A medium-high strength, high toughness, damage-tolerant titanium alloy, preparation method and application thereof

Abstract

The present invention belongs to the technical field of titanium alloy material preparation, and specifically relates to a titanium alloy with medium-high strength, high toughness and damage tolerance, a preparation method and its application. When preparing a titanium alloy with medium-high strength, high toughness and damage tolerance, the present invention reduces the content of impurity elements in the ingot by washing and machining the surface of the primary ingot and brushing the surface of the secondary ingot, and at the same time improves the purity of the ingot composition by multiple reversal smelting. The prepared titanium alloy has a tensile strength Rm ≥ 1000MPa and a yield strength Rp 0.2 ≥880MPa, elongation A≥18%, section shrinkage Z≥45%, fracture toughness K IC ≥120MPam 1 / 2 , fatigue crack growth rate da / dN≤8.92×10 ‑6 mm / cycle, its various mechanical properties have obvious advantages over TC4-DT, its strength is 100MPa lower than TC21, and its other properties are significantly better than TC21 alloy.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloy material preparation, and in particular relates to a titanium alloy with medium-high strength, high toughness and damage tolerance, a preparation method and application thereof. Background Art

[0002] With the rapid development of the aviation industry, aerospace structural components are facing new and diverse demands for lightweight, medium- and high-strength titanium alloys. No longer limited to highlighting a single performance advantage, the focus is now on actual service needs and design goals, focusing on multiple dimensions such as low cost, high performance, and high stability, striving to create new titanium alloy products with excellent overall performance.

[0003] Back in the 1970s, the U.S. Air Force took the lead in introducing the concept of "damage tolerance" in aircraft structural design. Based on this, it has successively developed titanium alloys such as Ti-6A1-4V (β-ELI, a titanium alloy containing β phase and ultra-low interstitial element content) with a strength of 900MPa and Ti-6-22-22S (Ti-6A12Sn-2Zr-2Mo-2Cr-0.2Si) with a strength of 1000MPa. They have excellent comprehensive mechanical properties. In the structural composition of the fourth-generation fighter F-22, Ti-6Al-4V and Ti-6-22-22S, two low-gap damage-tolerant titanium alloys, account for as much as 41% of the structure weight. It can be seen that damage-tolerant titanium alloys are gradually occupying a dominant position in the application of aircraft structural parts.

[0004] Based on the domestic situation, in order to meet the new international standards and requirements for titanium alloy damage tolerance, my country has actively made plans and carried out special research on high-strength, high-toughness and high damage tolerance titanium alloys. After years of research and exploration, we have successfully developed a high-strength, high-toughness and damage tolerance titanium alloy TC21 (nominal composition is Ti-6Al-2Zr-2Sn-3Mo-1Cr-2Nb-0.1Si, tensile strength Rm ≥ 1100MPa, fracture toughness K IC ≥70MPam 1 / 2 ), and medium-strength and high-toughness damage-tolerant titanium alloy TC4-DT (nominal composition Ti-6Al-4V, tensile strength Rm≥860MPa, fracture toughness K IC ≥90MPam 1 / 2 ), and has been applied on a large scale in scenarios of key load-bearing components of aircraft.

[0005] However, in the existing titanium alloy system, there is still a gap in the medium-high strength and high toughness damage tolerant titanium alloy between the high-strength and high-toughness damage tolerant titanium alloy TC21 and the medium-strength and high-toughness damage tolerant titanium alloy TC4-DT. Therefore, there is an urgent need to develop a medium-high strength and high toughness damage tolerant titanium alloy to improve the material layout of "high, medium and low" with a reasonable combination of different strength structural parts in my country's aerospace and other related fields.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a titanium alloy with medium-high strength, high toughness and damage tolerance, a preparation method and application thereof.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] On the one hand, the present invention provides a titanium alloy with medium-high strength, high toughness and damage tolerance, which includes, by weight percentage, Al: 5.0% to 7.0%, Cr: 2.5% to 4%, V: 2.5% to 5.0%, O: 0.05% to 0.15%, C≤0.02%, N≤0.01%, H≤0.01%, Si≤0.01%, Fe≤0.08%, and the balance is Ti and unavoidable impurity elements, wherein the total amount of impurity elements is less than 0.05%. In order to ensure damage tolerance related performance, the impurity elements in the product need to be controlled.

[0010] Specifically, the equivalent range of Al and Mo in the titanium alloy satisfies: 15wt.%≤[Al]eq+[Mo]eq≤17.5wt.%, and 0.9≤[Al]eq / [Mo]eq≤1.2, which can ensure a higher phase transition point of the alloy, facilitate alloy processing, and prevent the precipitation of brittle ɑ2 phase during heat treatment, thereby improving the strength and toughness of the alloy.

[0011] On the other hand, the present invention provides a method for preparing the above-mentioned titanium alloy with medium-high strength, high toughness and damage tolerance, the specific steps of which are as follows:

[0012] Step 1: Electrode preparation:

[0013] Complete weight calculation, weighing, mixing, electrode block pressing and electrode welding of titanium sponge, master alloy and other elemental metals according to weight percentage to form consumable electrodes;

[0014] Among them, sponge titanium should meet C≤0.008%, N≤0.005%, H≤0.003%, Si≤0.01%, Fe≤0.04%, Sn≤0.03%, Cl≤0.03%, and the particle size is less than 5mm; the intermediate alloy is vanadium aluminum alloy, and its impurity elements should meet C≤0.05%, N≤0.03%, H≤0.01%, S≤0.01%, P≤0.01%, B≤0.01%, Si≤0.02%, Fe≤0.10%, and the particle size is less than 1mm; in order to reduce the risk of Cr segregation, it is required that elemental Cr be added in the form of powder, and the impurity elements meet C≤0 0.005%, N≤0.01%, H≤0.005%, Si≤0.01%, Fe≤0.10%, and the powder particle size is less than 100 mesh; the remaining Al element is added in the form of simple Al, and the impurity elements meet the requirements of C≤0.01%, N≤0.001%, H≤0.003%, Si≤0.01%, Fe≤0.08%, and the particle size is less than 3 mm; the above raw materials are added to a mixer and mixed evenly, and then pressed into electrode blocks, the weight of a single electrode block is required to be 10 to 40 kg. In order to ensure the uniformity of the ingot composition, each electrode block is pressed separately, and then the electrode blocks are assembled and welded into a consumable electrode;

[0015] The electrode block assembly welding should be completed within 5 hours after the electrode block is pressed and placed in the welding box to evacuate. The welding should be completed in a plasma welding box under argon protection. The argon pressure inside the welding box is required to be 1×10 6 ~1×10 7 Pa, at the same time, monitor and detect the O and N elements inside the welding box before and during welding to ensure that the O content in the welding box is less than 500ppm and the N content is less than 800ppm;

[0016] Step 2: Ingot melting:

[0017] First, a vacuum consumable arc furnace is used to melt the consumable electrode once to obtain a primary ingot. Then, the primary ingot is turned around and melted twice to obtain a secondary ingot. Finally, the secondary ingot is turned around and melted three times to obtain a finished ingot. The time interval between the consumable electrode and the primary melting is required to be less than 8 hours, the time interval between the primary melting and the secondary melting is less than 12 hours, and the time interval between the secondary melting and the tertiary melting is less than 15 hours to ensure the uniformity of the ingot composition.

[0018] The primary ingot and the secondary ingot are both smelted using vacuum consumable arc melting. To ensure smooth electrode exhaust during the primary melting process, a crucible ratio (electrode diameter / crucible diameter) is required to be less than 0.71. The primary ingot is first rinsed with a high-pressure air gun and clean water to remove dust from its surface and then dried. The gray and blackened areas on the surface of the primary ingot are then machined to completely remove the solidified shell at areas with high impurity element content. The surface of the secondary ingot is then brushed and polished to remove some volatile impurities during the melting process.

[0019] The parameters of the three smelting processes are as follows: in the first smelting process, the vacuum degree of the smelting furnace is 0.5-0.8 Pa, the leakage rate is less than 0.6 Pa / min, the smelting current is 10-25 kA, and the smelting voltage is 26-38 V. After the first smelting process, the ingot is cooled in the crucible under vacuum for 7-9 hours, and the vacuum degree is less than 1 Pa. In the second smelting process, the leakage rate is controlled to be less than 0.5 Pa / min, the vacuum degree is less than 0.5 Pa, the smelting current is 13-27 kA, and the smelting voltage is 26-38 V. The melting voltage is 28-42V. After the secondary melting is completed, the secondary ingot is vacuumed and cooled in the crucible for 8-10 hours, and the vacuum degree is less than 0.8Pa. During the tertiary melting, the leakage rate is controlled below 0.3Pa / min, the vacuum degree is 0.01-0.1Pa, the melting current is 4-25kA, and the melting voltage is 20-43V. After the tertiary melting is completed, the finished ingot is vacuumed and cooled in the crucible for 9-12 hours, and the vacuum degree is less than 0.5Pa.

[0020] Step 3: Hot forming of bars:

[0021] The finished ingot is first heated to 930-1080°C for 1-2 rounds of blanking forging, then forged at 770-910°C for 2-4 rounds of intermediate forging, and finally forged at 750-800°C for 2-5 rounds of forming forging to form bars with a size of Φ150mm-Φ450mm.

[0022] Step 4: Heat treatment:

[0023] The obtained rod is kept at 750-800° C. for 2 hours and then subjected to AC ordinary annealing heat treatment to obtain a titanium alloy with medium-high strength, high toughness and damage tolerance.

[0024] Specifically, the titanium alloy has a tensile strength Rm ≥ 1000 MPa and a yield strength Rp 0.2 ≥880MPa, elongation A≥18%, section shrinkage Z≥45%, fracture toughness K IC ≥120MPam 1 / 2 , fatigue crack growth rate da / dN (ΔK=11)≤8.92×10 -6 mm / cycle.

[0025] In another aspect, the present invention provides a titanium alloy with medium-high strength, high toughness and damage tolerance as described above, or a titanium alloy prepared by the method for preparing the titanium alloy with medium-high strength, high toughness and damage tolerance as described above, and its use in aviation structural parts.

[0026] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0027] The titanium alloy with medium-high strength and high toughness and damage tolerance provided by the present invention has a tensile strength Rm≥1000MPa and a yield strength Rp 0.2 ≥880MPa, elongation A≥18%, section shrinkage Z≥45%, fracture toughness K IC ≥120MPam 1 / 2 , fatigue crack growth rate da / dN≤8.92×10 -6 mm / cycle, its various mechanical properties have obvious advantages over TC4-DT, its strength is 100MPa lower than TC21, and its other properties are significantly better than TC21 alloy.

[0028] Furthermore, when preparing titanium alloys with medium to high strength, high toughness and damage tolerance, only Al, V and Cr elements are added, and the more expensive V element is added in a smaller amount, while Al and Cr elements are relatively cheap. The raw material cost is lower than that of TC21 and TC4-DT, which further reduces the production cost and helps it be applied in more fields.

[0029] Furthermore, when preparing titanium alloys with medium to high strength and high toughness and damage tolerance, in order to reduce the influence of impurity elements on their damage tolerance-related properties, the requirements for the selection and use of raw materials, the requirements for the vacuum degree of the ingot preparation cooling process, and the air contact time are clarified, and the content of impurity elements in the ingot is reduced by flushing and machining the surface of the first ingot and brushing the surface of the second ingot to improve the purity of the ingot composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, serve to explain the principles of the invention.

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0032] Figure 1 This is a macroscopic structural photograph of the head of a titanium alloy Ø340 mm ingot according to Example 1 of the present invention;

[0033] Figure 2This is a low-magnification microstructure photograph of the head of a titanium alloy Ø200 mm bar according to Example 1 of the present invention;

[0034] Figure 3 The titanium alloy Ø200mm bar head T of Example 1 of the present invention β -25℃ air-burned tissue photos;

[0035] Figure 4 This is a metallographic photograph of the head of a titanium alloy Ø200 mm bar after ordinary annealing in Example 1 of the present invention;

[0036] Figure 5 This is a macroscopic structural photograph of the head of a titanium alloy Ø720 mm ingot according to Example 2 of the present invention;

[0037] Figure 6 This is a macroscopic structural photograph of the tail of the titanium alloy Ø720 mm ingot according to Example 2 of the present invention;

[0038] Figure 7 This is a graph showing the Al content at nine points in the transverse direction of the titanium alloy 720 mm diameter ingot according to Example 2 of the present invention;

[0039] Figure 8 This is a graph showing the V content results at nine points transversely from the head to the tail of a titanium alloy 720 mm diameter ingot according to Example 2 of the present invention;

[0040] Figure 9 This is a graph showing the Cr content at nine points in the transverse direction at the head and tail of a 720 mm diameter titanium alloy ingot according to Example 2 of the present invention;

[0041] Figure 10 This is a graph showing the O content at nine points transversely from the head to the tail of a titanium alloy 720 mm diameter ingot according to Example 2 of the present invention;

[0042] Figure 11 This is a low-magnification microstructure photograph of the head of the titanium alloy Ø400mm bar of Example 2 of the present invention;

[0043] Figure 12 This is a low-magnification microstructure photograph of the tail of the titanium alloy Ø400mm bar according to Example 2 of the present invention;

[0044] Figure 13 This is a metallographic photograph of the head of a titanium alloy Ø400 mm bar after conventional annealing in Example 2 of the present invention;

[0045] Figure 14 The flowchart of the preparation method of the high-strength, high-toughness and damage-tolerant titanium alloy in the present invention is shown. DETAILED DESCRIPTION

[0046] Exemplary embodiments will now be described in detail, with examples shown in the accompanying drawings. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present invention. Instead, they are merely examples consistent with some aspects of the present invention as detailed in the appended claims.

[0047] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is described in further detail below with reference to the accompanying drawings and embodiments.

[0048] On the one hand, the present invention provides a titanium alloy with medium-high strength, high toughness and damage tolerance, which includes, by weight percentage, Al: 5.0% to 7.0%, Cr: 2.5% to 4%, V: 2.5% to 5.0%, O: 0.05% to 0.15%, C≤0.02%, N≤0.01%, H≤0.01%, Si≤0.01%, Fe≤0.08%, and the balance is Ti and unavoidable impurity elements, wherein the total amount of impurity elements is less than 0.05%. In order to ensure damage tolerance related performance, the impurity elements in the product need to be controlled.

[0049] Specifically, the equivalent range of Al and Mo in the titanium alloy satisfies: 15wt.%≤[Al]eq+[Mo]eq≤17.5wt.%, and 0.9≤[Al]eq / [Mo]eq≤1.2, which can ensure a higher phase transition point of the alloy, facilitate alloy processing, and prevent the precipitation of brittle ɑ2 phase during heat treatment to improve the strength and toughness of the alloy.

[0050] On the other hand, the present invention provides a method for preparing the above-mentioned titanium alloy with medium-high strength, high toughness and damage tolerance, such as Figure 14 The specific steps are as follows:

[0051] Step 1: Electrode preparation:

[0052] Complete weight calculation, weighing, mixing, electrode block pressing and electrode welding of titanium sponge, master alloy and other elemental metals according to weight percentage to form consumable electrodes;

[0053] Among them, sponge titanium should meet C≤0.008%, N≤0.005%, H≤0.003%, Si≤0.01%, Fe≤0.04%, Sn≤0.03%, Cl≤0.03%, and the particle size is less than 5mm; the intermediate alloy is vanadium aluminum alloy, and its impurity elements should meet C≤0.05%, N≤0.03%, H≤0.01%, S≤0.01%, P≤0.01%, B≤0.01%, Si≤0.02%, Fe≤0.10%, and the particle size is less than 1mm; in order to reduce the risk of Cr segregation, it is required that elemental Cr be added in the form of powder, and the impurity elements meet C≤ 0.005%, N≤0.01%, H≤0.005%, Si≤0.01%, Fe≤0.10%, and the powder particle size is less than 100 mesh; the remaining Al element is added in the form of simple Al, and the impurity elements meet the requirements of C≤0.01%, N≤0.001%, H≤0.003%, Si≤0.01%, Fe≤0.08%, and the particle size is less than 3 mm; the above raw materials are added to a mixer and mixed evenly, and then pressed into electrode blocks, the weight of a single electrode block is required to be 10 to 40 kg, and each electrode block is pressed separately to ensure the uniformity of the ingot composition, and then the electrode blocks are assembled and welded into consumable electrodes;

[0054] The electrode block assembly welding should be completed within 5 hours after the electrode block is pressed and placed in the welding box to evacuate. The welding should be completed in a plasma welding box under argon protection. The argon pressure inside the welding box is required to be 1×10 6 ~1×10 7 Pa, at the same time, monitor and detect the O and N elements inside the welding box before and during welding to ensure that the O content in the welding box is less than 500ppm and the N content is less than 800ppm;

[0055] Step 2: Ingot melting:

[0056] First, a vacuum consumable arc furnace is used to melt the consumable electrode once to obtain a primary ingot. Then, the primary ingot is turned around and melted twice to obtain a secondary ingot. Finally, the secondary ingot is turned around and melted three times to obtain a finished ingot. The time interval between the consumable electrode and the primary melting is required to be less than 8 hours, the time interval between the primary melting and the secondary melting of the ingot is less than 12 hours, and the time interval between the secondary melting and the tertiary melting is less than 15 hours to ensure the uniformity of the ingot composition.

[0057] The primary ingot and the secondary ingot are both smelted using vacuum consumable arc melting. To ensure smooth electrode exhaust during the primary melting process, a crucible ratio (electrode diameter / crucible diameter) is required to be less than 0.71. The primary ingot is first rinsed with a high-pressure air gun and clean water to remove dust from its surface and then dried. The gray and blackened areas on the surface of the primary ingot are then machined to completely remove the solidified shell at areas with high impurity element content. The surface of the secondary ingot is then brushed and polished to remove some volatile impurities during the melting process.

[0058] The parameters of the three smelting processes are as follows: in the first smelting process, the vacuum degree of the smelting furnace is 0.5-0.8 Pa, the leakage rate is less than 0.6 Pa / min, the smelting current is 10-25 kA, and the smelting voltage is 26-38 V. After the first smelting process, the ingot is cooled in the crucible under vacuum for 7-9 hours, and the vacuum degree is less than 1 Pa. In the second smelting process, the leakage rate is controlled to be less than 0.5 Pa / min, the vacuum degree is less than 0.5 Pa, the smelting current is 13-27 kA, and the smelting voltage is 26-38 V. The smelting voltage is 28-42V. After the secondary smelting is completed, the secondary ingot is vacuumed and cooled in the crucible for 8-10 hours, and the vacuum degree is less than 0.8Pa. During the tertiary smelting, the leakage rate is controlled below 0.3Pa / min, the vacuum degree is 0.01-0.1Pa, the smelting current is 4-25kA, and the smelting voltage is 20-43V. After the tertiary smelting is completed, the finished ingot is vacuumed and cooled in the crucible for 9-12 hours, and the vacuum degree is less than 0.5Pa.

[0059] Step 3: Hot forming of bars:

[0060] The finished ingot is first heated to 930-1080°C for 1-2 rounds of blanking forging, then forged at 770-910°C for 2-4 rounds of intermediate forging, and finally forged at 750-800°C for 2-5 rounds of forming forging to form bars with a size of Φ150mm-Φ450mm.

[0061] Step 4: Heat treatment:

[0062] The obtained rod is kept at 750-800° C. for 2 hours and then subjected to AC ordinary annealing heat treatment to obtain a titanium alloy with medium-high strength, high toughness and damage tolerance.

[0063] In order to further verify the effect of the present invention, the inventors prepared a titanium alloy with medium-high strength, high toughness and damage tolerance by the following method:

[0064] Example 1

[0065] This embodiment provides a method for preparing a titanium alloy with medium-high strength, high toughness, and damage tolerance. The target alloy composition is Al: 5%, Cr: 2.5%, V: 2.5%, O: 0.06%, and the balance is Ti and unavoidable impurity elements. The specific preparation steps are as follows:

[0066] Step 1: Electrode preparation:

[0067] Use titanium sponge particles that comply with GB / T 2524, with a diameter range of 1 to 5 mm, and the impurity elements are C≤0.006%, N≤0.003%, H≤0.001%, Si≤0.01%, Fe≤0.02%, Sn≤0.025%, and Cl≤0.03%. The impurity elements of vanadium aluminum alloy are C≤0.02%, N≤0.01%, H≤0.01%, S≤0.01%, P≤0.01%, B≤0.01%, Si≤0.01%, and Fe≤0.05%, and the particle size is less than 1 mm. The impurity elements of Cr element powder meet the requirements of C≤0.005%, N≤0.01%, H≤0.003%, Si≤0.01%, and Fe≤0.05%, and the powder particle size is less than 100 mesh. The impurities of elemental Al meet the requirements of C≤0.006%, N≤0.01%, H≤0.003%, Si≤0.01%, and Fe≤0.05%, and the powder particle size is less than 100 mesh. ≤0.008%, N≤0.001%, H≤0.003%, Si≤0.01%, Fe≤0.05%, particle size less than 3mm, and the above raw materials all meet the alloy use requirements; the weight of a single electrode block is 15kg, and then the weight of the intermediate alloy used in the single electrode block is calculated according to the target composition, and the mixing is completed by a mixer, and the mixing time is 120s. After the mixing is completed, the above raw materials are pressed into an electrode block with a size of 400mm (length) × 100mm (width) × 100mm (height); then they are welded into a consumable electrode through a plasma welding box. The electrode block assembly welding should be completed within 5 hours after the electrode block is pressed, and the electrode block should be placed in a vacuum welding box. The welding should be completed in a plasma welding box under argon protection, and the argon pressure inside the welding box is required to be 1×10 6 Pa, monitor and test the O and N elements inside the welding box before and during welding to ensure that the O content in the welding box is less than 450ppm and the N content is less than 600ppm;

[0068] Step 2: Ingot melting:

[0069] A 1-ton vacuum consumable arc furnace (VAR) is used to first melt a consumable electrode to obtain a primary ingot. The crucible has a diameter of 200 mm. During the primary melting, the maximum vacuum degree of the melting furnace is 0.6 Pa, the leakage rate is less than 0.6 Pa / min, the melting current is 10.5 kA, and the melting voltage is 27 V. After the primary melting is completed, the primary ingot is vacuumed and cooled in the crucible for 7.5 hours. During the cooling process, the vacuum degree of the crucible is less than 1 Pa. The primary ingot is then rinsed with a high-pressure air gun and clean water, dried, and machined to remove impurities on the surface of the primary ingot.

[0070] The crucible diameter used for secondary smelting is 260 mm. The primary ingot obtained after machining is turned over and placed in the crucible for secondary smelting. During the secondary smelting, the leakage rate is less than 0.5 Pa / min, the vacuum degree is less than 0.5 Pa, the smelting current is 18 kA, and the smelting voltage is 32 V. After the secondary smelting is completed, the secondary ingot is vacuumed and cooled in the crucible for 8 hours with a vacuum degree less than 0.5 Pa. After being taken out of the furnace, the surface of the secondary ingot is brushed and polished to remove some volatile impurities during the smelting process.

[0071] The crucible diameter used for the tertiary smelting is Ф340mm. The secondary ingot obtained after the brushing treatment is turned over for the tertiary smelting. During the tertiary smelting, the leakage rate is less than 0.3Pa / min, the vacuum degree of the furnace is less than 0.1Pa, the smelting current is 15kA, and the smelting voltage is 31V. After the tertiary smelting, the finished ingot is vacuumed and cooled in the crucible for 9h, and the vacuum degree of the furnace is less than 0.3Pa. The macrostructure of the head of the Ф340mm finished ingot prepared by the above method is normal, without β-spot defects, such as Figure 1 As shown;

[0072] Step 3: Hot forming of bars:

[0073] First, the finished ingot after three VAR smelting is heated to 960℃ to complete 2-fire forging, then 2-fire intermediate forging is completed at 800℃, and then 3-fire forming forging is completed at 760℃ to form Φ200mm bars; the obtained bars are subjected to macroscopic microstructure inspection at the head. Figure 2 As shown, as well as T β -25℃ air burning tissue inspection Figure 3 As shown, the examinations were normal, and no β-plaque defects were found;

[0074] Step 4: Heat treatment:

[0075] The Φ200 mm rod was kept at 760°C for 2 hours and then subjected to AC conventional annealing heat treatment to obtain a titanium alloy rod A with medium-high strength, high toughness and damage tolerance.

[0076] The metallographic photographs of the head of the titanium alloy bar A after ordinary annealing were checked to see if they met the requirements. Figure 4 As shown;

[0077] The performance of titanium alloy bar A was tested: tensile strength Rm = 1039MPa, yield strength Rp 0.2 =897MPa, elongation A=23%, section reduction Z=49%, fracture toughness K IC =131MPam 1 / 2 , fatigue crack growth rate da / dN(ΔK=11)=8.35×10 -6 mm / cycle.

[0078] Example 2

[0079] This embodiment provides a method for preparing a titanium alloy with medium-high strength, high toughness, and damage tolerance. The target alloy composition is Al: 6.5%, Cr: 3%, V: 5%, O: 0.12%, and the balance is Ti and unavoidable impurity elements. The specific preparation steps are as follows:

[0080] Step 1: Electrode preparation:

[0081] Use titanium sponge particles that comply with GB / T 2524, with a diameter range of 2.5 to 5 mm, and the impurity elements are C≤0.006%, N≤0.003%, H≤0.001%, Si≤0.01%, Fe≤0.01%, Sn≤0.020%, and Cl≤0.02%; the impurity elements of vanadium aluminum alloy are C≤0.02%, N≤0.02%, H≤0.01%, S≤0.01%, P≤0.01%, B≤0.01%, Si≤0.01%, and Fe≤0.025%, and the particle size is less than 1 mm; the impurity elements of Cr element powder meet the requirements of C≤0.005%, N≤0.01%, H≤0.003%, Si≤0.01%, and Fe≤0.06%, and the powder particle size is less than 100 mesh; the impurity elements of elemental Al meet the requirements of The raw materials are C≤0.006%, N≤0.001%, H≤0.003%, Si≤0.01%, Fe≤0.08%, and the particle size is less than 3 mm. The above raw materials all meet the requirements for alloy use. The weight of a single electrode block is 25 kg. The weight of the intermediate alloy used in the single electrode block is calculated according to the target composition. The mixing is completed by a mixer. The mixing time is 180 s. After the mixing is completed, the above raw materials are pressed into an electrode block with a size of 350 mm (length) × 250 mm (width) × 200 mm (height). Then, a plasma welding box is used to weld the electrode blocks into consumable electrodes. The electrode block assembly welding should be completed within 4 hours after the electrode block is pressed. The electrode block should be placed in a vacuum-evacuated welding box. The welding should be completed in a plasma welding box under argon protection. The argon pressure inside the welding box is required to be 1×10 7 Pa, monitor and test the O and N elements inside the welding box before and during welding to ensure that the O content in the welding box is less than 400ppm and the N content is less than 600ppm;

[0082] Step 2: Ingot melting:

[0083] An 8-ton vacuum consumable arc furnace (VAR) is used to first melt a consumable electrode to obtain a primary ingot. The crucible has a diameter of 360 mm. During the primary melting, the maximum vacuum degree of the melting furnace is 0.5 Pa, the leakage rate is less than 0.5 Pa / min, the melting current is 14 kA, and the melting voltage is 34 V. After the primary melting is completed, the primary ingot is vacuumed and cooled in the crucible for 8 hours. During the cooling process, the vacuum degree of the crucible is less than 0.5 Pa. The primary ingot is then rinsed with a high-pressure air gun and clean water, dried, and machined to remove impurities on the surface of the primary ingot.

[0084] The crucible used for secondary smelting has a diameter of 440 mm. The machined primary ingot is turned around and placed in the crucible for secondary smelting. During the secondary smelting, the leakage rate is less than 0.4 Pa / min, the vacuum degree is less than 0.6 Pa, the smelting current is 18 kA, and the smelting voltage is 36 V. After the secondary smelting is completed, the secondary ingot is vacuumed and cooled in the crucible for 8.5 hours. The vacuum degree in the crucible is less than 0.5 Pa. After being taken out of the furnace, the surface of the secondary ingot is brushed and then cleaned with a hair dryer.

[0085] The crucible diameter used for the tertiary smelting is Ø520 mm. The secondary ingot after brushing is turned over and smelted for the tertiary smelting. During the tertiary smelting, the leakage rate is less than 0.2 Pa / min, the furnace vacuum is less than 0.1 Pa, the smelting current is 10 kA, and the smelting voltage is 26 V. After the tertiary smelting, the finished ingot is vacuumed and cooled in the crucible for 9 hours, and the furnace vacuum is less than 0.3 Pa.

[0086] The macrostructure of the head and tail of the Ø520mm finished ingot was inspected and found to be normal with no β-spot defects.

[0087] Step 3: Hot forming of bars:

[0088] The finished ingot after three VAR smeltings was first heated to 990°C for two rounds of blanking forging, then forged at 850°C for four rounds of intermediate forging, and then forged at 780°C for five rounds of forming forging, ultimately forming a Φ300mm bar. The macrostructure of the head and tail of the obtained bar was inspected and found to be normal.

[0089] Step 4: Heat treatment:

[0090] The Φ300 mm rod was kept at 790°C for 2 hours and then subjected to AC ordinary annealing heat treatment to obtain a titanium alloy rod B with medium-high strength, high toughness and damage tolerance.

[0091] Then the properties of titanium alloy bar B were tested: tensile strength Rm = 1025MPa, yield strength Rp 0.2 =887MPa, elongation A=22%, section reduction Z=48%, fracture toughness K IC=128MPam 1 / 2 , fatigue crack growth rate da / dN(ΔK=11)=8.42×10 -6 mm / cycle.

[0092] Example 3

[0093] This embodiment provides a method for preparing a titanium alloy with medium-high strength, high toughness, and damage tolerance. The target alloy composition is Al: 6%, Cr: 3.5%, V: 4%, O: 0.08%, and the balance is Ti and unavoidable impurity elements. The specific preparation steps are as follows:

[0094] Step 1: Electrode preparation:

[0095] Use titanium sponge particles that comply with GB / T 2524, with a diameter range of 2.5 to 5 mm, and the impurity elements are C≤0.005%, N≤0.004%, H≤0.001%, Si≤0.01%, Fe≤0.02%, Sn≤0.025%, and Cl≤0.03%. The impurity elements of vanadium aluminum alloy are C≤0.01%, N≤0.01%, H≤0.01%, S≤0.01%, P≤0.01%, B≤0.01%, Si≤0.01%, and Fe≤0.04%, and the particle size is less than 1 mm. The impurity elements of Cr element powder meet the requirements of C≤0.005%, N≤0.01%, H≤0.003%, Si≤0.01%, and Fe≤0.05%, and the powder particle size is less than 100 mesh. The impurity elements of elemental Al meet the requirements of The raw materials are C≤0.008%, N≤0.001%, H≤0.003%, Si≤0.01%, Fe≤0.05%, and the particle size is less than 3 mm. The above raw materials all meet the requirements for alloy use. The weight of a single electrode block is 40 kg. The weight of the intermediate alloy used in the single electrode block is calculated according to the target composition. The mixing is completed by a mixer. The mixing time is 180 s. After the mixing is completed, the above raw materials are pressed into an electrode block with a size of 400 mm (length) × 350 mm (width) × 250 mm (height). Then, a plasma welding box is used to weld the electrode blocks into consumable electrodes. The electrode block assembly welding should be completed within 5 hours after the electrode block is pressed. The electrode block should be placed in a vacuum-evacuated welding box. The welding should be completed in a plasma welding box under argon protection. The argon pressure inside the welding box is required to be 1×10 7 Pa, monitor and test the O and N elements inside the welding box before and during welding to ensure that the O content in the welding box is less than 500ppm and the N content is less than 700ppm;

[0096] Step 2: Ingot melting:

[0097] An 8-ton vacuum consumable arc furnace (VAR) is used to first melt a consumable electrode to obtain a primary ingot. The crucible has a diameter of 550 mm. During the primary melting, the maximum vacuum degree of the melting furnace is 0.6 Pa, the leakage rate is less than 0.4 Pa / min, the melting current is 18 kA, and the melting voltage is 37 V. After the primary melting is completed, the primary ingot is vacuumed and cooled in the crucible for 8.5 hours. During the cooling process, the vacuum degree of the crucible is less than 0.5 Pa. The primary ingot is then rinsed with a high-pressure air gun and clean water, dried, and machined to remove impurities on the surface of the primary ingot.

[0098] The crucible used for secondary smelting has a diameter of 660 mm. The primary ingot after machining is turned around and placed in the crucible for secondary smelting. During the secondary smelting, the leakage rate is less than 0.3 Pa / min, the vacuum degree is less than 0.4 Pa, the smelting current is 22 kA, and the smelting voltage is 39 V. After the secondary smelting is completed, the secondary ingot is vacuumed and cooled in the crucible for 9 hours. The vacuum degree in the crucible is less than 0.3 Pa. After being taken out of the furnace, the surface of the secondary ingot is brushed and then cleaned with a hair dryer.

[0099] The crucible diameter used for the tertiary smelting is 720 mm. The secondary ingot after brushing is turned over and smelted for the tertiary smelting. During the tertiary smelting, the leakage rate is less than 0.3 Pa / min, the vacuum degree of the furnace is less than 0.1 Pa, the smelting current is 12 kA, and the smelting voltage is 29 V. After the tertiary smelting, the finished ingot is vacuumed and cooled in the crucible for 10 hours, and the vacuum degree of the furnace is less than 0.1 Pa.

[0100] The macrostructure of the head of the 720mm finished ingot is as follows: Figure 5 As shown, and the tail low magnification tissue as Figure 6 As shown, the inspection was normal, without β-spot defects; the 9-point components of the head and tail were extremely poor as shown Figure 7-10 As shown: Al<2500ppm( Figure 7 )、V<1200ppm( Figure 8 )、Cr<2300ppm( Figure 9 )、O<170ppm( Figure 10 ), showing that the finished ingot has uniform composition throughout;

[0101] Step 3: Hot forming of bars:

[0102] First, the finished ingot after three VAR smeltings is heated to 1000℃ to complete 2-fire forging, then 4-fire intermediate forging is completed at 895℃, and then 5-fire forming forging is completed at 800℃ to finally form a Φ400mm bar. The macrostructure of the bar head is as follows: Figure 11 As shown, and the tail low magnification tissue as Figure 12 As shown, the examination was performed and all were normal;

[0103] Step 4: Heat treatment:

[0104] The obtained Φ400mm rod was kept at 780℃ for 2h and then subjected to AC ordinary annealing heat treatment to obtain titanium alloy rod C with medium-high strength, high toughness and damage tolerance.

[0105] The metallographic photographs of the head of the titanium alloy bar C after ordinary annealing were checked to see if they met the requirements. Figure 13 The mechanical properties of titanium alloy bar C are shown in Table 1, all of which meet the requirements.

[0106] Table 1 Performance results of Ø400mm bar after ordinary annealing

[0107]

[0108] The above examples illustrate that the titanium alloy prepared by the method for preparing the high-strength, high-toughness and damage-tolerant titanium alloy can be used in aviation structural parts.

[0109] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0110] It should be understood that the present invention is not limited to the above description and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a titanium alloy with medium-high strength, high toughness and damage tolerance, characterized in that: The medium-high strength, high toughness and damage tolerance titanium alloy comprises, by weight percentage, Al: 5.0%-7.0%, Cr: 2.5%-4%, V: 2.5%-5.0%, O: 0.05%-0.15%, C≤0.02%, N≤0.01%, H≤0.01%, Si≤0.01%, Fe≤0.08%, and the balance is Ti and unavoidable impurity elements, wherein the total amount of impurity elements is less than 0.05%; the raw materials of the above elements are sponge titanium, vanadium aluminum alloy, elemental Cr, and elemental Al; the equivalent range of Al and Mo in the titanium alloy satisfies: 15wt.%≤[Al]eq+[Mo]eq≤17.5wt.%, and 0.9≤[Al]eq / [Mo]eq≤1.2; the specific steps of the preparation method are as follows: Step 1: Electrode preparation: The weight of titanium sponge, master alloy and other elemental metals is calculated according to weight percentage, and then weighing, mixing, electrode block pressing and electrode welding are carried out to form a consumable electrode; Among them, sponge titanium meets C≤0.008%, N≤0.005%, H≤0.003%, Si≤0.01%, Fe≤0.04%, Sn≤0.03%, Cl≤0.03%; the intermediate alloy is vanadium aluminum alloy, and its impurity elements meet C≤0.05%, N≤0.03%, H≤0.01%, S≤0.01%, P≤0.01%, B≤0.01%, Si≤0.02%, Fe≤0.10%; the impurity elements of the single Cr powder are The elements meet the requirements of C≤0.005%, N≤0.01%, H≤0.005%, Si≤0.01%, and Fe≤0.10%; the remaining Al element is added in the form of elemental Al, and the impurity elements meet the requirements of C≤0.01%, N≤0.001%, H≤0.003%, Si≤0.01%, and Fe≤0.08%; the particle size of sponge titanium is less than 5mm, the particle size of vanadium-aluminum alloy is less than 1mm, the particle size of elemental Al is less than 3mm, and the particle size of elemental Cr powder is less than 100 mesh; Step 2: Ingot melting: First, a consumable electrode is melted once in a vacuum consumable arc furnace to obtain a primary ingot, then the primary ingot is turned around and melted twice to obtain a secondary ingot, and finally the secondary ingot is turned around and melted three times to obtain a finished ingot; During the primary smelting, the vacuum degree of the smelting furnace is 0.5-0.8 Pa, the leakage rate is less than 0.6 Pa / min, the smelting current is 10-25 kA, and the smelting voltage is 26-38 V. After the primary smelting is completed, the primary ingot is vacuumed and cooled in the crucible for 7-9 hours, and the vacuum degree is less than 1 Pa. During the secondary smelting, the leakage rate is controlled to be less than 0.5 Pa / min, the vacuum degree is less than 0.5 Pa, the smelting current is 13-27 kA, and the smelting voltage is 28-42 V. After the secondary smelting is completed, the secondary ingot is vacuumed and cooled in the crucible for 8-10 hours, and the vacuum degree is less than 0.8 Pa. During the tertiary smelting, the leakage rate is controlled to be less than 0.3 Pa / min, the vacuum degree is 0.01-0.1 Pa, the smelting current is 4-25 kA, and the smelting voltage is 20-43 V. After the tertiary smelting is completed, the finished ingot is vacuumed and cooled in the crucible for 9-12 hours, and the vacuum degree is less than 0.5 Pa. Step 3: Hot forming of bars: First, the finished ingot is heated to 930-1080℃ to complete 1-2 fires of blank forging, then 2-4 fires of intermediate forging are completed at 770-910℃, and finally 2-5 fires of forming forging are completed at 750-800℃ to finally obtain the required bar; Step 4: Heat treatment: The obtained rod is subjected to ordinary annealing heat treatment to obtain a titanium alloy with medium-high strength, high toughness and damage tolerance.

2. The method for preparing a titanium alloy with medium-high strength, high toughness and damage tolerance according to claim 1, characterized in that: In step 2, the dust on the surface of the obtained primary ingot is washed off with a high-pressure air gun and clean water and then dried. The gray and blackened parts of the surface of the primary ingot are then machined; the surface of the obtained secondary ingot is brushed and polished.

3. The method for preparing a titanium alloy with medium-high strength, high toughness and damage tolerance according to any one of claims 1 or 2, characterized in that: The tensile strength of the titanium alloy is Rm≥1000MPa, and the yield strength is Rp 0.2 ≥880MPa, elongation A≥18%, section shrinkage Z≥45%, fracture toughness K IC ≥120MPa·m 1 / 2 , fatigue crack growth rate da / dN≤8.92×10 -6 mm / cycle.

4. Use of the titanium alloy prepared by the method for preparing the medium-high strength, high toughness and damage tolerant titanium alloy according to any one of claims 1 or 2 in aviation structural parts.

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