A preparation method of ultra-high strength and plasticity TB8G titanium alloy

Abstract

A method for preparing an ultra-high-strength and plastic TB8G titanium alloy. The present invention relates to a method for preparing a titanium alloy. The present invention is to solve the problem of the urgent need for titanium alloys with higher strength-plasticity matching for weight reduction and performance improvement of aerospace structures in the prior art. The present invention uses high-strength and tough metastable β-type TB8 titanium alloy powder and Si powder as raw materials. By adopting a method of powder metallurgy combined with isothermal heat treatment and temperature-controlled hot extrusion, it breaks through the upper limit of 0.6wt.% Si in the melt casting method, successfully solves the brittleness induced by coarse silicides in high Si content, and precipitates dense and uniform nano-scale intracrystalline silicides in the crystal. A double-stage aging treatment is further adopted to regulate the microstructure of the heterogeneous cellular structure, thereby maintaining good plasticity while improving the room temperature strength of the material, and obtaining an ultra-high-strength and plastic TB8G titanium alloy. The present invention belongs to the field of non-ferrous metal preparation.

Description

Technical Field

[0001] The present invention relates to a method for preparing a titanium alloy, in particular to a method for preparing an ultra-high-strength and plastic TB8G titanium alloy. The present invention belongs to the technical field of non-ferrous metal preparation. Background Art

[0002] The application level of aviation titanium alloys has become one of the important indicators to measure the advancement of the new generation of aircraft and engines. However, existing titanium alloys are difficult to meet the comprehensive requirements of future aerospace for higher strength-plasticity (toughness) matching, high specific stiffness, etc., especially to meet the urgent needs of the new generation of hypersonic aircraft and cutting-edge weaponry for structural weight reduction and performance improvement. The development of ultra-high strength (tensile strength ≥1400MPa) and high plasticity and toughness titanium alloys has become one of the frontier hotspots in the research of new structural materials.

[0003] At present, alloying technology is generally used to introduce alloying elements by melt casting to obtain high-strength and toughness titanium alloys, and the Si element used to improve the strength of the alloy is controlled to be below 0.6wt% to prevent the brittleness of the material, which limits the potential of high Si enhancement. Although the strength of existing high-strength and toughness titanium alloys can still be improved through composition design and optimization of heat treatment system, the plasticity and toughness will deteriorate. Moreover, a single titanium alloy is difficult to meet the comprehensive requirements of future aviation aircraft for new structural materials such as higher strength-plasticity (toughness) matching, high stiffness and lightweight, which seriously limits its application. Therefore, it is urgent to develop new preparation technologies to improve the strength and stiffness of existing titanium alloys while maintaining sufficient plasticity and toughness. Summary of the Invention

[0004] The present invention aims to solve the urgent problem of the existing technology requiring higher strength-plasticity matching of titanium alloys for weight reduction and performance improvement of aerospace structures, and further proposes a method for preparing ultra-high strength and plasticity TB8G titanium alloy.

[0005] The technical solution adopted by the present invention to solve the above problems is:

[0006] The present invention comprises the steps of:

[0007] Step 1: Raw material powder preparation: The raw materials are spherical metastable β-type TB8 titanium alloy powder (nominal composition Ti-15Mo-2.7Nb-3Al-0.2Si, particle size 53-200 microns) and Si powder (99.96% purity, particle size 1-10 microns). The ratio of Si powder to TB8 titanium alloy powder is adjusted to design TB8-xSi alloys (x = 0.1% to 2.1% by mass) with different compositions (named TB8G). After weighing the raw material powder according to the desired alloy composition, the TB8 titanium alloy powder and Si powder are ball-milled to evenly adhere the Si powder to the surface of the TB8 particles.

[0008] Step 2: Alloy densification process: The mixed raw material powder is sintered in a vacuum hot pressing sintering furnace to finally obtain a dense TB8G alloy.

[0009] Step 3: Densification and homogenization of silicides: The sintered TB8G alloy is solution treated to completely dissolve the α phase and silicides and homogenize the Si element. The solution-state TB8G alloy is then isothermally heat treated to precipitate dense and uniform intragranular silicides, laying the foundation for subsequent temperature-controlled hot extrusion.

[0010] Step 4: Crushing of silicides and formation of heterogeneous lamellar structures: The TB8G alloy in the solution isothermal heat treatment state is hot extruded. During extrusion, the bulk material is first kept warm in a box-type heat treatment furnace. During the heat preservation, the silicides are transformed and coarsened based on the nano-scale silicides precipitated during the isothermal heat treatment, but the diameter still maintains a nano-scale size and is evenly distributed, ensuring the nano-scale size of the silicides after extrusion. At the same time, the extrusion die is kept warm, and water quenching is performed after extrusion to refine the β matrix grains and crush the grain boundary silicides. Finally, a microstructure consisting of silicide particles and a heterogeneous lamellar structure matrix composed of recrystallized layers and recovery layers is obtained.

[0011] Step 5: Controlling the Heterogeneous Cellular Structure: The extruded TB8G alloy was subjected to a two-stage aging treatment. The aging heat treatment modulated the microstructure of the extruded TB8G alloy into a heterogeneous cellular structure: the material is composed of uniformly distributed nanoscale Ti5Si3 particles, with cellular boundaries formed by nano-Widmanstätten α grain boundaries. Within the cells, a mixture of coarse and fine nano-graded α phases and pyramidal α phases distributed near the grain boundaries and Ti5Si3 particles are present, achieving a perfect balance between ultra-high strength and excellent ductility.

[0012] The excellent comprehensive performance is that the room temperature yield strength reaches 1720MPa, the tensile strength reaches 1839MPa, and the elongation is 5.5%.

[0013] The beneficial effects of the present invention are:

[0014] 1. The matrix is ​​made of TB8 metastable β titanium alloy, which has high strength exceeding 1300MPa while maintaining sufficient elongation. Compared with Ti-6Al-4V, it has better formability and lower cost than developing new alloy grades.

[0015] 2. Conventional alloying techniques, such as melt casting, control the Si content below 0.6 wt.% to prevent material brittleness, limiting the potential for high-Si enhancement. The present invention utilizes powder metallurgy combined with isothermal heat treatment to break through the 0.6 wt.% upper limit, effectively controlling silicide coarsening and resulting in the precipitation of dense and uniform nano-scale intragranular silicides.

[0016] 3. This invention utilizes temperature-controlled hot extrusion combined with a two-stage aging treatment to refine the β matrix grains and break up grain boundary silicides, ultimately achieving a microstructure composed of silicide particles and a heterogeneous lamellar matrix composed of recrystallized and recovered layers. The two-stage aging treatment further modulates the TB8G alloy microstructure into a heterogeneous cellular structure, achieving a balance between ultrahigh strength and excellent ductility.

[0017] 4. The present invention gives full play to the role of high Si reinforcement: it plays a role of solid solution strengthening; solid solution Si reduces the ability of dislocation movement, inhibits dynamic recrystallization, and refines grains; promotes the precipitation of nano-graded α phase within the grain, enhances the ability of intracrystalline work hardening, and improves strength; inhibits the continuous grain boundary α phase, promotes the precipitation of nano-Widmanstätten structure α phase at the grain boundary, strengthens the grain boundary, improves the matching of grain boundary / intracrystalline deformation, and is beneficial to plasticity; high addition of Si promotes the precipitation of Ti5Si3, which acts as a second relative material for strengthening. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a preparation flow chart of the present invention;

[0019] Figure 2 This is the TEM characterization of the double-stage aging microstructure cellular structure of the present invention. Among them, (a) TEM morphology; (b) statistics of nano-graded α phase in the grain; (c) pyramidal α atomic image; (d) α atomic image of nano-Widmanstätten structure at the grain boundary;

[0020] Figure 3 This is the room temperature tensile engineering stress-strain curve of the double-stage aged TB8G alloy. DETAILED DESCRIPTION

[0021] Specific embodiment 1: This embodiment adopts a powder metallurgy preparation method, introduces a high-mass fraction of Si element; adopts a solid solution combined with isothermal heat treatment method to precipitate dense and uniform nano-scale intracrystalline silicide in the crystal, which serves as a precursor for the precipitation of Ti5Si3 in the subsequent hot extrusion and heat preservation process; adopts a temperature-controlled hot extrusion combined with a two-stage aging treatment method to control the microstructure of the TB8G alloy into a heterogeneous cellular structure. This embodiment is prepared according to the following steps:

[0022] Step 1: Prepare raw powder: Adjust the ratio of Si powder and TB8 titanium alloy powder to design TB8-xSi alloys with different compositions. After weighing the raw powder according to the required alloy composition, the TB8 titanium alloy powder and Si powder are ball-milled to mix them so that the Si powder is evenly attached to the surface of the TB8 particles.

[0023] Step 2: Alloy densification process: The mixed raw material powder is sintered in a vacuum hot pressing sintering furnace to obtain a dense TB8G alloy.

[0024] Step 3: Densification and homogenization of silicide: Solution treatment and isothermal heat treatment are performed on the sintered TB8G alloy to lay the organizational foundation for subsequent temperature-controlled hot extrusion;

[0025] Step 4: Crushing of silicide and formation of heterogeneous lamellar structure: hot extruding the TB8G alloy in the solid solution isothermal heat treatment state to obtain the extruded TB8G alloy;

[0026] Step 5. Regulation of heterogeneous cellular structure: The extruded TB8G alloy is subjected to a double-stage aging treatment to obtain an aged TB8G alloy.

[0027] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the mass percentage of x in the TB8-xSi alloy described in step 1 of this embodiment is 0.1% to 2.1%; the TB8 titanium alloy powder and Si powder are ball-milled, wherein the rotation speed is 100 to 340 rpm, the ball-to-material ratio is 2:1 to 10:1, the mixing time is 2 to 15 hours, and the ball-milling atmosphere is Ar gas.

[0028] The rest is the same as the first specific implementation method.

[0029] Specific embodiment three: The difference between this embodiment and specific embodiment one or two is that the raw materials described in step one of this embodiment are spherical metastable TB8 titanium alloy powder and Si powder, wherein the nominal composition of the TB8 titanium alloy powder is Ti-15Mo-2.7Nb-3Al-0.2Si, and the particle size is 53 to 200 microns; the purity of the Si powder is 99.96%, and the particle size is 1 to 10 microns.

[0030] The rest is the same as the first or second embodiment.

[0031] Specific embodiment 4: This embodiment differs from one of specific embodiments 1 to 3 in that the solution temperature of the solution treatment in step 3 of this embodiment is 800-1300° C., and the solution is kept at this temperature for 0.5-5 hours before water quenching.

[0032] The rest is the same as that of the first to third embodiments.

[0033] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the temperature of the isothermal heat treatment in step 3 of this embodiment is 500° C. to 1100° C., and the isothermal treatment is carried out for 15 min to 5 h before water quenching.

[0034] The rest is the same as that of the first to fourth embodiments.

[0035] Specific embodiment six: The difference between this embodiment and any one of specific embodiments one to five is that the purpose of the isothermal heat treatment described in step three of this embodiment is to precipitate dense and uniform intracrystalline silicide in the crystal, which serves as a precursor for the precipitation of Ti5Si3 in the subsequent hot extrusion and insulation process.

[0036] The rest is the same as that of the specific implementation modes 1 to 5.

[0037] Specific embodiment seven: The difference between this embodiment and any one of specific embodiments one to six is ​​that the temperature-controlled hot extrusion described in step four of this embodiment is to first heat treat the block material in a box-type heat treatment furnace, keep it warm at 800-1300°C for 0.5-5h, the insulation temperature of the extrusion die is 300-1000°C, the extrusion ratio is 6:1-16:1, and water quenching is performed after extrusion.

[0038] The rest is the same as that of the specific embodiments 1 to 6.

[0039] Specific embodiment eight: The difference between this embodiment and any one of specific embodiments one to seven is that the purpose of the temperature-controlled hot extrusion described in step four of this embodiment is to refine the β matrix grains and crush the grain boundary silicides; and ultimately obtain a microstructure composed of silicide particles and a heterogeneous lamellar structure matrix composed of recrystallized layers and recovery layers.

[0040] The rest is the same as that of the specific implementation modes 1 to 7.

[0041] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the double-stage aging treatment described in step 5 of this embodiment is to keep the temperature at 300-400°C for 8-150 hours and then air-cool, and then keep the temperature at 500-800°C for 2-72 hours and then air-cool.

[0042] The rest is the same as that of Specific Embodiments 1 to 8.

[0043] Specific embodiment ten: This embodiment differs from any one of specific embodiments one to nine in that the microstructure of the TB8G alloy after the double-stage aging treatment described in step five of this embodiment is controlled to be a heterogeneous cellular structure: that is, the material as a whole is composed of uniformly distributed nano-scale Ti5Si3 particles, cellular boundaries composed of nano-Widmanstätten structure α grain boundaries, and the cells are composed of a coarse and fine mixed nano-graded α phase and a pyramidal α phase distributed near the grain boundaries and near the Ti5Si3 particles.

[0044] The rest is the same as that of Specific Embodiments 1 to 9.

[0045] Example 1:

[0046] 1. Raw material powder preparation. The raw materials are spherical metastable β-type TB8 titanium alloy powder (nominal composition Ti-15Mo-2.7Nb-3Al-0.2Si, particle size 53-200 microns) and Si powder (purity 99.96%, particle size 1-10 microns). The ratio of Si powder to TB8 titanium alloy powder was adjusted to design TB8-xSi (x = 0.1% to 2.1%, mass fraction) alloys with different compositions (named TB8G). After weighing the raw material powder according to the required alloy composition, the TB8 titanium alloy powder and Si powder were ball-milled (rotation speed 100-340 rpm, ball-to-powder ratio 2:1-10:1, mixing time 2-15 hours, ball-to-powder atmosphere in Ar gas) to ensure that the Si powder is evenly attached to the surface of the TB8 particles.

[0047] 2. Alloy densification process: The mixed raw material powder is sintered in a vacuum hot pressing sintering furnace (sintering temperature is 900-1400℃, pressure is 50Mpa, and sintering time is 1-10h) to finally obtain a dense TB8G alloy.

[0048] 3. Densification and homogenization of silicides. Solution treatment was performed on the sintered TB8G alloy. The solution temperature was 800-1300°C, and the solution was kept at this temperature for 0.5-5 hours before water quenching. Isothermal heat treatment was performed on the solution-state TB8-0.9Si alloy (temperature was 500-1100°C, and the solution was kept at this temperature for 15 minutes to 5 hours before water quenching).

[0049] 4. Crushing of silicides and formation of heterogeneous lamellar structures. The TB8G alloy after solid solution isothermal heat treatment was hot extruded at an extrusion temperature of 8000-1300℃, a preheating time of 0.5-5h, an extrusion die insulation temperature of 300-1000℃, an extrusion ratio of 6:1-16:1, and water quenching after extrusion.

[0050] 5. Control of heterogeneous cellular structure: The extruded TB8G alloy was subjected to a double-stage aging treatment (holding at 300-400°C for 8-150 hours followed by air cooling, and then holding at 500-800°C for 2-72 hours followed by air cooling).

[0051] In this embodiment, the microstructure of the extruded TB8G alloy is regulated to a heterogeneous cellular structure after aging heat treatment: that is, the material as a whole is composed of uniformly distributed nano-sized Ti5Si3 particles, nano-Widmanstätten structure α grain boundaries (α WGB ) form a cellular boundary with an average size of ~5 μm, and the cell is composed of a nano-graded α phase (α HS ) and the pyramidal α phase (α pyramid ) to achieve a match between ultra-high strength and good plasticity. The cellular boundary is composed of nano-Widmanstätten structure α grain boundaries, and the cell is composed of coarse and fine mixed nano-graded α phase and pyramidal α distributed near the grain boundaries and particles.

[0052] The excellent comprehensive performance is that the room temperature yield strength reaches 1720MPa, the tensile strength reaches 1839MPa, and the elongation is 5.5%.

[0053] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement of the above embodiments made according to the technical essence of the present invention, within the spirit and principles of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing ultra-high strength and plasticity TB8G titanium alloy, characterized by: It includes the following steps: Step 1: Prepare raw powder: Adjust the ratio of Si powder and TB8 titanium alloy powder to design a TB8-xSi alloy, named TB8G. After weighing the raw powder according to the desired alloy composition, the TB8 titanium alloy powder and Si powder are ball-milled to uniformly adhere the Si powder to the surface of the TB8 particles. The mass percentage of x in the TB8-xSi alloy is 0.1% to 2.1%. The composition of the TB8 titanium alloy powder is Ti-15Mo-2.7Nb-3Al-0.2Si. Step 2: Alloy densification process: The mixed raw material powder is sintered in a vacuum hot pressing sintering furnace to obtain a dense TB8G alloy; Step 3: Densification and homogenization of silicide: The sintered TB8G alloy is subjected to solution treatment and isothermal heat treatment to lay the foundation for the subsequent temperature-controlled hot extrusion. The isothermal heat treatment temperature in step 3 is 500°C to 1100°C, and the temperature is kept for 15 minutes to 5 hours before water quenching. Step 4: Crushing of silicides and formation of heterogeneous lamellar structures: The TB8G alloy in the solution isothermal heat treatment state is subjected to temperature-controlled hot extrusion to obtain an extruded TB8G alloy; the temperature-controlled hot extrusion is performed by placing the bulk material in a box-type heat treatment furnace for heat treatment at a treatment temperature of 800-1300°C for a holding time of 0.5-5 hours, the holding temperature of the extrusion die is 300-1000°C, the extrusion ratio is 6:1-16:1, and water quenching is performed after extrusion; Step 5. Regulation of heterogeneous cellular structure: The extruded TB8G alloy is subjected to a double-stage aging treatment to obtain an aged TB8G alloy.

2. The method for preparing an ultra-high strength and plasticity TB8G titanium alloy according to claim 1, characterized in that: In step 1, TB8 titanium alloy powder and Si powder are ball-milled at a rotation speed of 100-340 rpm, a ball-to-material ratio of 2:1-10:1, a mixing time of 2-15 h, and an Ar gas atmosphere.

3. The method for preparing an ultra-high strength and plasticity TB8G titanium alloy according to claim 1, characterized in that: The raw material powders described in step 1 are spherical metastable TB8 titanium alloy powder and Si powder with a particle size of 53 to 200 microns; the purity of the Si powder is 99.96% and the particle size is 1 to 10 microns.

4. The method for preparing an ultra-high strength and plasticity TB8G titanium alloy according to claim 1, characterized in that: The solution temperature of the solution treatment described in step 3 is 800~1300℃, and it is kept at this temperature for 0.5~5h and then water quenched.

5. The method for preparing an ultra-high strength and plasticity TB8G titanium alloy according to claim 1, characterized in that: The double-stage aging treatment described in step 5 is to keep the temperature at 300-400°C for 8-150 hours and then air cool, and then keep the temperature at 500-800°C for 2-72 hours and then air cool.

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