A method for improving the high-temperature strength and plasticity of TC4 alloy plate

Abstract

The application discloses a plate composite method for improving high-temperature strength and plasticity of TC4 alloy, and belongs to the field of alloy materials and preparation technologies. The application solves the problem that the existing TC4 alloy cannot maintain high strength and poor plasticity for a long time when serving at a temperature of 400 DEG C or above for a long time. The TC4 and TC17 are compounded by using a three-layer composite plate preparation method, the TC17 is used as an intermediate functional layer, and the TC17 has excellent high-temperature strength, fracture toughness and thermal stability, and can bear the main load at high temperature; the TC4 is used as a surface layer, the TC4 has good high-temperature plasticity, medium-temperature strength and mature process characteristics, and can ensure the overall plasticity and processability of the composite plate at room temperature and at medium temperature, the composite plate has excellent high-temperature strength and long-term service reliability, the comprehensive performance of the TC4 alloy at a temperature of 400 DEG C or above is improved, and a solution is provided for solving the high-temperature performance and weight reduction demand of key components in aviation and aerospace equipment.

Description

Technical Field

[0001] This invention belongs to the field of alloy materials and their preparation technology, and relates to a method for improving the high-temperature strength and plasticity of TC4 alloy composite plates. Background Technology

[0002] Titanium and titanium alloys, due to their excellent specific strength, corrosion resistance, and good mid-temperature properties, have become indispensable key structural materials in cutting-edge fields such as aerospace, shipbuilding, petrochemicals, and biomedicine since the mid-20th century. Among them, TC4 (Ti-6Al-4V) titanium alloy, as a typical representative of α+β type two-phase titanium alloys, is currently the most widely used and consumed titanium alloy due to its good comprehensive mechanical properties, mature processing technology, and relatively low manufacturing cost, earning it the title of "universal titanium alloy." TC4 alloy is extremely commonly used in critical load-bearing components of aero-engines, such as fan blades, compressor disks, and casings, as well as in aircraft fuselage beams, bulkheads, and skins.

[0003] However, with the continuous development of aerospace technology towards high speed, high maneuverability, long lifespan, and high reliability, modern aircraft and their propulsion systems place increasingly stringent demands on the performance of high-temperature structural materials. Especially for high thrust-to-weight ratio engines and thermal protection structures of high-speed aircraft, their service temperatures far exceed the limits of conventional TC4 alloys. As a medium-strength titanium alloy, the long-term operating temperature of TC4 alloy is typically limited to below 400℃. When the ambient temperature exceeds 400℃, the mechanical properties of TC4 alloy face two major bottlenecks: first, a sharp decrease in high-temperature strength, mainly manifested in a significant reduction in tensile strength and yield strength, leading to excessive plastic deformation or even fracture under high-temperature loads; second, insufficient high-temperature oxidation resistance and thermal stability, with a loose oxide layer easily forming on the surface, and the β phase in the microstructure potentially decomposing, leading to material embrittlement and severely affecting the service life and reliability of components. Therefore, how to break through the upper limit of the operating temperature of TC4 alloy while maintaining or improving its strength-toughness balance under high-temperature environments has become a critical problem that urgently needs to be solved.

[0004] Material composite technology offers a new approach to solving the aforementioned problems. In the development of composite materials, interfacial bonding strength is a core factor determining the overall performance of the material, especially for titanium-based composites in high-temperature environments. Currently, existing research still has significant shortcomings in core areas such as interface design, high-temperature strengthening, and precision manufacturing of high-performance titanium alloy-based composite structures. The potential for improving the high-temperature performance of monolithic material composite structures is very limited. Traditional adhesive or welded interfaces are prone to stress concentration and interface failure under thermal cycling loads, severely restricting the long-term reliability of materials in extreme environments. Therefore, there is an urgent need to develop a TC4 composite material with high interfacial bonding strength. Summary of the Invention

[0005] In order to solve the problem that existing TC4 alloys cannot maintain high strength and poor plasticity for long-term service at temperatures of 400°C and above, this invention provides a plate composite method to improve the high-temperature strength and plasticity of TC4 alloys.

[0006] The technical solution of the present invention is as follows: One objective of this invention is to provide a method for improving the high-temperature strength and plasticity of TC4 alloy sheet composites, the method comprising the following steps: Step 1: Sand the TC4 and TC17 boards, then pickle them, clean them with ethanol and blow them dry, and set them aside. Step 2: Spray a release agent onto the inner wall and bottom of the mold; Step 3: Take two TC4 sheets and one TC17 sheet, and stack them in the order of TC4, TC17 and TC4 from bottom to top. Place the stacked sheets into the mold that has been sprayed with release agent. Step 4: Press the mold, heat it step by step to the hot pressing temperature under vacuum and certain pressure conditions, and keep it at the temperature. After the holding time is completed, cool it to obtain TC4 composite board.

[0007] Further specifying, the TC4 plate in step 1 is a thin plate with a thickness of 1mm obtained by rolling, which is homogenized and annealed, and has a size of 50mm×50mm×1mm.

[0008] Furthermore, the homogenization annealing parameters are specified as follows: 940-960℃ for 1.5-2 hours, followed by air cooling. This process effectively eliminates the segregation of internal components in the material, achieves homogenization of the microstructure, and lays the foundation for subsequent heat treatment.

[0009] Further specifying, in step 1, TC17 is a block material obtained by forging, and a 1mm plate obtained by thin cutting, with dimensions of 50mm×50mm×1mm.

[0010] To further specify, in step 1, 400-grit sandpaper is used to sand the TC4 and TC17 plates until the surface has scratches in only one direction.

[0011] Further specifying, the liquid used for pickling in step 1 is a mixture of hydrofluoric acid, nitric acid and water in a volume ratio of 1:3:6.

[0012] Further specifying, the pickling time in step 1 is 1-5 minutes.

[0013] To further specify, in step 4, before pressing the mold, the mold with the plate material is placed into the vacuum hot press furnace, and when placing it in, ensure that the mold is located in the center position of the press slide.

[0014] Further specifying, the vacuum condition in step 4 is to evacuate to 10... -2 Pa, with a pressure of 2-10 MPa.

[0015] Further specifying, the step-by-step heating process in step 4 is as follows: first, heat to 100-300℃ in 20-60 minutes, do not hold the temperature, and then continue to heat to the hot-pressing temperature in 40-80 minutes.

[0016] To further define the process, the step-by-step heating process in step 4 is as follows: first, heat the temperature to 200°C for 40 minutes, and then continue heating to the hot-pressing temperature for 60 minutes without holding the temperature.

[0017] Further specified, the hot pressing temperature in step 4 is 750-850℃, and the holding time is 30-90min.

[0018] Furthermore, the hot pressing temperature in step 4 is 800℃, and the holding time is 60min.

[0019] To further specify, in step 4, after the heat preservation is completed, the heating system should be turned off first, followed by the pressure system.

[0020] Further specifying, in step 4, after cooling, the vacuum system is shut off, and then the furnace is opened to remove the workpiece.

[0021] The second objective of this invention is to provide a TC4 composite board prepared by the above method, which has a tensile strength ≥778MPa and an elongation ≥17.5% at 400℃, and a tensile strength ≥691MPa and an elongation ≥27% at 500℃.

[0022] The beneficial effects of this invention are as follows: (1) This invention forms a sandwich-structured TC4 composite plate by layering TC4 alloy and TC17 alloy. The synergistic effect of TC4 alloy and TC17 alloy structure achieves a synergistic effect of 1+1>2. The surface layer of TC4 alloy gives the plate excellent high-temperature plasticity, medium-temperature strength and mature machinability, ensuring the overall molding capability of the composite plate under normal temperature and medium temperature conditions; the core layer of TC17 alloy is rich in β-stabilizing elements such as Mo and Cr, which makes the composite plate have excellent high-temperature strength, fracture toughness and thermal stability. When the composite board is used in a high-temperature environment of 400℃-500℃, the strength of the TC4 surface layer decreases due to the temperature rise, which is effectively compensated by the strong load-bearing TC17 core layer. This is a deep synergy between the two under thermo-mechanical coupling conditions: the core layer makes up for the high-temperature shortcomings of TC4, while the surface layer provides plastic protection and process feasibility for TC17, which has a higher tendency to brittleness. This increases the overall high-temperature service temperature of the composite board to about 500℃, while achieving both high-temperature strength and fracture toughness. This comprehensive performance of high strength and good plasticity cannot be achieved by TC4 or TC17 materials alone, realizing the synergistic effect of high-temperature strength and fracture toughness.

[0023] (2) The TC4 three-layer composite plate prepared by this invention has an interface constraint effect. When subjected to external loads, if a crack initiates in the surface TC4 layer and extends to the TC4 / TC17 interface, the high strength and high elastic modulus of the TC17 core layer will blunt or deflect the crack tip, hindering the rapid penetration of the crack, thereby significantly improving the material's resistance to crack propagation. At the same time, the good plasticity of the TC4 surface layer can absorb some of the impact energy, avoiding the risk of brittle fracture caused by the relatively insufficient plasticity of the core layer TC17. This structural design enables the composite plate to obtain high strength while retaining good toughness, exhibiting excellent damage tolerance characteristics, and is particularly suitable for aerospace structural components subjected to complex alternating loads.

[0024] (3) This invention employs vacuum diffusion bonding technology. Under conditions of hot pressing temperature of 750-850℃, holding time of 30-60min, and pressure of 2-10MPa, interatomic diffusion occurs at the interface between TC4 and TC17, forming a strong metallurgical bonding layer. Compared with traditional explosive welding or fusion welding, this method has high interface bonding strength, no porosity or inclusion defects, and can precisely control the thickness of the interface diffusion layer, avoiding the formation of brittle intermetallic compounds at the interface due to excessive alloying diffusion. This high-integrity interface not only ensures the continuity of interlayer stress transmission but also prevents cracking or peeling of the interface during subsequent hot working or heat treatment of the composite plate, ensuring the long-term reliability of the product.

[0025] (4) The method provided by the present invention is simple and the key parameters such as vacuum degree, temperature, pressure and time are easy to control accurately and repeat, which ensures the stability and consistency of product quality and meets the requirements of large-scale industrial production. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the stacking of TC4 composite panels in Example 1; Figure 2 Comparison of the high-temperature tensile curves of TC4 alloy alone and TC4 composite plate prepared in Example 1 at 400℃; Figure 3 Comparison of the high-temperature tensile curves of TC4 alloy alone and TC4 composite plates prepared in Example 1 at 500℃; Figure 4 The diffusion bonding interface of TC4 / TC17 in the TC4 composite plate prepared in Example 1; Figure 5 Comparison of high-temperature tensile curves at 400°C for composite plates prepared with TC4 alloy alone, Example 1, and Comparative Examples 1-2; Figure 6 The diffusion bonding interface of TC4 / TC17 in the TC4 composite plate prepared in Comparative Example 3. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0031] Example 1 Step 1: Sand two TC4 boards measuring 50mm×50mm×1mm and one TC17 board measuring 50mm×50mm×1mm until smooth. During the sanding process, ensure that the scratches on each board are in the same direction. Then remove surface oil and wash the three boards with a combination of hydrofluoric acid, nitric acid and water (volume ratio) of 1:3:6 for 2 minutes to remove impurities. After washing, clean them with anhydrous ethanol and dry them for later use. Step 2: Spray boron nitride as a release agent onto the inner wall and bottom of the mold; Step 3: Stack the two processed TC4 sheets and one TC17 sheet in the order of TC4, TC17 and TC4 from bottom to top, and then place them into the mold that has been sprayed with release agent. Step 4: Place the mold with the plate material loaded in Step 4 into the vacuum hot press furnace, ensuring that the mold is located in the center of the press slide, and press the mold tightly; Step 5: Evacuate to 10 -2 Pa, set the pressure to 10MPa, heat to 200℃ in 40min, then heat to 800℃ in 60min and hold for 60min. After holding, first turn off the heating system and then the pressure system, cool, then turn off the vacuum system, open the furnace and take out the part to obtain a TC4 / TC17 / TC4 three-layer composite plate, which is denoted as TC4 composite plate. TC4 plate is used as tough matrix and TC17 is used as high temperature and high strength core layer.

[0032] The preparation process in this embodiment is as follows: Figure 1 As shown. Figure 2 The high-temperature tensile stress-strain curves of the TC4 sheet alone and the TC4 composite sheet of this embodiment at 400℃ show that the tensile strength of the TC4 sheet is 675MPa in the high-temperature tensile test at 400℃, while the tensile strength of the TC4 composite sheet of this invention is 778MPa, an increase of 15.2%; the elongation of the TC4 sheet is 15%, while the elongation of the TC4 composite sheet of this invention is 17.5%, an increase of 16.6%. At the service temperature of the TC4 sheet, the tensile strength and elongation of the TC4 composite sheet are both improved, exhibiting both good high-temperature strength and plasticity.

[0033] Figure 3The high-temperature tensile stress-strain curves of TC4 sheet and TC4 composite sheet of this embodiment at 500℃ show that the tensile strength of TC4 sheet is 598MPa in the 500℃ high-temperature tensile test, while the tensile strength of TC4 composite sheet of this invention is 691MPa, an increase of 15.5%; the elongation of TC4 sheet is 19%, while the elongation of TC4 composite sheet of this invention is 27%, an increase of 42.1%. In the 500℃ high-temperature tensile test, which is higher than the service temperature of TC4 sheet, the tensile strength and elongation of TC4 composite sheet are both higher than those of the original TC4 sheet, demonstrating both good high-temperature strength and plasticity.

[0034] The microstructure of the diffusion interface of TC4 / TC17 prepared in this embodiment is as follows: Figure 4 As shown, the diffusion interface is mainly composed of lath-like structures, with the grains of the parent materials on both sides continuously growing across the original interface, forming a reliable metallurgical bond. The absence of defects such as pores, microcracks, or unconnected areas in the interface region indicates that atomic diffusion was sufficient and the interface structure was dense and complete under the set temperature, pressure, and holding time.

[0035] Comparative Example 1 The difference between this comparative example and Example 1 is that: in step 1, the TC17 plate is replaced with a Ti55 plate, that is, the core material of the composite plate is Ti55; in step 5, the pressure is 20MPa, the temperature is raised to 200℃ in 60 minutes, and then raised to 950℃ in 90 minutes; the remaining process operations and parameter settings are the same as in Example 1, and a three-layer composite plate of TC4 / Ti55 / TC4 is obtained, which is denoted as TC4 composite plate. The TC4 plate is used as a tough matrix, and Ti55 is used as a high-temperature and high-strength core layer.

[0036] Comparative Example 2 The difference between this comparative example and Example 1 is that: in step 1, the TC17 plate is replaced with a Ti750S plate, that is, the core material of the composite plate is Ti750S; in step 5, the pressure is 30MPa, the temperature is raised to 200℃ in 60 minutes, and then raised to 900℃ in 90 minutes; the remaining process operations and parameter settings are the same as in Example 1, and a three-layer composite plate of TC4 / Ti750S / TC4 is obtained, which is referred to as TC4 composite plate. TC4 plate is used as a tough matrix, and Ti750S is used as a high-temperature and high-strength core layer.

[0037] Figure 5 Comparison of tensile stress-strain curves at 400°C for individual TC4 sheets, TC4 composite sheets of Example 1, and Comparative Examples 1-2. Figure 5It can be seen that in the high-temperature tensile test at 400℃, the tensile strength of the TC4 sheet alone is 675MPa, and the elongation is 15%; the tensile strength of the TC4 / Ti750S / TC4 three-layer composite sheet is 691MPa, which is an increase of 2.3%, and the elongation is 15.5%, which is an increase of 3.3%; the tensile strength of the TC4 / Ti55 / TC4 three-layer composite sheet is the same as that of the TC4 sheet alone, which is 675MPa, and the elongation is 16%, which is an increase of 6.7%; while the tensile strength of the TC4 / TC17 / TC4 three-layer composite sheet of the present invention is 778MPa, which is an increase of 15.2%, and the elongation is 17.5%, which is an increase of 16.6%. In summary, the tensile strength and elongation of the TC4 / TC17 / TC4 three-layer composite plates, TC4 / Ti55 / TC4 three-layer composite plates, and TC4 / Ti750S / TC4 three-layer composite plates all improved compared to the pure TC4 plate in the high-temperature tensile test at 400℃, but still could not exceed 700MPa. The TC4 / TC17 / TC4 three-layer composite plate had the best overall performance.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that: a vacuum was drawn to 10... -2 Pa, set the pressure to 10MPa, heat to 200℃ in 30min, then heat to 700℃ in 60min and hold for 30min. The remaining process operations and parameter settings are the same as in Example 1, and a TC4 / TC17 / TC4 three-layer composite board is obtained, which is denoted as TC4 composite board.

[0039] The microstructure of the diffusion interface of TC4 / TC17 prepared in this comparative example is as follows: Figure 6 As shown, it can be seen that lowering the temperature leads to insufficient atomic activity, hindered interface closure and diffusion behavior, and the two parent materials fail to achieve complete metallurgical bonding, resulting in obvious unclosed pores.

[0040] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for improving the high-temperature strength and plasticity of TC4 alloy sheet composites, characterized in that, The method includes the following steps: Step 1: Sand the TC4 and TC17 boards, then pickle them, clean them with ethanol and blow them dry, and set them aside. Step 2: Spray a release agent onto the inner wall and bottom of the mold; Step 3: Take two TC4 sheets and one TC17 sheet, and stack them in the order of TC4, TC17 and TC4 from bottom to top. Place the stacked sheets into the mold that has been sprayed with release agent. Step 4: Press the mold, heat it step by step to the hot pressing temperature under vacuum and certain pressure conditions, and keep it at the temperature. After the holding time is completed, cool it to obtain TC4 composite board.

2. The method according to claim 1, characterized in that, In step 1, the TC4 sheet is a thin sheet with a thickness of 1 mm obtained by rolling. The sheet is homogenized and annealed, and its dimensions are 50 mm × 50 mm × 1 mm.

3. The method according to claim 2, characterized in that, Homogenization annealing parameters: 940-960℃, hold for 1.5-2 hours, then air cool.

4. The method according to claim 1, characterized in that, In step 1, TC17 is a block material obtained by forging, and a 1mm plate obtained by thin cutting, with a size of 50mm×50mm×1mm.

5. The preparation method according to claim 1, characterized in that, The liquid used for pickling in step 1 is a mixture of hydrofluoric acid, nitric acid and water in a volume ratio of 1:3:

6.

6. The preparation method according to claim 1, characterized in that, The pickling time in step 1 is 1-5 minutes.

7. The preparation method according to claim 1, characterized in that, In step 4, the vacuum condition is to evacuate to 10... -2 Pa, with a pressure of 2-10 MPa.

8. The method according to claim 1, characterized in that, The step-by-step heating process in step 4 is as follows: First, heat the temperature to 100-300℃ for 20-60 minutes, do not hold the temperature, and then continue to heat the temperature to the hot pressing temperature for 40-80 minutes.

9. The method according to claim 1, characterized in that, In step 4, the hot pressing temperature is 750-850℃, and the holding time is 30-90 minutes.

10. A TC4 composite sheet obtained by the composite method according to any one of claims 1-9, characterized in that, Tensile strength at 400℃ ≥778MPa, elongation ≥17.5%; tensile strength at 500℃ ≥691MPa, elongation ≥27%.

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