A 1800mpa grade ultra-high strength titanium alloy prepared by a non-quenching process

Abstract

This invention discloses an 1800MPa-grade ultra-high strength titanium alloy prepared without quenching. The alloy's elemental mass percentages are: Al: 3%–5%, Mo: 5%–7.5%, Cr: 2%–3%, Zr: 1.5%–3%, Cu: 1.5%–3%, with the balance being Ti and unavoidable impurities. After melting, billet forging, two-phase rolling, solution treatment, air cooling, and aging treatment, the alloy exhibits a room temperature tensile strength exceeding 1800MPa and an elongation greater than 5%, significantly superior to traditional high-strength titanium alloys, while also possessing a certain degree of plasticity. Furthermore, traditional high-strength titanium alloys mostly employ a heat treatment process of "solution + water quenching + aging." The preparation process of the ultra-high strength titanium alloy described in this invention allows for air cooling instead of water quenching, avoiding problems such as deformation and cracking caused by excessive quenching stress and uneven microstructure and properties due to insufficient hardenability. This significantly reduces the production cost of high-strength titanium alloys, improves the yield of finished products, and has significant engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy technology, specifically relating to an 1800MPa grade ultra-high strength titanium alloy prepared without quenching process. Background Technology

[0002] Titanium alloys, due to their low density, high specific strength, high toughness, and excellent corrosion resistance, are widely used in aerospace, petrochemical, and marine engineering fields, gradually becoming the preferred material for high-performance and lightweight structural materials. High-strength titanium alloys are widely used in important structural components such as aerospace fasteners, fuselage load-bearing beams, and torsion arms and struts of aircraft landing gear. The tensile strength of traditional high-strength titanium alloys ranges from 1100 MPa to 1600 MPa. When the strength is further increased, the alloy's plasticity deteriorates significantly to below 3%, making it unsuitable for application requirements. Therefore, components with service strengths above 1600 MPa still use alloy steel. To meet the urgent need for lightweighting of the main load-bearing structures in next-generation aircraft, there is a pressing need to design a new type of ultra-high-strength titanium alloy with a room temperature tensile strength above 1600 MPa, while also possessing certain plasticity and toughness. This will significantly promote the development of my country's aerospace industry.

[0003] In addition, traditional high-strength titanium alloys mostly adopt the heat treatment process of "solution + water quenching + aging" to obtain ultra-high strength: through high-temperature solution and water quenching, the alloy retains the metastable β phase at room temperature, and then through aging treatment, fine secondary α phases are precipitated in the metastable β phase. The increased α / β phase interface can hinder dislocation slip and significantly improve the strength of the alloy. However, the quenching process in this process has obvious drawbacks: (1) Titanium alloys have a large coefficient of thermal expansion, and rapid cooling can easily generate large internal stress, leading to workpiece deformation and cracking; (2) For titanium alloy components with large thickness, due to insufficient hardenability, the cooling rate of the component surface and core is significantly different, resulting in uneven overall structure and properties, which seriously affects the service performance of the component; (3) The equipment required for the quenching process is complex, the operation process is cumbersome, and it is difficult to correct and detect the deformation and cracks generated during the quenching process, resulting in high process costs. In summary, the production of high-strength titanium alloys through a heat treatment process without quenching can significantly reduce production costs and improve the workpiece yield, which has important engineering application significance. Summary of the Invention

[0004] To address the shortcomings of traditional high-strength titanium alloys and their heat treatment processes, this invention aims to provide an 1800MPa-grade ultra-high-strength titanium alloy that can be prepared without quenching. This alloy can be manufactured through a heat treatment process without quenching, while maintaining a room-temperature tensile strength greater than 1800MPa and acceptable plasticity. This alloy overcomes the trade-off between strength and plasticity, and its preparation process is simple and easy to implement, avoiding various drawbacks of water quenching and significantly reducing manufacturing costs. It has broad application prospects in the aerospace field.

[0005] The technical solution of the present invention is as follows:

[0006] A 1800MPa grade ultra-high strength titanium alloy prepared without quenching process has the following alloy composition by mass percentage: Al: 3%~5%, Mo: 5%~7.5%, Cr: 2%~3%, Zr: 1.5%~3%, Cu: 1.5%~3%, with the balance being Ti and unavoidable impurities.

[0007] A method for preparing 1800MPa-grade ultra-high strength titanium alloy without quenching includes the following steps:

[0008] Step 1: Mix the raw materials according to the above mass percentages and then perform multiple smelting processes to obtain a cast ingot with uniform composition. Measure the β-phase transformation temperature of the cast ingot.

[0009] Step 2: Perform β single-phase region forging on the ingot obtained in Step 1 to obtain a flat ingot;

[0010] Step 3: Roll the flat ingot obtained in Step 2 in the α+β two-phase region;

[0011] Step 4: Perform a solution treatment on the alloy obtained in Step 3, and then cool it to room temperature;

[0012] Step 5: The alloy obtained in Step 4 is subjected to aging treatment, and then cooled to room temperature to obtain an ultra-high strength titanium alloy.

[0013] Preferably, the smelting process described in step 1 is as follows: 3 to 5 vacuum suspension smelting processes are carried out in a high-purity argon atmosphere.

[0014] Preferably, the method for determining the β-phase transformation temperature of the ingot in step 1 is metallographic method.

[0015] Preferably, the single-phase region forging temperature in step 2 is 50°C to 200°C above the β-phase transformation temperature, and the deformation is not less than 50%.

[0016] Preferably, the rolling temperature of the two-phase region in step 3 is 20°C to 60°C below the β-phase transformation temperature, and the deformation is not less than 80%.

[0017] Preferably, the solution treatment process in step 4 is as follows: keep warm at 10°C to 30°C below the β phase transformation temperature for 30 minutes, and then air cool to room temperature.

[0018] Preferably, the aging process described in step 5 is as follows: heat treatment at 480℃~550℃ for 6 hours, followed by air cooling to room temperature.

[0019] Preferably, the ultra-high strength titanium alloy obtained in step 5 has a room temperature tensile strength greater than 1800 MPa and an elongation greater than 5%.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The 1800MPa grade ultra-high strength titanium alloy prepared by the present invention without quenching process has the following composition by mass percentage: Al: 3%~5%, Mo: 5%~7.5%, Cr: 2%~3%, Zr: 1.5%~3%, Cu: 1.5%~3%, with the balance being Ti and unavoidable impurities. This alloy is strengthened by solid solution treatment with a large amount of β-stabilizing elements Mo, Cr, and Cu, thereby improving the alloy strength. Furthermore, the highly diffusing element Cr can significantly reduce the size of the secondary α phase precipitated during aging; the eutectoid element Cu will cause a large number of Ti2Cu particles to precipitate in the alloy, which will promote the nucleation of the secondary α phase during aging, increasing the number and reducing the size of the secondary α phase. The significantly increased α / β phase interface can hinder dislocation slip, significantly improving the strength of the alloy. The addition of the α-stabilizing element Al and the neutral element Zr to the alloy aims to retain a certain proportion of equiaxed primary α phases and exert a solid solution strengthening effect on them, thereby increasing the critical shear stress of dislocation slip within the α phase and further improving the overall strength of the alloy. Simultaneously, the primary α phases, with their strong plastic deformation capacity, can coordinate the plastic deformation between β-transformation structures, reducing the possibility of crack initiation at phase interfaces. This allows the alloy to retain a certain degree of plasticity while possessing ultra-high strength. Therefore, the ultra-high strength titanium alloy described in this invention achieves an unprecedentedly excellent strength-plasticity balance, with a room temperature tensile strength greater than 1800 MPa and an elongation greater than 5%.

[0022] (2) By adding a large amount of β-stabilizing elements Mo, Cr, and Cu, this invention significantly improves the stability of the β phase. This prevents the secondary α phase from nucleating at the β interface and growing lamellarly into the β grains during the air cooling process after solution treatment. Instead, it precipitates as nano-needle-like particles from inside the β grains during subsequent aging. Therefore, the alloy described in this invention can be prepared with the same microstructure as that produced by traditional quenching processes without quenching, and it also exhibits higher strength and elongation. The preparation process of the ultra-high strength titanium alloy described in this invention is simple and easy to implement, while avoiding various drawbacks of water quenching: excessive quenching stress leading to deformation and cracking, insufficient hardenability leading to uneven microstructure and properties, etc. This can significantly reduce preparation costs and improve the yield of finished products, which has important engineering significance. Attached Figure Description

[0023] Figure 1 Microscopic images and room temperature quasi-static tensile stress-strain curves of the 1800MPa grade ultra-high strength titanium alloy prepared by the quench-free process described in Example 1 are shown: (a) Microscopic image; (b) Room temperature quasi-static tensile stress-strain curve.

[0024] Figure 2 Microscopic images and room temperature quasi-static tensile stress-strain curves of the 1800MPa grade ultra-high strength titanium alloy prepared by the quench-free process described in Example 2 are shown: (a) Microscopic image; (b) Room temperature quasi-static tensile stress-strain curve.

[0025] Figure 3 Microscopic images and room temperature quasi-static tensile stress-strain curves of the 1800MPa grade ultra-high strength titanium alloy prepared by the quench-free process described in Example 3 are shown: (a) Microscopic image; (b) Room temperature quasi-static tensile stress-strain curve. Detailed Implementation

[0026] The technical solution of a 1800MPa grade ultra-high strength titanium alloy prepared by a quenching-free process according to the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, the scope of protection of the present invention is not limited to these embodiments. Any changes or equivalent substitutions that do not depart from the concept of the present invention are included within the scope of protection of the present invention.

[0027] The raw materials used in the following examples include: high-purity titanium, high-purity aluminum, high-purity molybdenum, high-purity chromium, high-purity zirconium, and high-purity copper.

[0028] Example 1

[0029] The 1800MPa grade ultra-high strength titanium alloy prepared by a non-quenching process in this embodiment is composed of the following components by mass percentage: Al 4%, Mo 6%, Cr 2%, Zr 2%, Cu 2%, with the balance being Ti and unavoidable impurities.

[0030] The preparation method of 1800MPa grade ultra-high strength titanium alloy without quenching process in this embodiment is as follows:

[0031] Step 1: After mixing the raw materials according to the above-mentioned mass percentages, perform three vacuum suspension melting processes in a high-purity argon atmosphere. Before each melting process, the ingot is loaded into the furnace with its head and tail reversed. After cooling, the riser is removed to obtain a homogeneous ingot. The β-phase transformation temperature of the ingot was determined to be 820℃ by metallographic analysis.

[0032] Step 2: The ingot obtained in Step 1 is forged in one direction at 950℃ to obtain a flat ingot with a deformation of 65%.

[0033] Step 3: Roll the flat ingot obtained in Step 2 at 770°C in the two-phase region, with a rolling deformation of 85%.

[0034] Step 4: Perform solution treatment on the alloy obtained in Step 3: hold at 810℃ for 30 minutes, and then air cool to room temperature;

[0035] Step 5: Aging treatment is performed on the alloy obtained in Step 4: the alloy is held at 500℃ for 6 hours and then air-cooled to room temperature to finally obtain the 1800MPa grade ultra-high strength titanium alloy prepared by the quench-free process described in this invention.

[0036] Microstructure photographs of an 1800MPa grade ultra-high strength titanium alloy prepared by a non-quenching process in this embodiment are shown below. Figure 1 As shown in (a), after solid solution treatment in the two-phase region, the alloy retains some equiaxed primary α phases with a size less than 2 μm. After aging, nanoscale needle-like secondary α phases precipitate in the β matrix. This dual-phase structure allows the alloy to maintain a certain degree of plasticity while possessing ultra-high strength. According to the requirements of GB / T 228.1-2010 standard, the room temperature tensile strength of the titanium alloy prepared in this embodiment was measured to be 1845 MPa, and the elongation was 6.3%. Its stress-strain curve is shown below. Figure 1 As shown in (b).

[0037] Example 2

[0038] The 1800MPa grade ultra-high strength titanium alloy prepared by a non-quenching process in this embodiment is composed of the following components by mass percentage: Al 3.5%, Mo 5%, Cr 2.5%, Zr 2.5%, Cu 2%, with the balance being Ti and unavoidable impurities.

[0039] The preparation method of 1800MPa grade ultra-high strength titanium alloy without quenching process in this embodiment is as follows:

[0040] Step 1: After mixing the raw materials according to the above-mentioned mass percentages, the mixture is subjected to four vacuum suspension melting processes in a high-purity argon atmosphere. Before each melting process, the ingot is loaded into the furnace with its head and tail reversed. After cooling, the riser is removed to obtain an ingot with uniform composition. The β-phase transformation temperature of the ingot is determined to be 805℃ by metallographic analysis.

[0041] Step 2: The ingot obtained in Step 1 is forged in one direction at 950℃ to obtain a flat ingot with a deformation of 70%.

[0042] Step 3: Roll the flat ingot obtained in Step 2 at 765°C in the two-phase region, with a rolling deformation of 80%.

[0043] Step 4: Perform a solution treatment on the alloy obtained in Step 3: hold at 790℃ for 30 minutes, and then air cool to room temperature;

[0044] Step 5: Aging treatment is performed on the alloy obtained in Step 4: the alloy is held at 520℃ for 6 hours and then air-cooled to room temperature to finally obtain the 1800MPa grade ultra-high strength titanium alloy prepared by the quench-free process described in this invention.

[0045] Microstructure photographs of an 1800MPa grade ultra-high strength titanium alloy prepared by a non-quenching process in this embodiment are shown below. Figure 2 As shown in (a), the microstructure is similar to that of Example 1. After solid solution treatment in the two-phase region, the alloy retains some equiaxed primary α phases with a size of less than 2 μm. After aging, nanoscale needle-like secondary α phases precipitate in the β matrix. This dual-state microstructure allows the alloy to maintain a certain degree of plasticity while possessing ultra-high strength. According to the requirements of GB / T 228.1-2010 standard, the room temperature tensile strength of the titanium alloy prepared in this example was measured to be 1834 MPa, and the elongation was 6.7%. Its stress-strain curve is shown below. Figure 2 As shown in (b).

[0046] Example 3

[0047] The 1800MPa grade ultra-high strength titanium alloy prepared by a non-quenching process in this embodiment is composed of the following components by mass percentage: Al 4.5%, Mo 5.5%, Cr 2%, Zr 3%, Cu 2.5%, with the balance being Ti and unavoidable impurities.

[0048] The preparation method of 1800MPa grade ultra-high strength titanium alloy without quenching process in this embodiment is as follows:

[0049] Step 1: After mixing the raw materials according to the above-mentioned mass percentages, perform five vacuum suspension melting processes in a high-purity argon atmosphere. Before each melting process, the ingot is loaded into the furnace with its head and tail reversed. After cooling, the riser is cut off to obtain an ingot with uniform composition. The β-phase transformation temperature of the ingot was determined to be 815℃ by metallographic method.

[0050] Step 2: The ingot obtained in Step 1 is forged in one direction at 1000℃ to obtain a flat ingot with a deformation of 60%.

[0051] Step 3: Roll the flat ingot obtained in Step 2 at 760°C in the two-phase region, with a rolling deformation of 90%.

[0052] Step 4: Perform solution treatment on the alloy obtained in Step 3: hold at 800℃ for 30 minutes, and then air cool to room temperature;

[0053] Step 5: Aging treatment is performed on the alloy obtained in Step 4: the alloy is held at 480℃ for 6 hours and then air-cooled to room temperature to finally obtain the 1800MPa grade ultra-high strength titanium alloy prepared by the quench-free process described in this invention.

[0054] Microstructure photographs of an 1800MPa grade ultra-high strength titanium alloy prepared by a non-quenching process in this embodiment are shown below. Figure 3 As shown in (a), similar to the microstructure of Examples 1 and 2, the alloy retains some equiaxed primary α phases with a size less than 2 μm after solid solution treatment in the two-phase region. After aging, nanoscale needle-like secondary α phases precipitate in the β matrix. This dual-state microstructure allows the alloy to maintain a certain degree of plasticity while possessing ultra-high strength. According to the requirements of GB / T 228.1-2010 standard, the room temperature tensile strength of the titanium alloy prepared in this example was measured to be 1807 MPa, and the elongation was 5.9%. Its stress-strain curve is shown below. Figure 3 As shown in (b).

[0055] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A 1800MPa grade ultra-high strength titanium alloy prepared without quenching process, wherein the alloy composition by mass percentage is as follows: Al: 3%~5%, Mo: 6%~7.5%, Cr: 2%~2.5%, Zr: 2%~3%, Cu: 2%~2.5%, with the balance being Ti and unavoidable impurities.

2. The method of claim 1, wherein the non-quenched process produced 1800 MPa grade ultra-high strength titanium alloy is produced by the steps of: Includes the following steps: ​ Step 1: Mix the raw materials according to the above mass percentages and then perform multiple smelting processes to obtain a cast ingot with uniform composition. Measure the β-phase transformation temperature of the cast ingot. Step 2: Perform β single-phase region forging on the ingot obtained in Step 1 to obtain a flat ingot; Step 3: Roll the flat ingot obtained in Step 2 into the α+β two-phase region; Step 4: Perform a solution treatment on the alloy obtained in Step 3, and then cool it to room temperature; Step 5: The alloy obtained in Step 4 is subjected to aging treatment, and then cooled to room temperature to obtain an ultra-high strength titanium alloy.

3. The method of claim 2, wherein: The melting process described in step 1 involves 3 to 5 vacuum suspension melting processes in a high-purity argon atmosphere.

4. The method of claim 2, wherein: The forging temperature for the single-phase region described in step 2 is 50°C to 200°C above the β-phase transformation temperature, and the deformation is not less than 50%.

5. The method of claim 2, wherein: The rolling temperature in step 3 for the two-phase region is 20°C to 60°C below the β-phase transformation temperature, and the deformation is not less than 80%.

6. The method of claim 2, wherein: The solution treatment in step 4 involves holding the solution at 10°C to 30°C below the β-phase transformation temperature for 30 minutes.

7. The method of claim 2, wherein: The cooling method described in step 4 is air cooling.

8. The method of claim 2, wherein: The aging treatment described in step 5 involves holding the temperature at 480℃~550℃ for 6 hours.

9. The method of claim 2, wherein: The cooling method described in step 5 is air cooling.

10. The 1800 MPa grade ultra-high strength titanium alloy produced by the quenching-free process of claim 1, wherein, After heat treatment, the tensile strength of the titanium alloy is greater than 1800 MPa, and the elongation is greater than 5%.

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