As-cast direct rolling process of ultra-fine-grained tc11 titanium alloy bar

Abstract

The application discloses a kind of ultrafine-grain TC11 titanium alloy bar's as-cast direct rolling process, belong to titanium alloy bar rolling technical field, including the following steps: selecting TC11 titanium alloy as-cast blank, the surface of blank is cleaned, remove oxide skin and dirt, after cleaning blank surface roughness Ra≤10 μm;The blank after cleaning is placed into heating furnace, with 8-15 ℃ / min heating rate to 750-850 ℃.The application is by being set as double-curved surface class circular table shape roller, its generatrix is connected by first curve and second curve, and the one side of guide plate is set as curved surface, two guide plates and two rollers enclose the deformation zone with constant ellipticity 1.02-1.04, cooperate with 20.5-22.5 degrees of feed angle, 21-23 degrees of rolling angle and reverse feeding type rolling mode, so that blank is sequentially passed through rolling area and rounding area along spiral path in deformation zone to carry out variable cross-section rolling, so as to realize the direct rolling of as-cast blank, without being subjected to forging breakdown, significantly shorten the process flow, reduce production cost.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy bar rolling technology, and more specifically, to a direct casting rolling process for ultrafine-grained TC11 titanium alloy bars. Background Technology

[0002] Titanium alloys, due to their high specific strength, excellent corrosion resistance, and good high-temperature performance, have broad application prospects in aerospace, marine engineering, and biomedical fields. TC11 titanium alloy, as a novel α+β type two-phase titanium alloy, possesses high strength, good toughness, and weldability, making it an important material for manufacturing aircraft structural components, engine parts, and marine engineering equipment. Bar stock is one of the most common semi-finished product forms of titanium alloys, and its grain size directly determines the mechanical properties and service life of subsequently processed products. Obtaining ultrafine-grained (grain size ≤ 5μm) titanium alloy bars can significantly improve the material's strength, fatigue performance, and superplastic forming ability. Traditional titanium alloy bar production processes typically employ a long process route of "casting → forging → multi-pass hot rolling → heat treatment." Forging requires multiple heating and forging processes, resulting in complex procedures, high energy consumption, low yield, and difficulty in obtaining a uniform and fine grain structure. As a short-process technology, direct as-cast rolling technology has the potential to improve production efficiency and reduce production costs. However, its application in the field of titanium alloys faces technical challenges such as poor plasticity of the as-cast structure, high deformation resistance, and difficulty in grain refinement.

[0003] In existing technologies, the direct casting process for titanium alloy bars has the following drawbacks: First, conventional rolls are insufficient to achieve sufficient fragmentation and uniform refinement of the as-cast microstructure under single-pass high reduction conditions, and lack precise control over the geometric parameters of the deformation zone. Uneven stress distribution on the billet during deformation easily leads to defects such as surface spiral marks and excessive ellipticity, affecting the surface quality and dimensional accuracy of the bar. Grain size typically only reaches 10μm or larger, making it difficult to obtain an ultrafine grain structure of 1-5μm. Second, the ratio of roll diameter to billet diameter, the length ratio of the rolling zone to the rounding zone, and the roll surface cone angle all have limitations. When key geometric parameters are not designed properly, the early rolling deformation and the later rounding correction of the billet during the deformation process will not match, resulting in poor roundness and low diameter accuracy of the bar, which cannot meet the requirements of high-end applications for bar dimensional accuracy. Thirdly, titanium alloys are very prone to react with oxygen in the air during high-temperature heating (750-850℃). The dense oxide scale formed on the surface will be pressed into the bar matrix during subsequent rolling, forming surface oxidation defects that are difficult to eliminate. This seriously reduces the surface quality and yield of the product. At the same time, oxidation will also lead to the depletion of surface alloy elements, affecting the mechanical properties and corrosion resistance of the bar.

[0004] Based on this, the present invention designs a direct casting rolling process for ultrafine-grained TC11 titanium alloy bars to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a direct casting process for ultrafine-grained TC11 titanium alloy bars to solve the problems mentioned in the background art.

[0006] A direct rolling process for ultrafine-grained TC11 titanium alloy bars in the as-cast state includes the following steps: S1. Select TC11 titanium alloy as-cast billet, clean the surface of the billet to remove oxide scale and oil stains, and the surface roughness Ra of the billet after cleaning is ≤10μm; The specific cleaning method is as follows: The oxide scale on the surface of the billet is removed by mechanical grinding using a belt grinder with belt mesh sizes of 60, 120, and 240 mesh, each grinding stage lasting 5-10 minutes. The grinding direction is alternately performed at a 45° angle to the billet axis. After grinding, high-pressure water jet cleaning is used to remove residual grinding debris and oil stains. The high-pressure water jet pressure is 10-20 MPa, the water temperature is controlled at 40-60℃, and the cleaning time is 3-5 minutes. After cleaning, compressed air is used for drying, with a compressed air pressure of 0.5-0.8 MPa, and a drying time of 2-3 minutes. After cleaning, the surface roughness Ra of the billet is controlled within 10 μm. S2. Place the cleaned billet into the heating furnace and heat it to 750-850℃ at a heating rate of 8-15℃ / min. Hold it at this temperature for 45-90 minutes to ensure that the temperature of the core and surface of the billet is uniform and the temperature difference is controlled within ±15℃. When the billet is placed into the heating furnace, the distance between the two ends of the billet and the furnace door shall not be less than 200mm, and a gap of 100-150mm shall be maintained between the billets to ensure uniform airflow in the furnace. The heating furnace adopts a resistance heating bogie furnace, and a circulating fan is installed inside the furnace. The furnace temperature uniformity is controlled within ±10℃. During the heat preservation process, the temperature of the billet core is monitored in real time by inserting a sheathed thermocouple into the core of the billet. When the temperature difference between the core and the surface exceeds 15℃, the heat preservation time is extended until the temperature difference is reduced to within 15℃. S3. The roll is configured as a hyperboloid frustum-shaped roll. The generatrix of the roll is formed by connecting the first curve and the second curve. The first curve corresponds to the large end of the roll, and the second curve corresponds to the small end of the roll. One side of the guide plate is configured as a curved surface. The curved surfaces of the two guide plates are placed opposite each other. The two rolls are placed between the two guide plates. The area enclosed by the two guide plates and the two rolls is the deformation zone. The rolls are made of alloy tool steel, and the roll surface is nitrided with a nitriding layer thickness of 0.3-0.5 mm and a surface hardness of not less than HRC58. The guide plates are cast from high-chromium cast iron, and the curved surfaces of the guide plates are precision ground, with the surface profile tolerance controlled within 0.05 mm. During the assembly of the rolls and guide plates, a laser alignment instrument is used to adjust the relative position of the roll axis and the curved surface of the guide plate, and the assembly accuracy is controlled within 0.1 mm. S4. Adjust the relative positions of the two rolls and the two guide plates to keep the ellipticity at any cross section in the deformation zone constant. The ellipticity is the ratio of the maximum distance between the two guide plates to the distance between the two rolls in the same cross section of the deformation zone. The ellipticity is controlled to be 1.02-1.04. Adjust the feed angle of the rolls to 20.5-22.5 degrees and the rolling angle to 21-23 degrees. The method for adjusting the ellipticity is as follows: measure the guide plate spacing and roll spacing at the entrance, middle, and exit ends of the deformation zone, calculate the ellipticity at each cross-section, and adjust the thickness of the adjusting shims at the rear of the guide plates and the eccentric sleeve angle of the roll bearing seat to ensure that the difference in ellipticity at each cross-section does not exceed 0.005. The feed angle and rolling angle are adjusted using a digital inclinometer, and the adjustment accuracy is controlled within ±0.1 degrees. S5. The heated TC11 titanium alloy cast billet is fed into the deformation zone from the large end of the roll using a reverse rolling method. The billet feed speed is 10-30 mm / s. The billet feeding is driven by a hydraulic pusher mechanism, which includes a hydraulic cylinder, a pusher rod, and a clamping head. The hydraulic cylinder operates at a pressure of 10-16 MPa, and the pusher rod has a stroke of 2-4 m. The clamping head is a three-jaw self-centering chuck structure. The contact area between the jaws and the end face of the billet is inlaid with high-temperature resistant copper alloy gaskets with a thickness of 3-5 mm to prevent damage to the end face of the billet. The feed speed is adjusted in real time by a proportional servo valve, with a speed control accuracy of ±1 mm / s. S6. Start the two rolls at a speed of 28-55 r / min. The rolls rotate in the same direction around their central axis. The billet is constrained by the hyperboloid rolls and curved guide plates in the deformation zone and moves along the spiral path. The billet diameter reduction rate in the deformation zone is 36-55%. The billet passes through the rolling zone and the rounding zone in sequence during its forward movement to achieve variable cross-section rolling. The roll drive uses two AC variable frequency motors driven independently, each with a power of 200-350kW. The motors are connected to the rolls via universal couplings. During the rolling process, the rolling force is monitored in real time by pressure sensors installed on the roll bearing housings. The upper limit of the rolling force is set at 3000kN. When the rolling force exceeds the upper limit, the control system automatically reduces the feed speed or stops the feed. The spiral forward path of the billet in the deformation zone is formed by the rotational motion of the rolls and the axial feed of the billet. The axial feed distance is 10-30mm for each revolution of the billet. S7. The billet is output from the small end of the roll, and the output bar is cooled to room temperature in the air to obtain an ultrafine-grained TC11 titanium alloy bar with a grain size of 1-5 μm. A set of guide rollers is installed at the output end of the bar. The guide rollers are arranged in a V-shape with a spacing of 300-500mm. The surface of the guide rollers is covered with high-temperature resistant asbestos cloth to prevent surface scratches during the output process. After the bar is output, it is conveyed to the cooling bed along the roller conveyor. The length of the cooling bed is 10-15m. The bar is naturally cooled on the cooling bed. During the cooling process, the bar is turned over every 2-3 minutes to ensure uniform cooling. After the bar is cooled to below 50℃, it is subjected to online flaw detection using an ultrasonic flaw detector with a flaw detection sensitivity of Φ0.8mm equivalent flat bottom hole.

[0007] Preferably, the line connecting the two ends of the first curve near the large end of the roll on the roll generatrix is ​​the first centerline, and the line connecting the two ends of the second curve near the small end of the roll is the second centerline. The included angle between the first centerline and the second centerline is 4-7 degrees. The diameter of the large end of the roll is 3-6 times the diameter of the billet, and the diameter of the small end of the roll is 2.5-4 times the diameter of the billet.

[0008] Preferably, the area corresponding to the deformation zone formed by the first curve on the roll rotating around the roll axis is the rolling zone, and the area corresponding to the deformation zone formed by the second curve on the roll rotating around the roll axis is the rounding zone. The length of the rolling zone is 2.5-5 times the length of the rounding zone, and the roll surface cone angle slope is 4.5-5.5 degrees during the rolling process.

[0009] The roll surface taper angle is defined as the angle between the roll generatrix and the roll axis, averaged along the roll length. The control method for the roll surface taper angle is as follows: During the roll finishing process, a CNC grinding machine is used to grind according to the designed taper angle. The diameter is measured every 100mm of length during grinding, and the diameter deviation is controlled within ±0.05mm. During rolling, the bar diameter is monitored online using a laser diameter gauge. When the diameter deviation exceeds ±0.5mm, the rolling angle of the roll is automatically adjusted for compensation.

[0010] Preferably, in step S2, before the billet enters the heating furnace, an anti-oxidation coating with a thickness of 0.5-1.5 mm is applied to the surface of the billet. The anti-oxidation coating is made by mixing glass powder, alumina and binder in a mass ratio of (5-8):(2-4):(1-2). After the billet is coated, it is dried for 30-60 minutes before heating.

[0011] The glass powder has a particle size of 10-50 μm and a softening point of 600-700℃. Its main components are SiO2 (65-75%), B2O3 (10-20%), and Na2O (5-10%). The alumina has a particle size of 1-10 μm and a purity of over 99.5%. The binder is water glass or aluminum dihydrogen phosphate, with a solid content of 30-45%.

[0012] The preparation method of the anti-oxidation coating is as follows: Glass powder, alumina, and binder are weighed according to the specified ratio and mixed in a planetary ball mill. The milling speed is 200-400 r / min, and the milling time is 30-60 min to obtain a uniform slurry. The slurry is then sprayed onto the surface of the workpiece using air spraying. The spray gun nozzle diameter is 1.0-1.5 mm, the spraying pressure is 0.3-0.5 MPa, and the distance between the spray gun and the workpiece surface is 150-250 mm. During spraying, the workpiece rotates at a speed of 5-10 r / min. Two to four coats are applied, and each coat is allowed to air dry for 10-15 min. The coating thickness is measured using an eddy current thickness gauge, and the thickness deviation is no more than ±0.1 mm.

[0013] Preferably, after step S7, the obtained bar is subjected to differential temperature heat treatment: first, the bar is heated to 880-920℃ and held at that temperature for 15-30 minutes, then the bar is rapidly cooled through a temperature range of 880-950℃ at a cooling rate of 30-50℃ / s. This temperature range covers the TC11 titanium alloy. The phase transition point is cooled to 400-500℃ and then immediately heated to 550-620℃ and held for 60-120 minutes. Finally, it is air-cooled to room temperature. The method of rapidly passing through the 880-950℃ temperature range is high-pressure air mist cooling or water mist cooling.

[0014] Preferably, in step S2, before applying the anti-oxidation coating, the surface of the blank is first subjected to laser roughening treatment to form a micro-pit array with a depth of 0.1-0.3 mm and a surface coverage of 40-60% on the surface of the blank. The anti-oxidation coating is applied to the surface of the blank after roughening treatment, and the coating thickness is 1.5-2.5 times the depth of the micro-pits.

[0015] Preferably, in the differential temperature heat treatment process, a cryogenic pretreatment step is added before the rapid cooling stage: the bar is cooled to -120℃ to -80℃ and held for 10-20 minutes, and then rapidly heated to 880-920℃ at a heating rate of 80-120℃ / s. The cryogenic pretreatment is carried out in a protective atmosphere, which is argon or nitrogen.

[0016] Preferably, the rapid cooling stage adopts a staged cooling method: first, the surface of the bar is cooled to 650-700℃ at a cooling rate of 50-80℃ / s, and held for 3-8s to reduce the temperature difference between the core and the surface to within 50℃, and then cooled to 400-500℃ at a cooling rate of 20-40℃ / s. During the staged cooling process, the cooling medium is switched from high-pressure gas mist to compressed air or water mist.

[0017] Preferably, the laser texturing process uses a pulsed laser with a laser power of 50-100W, a pulse frequency of 10-30kHz, and a scanning speed of 200-500mm / s. After the texturing process, a micron-level uneven structure is formed on the surface of the blank, and the average roughness Ra of the uneven structure is 5-15μm.

[0018] Compared with the prior art, the advantages of this invention are: 1. This invention sets the rolls as hyperboloid frustum-shaped rolls, whose generatrix is ​​formed by connecting the first curve and the second curve. One side of the guide plate is set as a curved surface. The two guide plates and the two rolls form a deformation zone with a constant ellipticity of 1.02-1.04. With a feed angle of 20.5-22.5 degrees, a rolling angle of 21-23 degrees, and a reverse rolling method, the billet passes through the rolling zone and the rounding zone along a spiral path in the deformation zone for variable cross-section rolling. This realizes the direct rolling of the cast billet without the need for forging, which significantly shortens the process and reduces production costs.

[0019] 2. This invention controls the angle between the first and second center lines on the roll generatrix to be 4-7 degrees, the large end diameter of the roll to be 3-6 times the billet diameter, the small end diameter to be 2.5-4 times the billet diameter, and sets the length of the rolling zone to be 2.5-5 times the length of the rounding zone and the roll surface cone angle to be 4.5-5.5 degrees. This allows the billet to first pass through the rolling zone to achieve a large reduction rate deformation (36-55%) during the deformation process, and then pass through the rounding zone for roundness correction. This ensures the diameter accuracy and roundness of the bar and avoids surface defects caused by uneven deformation in traditional rolling.

[0020] 3. The present invention coats the billet with an anti-oxidation coating made of glass powder, alumina and binder in a mass ratio of (5-8):(2-4):(1-2) before heating. The coating thickness is 0.5-1.5mm. This effectively prevents the surface oxidation of titanium alloy billet during high-temperature heating, reduces the impact of oxide scale on the surface quality of rolling, and avoids the depletion of alloy elements caused by oxidation, thus ensuring the surface quality and compositional uniformity of the bar. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the direct rolling process for ultrafine-grained TC11 titanium alloy bars in the cast state, as proposed in this invention. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 A direct rolling process for ultrafine-grained TC11 titanium alloy bars in the as-cast state includes the following steps: S1. Select TC11 titanium alloy cast blank with a diameter of Φ80mm. Use a belt grinder to grind the blank sequentially with 60-grit, 120-grit, and 240-grit abrasive belts, grinding for 8 minutes at each level. The grinding direction is alternately at 45° to the axis. Then, use high-pressure water jet cleaning at a pressure of 15MPa and a water temperature of 50℃ for 4 minutes. Dry the blank with compressed air until the surface roughness Ra≤8μm.

[0024] S2. Apply an anti-oxidation coating to the surface of the billet with a thickness of 1.0 mm. The coating is made of glass powder, alumina and binder mixed in a mass ratio of 6:3:2 and dried for 45 min. Place the billet in a heating furnace and heat it to 800℃ at a rate of 12℃ / min. Hold it at that temperature for 60 min, with a core-to-surface temperature difference of ±12℃.

[0025] S3. A hyperboloid frustum-shaped roll is used, with a large end diameter of Φ400mm and a small end diameter of Φ280mm. The ratio of the rolling zone length to the rounding zone length is 3.5:1, and the roll surface cone angle is 5.0°. The guide plate surface profile tolerance is 0.04mm.

[0026] S4. Adjust the ellipticity to 1.03, feed angle to 21.5°, rolling angle to 22°, and ellipticity difference between each section to ≤0.005.

[0027] S5. Reverse rolling is adopted, with the billet fed from the large end at a feed speed of 20 mm / s.

[0028] S6, the roll speed is 40 r / min, the diameter reduction rate is 45%, and the billet moves along the spiral path.

[0029] S7. The bar is output from the small end of the roll and air-cooled to room temperature to obtain an ultrafine-grained TC11 titanium alloy bar with a grain size of 2-4μm.

[0030] Example 2 Based on Example 1, step S2 adds a laser texturing process: a pulsed laser power of 70W, a frequency of 20kHz, and a scanning speed of 300mm / s, forming a micro-pit array with a depth of 0.2mm and a coverage of 50%, and a coating thickness of 0.4mm (twice the depth of the micro-pits). This results in a rod grain size of 1.5-3.5μm and significantly improved coating adhesion.

[0031] Example 3 Based on Example 1, a differential temperature heat treatment is added after step S7: Heat to 900℃ and hold for 20 minutes; It rapidly passes through the 900-940℃ range (covering the β phase transition point) at a cooling rate of 40℃ / s (high-pressure gas mist). After cooling to 450℃, immediately heat to 580℃ and hold for 90 minutes; Air cool to room temperature.

[0032] The final bar grain size is 1-2.5μm, and the strength is increased by about 12% compared with the untreated bar.

[0033] Example 4 Based on Example 3, a cryogenic pretreatment was added before the differential temperature heat treatment: the bar was cooled to -100℃ and held for 15 minutes (argon atmosphere), and then heated to 900℃ at a rate of 100℃ / s. The resulting bar had a grain size of 1-2μm, a more uniform microstructure, and a significant reduction in β-phase residue.

[0034] Example 5 Based on Example 3, the rapid cooling stage employs staged cooling: First, cool the surface to 680°C at 65°C / s and hold for 5s (high-pressure mist). Then cool to 450°C at 30°C / s (compressed air).

[0035] The resulting bar material has a grain size of 1.2-2.8 μm, with little difference between the core and surface microstructure and low residual stress.

[0036] Comparative Example 1 It is basically the same as Example 1, except that: Instead of using hyperboloid-shaped frustum rolls, ordinary cylindrical rolls were used. Uncontrolled ellipticity (ellipticity approximately 1.15).

[0037] Results: Obvious spiral marks appeared on the surface of the bar, with a diameter deviation of ±1.2 mm, uneven grain size (2-12 μm), and coarse grains in some areas.

[0038] Comparative Example 2 It is basically the same as Example 1, except that: No antioxidant coating treatment was applied; The heating temperature is increased to 900℃ (to compensate for oxidation and diameter reduction).

[0039] Results: The billet surface was severely oxidized, and the rolled bar surface had oxide scale indentation defects. The grain size was 5-10μm, which did not meet the ultrafine grain requirement (1-5μm), and the yield was reduced by about 25%.

[0040] Comparative Analysis of Examples and Comparative Cases in conclusion The comparison of Examples 1-5 shows that the cast-state direct rolling process proposed in this invention (using hyperboloid frustoconical rolls with ellipticity control) can stably produce ultrafine-grained TC11 titanium alloy bars with a grain size of 1-5 μm. Further, by combining optimized processes such as laser texturing anti-oxidation coating, differential temperature heat treatment, cryogenic pretreatment, or staged cooling, the grain size can be refined to 1-2.5 μm, while surface quality, microstructure uniformity, and the consistency of microstructure between the core and surface are significantly improved.

[0041] Comparative Examples 1-2 demonstrate the necessity of the key features of this invention from the opposite perspective: when using ordinary cylindrical rolls and without controlling ellipticity, the grains are coarse and uneven (2-12 μm), and spiral marks are generated on the surface; while without using an anti-oxidation coating and increasing the heating temperature, the oxide scale on the surface of the bar is severely pressed in, and the grain size only reaches 5-10 μm, which cannot meet the requirements for ultrafine grains. The above comparison fully demonstrates the innovation and technical advantages of this invention in terms of roll geometry, ellipticity control in the deformation zone, and heating protection.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A direct rolling process for ultrafine-grained TC11 titanium alloy bars in the cast state, characterized in that, Includes the following steps: S1. Select TC11 titanium alloy as-cast billet, clean the surface of the billet to remove oxide scale and oil stains, and the surface roughness Ra of the billet after cleaning is ≤10μm; S2. Place the cleaned billet into the heating furnace and heat it to 750-850℃ at a heating rate of 8-15℃ / min. Hold it at this temperature for 45-90 minutes to ensure that the temperature of the core and surface of the billet is uniform and the temperature difference is controlled within ±15℃. S3. The roll is configured as a hyperboloid frustum-shaped roll. The generatrix of the roll is formed by connecting the first curve and the second curve. The first curve corresponds to the large end of the roll, and the second curve corresponds to the small end of the roll. One side of the guide plate is configured as a curved surface. The curved surfaces of the two guide plates are placed opposite each other. The two rolls are placed between the two guide plates. The area enclosed by the two guide plates and the two rolls is the deformation zone. S4. Adjust the relative positions of the two rolls and the two guide plates to keep the ellipticity at any cross section in the deformation zone constant. The ellipticity is the ratio of the maximum distance between the two guide plates to the distance between the two rolls in the same cross section of the deformation zone. The ellipticity is controlled to be 1.02-1.

04. Adjust the feed angle of the rolls to 20.5-22.5 degrees and the rolling angle to 21-23 degrees. S5. The heated TC11 titanium alloy cast billet is fed into the deformation zone from the large end of the roll using a reverse rolling method. The billet feed speed is 10-30 mm / s. S6. Start the two rolls at a speed of 28-55 r / min. The rolls rotate in the same direction around their central axis. The billet is constrained by the hyperboloid rolls and curved guide plates in the deformation zone and moves along the spiral path. The billet diameter reduction rate in the deformation zone is 36-55%. The billet passes through the rolling zone and the rounding zone in sequence during its forward movement to achieve variable cross-section rolling. S7. The billet is output from the small end of the roll, and the output bar is cooled to room temperature in the air to obtain an ultrafine-grained TC11 titanium alloy bar with a grain size of 1-5 μm.

2. The direct casting rolling process for ultrafine-grained TC11 titanium alloy bars according to claim 1, characterized in that, The line connecting the two ends of the first curve near the large end of the roll on the roll generatrix is ​​the first centerline, and the line connecting the two ends of the second curve near the small end of the roll is the second centerline. The included angle between the first centerline and the second centerline is 4-7 degrees. The diameter of the large end of the roll is 3-6 times the diameter of the billet, and the diameter of the small end of the roll is 2.5-4 times the diameter of the billet.

3. The direct casting rolling process for ultrafine-grained TC11 titanium alloy bars according to claim 2, characterized in that, The area corresponding to the deformation zone formed by the first curve on the roll rotating around the roll axis is the rolling zone, and the area corresponding to the deformation zone formed by the second curve on the roll rotating around the roll axis is the rounding zone. The length of the rolling zone is 2.5-5 times the length of the rounding zone. During the rolling process, the roll surface cone angle is 4.5-5.5 degrees.

4. The direct casting rolling process for ultrafine-grained TC11 titanium alloy bars according to claim 1, characterized in that, In step S2, before the billet enters the heating furnace, an anti-oxidation coating with a thickness of 0.5-1.5 mm is applied to the surface of the billet. The anti-oxidation coating is made by mixing glass powder, alumina and binder in a mass ratio of (5-8):(2-4):(1-2). After the billet is coated, it is dried for 30-60 minutes before heating.

5. The direct casting rolling process for ultrafine-grained TC11 titanium alloy bars according to claim 3, characterized in that, Following step S7, the obtained bar undergoes differential temperature heat treatment: first, the bar is heated to 880-920℃ and held at that temperature for 15-30 minutes; then, the bar is rapidly cooled through the 880-950℃ temperature range at a rate of 30-50℃ / s. This temperature range covers the TC11 titanium alloy. The phase transition point is cooled to 400-500℃ and then immediately heated to 550-620℃ and held for 60-120 minutes. Finally, it is air-cooled to room temperature. The method of rapidly passing through the 880-950℃ temperature range is high-pressure air mist cooling or water mist cooling.

6. The direct casting rolling process for ultrafine-grained TC11 titanium alloy bars according to claim 4, characterized in that, In step S2, before applying the anti-oxidation coating, the surface of the blank is first subjected to laser roughening treatment to form a micro-pit array with a depth of 0.1-0.3 mm and a surface coverage of 40-60%. The anti-oxidation coating is applied to the roughened blank surface, and the coating thickness is 1.5-2.5 times the depth of the micro-pits.

7. The direct casting rolling process for ultrafine-grained TC11 titanium alloy bars according to claim 5, characterized in that, In the differential temperature heat treatment process, a cryogenic pretreatment step is added before the rapid cooling stage: the bar is cooled to -120℃ to 80℃ and held for 10-20 minutes, and then rapidly heated to 880-920℃ at a heating rate of 80-120℃ / s. The cryogenic pretreatment is carried out in a protective atmosphere, which is argon or nitrogen.

8. The direct casting rolling process for ultrafine-grained TC11 titanium alloy bars according to claim 7, characterized in that, The rapid cooling stage adopts a staged cooling method: first, the surface of the bar is cooled to 650-700℃ at a cooling rate of 50-80℃ / s, and held for 3-8s to reduce the temperature difference between the core and the surface to within 50℃. Then, the bar is cooled to 400-500℃ at a cooling rate of 20-40℃ / s. During the staged cooling process, the cooling medium is switched from high-pressure gas mist to compressed air or water mist.

9. The direct casting rolling process for ultrafine-grained TC11 titanium alloy bars according to claim 6, characterized in that, The laser texturing process uses a pulsed laser with a power of 50-100W, a pulse frequency of 10-30kHz, and a scanning speed of 200-500mm / s. After texturing, a micron-level uneven structure is formed on the surface of the blank, and the average roughness Ra of the uneven structure is 5-15μm.

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