Titanium matrix composite sheet having equiaxed microstructure and method of heat treating the same

Abstract

The present application relates to a kind of titanium matrix composite sheet with equiaxed structure and its heat treatment method, comprising the following steps: on the side of pure titanium plate and / or titanium alloy plate and titanium matrix composite sheet contact, coating stop solder, as the upper and lower cladding of sandwich titanium matrix composite sheet;The upper and lower cladding are placed in the uppermost layer and the lowermost layer of titanium matrix composite sheet or titanium matrix composite sheet stack respectively;The stack of the above-mentioned step is sealed after being placed as a whole, then vacuumizing, obtain the cladding with vacuum inside;The cladding with vacuum inside is heat treated, obtain the titanium matrix composite sheet with equiaxed structure;The titanium matrix composite sheet with equiaxed structure is diffusion connected;Its purpose is to realize the diffusion connection of high welding rate, reach the purpose of high quality weld and superplastic deformation capacity.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy heat treatment technology, and particularly relates to a titanium-based composite sheet with equiaxed structure and its heat treatment method. Background Technology

[0002] Titanium-based composites, as high-temperature structural materials for aerospace applications, can be used for hypersonic skins and forgings. Superplastic forming and superplastic forming / diffusion bonding (SPF / DB) technology is a low-cost, high-efficiency, and near-marginal component manufacturing technology that can produce integral hollow structural components in a single thermal cycle, thus reducing structural weight. Due to the addition of reinforcing phases to titanium-based composites, their microstructure is more complex, their phase transformation point is higher, and their deformation resistance is increased. Therefore, the diffusion bonding requirements for titanium-based composites are higher than those for conventional titanium alloys (such as TC4, TA15, and TA32), and it is even difficult to achieve high-weld-rate diffusion bonding on engineered equipment, severely impacting the application of titanium-based composites in SPF / DB technology. Currently, methods to achieve a high weld rate of 90% for titanium-based composites include high-temperature and high-pressure methods, with diffusion bonding temperatures exceeding 970℃, diffusion bonding pressures reaching 3.0 MPa to 5.0 MPa, and diffusion bonding times of 3 to 4 hours. From the perspective of diffusion bonding theory, equiaxed fine-grained microstructure is a relatively ideal microstructure for diffusion bonding. Increased grain boundary density and reduced grain boundary size are beneficial for achieving high-quality welds. For ordinary titanium alloys, equiaxed fine-grained microstructure is usually obtained by controlling rolling process parameters. However, for titanium-based composites, it is difficult to obtain equiaxed fine-grained microstructure through low-temperature rolling and static recrystallization. In addition, equiaxed fine-grained microstructure is also beneficial for improving the superplastic deformation capacity of materials.

[0003] Traditional methods for preparing equiaxed fine-grained microstructures mainly involve controlling the rolling process. For example, for titanium alloys such as TC4, TA15, and TA32, T... β Rolling at -40 to 60℃ with multiple passes and varying deformation amounts achieves grain breakage and dynamic recrystallization to obtain an equiaxed fine-grained microstructure. However, titanium-based composites are highly sensitive to deformation temperature; low temperatures easily lead to cracking. Therefore, titanium-based composites are typically rolled in the transphase region, resulting in a lamellar microstructure. Figure 1 The microstructure of a 1.2 mm thick titanium-based composite sheet is shown. Summary of the Invention

[0004] This invention addresses the above-mentioned problems by proposing a titanium-based composite sheet with equiaxed structure and its heat treatment method. The purpose is to achieve diffusion bonding with high weldability, resulting in high-quality welds and superplastic deformation capabilities.

[0005] To achieve the above objectives, the present invention provides a heat treatment method for a titanium-based composite sheet with an equiaxed microstructure for diffusion bonding, comprising the following steps:

[0006] A weld nugget is applied to the side of the pure titanium plate and / or titanium alloy plate that is in contact with the titanium-based composite sheet, serving as an upper and lower sleeve for enclosing the titanium-based composite sheet.

[0007] The upper sleeve and the lower sleeve are respectively placed on the top and bottom layers of the titanium-based composite sheet or the titanium-based composite sheet stack;

[0008] After the above steps are completed, the entire stack is encased, welded, and sealed, and then a vacuum is drawn to obtain an encasing with an internal vacuum.

[0009] The inner vacuum of the cladding is heat-treated to obtain a titanium-based composite sheet with an equiaxed structure.

[0010] The titanium-based composite sheet with equiaxed structure is diffuse-bonded.

[0011] Furthermore, the heat treatment step of the vacuum-filled cladding includes: placing the vacuum-filled cladding in a gas diffusion furnace or a heat treatment furnace capable of applying gas pressure, heating it to 950-970°C, applying a gas pressure of 0.5-3 MPa after reaching the temperature, holding it at the temperature and pressure for 2-3 hours, and then cooling it in the furnace.

[0012] Furthermore, after heat treatment, the process also includes conventional surface pickling of the heat-treated titanium-based composite sheet.

[0013] Furthermore, the process parameters for the diffusion connection include: a diffusion connection temperature of 940–960°C, a diffusion connection pressure of 1.5–2.0 MPa, and a heat and pressure holding period of 1.5–2 hours.

[0014] Furthermore, before placing the upper and lower sleeves on the top and bottom layers of the titanium-based composite sheet or the titanium-based composite sheet stack, respectively, the surface of the titanium-based composite sheet or the titanium-based composite sheet stack is pretreated according to the requirements for surface flatness and cleanliness.

[0015] Furthermore, the surface pretreatment of the titanium-based composite sheet or the titanium-based composite sheet stack includes: pretreatment of the surface by steel brush grinding, mechanical grinding, sanding or chemical cleaning.

[0016] Furthermore, the grain size of the equiaxed structure is less than 10 μm.

[0017] To achieve the above objectives, the present invention provides a titanium-based composite sheet with an equiaxed structure, characterized in that it is prepared by the heat treatment method of the titanium-based composite sheet with an equiaxed structure based on diffusion bonding.

[0018] The above-mentioned technical solution of the present invention has the following advantages: by sandwiching a titanium-based composite thin plate or a titanium-based composite thin plate stack between a pure titanium plate and / or a titanium alloy plate, then performing encapsulation welding and sealing, and then performing vacuuming to obtain an encapsulation with an internal vacuum, and then performing heat treatment within a certain temperature range by applying a certain pressure to the encapsulation, an equiaxed structure with a grain size of less than 10 μm is obtained. The heat-treated thin plate is then diffusion-bonded, which can reduce the diffusion bonding temperature, pressure and time, and achieve diffusion bonding with a high welding rate. Attached Figure Description

[0019] Figure 1 This invention discloses the microstructure of a 1.2 mm thick titanium-based composite sheet.

[0020] Figure 2 This is a micrograph of a titanium-based composite sheet with an equiaxed structure obtained in an embodiment of the present invention.

[0021] Figure 3 This describes the high-quality weld microstructure obtained by diffusion bonding of a titanium-based composite sheet with an equiaxed structure prepared using the method of this invention. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] This invention addresses the problems and shortcomings of existing technologies in achieving high-weld-rate diffusion bonding by proposing a heat treatment method for equiaxed titanium-based composite thin plates for diffusion bonding. This method leverages the sensitivity of titanium-based composites to deformation temperature and their tendency to crack at low temperatures. Pure titanium plates or other titanium alloy plates coated with anti-weld flux are placed at the top and bottom of the titanium-based composite thin plate stack for encapsulation welding and sealing. After vacuuming, an internal vacuum encapsulation is obtained. Heat treatment is then performed within a specific temperature range using this vacuum encapsulation and by applying a certain pressure to the encapsulation, resulting in an equiaxed structure with a grain size of less than 10 μm. This yields a titanium-based composite thin plate with an equiaxed structure. Diffusion bonding of this equiaxed titanium-based composite thin plate reduces the diffusion bonding temperature, pressure, and time, facilitating high-quality welds at the interface and improving the material's superplastic deformation capability.

[0025] Please see Figure 2 and Figure 3 The heat treatment method for a titanium-based composite sheet with equiaxed structure for diffusion bonding provided by this invention mainly includes the following steps:

[0026] Step 1: Apply a weld nugget to the side of the pure titanium plate and / or titanium alloy plate that is in contact with the titanium-based composite sheet, as an upper and lower sleeve to enclose the titanium-based composite sheet.

[0027] Specifically, a weld nugget is applied to one side of two pure titanium plates, two titanium alloy plates, or one pure titanium plate and one titanium alloy plate. The side coated with the weld nugget is used as the contact surface for sandwiching the titanium-based composite sheet, thus preventing the titanium-based composite sheet from being welded to the side of the pure titanium plate or titanium alloy plate that is in contact with it.

[0028] Step 2: Place the upper sleeve and the lower sleeve on the top and bottom layers of the titanium-based composite sheet or the titanium-based composite sheet stack, respectively.

[0029] Step 3: After the above steps, the entire stack is encased, welded, and sealed, and then a vacuum is drawn to obtain an encasing with an internal vacuum.

[0030] Specifically, the surface of the titanium-based composite sheet is first pretreated according to the requirements of surface flatness, cleanliness, and roughness to clean the surface of the titanium-based composite sheet and remove impurities. In this embodiment, one example of pretreatment of the surface of the titanium-based composite sheet may include pretreatment of the surface by means of steel brush grinding, mechanical grinding, sanding, chemical cleaning, etc.

[0031] Secondly, titanium-based composite sheets can be stacked, or a single titanium-based composite sheet can be used for subsequent processing. The upper and lower sleeves coated with anti-welding agent are placed on the top and bottom layers of the titanium-based composite sheet or the stack of titanium-based composite sheets, respectively.

[0032] Finally, the entire assembly is sealed by welding, with a vacuum evacuation channel provided. The entire assembly is then evacuated to obtain an internally vacuum-sealed assembly.

[0033] Step 4: Heat-treat the vacuum-sealed enclosure to obtain a titanium-based composite sheet with an equiaxed structure;

[0034] Specifically, the vacuum-sealed cladding is placed in a gas diffusion furnace or a heat treatment furnace capable of applying gas pressure. The cladding is heated to 950–970°C, and after reaching the temperature, a gas pressure of 0.5–3 MPa is applied. The cladding is held at this temperature and pressure for 2–3 hours, followed by furnace cooling to obtain the desired result. Figure 2 The equiaxed microstructure shown in this method, compared to existing methods for preparing titanium-based composite thin plates, has a grain size of less than 10 μm. This equiaxed microstructure is a more ideal microstructure for diffusion bonding, enabling a reduction in diffusion bonding temperature, pressure, and time, and achieving a bonding rate of over 95%. Before diffusion bonding, the heat-treated titanium-based composite thin plate also needs to undergo conventional surface pickling treatment.

[0035] Step 5: Diffusion bonding is performed on the titanium-based composite sheet with equiaxed structure.

[0036] Specifically, for titanium-based composites, the process parameters for diffusion bonding include: a diffusion bonding temperature of 940–960℃, a diffusion bonding pressure of 1.5–2.0 MPa, and a holding time of 1.5–2 hours. Based on this process, the resulting weld microstructure is as follows: Figure 3 As shown, it has high-quality welds.

[0037] The present invention also provides a titanium-based composite sheet with an equiaxed structure, wherein the titanium-based composite sheet with an equiaxed structure is prepared by a heat treatment method for a titanium-based composite sheet with an equiaxed structure for diffusion bonding as described above.

[0038] The present invention will be further described in detail below with reference to specific embodiments.

[0039] Example 1

[0040] The heat treatment method for preparing titanium-based composite thin plates with equiaxed structures based on diffusion bonding provided in Example 1 mainly includes the following steps:

[0041] S1: Clean the surface of the titanium-based composite sheet to remove impurities;

[0042] S2: Stack and arrange titanium-based composite thin plates;

[0043] S3: A pure titanium plate or other titanium alloy plate with a weld nugget coated on the contact surface with the titanium-based composite sheet is placed on the top and bottom of the titanium-based composite sheet stack, and then a sheath welding seal is performed, leaving a vacuum channel.

[0044] S4: Vacuum the entire package;

[0045] S5: Place the vacuum-sealed enclosure into a gas diffusion furnace or a heat treatment furnace that can apply gas pressure;

[0046] S6: Heat the cladding to 950–970℃, apply a pressure of 0.5–3 MPa after reaching the temperature, maintain the temperature and pressure for 2–3 hours, and then cool it in the furnace to obtain the desired result. Figure 2 As shown, a titanium-based composite sheet with an equiaxed structure.

[0047] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, those skilled in the art will know that there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A heat treatment method for a titanium-based composite sheet with equiaxed microstructure based on diffusion bonding, characterized in that, Includes the following steps: A weld nugget is applied to the side of the pure titanium plate and / or titanium alloy plate that is in contact with the titanium-based composite sheet, serving as an upper and lower sleeve for enclosing the titanium-based composite sheet. The upper sleeve and the lower sleeve are respectively placed on the top and bottom layers of the titanium-based composite sheet or the titanium-based composite sheet stack; After the above steps are completed, the entire stack is encased, welded, and sealed, and then a vacuum is drawn to obtain an encasing with an internal vacuum. The inner vacuum of the cladding is heat-treated to obtain a titanium-based composite sheet with an equiaxed structure. The titanium-based composite sheet with equiaxed structure is diffuse-bonded; The steps for heat-treating a vacuum-sealed cladding include: placing the vacuum-sealed cladding in a gas diffusion furnace or a heat treatment furnace capable of applying gas pressure, heating it to 950–970°C, applying a gas pressure of 0.5–3 MPa after reaching the temperature, holding it at the temperature and pressure for 2–3 hours, and then cooling it in the furnace.

2. The heat treatment method for a titanium-based composite sheet with equiaxed structure for diffusion bonding as described in claim 1, characterized in that, After heat treatment, the process also includes routine surface pickling of the heat-treated titanium-based composite sheet.

3. The heat treatment method for a titanium-based composite thin plate with equiaxed structure for diffusion bonding as described in claim 1, characterized in that, The process parameters for diffusion bonding include: diffusion bonding temperature of 940-960℃, diffusion bonding pressure of 1.5-2.0MPa, and heat and pressure holding for 1.5-2 hours.

4. The heat treatment method for a titanium-based composite sheet with equiaxed structure for diffusion bonding as described in claim 1, characterized in that, Before placing the upper and lower sleeves on the top and bottom layers of the titanium-based composite sheet or the titanium-based composite sheet stack, respectively, the surface of the titanium-based composite sheet or the titanium-based composite sheet stack is pretreated according to the requirements of surface flatness and cleanliness.

5. The heat treatment method for a titanium-based composite sheet with equiaxed structure for diffusion bonding as described in claim 4, characterized in that, The surface pretreatment of the titanium-based composite sheet or titanium-based composite sheet stack includes: pretreatment of the surface by mechanical grinding or chemical cleaning.

6. The heat treatment method for a titanium-based composite sheet with equiaxed structure for diffusion bonding as described in claim 1, characterized in that, The grain size of the equiaxed structure is less than 10 μm.

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