Preparation method of large-size high-strength high-toughness titanium alloy hollow shaft blank

Abstract

The invention relates to a preparation method of a large-size high-strength high-toughness titanium alloy hollow shaft blank, and belongs to the technical field of hot working. The metastable beta-type high-strength and high-toughness titanium alloy hollow shaft blank is prepared by innovatively adopting near beta backward extrusion, quasi beta forward extrusion and (alpha + beta) solid solution aging processes to solve the problems that the structure of the large-size high-strength and high-toughness titanium alloy hollow shaft blank is difficult to control, and the performance is difficult to match and regulate. The method comprises the following steps of bar blank specification selection, bar blank machining and sheathing, near-beta backward extrusion, backward extrusion intermediate blank machining and sheathing, quasi-beta backward extrusion, hollow shaft blank finishing and (alpha + beta) solid solution aging. According to the method, the large-specification high-strength high-toughness titanium alloy hollow shaft blank can obtain a uniform, fine and fully-woven basket structure, and comprehensive matching of strength, plasticity, toughness and fatigue is considered.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a large-specification high-strength high-toughness titanium alloy hollow shaft blank, and belongs to the technical field of hot working, and particularly relates to an innovative preparation method of a large-specification high-strength high-toughness titanium alloy hollow shaft blank with a diameter of greater than or equal to 200 mm. BACKGROUND

[0002] Titanium alloy hollow shafts are widely used in the transmission systems of aerospace vehicles. In addition to requiring high strength, such load-bearing transmission shafts often also require high toughness to meet complex load conditions and damage tolerance use requirements. In recent years, the large-scale of aerospace equipment has made the size of hollow transmission shafts increasingly larger, and the requirements for strength, toughness, plasticity and fatigue comprehensive performance are increasingly higher.

[0003] Metastable beta titanium alloys have become ideal materials for high-strength high-toughness titanium alloy transmission shafts due to their high strength, deep quenching properties and high fracture toughness. However, there are still problems in controlling the microstructure and properties of large-diameter hollow shaft blanks made of metastable beta titanium alloys. Firstly, large-specification bars with a diameter of greater than or equal to 300 mm are often required for the preparation of large-specification hollow shaft blanks. The microstructure of large-specification bars of metastable beta titanium alloys is not easy to control, and open-die forging may cause residual as-cast microstructure in the local part (especially the core) of the bar, and the microstructure inheritance of the bar may cause uneven microstructure of the hollow shaft blank. Secondly, the microstructure and properties of metastable beta titanium alloys are sensitive to deformation processes, making it difficult to control the microstructure and properties of large-specification hollow shaft blanks. It is difficult to match the comprehensive performance of strength-plasticity-toughness-fatigue using existing process methods, thereby limiting the application range of high-strength high-toughness titanium alloy hollow shaft blanks. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a metastable beta high-strength high-toughness titanium alloy large-specification hollow shaft blank. The hollow shaft blank is prepared by using a reverse extrusion+forward extrusion composite extrusion process with different temperature matching, and is combined with solid solution and aging heat treatment to obtain fine and uniform net basket microstructure, thereby solving the problems of uneven microstructure and difficult performance matching of large-specification high-strength high-toughness titanium alloy hollow shaft blanks. By sequentially performing near-beta reverse extrusion, quasi-beta forward extrusion and (alpha+beta) solid solution and aging, the recrystallization crushing of the uneven microstructure of the bar and the uniform net basket of the hollow shaft blank are realized while the large-specification bar gradually transitions to the shape of the hollow shaft blank, and finally the comprehensive matching of the performance is realized.

[0005] The technical solution of the present application is as follows: A preparation method of a large-specification high-strength high-toughness titanium alloy hollow shaft blank, the specific steps are as follows: (1) Bar blank specification selection: according to the forming path of bar blank → backward extrusion → backward extrusion intermediate blank → forward extrusion → hollow shaft blank, the backward extrusion intermediate blank and the bar blank specification are determined by reverse calculation, wherein the inner diameter of the backward extrusion intermediate blank is 3 mm to 5 mm larger than the inner diameter of the hollow shaft blank, and the outer diameter size should ensure that the forward extrusion extrusion ratio is between 2.5 and 5.

[0006] (2) Bar blank processing and sleeve: the bar blank sharp corner is rounded, one side end face is processed with a center positioning groove, copper sleeve is tightly attached to the bar blank, and the positioning groove on one side is not sleeved, thereby obtaining a backward extrusion blank; (3) Near-β backward extrusion: the backward extrusion blank is preheated to T β - (10-20) ℃, wherein T β is the β transformation temperature of the alloy, the backward extrusion blank is transferred to the preheated extrusion cylinder after being heated through, a glass powder solidified bonding pad is arranged between the backward extrusion blank and the extrusion cone head, the extrusion cone head is pushed to perform backward extrusion, and the backward extrusion blank is air-cooled after backward extrusion, thereby obtaining a backward extrusion intermediate blank; (4) Backward extrusion intermediate blank processing and sleeve: the copper sleeve and surface defects of the backward extrusion intermediate blank are removed, the flat end face is rounded, and the copper sleeve is reattached to the whole surface; (5) Quasi-β backward extrusion: the backward extrusion intermediate blank obtained in step (4) is preheated to T β + (10-20) ℃, the intermediate blank is transferred to the same specification and preheated extrusion cylinder as in step (3), a glass powder solidified bonding pad is arranged between the intermediate blank and the extrusion die, the extrusion rod is pushed to perform forward extrusion, thereby obtaining a hollow shaft blank, and the hollow shaft blank is quickly wrapped with an aluminum silicate fiber felt for slow cooling after extrusion; (6) Hollow shaft blank finishing processing: the sleeve and surface defects of the hollow shaft blank are removed; (7) (α+β) solution aging: the hollow shaft blank is subjected to (α+β) two-phase zone solution aging heat treatment.

[0007] Further, the backward extrusion intermediate blank in step (1) is a cylinder blank.

[0008] Further, the cross-sectional area of the backward extrusion intermediate blank determined by the inner and outer diameters in step (1) should be 2.5 to 5 times the cross-sectional area of the forward extrusion hollow shaft blank.

[0009] Further, the copper sleeve thickness in steps (2) and (4) is 0.5 mm to 2 mm.

[0010] Further, the preheating in steps (3) and (5) adopts a furnace temperature rising mode.

[0011] Further, the heating through time T 反 in step (3) is D × time coefficient t 反 , t 反 = (1.0-2.0) min / mm.

[0012] Further, the heat penetration time T in step (5) is 正 = intermediate blank wall thickness delta x time coefficient t 正 , t 反 = (2.0~3.0) min / mm.

[0013] Further, the ingot blank is transported to the extrusion cylinder in step (3) and step (5) for less than or equal to 180 seconds, the extrusion cylinder is preheated to a temperature of greater than or equal to 200 DEG C, and the hot extrusion speed is (30~150) mm / s.

[0014] Further, the heat treatment system in step (7) is: solution temperature T β - (20~50) DEG C, holding for 1h~3h, air cooling or air cooling; aging temperature 540 DEG C~600 DEG C, holding for 4h~8h, air cooling or furnace cooling.

[0015] The present application has the characteristics and beneficial effects of: The present application aims at the problems of difficult control of the microstructure and difficult matching of the performance of large-size high-strength high-toughness titanium alloy hollow shaft blanks, and innovatively adopts near-beta backward extrusion + quasi-beta forward extrusion + (alpha+beta) solution and aging process to prepare metastable beta type high-strength high-toughness titanium alloy hollow shaft blanks.

[0016] The basic principle of the present application is: after the large-size rod blank is sleeved, backward extrusion is performed at T β - (10~20) DEG C, which can make the core of the rod blank obtain large extrusion deformation without obvious coarsening of the grain of the rod blank, so as to break the original coarse residual as-cast structure. β + (10~20) DEG C and extrusion ratio 2.5~5 forward extrusion is performed on the backward extruded intermediate blank, which can make the microstructure of the hollow shaft blank completely net basket, and the control of the quasi-beta extrusion temperature and holding time ensures that the beta heating grain structure does not obviously coarsen, so that the hollow shaft blank with uniform and fine net basket structure is finally obtained, and the comprehensive matching of various performances is considered.

[0017] The main innovation of the present application is: (1) near-beta backward extrusion + quasi-beta forward extrusion across phase zone composite extrusion: firstly, the deformation of the core of the backward extruded rod blank is greater than the outer edge, while the deformation of the outer edge of the forward extruded blank is greater than the core, and the composite extrusion process can make each region of the blank obtain sufficient deformation, which helps the non-uniform structure of the large-size rod blank to break through dynamic recrystallization at high temperature near the phase transition point; secondly, the composite extrusion across the phase zone is heated only by one fire beta and preheated by temperature control, which can realize the effect of fine-grained basket by a large extrusion ratio. (2) Quasi-beta extrusion + (α+β) heat treatment process balances various properties: the fine-grained basket structure of quasi-beta extrusion can be retained by two-phase zone solid solution aging heat treatment, and good strength, plasticity and fatigue performance can be obtained, and the quasi-beta extrusion coating slow cooling process can make the lamellar α phase fully analyze and weave the basket, which makes up for the lack of toughness caused by fine-grain, and finally realizes the comprehensive balance of strength-plasticity-toughness-fatigue performance of the shaft blank. BRIEF DESCRIPTION OF DRAWINGS

[0018] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0019] Figure 1 is the deformation distribution diagram of the backward extrusion and forward extrusion in the embodiment 1 of the present application; Figure 2 is the low-magnification structure of the rod and shaft blank in the embodiment 1 of the present application; Figure 3 is the high-magnification structure of the shaft blank in the embodiment 1 of the present application; Figure 4 is the high-magnification structure of the shaft blank in the embodiment 2 of the present application. DETAILED DESCRIPTION

[0020] The technical scheme of the present application will be further described in combination with the embodiments as follows: A preparation method of a large-size high-strength high-toughness titanium alloy hollow shaft blank, the specific steps are as follows: (1) Selection of rod blank specification: according to the forming path of rod blank→ backward extrusion→ backward extruded intermediate blank→ forward extrusion→ hollow shaft blank, the backward extruded intermediate blank and rod blank specification are determined by reverse calculation, wherein the inner diameter of the backward extruded intermediate blank (cylinder blank) is 3mm~5mm larger than the inner diameter of the hollow shaft blank, and the outer diameter size should ensure that the forward extrusion extrusion ratio is between 2.5~5 (the cross-sectional area of the backward extruded intermediate blank determined by the inner and outer diameters should be 2.5~5 times the cross-sectional area of the forward extruded hollow shaft blank).

[0021] (2) Rod blank processing and sleeving: the rod blank is rounded at the sharp corners, the center positioning groove is processed on one side end face, the copper sleeve is tightly sleeved on the rod blank, the thickness of the copper sleeve is 0.5mm~2mm, one side of the positioning groove is not sleeved, and the backward extruded blank is obtained.

[0022] (3) Near-beta backward extrusion: the backward extruded blank is preheated to T β(10~20)℃, wherein T β After the alloy β-transus temperature T β + (10~20)℃, the intermediate billet is transferred to the preheated extrusion cylinder after being heated through, and a glass powder solidified adhesive pad is arranged between the intermediate billet and the extrusion cone, the extrusion cone is pushed to perform backward extrusion, and the backward extrusion intermediate billet is obtained after being air-cooled.

[0023] (4) Intermediate billet processing and copper sheath: the copper sheath and possible surface defects such as cracks of the intermediate billet are removed, the flat end face is rounded, and then the whole surface is re-coppered, and the copper sheath thickness is 0.5mm~2mm.

[0024] (5) Quasi-β backward extrusion: the backward extrusion intermediate billet is preheated to T β + (10~20)℃, the intermediate billet is transferred to the preheated extrusion cylinder after being heated through, and a glass powder solidified adhesive pad is arranged between the intermediate billet and the extrusion cone, the extrusion cone is pushed to perform backward extrusion, and the backward extrusion intermediate billet is obtained after being air-cooled.

[0025] (6) Hollow shaft billet finishing: the copper sheath and possible surface defects such as cracks of the hollow shaft billet are removed.

[0026] (7) (α+β) solution and aging: the hollow shaft billet is subjected to (α+β) two-phase zone solution and aging heat treatment.

[0027] The preheating in steps (3) and (5) is performed in a furnace in a temperature rising mode, the heating through time T 反 = rod billet diameter D x time coefficient t 反 , t 反 = (1.0~2.0) min / mm in step (3); and the heating through time T 正 = intermediate billet wall thickness δ x time coefficient t 正 , t 反 = (2.0~3.0) min / mm in step (5).

[0028] The time for transferring the ingot billet to the extrusion cylinder in steps (3) and (5) is ≤180s, the preheating temperature of the extrusion cylinder is ≥200℃, and the hot extrusion speed is (30~150) mm / s.

[0029] The heat treatment system in step (7) is: solution temperature T β - (20~50)℃, holding for 1h~3h, air cooling or air cooling; aging temperature 540℃~600℃, holding for 4h~8h, air cooling or furnace cooling.

[0030] Example 1 The steps for preparing a Φ250mm x Φ160mm x 2500mm specification TB17 high-strength high-toughness titanium alloy (transus temperature T β = 845℃) hollow shaft billet are as follows: (1) Bar blank specification selection: according to the hollow shaft blank specification Φ250mmxΦ160mmx2500mm, the reverse determination of the intermediate blank size Φ345mmxΦ163mmx1000mm, the reverse determination of the bar blank specification Φ345mmx800mm, the positive extrusion extrusion ratio 2.5.

[0031] (2) Bar blank processing and cladding: the bar blank sharp corner is rounded R10, one side end face is processed with a center positioning groove (cooperating with the extrusion cone), a thickness of 0.5mm copper skin is tightly cladded on the bar blank, one side of the positioning groove is not cladded, and the reverse extrusion blank is obtained.

[0032] (3) Near-β reverse extrusion: the reverse extrusion blank is preheated to 835℃ (T β -10℃) in the furnace, the holding time after reaching temperature is 5h45min (thermal penetration coefficient t 反 1.0min / mm), after the holding of the blank ends, the blank is quickly transferred to the preheated Φ355mm specification extrusion cylinder (preheating temperature 240℃) in 60s~80s. Glass powder solidification bonding pad is placed between the blank and the extrusion cone, the extrusion cone (considering cold shrinkage, the working diameter of the cone is Φ164.5mm) is pushed to perform reverse extrusion, the extrusion speed is controlled at 30mm / s~80mm / s, and the reverse extrusion is air cooled to obtain the reverse extrusion intermediate blank Φ348mmxΦ163mmx1005mm with cladding.

[0033] (4) Reverse extrusion intermediate blank processing and cladding: the lathe is used to remove the copper cladding and surface defects on the outer edge of the intermediate blank, the flat end face is turned, and the rounded corner R10 is obtained. The Φ345mmxΦ163mmx1000mm reverse extrusion intermediate blank is obtained, and the copper cladding with a thickness of 0.5mm is re-cladded on the whole surface of the cylindrical reverse extrusion intermediate blank.

[0034] (5) Quasi-β reverse extrusion: the cladded reverse extrusion intermediate blank is preheated to 855℃ (T β +10℃) in the furnace, the holding time after reaching temperature is 184min (thermal penetration coefficient t 正 2.0min / mm), after the holding of the reverse extrusion intermediate blank ends, the blank is transferred to the preheated Φ355mm specification extrusion cylinder (preheating temperature 240℃), and glass powder solidification bonding pad is arranged between the intermediate blank and the extrusion die, the extrusion rod is pushed to perform positive extrusion with an extrusion ratio of 2.5 (considering cold shrinkage, the working diameter of the hollow extrusion die is Φ256mm, and the diameter of the hollow extrusion mandrel is Φ161.5mm), the extrusion speed is controlled at 30mm / s~80mm / s, and the hollow extrusion shaft blank is obtained. After extrusion, the shaft blank is quickly wrapped with aluminum silicate fiber felt for slow cooling.

[0035] (6) Hollow shaft blank finishing processing: the lathe is used to remove the cladding and surface defects of the hollow shaft blank, and the Φ250mmxΦ160mmx2500mm hollow shaft blank is obtained.

[0036] (7) (α+β) solution and aging: hollow shaft blank is solution and aging, solution temperature 825℃ (T β -20℃), insulation 2h, air cooling; aging temperature 540℃, insulation 4h, air cooling.

[0037] Mechanical property test standard is carried out on the hollow shaft blank after heat treatment, and the mechanical property data is shown in Table 1.

[0038] Table 1 Mechanical property of TB17 hollow shaft blank prepared in Example 1

[0039] Example 2 Φ270mm×Φ220mm×2500mm specification Ti55531 high-strength and high-toughness titanium alloy (transformation point T β =850℃) hollow shaft blank steps are as follows: (1) Selection of bar blank specification: according to the specification of hollow shaft blank Φ270mm×Φ220mm×2500mm, the intermediate blank size Φ420mm×Φ228mm×520mm is determined reversely, and the bar blank specification Φ420mm×380mm is determined reversely, and the extrusion is 5.0.

[0040] (2) Bar blank reverse extrusion blank processing and cladding: Φ420mm×380mm bar blank sharp corner is rounded R20, one side end face is processed center positioning groove (cooperating with extrusion cone), 2mm thick copper skin is tightly cladded on the bar blank, one side of the positioning groove is not cladded, and the reverse extrusion blank is obtained.

[0041] (3) Near-β reverse extrusion: the reverse extrusion blank is preheated to 830℃ (T β -20℃) in the furnace, the insulation time is 848min (hot penetration coefficient t 反 is 2.0min / mm), the blank is taken out of the furnace and transferred to the preheated Φ435mm specification extrusion cylinder (preheating temperature 300℃) after the insulation of the blank is finished, and the transfer time is controlled within 90s~120s. Glass powder solidification adhesive pad is placed between the blank and the extrusion cone, and the reverse extrusion is carried out by pushing the extrusion cone (considering cold shrinkage, the working diameter of the cone is Φ230.5mm), and the extrusion speed is controlled within 100mm / s~120mm / s. After reverse extrusion, air cooling is carried out, and the Φ426mm×Φ228mm×525mm reverse extrusion intermediate blank with cladding is obtained.

[0042] (4) Reverse extrusion intermediate blank processing and cladding: the copper cladding and surface defects of the outer edge of the reverse extrusion intermediate blank are removed by lathe, the end face is turned, and the corner is rounded R20, and the Φ420mm×Φ228mm×520mm reverse extrusion intermediate blank is obtained. The cylindrical reverse extrusion intermediate blank is re-cladded with copper, and the copper cladding thickness is 2.0mm.

[0043] (5) Quasi-β backward extrusion: the cladded backward extrusion intermediate billet is preheated to 870°C (T β +20°C) in the furnace, and after being heated to the temperature, it is kept for 4h48min (hot penetration coefficient t 正 =3.0 min / mm), and after the intermediate billet is kept for the time, it is quickly taken out of the furnace and transferred to a Φ435 mm specification extrusion cylinder preheated to 300°C. A glass powder solidification bonding pad is arranged between the intermediate billet and the extrusion die, and forward extrusion with an extrusion ratio of 5 is performed by pushing the extrusion rod (considering the cladding thickness and cold shrinkage effect, the working belt diameter of the hollow extrusion die is Φ276.5 mm, and the hollow extrusion mandrel diameter is Φ221.5 mm). The extrusion speed is controlled at 100 mm / s-120 mm / s, and a hollow extrusion shaft blank is obtained. After extrusion, the shaft blank is quickly wrapped with an aluminum silicate fiber felt for slow cooling.

[0044] (6) Hollow shaft blank finishing: a lathe is used to remove the cladding and surface defects of the hollow shaft blank, and a Φ270 mm×Φ220 mm×2500 mm hollow shaft blank is obtained.

[0045] (7) (α+β) solution and aging: the hollow shaft blank is subjected to (α+β) two-phase zone solution and aging. The solution temperature is 800°C (T β -50°C), the holding time is 3h, and the cooling method is air cooling; the aging temperature is 600°C, the holding time is 8h, and the cooling method is furnace cooling.

[0046] Table 2 Mechanical properties of the Ti55531 hollow shaft blank prepared in Example 2

Claims

1. A method for preparing large-size, high-strength, high-toughness titanium alloy hollow shaft blanks, characterized in that, The specific steps are as follows: (1) Selection of billet specifications: Based on the forming path of billet → reverse extrusion → reverse extrusion intermediate billet → forward extrusion → hollow shaft billet, the specifications of reverse extrusion intermediate billet and billet are determined by reverse calculation. The inner diameter of the reverse extrusion intermediate billet is 3mm~5mm larger than the inner diameter of the hollow shaft billet, and the outer diameter should ensure that the forward extrusion ratio is between 2.5 and 5. (2) Billet processing and sheathing: The sharp corners of the billet are rounded, and a center positioning groove is machined on one end face. A copper sleeve is wrapped tightly around the billet, and the side with the positioning groove is not wrapped to obtain a reverse extrusion billet. (3) Near β reverse extrusion: Preheat the reverse extrusion billet to T β -(10~20)℃, where T β The β transformation temperature of the alloy is used. After the reverse extrusion billet is heated through, it is transferred to the preheated extrusion cylinder. A glass powder curing and bonding pad is placed between the reverse extrusion billet and the extrusion cone. The extrusion cone is pushed forward to perform reverse extrusion. After reverse extrusion, it is air-cooled to obtain the reverse extrusion intermediate billet. (4) Reverse extrusion intermediate billet processing and cladding: Remove the copper cladding and surface defects from the reverse extrusion intermediate billet, round the end face, and then re-clad the entire surface with copper cladding; (5) Quasi-β reverse extrusion: Preheat the reverse extrusion intermediate billet obtained in step (4) to T β + (10~20)℃, after the intermediate billet is heated through, it is transferred to the extrusion cylinder of the same specification as in step (3) and preheated. A glass powder curing bonding pad is arranged between the intermediate billet and the extrusion die. The extrusion rod is pushed to perform positive extrusion to obtain a hollow shaft billet. After extrusion, the hollow shaft billet is quickly wrapped with aluminum silicate fiber felt for slow cooling. (6) Finishing of hollow shaft blanks: removing the sheath and surface defects from the hollow shaft blanks; (7) (α+β) solution aging: Hollow shaft blanks are subjected to (α+β) two-phase region solution aging heat treatment.

2. The method for preparing large-size high-strength and high-toughness titanium alloy hollow shaft blanks according to claim 1, characterized in that, The intermediate billet in step (1) is a cylindrical billet.

3. The method for preparing large-size high-strength and high-toughness titanium alloy hollow shaft blanks according to claim 1, characterized in that, In step (1), the cross-sectional area of ​​the reverse extrusion intermediate billet, determined by the inner and outer diameters, should be 2.5 to 5 times that of the cross-sectional area of ​​the forward extrusion hollow shaft billet.

4. The method for preparing large-size high-strength and high-toughness titanium alloy hollow shaft blanks according to claim 1, characterized in that, The thickness of the copper sleeve in steps (2) and (4) is 0.5mm to 2mm.

5. The method for preparing large-size high-strength and high-toughness titanium alloy hollow shaft blanks according to claim 1, characterized in that, The preheating in steps (3) and (5) is carried out by heating along with the furnace.

6. The method for preparing large-size high-strength and high-toughness titanium alloy hollow shaft blanks according to claim 1, characterized in that, In step (3), the heat penetration time T 反 =Ball diameter D × Time coefficient t 反 , t 反 = (1.0~2.0) min / mm.

7. The method for preparing large-size high-strength and high-toughness titanium alloy hollow shaft blanks according to claim 1, characterized in that, In step (5), the heat penetration time T 正 =Intermediate billet wall thickness δ × Time coefficient t 正 , t 反 = (2.0~3.0) min / mm.

8. The method for preparing large-size high-strength and high-toughness titanium alloy hollow shaft blanks according to claim 1, characterized in that, In steps (3) and (5), the time for transferring the billet to the extrusion cylinder is ≤180s, the preheating temperature of the extrusion cylinder is ≥200℃, and the hot extrusion speed is (30~150)mm / s.

9. The method for preparing large-size high-strength and high-toughness titanium alloy hollow shaft blanks according to claim 1, characterized in that, The heat treatment process in step (7) is as follows: solution temperature T β - (20~50)℃, heat preservation for 1h~3h, air cooling or air cooling; aging temperature 540℃~600℃, heat preservation for 4h~8h, air cooling or furnace cooling.

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