept for 25 minutes, so that the billet temperature is evenly distributed along the entire cross-section. After the required total deformation cycle passes are completed, the TC4 cylindrical blank is water-cooled.

4) Heat treatment: Heat the water-cooled TC4 titanium alloy cylinder to 750°C, keep it for 2h, and perform AC (air cooling) annealing heat treatment to uniform the structure and refine the grains.

原始坯料沿径向的显微组织分布。可以看出，原始坯料沿径向的组织比较均匀，晶粒尺寸约为15um。As shown in Figure 2(a)-Figure 2(c), the diameter

The microstructure distribution of the original billet along the radial direction. It can be seen that the structure of the original billet along the radial direction is relatively uniform, and the grain size is about 15um.

钛合金棒材沿径向从边部至中心均为等轴细小状、分布均匀，且中心处组织相对更细小的组织，晶粒尺寸约为3um，但少部分组织仍保留着一些变形特征。As shown in Fig. 3(a)-Fig. 3(c), the mold angle is 6°, after 6 cycles of deformation at 900 °C,

The titanium alloy rods are equiaxed and finely distributed from the edge to the center in the radial direction, and the structure at the center is relatively finer, and the grain size is about 3um, but a small part of the structure still retains some deformation characteristics.

钛合金棒材的晶粒大小与仅经变形的试样相比变化较小，其晶粒尺寸约为4um，但α晶粒的等轴化程度和沿径向分布的均匀性明显增加。As shown in Fig. 4(a)-Fig. 4(c), after annealing heat treatment at 750℃/2h, AC,

The grain size of the titanium alloy bar has little change compared with the deformed sample, the grain size is about 4um, but the degree of equiaxing of α grains and the uniformity of distribution along the radial direction are obviously increased.

细晶TC4钛合金棒材。After a large number of experiments, it has been shown that: first, 850~900℃, 6~8 passes of deformation, WC CVCE deformation, and then 750~800℃/2~3h, AC annealing heat treatment, the grain size of about 4um can be obtained, and more evenly distributed in the radial direction

Fine grained TC4 titanium alloy rods.

The analysis of the TC4 fine-grained titanium alloy billet prepared by CVCE shows that:

1) When upsetting a billet with a height-to-diameter ratio of H/D=3.5, bending and instability did not occur. This is because the upsetting process is a process of "chain reaction deformation", that is, each time plastic deformation occurs in the sample. The height is very small (H/D<<2.5～3), so the bending instability or even folding phenomenon that occurs in the free forging process of ordinary upsetting-stretching will not occur.

2) When the upsetting-stretching free forging process and the continuous variable section cyclic extrusion method are used to deform the samples of the same shape and size for the same number of cycles, the cumulative strain obtained by the continuous variable section cyclic extrusion is larger. , the deformation efficiency is high, so the grain refinement effect is good.

H＝142mm的TC4钛合金圆柱体试样，经过最佳变形循环次数6时，采用两种不同变形方法所获得的应变量分别为：like

H=142mm TC4 titanium alloy cylinder sample, when the optimal number of deformation cycles is 6, the strain amounts obtained by using two different deformation methods are:

(1) When the round bar sample adopts the free forging process of upsetting-drawing 6 times, its cumulative strain (n is the total number of upsetting-drawing):

Among them, h- the height of the blank after drawing, H- the original height of the blank.

(Note: According to the height-diameter ratio H/D ≤ 2.5 and the deformation amount ≤ 70% during upsetting of the titanium alloy, the diameter of the blank after drawing is D=83mm, and the height of the blank at this time is H=206.13mm)

(2) When the round bar sample adopts a die angle of 6°, and the height-diameter ratio h/[(D+d)/2]=3.4, after 6 cycles of continuous variable cross-section cyclic extrusion deformation, the cumulative stress Variables (n is the number of loops):

(Note: According to the principle that the volume does not change during deformation, the volume of the extruded continuously variable cross-section body V truncated _body = V _cylinder , that is, πh(R ² +Rr+r ² )/3=πR ² H, calculate Circular truncated body height h=252.21mm)

Wherein h - the height of the blank when it is drawn into a truncated cone with 6°, and H - the height of the cylindrical blank.

3) During cyclic extrusion with continuous variable cross-section, the extrusion process is a three-way compressive stress state, and the edge of the sample is simultaneously subjected to shear deformation and extrusion force generated by the friction between the die surface and the billet. It is extended and deformed, so the edge of the blank is a large deformation area and the deformation is relatively deep; while in the upsetting process, the center of the blank is a large deformation area. Therefore, after several cycles of deformation, the distribution of the material along the radial direction is relatively uniform and fine.

In addition, since the alloy is deformed at a lower temperature above the recrystallization temperature, and then annealed at a temperature above the recrystallization temperature near the recrystallization temperature, not only can the plastically deformed metal be recrystallized and appear equiaxed, but also Because the temperature is too high, it grows and coarsens.

In order to make the objectives, technical solutions and advantages of the present invention clearer, further detailed descriptions are given below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments.

The components described and illustrated in the drawings and embodiments of the present invention may be arranged and designed in a variety of different configurations, therefore, the detailed descriptions of the embodiments of the present invention provided in the following drawings are not intended to limit the claimed invention. scope, but only represents a selected embodiment of the present invention. Based on the drawings and embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present invention.

Claims (8)

1. a method for preparing large-size titanium alloy fine-grained billet based on CVCE method, is characterized in that, comprises the following steps: S1. Calculate the size of the billet, and perform blanking to obtain a titanium alloy billet; S2, heating the titanium alloy billet to 850°C to 900°C, and performing continuous variable cross-section cyclic extrusion deformation to obtain a titanium alloy cylinder; After the required total deformation cycle is completed, the titanium alloy cylinder is water-cooled; S3, heating the water-cooled titanium alloy cylinder to 750-800° C., holding the temperature for 2-3 hours, and performing annealing heat treatment to obtain a titanium alloy fine-grained billet with uniform distribution along the radial direction. 2 . The method for preparing large-scale titanium alloy fine-grained billets based on the CVCE method according to claim 1 , wherein the titanium alloy billets have a height-diameter ratio of ≤3.5 and a diameter of ≥100 mm. 3 . 3. a kind of method for preparing large-size titanium alloy fine-grained billet based on CVCE method according to claim 1, is characterized in that, in S2, continuously variable section cyclic extrusion deformation specifically comprises the following steps: 2.1. First, according to the diameter specification and height-diameter ratio of the titanium alloy billet, the deformation equipment and extrusion die are selected, and the heated bar billet is extruded into a circular truncated body with 6° to 9°; 2.2. Turn the small diameter end of the circular truncated body upward and the large diameter end downward, and continue to use the deformation equipment to upset the circular truncated body into a cylinder with the same diameter as the original blank; 2.3. Then rotate the upsetting cylinder by 180°, and then extrude it into a truncated truncated body with 6° to 9°; the taper of the truncated truncated body is the same as that of the truncated truncated body extruded in step 2.1; 2.4. Finally, turn the small diameter end of the circular truncated body downward and the large diameter end upward, and use the deformation equipment to upset it into a cylinder with the same diameter as the original blank; so far, one deformation cycle has been completed; 2.5. Repeat 2.1-2.4 until the required number of deformation cycles is reached, obtain the corresponding cumulative strain amount, and stop. 4. a kind of method for preparing large-scale titanium alloy fine-grained billet based on CVCE method according to claim 1, is characterized in that, in S2, titanium alloy billet heating temperature is on the basis of recrystallization temperature plus 100 ℃～150 ℃ °C. 5. a kind of method for preparing large-size titanium alloy fine-grained billet based on CVCE method according to claim 1, is characterized in that, between the deformation process of continuous variable section cyclic extrusion deformation, if billet temperature＜700 ℃, Then put it into a heating furnace to be heated to 850-900° C. and then keep the temperature (D _{cylindrical blank} /4) min. 6. a kind of method for preparing large-size titanium alloy fine-grained billet based on CVCE method according to claim 1, is characterized in that, in S1, according to the die angle of extrusion die, determine the height h and the minor diameter of the continuously variable section body End radius r: According to the principle that the volume does not change during deformation, the volume of the extruded continuously variable cross-section body is V truncated _body = V _cylinder , that is, πh(R ² +Rr+r ² )/3=πR ² H, and the height of the cylinder is calculated. H, and control the height-diameter ratio of the continuously variable section body h/[(D+d)/2]≤3.5, where R and D are the radius of the cylinder and the diameter of the cylinder, respectively; Then, according to the calculated height H, blank the titanium alloy billet of known diameter. 7 . The method for preparing large-size titanium alloy fine-grained billets based on the CVCE method according to claim 6 , wherein the die angle is 6° to 9°. 8 . 8 . The method for preparing a large-sized titanium alloy fine-grained billet based on the CVCE method according to claim 1 , wherein, in S3 , the method of annealing and heat treatment is air cooling. 9 .

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