A method for preparing a NiAl / Ni3Al gradient structure special-shaped shell part by integrating in-situ reaction with gas pressure forming

Abstract

A method for preparing a NiAl / Ni3Al gradient structure special-shaped shell part by integrating in-situ reaction and gas pressure forming belongs to the technical field of forming of special-shaped plate shell parts for aerospace. The method aims to solve the problems of long cycle, complex process, high equipment requirement, many hollow defects and high cost of the existing forming method of NiAl-based alloy laminated shell parts, and solve the problem of low high-temperature strength of the existing single-phase NiAl intermetallic compound. The method comprises the following steps: I. stacking Ni foils and Al foils alternately in a forming lower die to obtain a laminated structure; II. closing and sealing a forming upper die and the forming lower die, and filling inert gas through a central air hole of the forming lower die; III. first-stage reaction; IV. gas pressure forming; and V. second-stage reaction. The method is used for preparing a NiAl / Ni3Al gradient structure special-shaped shell part.

Description

Technical Field

[0001] The invention belongs to the technical field of forming special-shaped plate and shell parts for aerospace. Background Art

[0002] With the development of aerospace industry, the demand for lightweight and high temperature resistant structural materials is increasing. Currently, the key hot end shell parts serving at 700℃~900℃ mainly rely on nickel-based high temperature alloys. However, the high density of nickel-based high temperature alloys (7.9g / cm 3 ~8.5g / cm 3 ) not only leads to excessive weight of structural parts, thereby increasing the energy consumption of aircraft, but also may aggravate safety risks and pose a potential threat to flight performance and stability. Therefore, it is urgent to develop new lightweight and high-temperature resistant structural materials to meet the needs of the new generation of flight equipment for high-temperature yield strength, creep performance, oxidation resistance, etc. NiAl intermetallic compounds have low density, excellent oxidation resistance and high thermal conductivity, making them a class of highly potential high-temperature resistant structural materials that have emerged in recent years. However, the low-temperature brittleness and large hot forming resistance of NiAl intermetallic compounds make it difficult to form even at high temperatures, making it difficult to form large-sized NiAl alloy thin-walled components using traditional preparation and processing technologies. Publication No. CN 103057203 A proposes a layered NiAl material and a preparation method thereof, which comprises stacking Ni foil and Al foil in an alternating manner, reacting in a vacuum reaction hot pressing sintering furnace to form NiAl alloy plates, and then taking them out and reheating them to a suitable deformation temperature to prepare NiAl thin-walled components. This method can produce large-sized NiAl-based alloy thin-walled components, but the implementation of this method depends on specific equipment. In the vacuum hot pressing sintering process, not only are complex steps of heating and pressurizing involved, but after completing the primary reaction, the pressure and temperature in the furnace must be lowered to room temperature before the laminated material can be taken out. This process takes a long time, seriously affecting production efficiency and increasing processing costs. At the same time, during the primary reaction, when Al atoms penetrate into the Ni layer, pores are often induced inside the Al layer. However, when applying pressure to the composite plate in the vacuum hot pressing process, it is difficult to achieve uniform distribution of pressure at all points, which makes it difficult to effectively bridge the pores formed in areas that are not subjected to sufficient pressure. Therefore, the use of traditional processes often leads to a large number of relatively large pore defect problems. In addition, although single-phase NiAl intermetallic compounds have excellent oxidation resistance, their high-temperature strength is low, which limits their application. Summary of the Invention

[0003] The present invention aims to solve the problems of long cycle, complex process, high equipment requirements, many void defects and high cost in the existing NiAl-based alloy laminated shell forming method, and at the same time solve the problem of low high-temperature strength of the existing single-phase NiAl intermetallic compound, and further provide a method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming.

[0004] A method for preparing a NiAl / Ni3Al gradient structure special-shaped shell part by integrating in-situ reaction and gas pressure forming is carried out according to the following steps:

[0005] First, according to the gradient layer thickness design, Ni foil and Al foil are alternately stacked in the forming lower mold to obtain a laminated structure, and the upper and lower surfaces of the laminated structure are both Ni foil;

[0006] 2. Close and seal the upper and lower forming molds, and fill the inert gas through the central vent hole of the lower forming mold to maintain the pressure in the lower mold cavity at 2MPa to 15MPa;

[0007] 3. Under the conditions of a pressure of 2MPa to 15MPa in the lower die cavity and a primary reaction temperature, a primary reaction of Ni foil and Al foil is carried out to obtain a Ni2Al3 / Ni composite structure;

[0008] 4. After the primary reaction is completed, the temperature is raised to the bulging temperature. During the heating process, the vacuum is evacuated through the central vent hole of the forming lower mold to a vacuum degree of ≤1Pa, and inert gas is filled through the central vent hole of the forming upper mold until the pressure in the upper mold cavity is 5MPa~30MPa. Then, under the conditions of bulging temperature, vacuum degree in the lower mold cavity of ≤1Pa and pressure in the upper mold cavity of 5MPa~30MPa, the pressure difference between the upper and lower molds is used to drive the Ni2Al3 / Ni composite structure to undergo plastic deformation and expand to fill the entire special-shaped mold cavity, thereby obtaining a Ni2Al3 / Ni composite structure after gas pressure forming;

[0009] 5. After gas pressure forming, the pressure difference between the upper and lower molds is maintained and the temperature is raised to the secondary reaction temperature. Under the conditions of the secondary reaction temperature, the vacuum degree in the lower mold cavity ≤1Pa and the pressure in the upper mold cavity of 5MPa~30MPa, the Ni2Al3 / Ni composite structure after gas pressure forming is subjected to secondary reaction to obtain a NiAl / Ni3Al gradient structure special-shaped shell part.

[0010] The beneficial effects of the present invention are:

[0011] 1. The NiAl and Ni3Al composition ratios of the special-shaped shell components described in the present invention can be controlled based on the single-layer thickness ratio of the Ni foil and the Al foil. The composition ratios of the NiAl / Ni3Al gradient structure components can be flexibly and variably set as needed. By designing a gradient structure with NiAl on the surface and Ni3Al in the core through different thickness ratios of Ni and Al foil from the surface to the inside, the component can have both excellent oxidation resistance and high-temperature strength.

[0012] 2. The present invention integrates the two steps of reaction and forming of Ni foil and Al foil, has high efficiency and low cost, and can prepare NiAl-based alloy thin-walled special-shaped components of larger size.

[0013] 3. During the primary reaction, gas pressure loading ensures uniform gas pressure at every point on the composite plate. This uniform pressure distribution promotes effective closure of holes under the action of gas pressure, significantly reducing hole defects in the composite plate. This improvement is extremely beneficial for the subsequent secondary reaction process of the composite plate.

[0014] 4. The pressure differential design of applying low pressure in the concave die cavity of the forming lower die and high pressure in the convex die cavity of the forming upper die can effectively promote a more thorough film bulging deformation of the laminated material inside the concave die cavity, thereby significantly improving the dimensional accuracy of the bulged part.

[0015] 5. The prepared NiAl / Ni3Al gradient structure special-shaped shell has a room temperature tensile strength of 620MPa and an elongation of 7%; the tensile strength at 1000℃ is 125MPa and the elongation is 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Scanning electron micrographs of the interfaces of the Ni2Al3 / Ni composite structures prepared in Example 1 and the comparative experiment, (a) comparative experiment, (b) Example 1;

[0017] Figure 2 This is a flow chart of the present invention for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming;

[0018] Figure 3 1 is an exploded view of the structure of the forming device used in the preparation method of Example 1, 1 is the upper support base, 2 is the central ventilation pipe of the forming upper mold, 3 is the forming upper mold, 4 is the induction coil, 5 is the forming lower mold, 6 is the lower support base, and 7 is the central ventilation pipe of the forming lower mold;

[0019] Figure 4 Schematic diagram of the assembly of the forming device used in the preparation method of Example 1;

[0020] Figure 5 It is an assembly cross-sectional view of the forming upper mold and the forming lower mold used in the preparation method of Example 1. DETAILED DESCRIPTION

[0021] Specific implementation method 1, combined with Figure 2 Specific description: This embodiment is a method for preparing a NiAl / Ni3Al gradient structure special-shaped shell part by integrating in-situ reaction and gas pressure forming, which is carried out in the following steps:

[0022] First, according to the gradient layer thickness design, Ni foil and Al foil are alternately stacked in the forming lower mold to obtain a laminated structure, and the upper and lower surfaces of the laminated structure are both Ni foil;

[0023] 2. Close and seal the upper and lower forming molds, and fill the inert gas through the central vent hole of the lower forming mold to maintain the pressure in the lower mold cavity at 2MPa to 15MPa;

[0024] 3. Under the conditions of a pressure of 2MPa to 15MPa in the lower die cavity and a primary reaction temperature, a primary reaction of Ni foil and Al foil is carried out to obtain a Ni2Al3 / Ni composite structure;

[0025] 4. After the primary reaction is completed, the temperature is raised to the bulging temperature. During the heating process, the vacuum is evacuated through the central vent hole of the forming lower mold to a vacuum degree of ≤1Pa, and inert gas is filled through the central vent hole of the forming upper mold until the pressure in the upper mold cavity is 5MPa~30MPa. Then, under the conditions of bulging temperature, vacuum degree in the lower mold cavity of ≤1Pa and pressure in the upper mold cavity of 5MPa~30MPa, the pressure difference between the upper and lower molds is used to drive the Ni2Al3 / Ni composite structure to undergo plastic deformation and expand to fill the entire special-shaped mold cavity, thereby obtaining a Ni2Al3 / Ni composite structure after gas pressure forming;

[0026] 5. After gas pressure forming, the pressure difference between the upper and lower molds is maintained and the temperature is raised to the secondary reaction temperature. Under the conditions of the secondary reaction temperature, the vacuum degree in the lower mold cavity ≤1Pa and the pressure in the upper mold cavity of 5MPa~30MPa, the Ni2Al3 / Ni composite structure after gas pressure forming is subjected to secondary reaction to obtain a NiAl / Ni3Al gradient structure special-shaped shell part.

[0027] To prevent gas leakage during inflation, this embodiment features a ring of male and female stoppers at the flange junction of the upper and lower molds. When the upper and lower molds are closed, the male and female stoppers fit tightly and securely together, creating a distinct ridge at the flange edge of the sheet material. This ridge not only enhances structural stability but also creates a reliable seal.

[0028] The beneficial effects of this embodiment are:

[0029] 1. The NiAl and Ni3Al composition ratios of the special-shaped shell member described in this embodiment can be controlled based on the single-layer thickness ratio of the Ni foil and the Al foil. The composition ratios of the NiAl / Ni3Al gradient structure components can be flexibly and variably set as needed. By designing a gradient structure with NiAl on the surface and Ni3Al in the core through Ni and Al foils with different thickness ratios from the surface to the inside, the component can have both excellent oxidation resistance and high-temperature strength.

[0030] 2. This embodiment integrates the two steps of reaction and forming of Ni foil and Al foil, has high efficiency and low cost, and can produce large-sized NiAl-based alloy thin-walled special-shaped components.

[0031] 3. During the primary reaction, gas pressure loading ensures uniform gas pressure at every point on the composite plate. This uniform pressure distribution promotes effective closure of holes under the action of gas pressure, significantly reducing hole defects in the composite plate. This improvement is extremely beneficial for the subsequent secondary reaction process of the composite plate.

[0032] 4. The pressure differential design of applying low pressure in the concave die cavity of the forming lower die and high pressure in the convex die cavity of the forming upper die can effectively promote a more thorough film bulging deformation of the laminated material inside the concave die cavity, thereby significantly improving the dimensional accuracy of the bulged part.

[0033] 5. The prepared NiAl / Ni3Al gradient structure special-shaped shell has a room temperature tensile strength of 620MPa and an elongation of 7%; the tensile strength at 1000℃ is 125MPa and the elongation is 30%.

[0034] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the Ni foil and Al foil described in step 1 are pretreated Ni foil and pretreated Al foil, and the pretreatment is specifically carried out according to the following steps:

[0035] ① Heat-treating the Ni foil at a temperature of 500° C. to 700° C. for 0.5 h to 1 h to obtain a heat-treated Ni foil;

[0036] ② heat-treating the Al foil at a temperature of 300° C. to 400° C. for 0.5 h to 1 h to obtain a heat-treated Al foil;

[0037] ③ The surfaces of the heat-treated Ni foil and the heat-treated Al foil were shot peened to remove the surface oxide layer. Finally, the surfaces were ultrasonically cleaned with anhydrous ethanol for 5 to 15 minutes at an ultrasonic power of 100 W to 300 W, and then dried to obtain the pretreated Ni foil and pretreated Al foil. Other steps are the same as those in the first embodiment.

[0038] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the thickness of the Ni foil in step 1 is 50 μm to 100 μm, and the thickness of the Al foil in step 1 is 25 μm to 115 μm. Other aspects are the same as specific embodiment 1 or 2.

[0039] Specific embodiment 4: This embodiment differs from Specific embodiments 1 to 3 in that the laminated structure in step 1 consists of two outer composite unit layers and one central composite unit layer, and the thickness of the two outer composite unit layers is ≥ 0.45 mm; the thickness of the central composite unit layer is ≥ 0.5 mm. Otherwise, this embodiment is the same as Specific embodiments 1 to 3.

[0040] In this embodiment, the outer composite unit layer ultimately reacts to form NiAl, which provides surface antioxidant properties. The central composite unit layer ultimately reacts to form Ni3Al, which exhibits high high-temperature strength. This allows the production of gradient-structured thin-walled components with both excellent oxidation resistance and high-temperature strength.

[0041] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the thickness ratio of the Ni foil to the Al foil in the outer composite unit layer is 1:1.5. Other aspects are the same as specific embodiments 1 to 4.

[0042] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the thickness ratio of the Ni foil to the Al foil in the central composite unit layer is 2:1. Other aspects are the same as specific embodiments 1 to 5.

[0043] Specific embodiment 7: This embodiment differs from Specific embodiments 1 to 6 in that the primary reaction temperature in step 3 is 630° C. to 650° C. The rest is the same as Specific embodiments 1 to 6.

[0044] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the primary reaction time in step 3 is 2 to 4 hours. Other aspects are the same as specific embodiments 1 to 7.

[0045] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the bulging temperature in step 4 is 750° C. to 850° C. The rest is the same as specific embodiments 1 to 8.

[0046] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that the secondary reaction temperature in step 5 is 1050°C to 1150°C and the secondary reaction time in step 5 is 2h to 4h. Other aspects are the same as specific embodiments 1 to 9.

[0047] The following examples are used to verify the beneficial effects of the present invention:

[0048] Example 1:

[0049] A method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming is combined Figures 3 to 5 The forming device shown in FIG, and follow the steps below:

[0050] First, according to the gradient layer thickness design, Ni foil and Al foil are alternately stacked in the forming lower mold to obtain a laminated structure, and the upper and lower surfaces of the laminated structure are both Ni foil;

[0051] The laminated structure consists of two outer composite unit layers and one central composite unit layer, and the thickness of the two outer composite unit layers is 0.45 mm; the thickness of the central composite unit layer is 0.51 mm;

[0052] The thickness of the Ni foil in the outer composite unit layer is 0.06 mm, the thickness of the Al foil is 0.09 mm, and the thickness ratio of the Ni foil to the Al foil is 1:1.5; the thickness of the Ni foil in the central composite unit layer is 0.06 mm, the thickness of the Al foil is 0.03 mm, and the thickness ratio of the Ni foil to the Al foil is 2:1;

[0053] 2. Close and seal the upper and lower forming molds, and fill argon gas through the central vent hole of the lower forming mold to maintain the pressure in the lower mold cavity at 10 MPa;

[0054] 3. Under the conditions of a pressure of 10 MPa and a primary temperature of 650°C in the lower die cavity, the Ni foil and the Al foil were subjected to a primary reaction for 2 hours to obtain a Ni2Al3 / Ni composite structure;

[0055] 4. After the primary reaction is completed, the temperature is raised to a bulging temperature of 800°C. During the heating process, vacuum is drawn through the central vent hole of the forming lower mold until the vacuum degree is ≤1Pa, and argon is filled through the central vent hole of the forming upper mold until the pressure in the upper mold cavity is 20MPa. Then, under the conditions of a bulging temperature of 800°C, a vacuum degree in the lower mold cavity ≤1Pa, and a pressure in the upper mold cavity of 20MPa, the pressure difference between the upper and lower molds is used to drive the Ni2Al3 / Ni composite structure to undergo plastic deformation and expand to fill the entire special-shaped mold cavity, thereby obtaining a Ni2Al3 / Ni composite structure after gas pressure forming;

[0056] 5. After gas pressure forming, the pressure difference between the upper and lower molds is maintained and the temperature is raised to a secondary reaction temperature of 1100°C. Under the conditions of a temperature of 1100°C, a vacuum degree in the lower mold cavity ≤1Pa and a pressure in the upper mold cavity of 25MPa, the Ni2Al3 / Ni composite structure after gas pressure forming is subjected to a secondary reaction for 3h to obtain a NiAl / Ni3Al gradient structure special-shaped shell part.

[0057] The Ni foil and Al foil described in step 1 are pretreated Ni foil and pretreated Al foil, and the pretreatment is specifically carried out according to the following steps:

[0058] ① Heat-treating the Ni foil at 500°C for 1 hour to obtain a heat-treated Ni foil;

[0059] ② Heat-treating the Al foil at 400° C. for 0.5 h to obtain heat-treated Al foil;

[0060] ③ The surfaces of the heat-treated Ni foil and the heat-treated Al foil were shot peened to remove the surface oxide layer. Finally, they were ultrasonically cleaned with anhydrous ethanol for 10 minutes under an ultrasonic power of 200 W, and finally dried to obtain the pretreated Ni foil and the pretreated Al foil.

[0061] The working surfaces of the upper forming mold and the lower forming mold described in the first embodiment are evenly coated with boron nitride solder resist.

[0062] Figure 4 This is a schematic assembly diagram of the forming device used in the preparation method of Example 1. As shown, the upper support base is bolted to the movable beam of the hydraulic press, and the lower support base is fixed to the workbench of the hydraulic press. The hydraulic press adopts an existing structure as needed. An upper forming die is located below the upper support base and bolted to the upper support base. A lower forming die is located above the lower support base and bolted to the lower support base. The central ventilation line of the upper forming die is fixed to the upper forming die, and the central ventilation line of the lower forming die is fixed to the lower forming die. An induction coil is installed on the lower support base and located outside the upper and lower forming dies. The induction coil is used to heat the upper and lower forming dies, thereby heating the nickel-aluminum laminate, facilitating the reaction and forming of the nickel-aluminum laminate. Using the induction coil to heat the nickel-aluminum laminate achieves rapid and uniform heating. The heating power can be controlled by adjusting the frequency and amplitude of the high-frequency current, enabling precise control of the heating process.

[0063] Figure 5This is a cross-sectional view of the upper and lower forming dies used in the preparation method of Example 1. As shown, a ring of convex stoppers is designed around the flange of the upper die, while a ring of concave stoppers is provided around the flange of the lower die. When the upper and lower dies are precisely closed, the convex and concave stoppers fit tightly and securely together, creating a distinct ridge at the flange edge of the sheet material. This ridge not only enhances structural stability but also provides a reliable sealing barrier.

[0064] Comparative experiment: To verify the traditional vacuum hot pressing sintering process, the comparative experiment used a vacuum heating sintering furnace equipment to perform a first-order reaction on the two laminated structures in step 1 of Example 1. The reaction process parameters were: the equipment heating rate was 5°C / min, the vacuum degree was 0.1Pa, the pressure was 10MPa, the operating temperature was 650°C, and the heat preservation was 2h to obtain a Ni2Al3 / Ni composite structure.

[0065] Figure 1 Interface scanning electron microscope images of the Ni2Al3 / Ni composite structure prepared in Example 1 and the comparative experiment, (a) comparative experiment, (b) Example 1; it can be seen from the figure that through the traditional vacuum hot pressing sintering process, a large number of large-sized holes are formed at the interface of the composite material layer after the primary reaction, while the number of holes in the primary reaction composite material prepared by the air pressure loading reaction process in Example 1 is relatively small.

[0066] According to GB / T 228.1-2021 "Tensile test of metallic materials - Part 1: Room temperature test method" and GB / T228.2-2015: "Tensile test of metallic materials - Part 2: High temperature test method", the NiAl / Ni3Al gradient structure special-shaped shell prepared in Example 1 was subjected to room temperature mechanical property tests and high temperature mechanical property tests. The tensile strength at room temperature was 620 MPa and the elongation was 7%; the tensile strength at 1000°C was 125 MPa and the elongation was 30%.

Claims

1. A method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming, characterized in that It is carried out in the following steps: First, according to the gradient layer thickness design, Ni foil and Al foil are alternately stacked in the forming lower mold to obtain a laminated structure, and the upper and lower surfaces of the laminated structure are both Ni foil; 2. Close and seal the upper and lower forming molds, and fill the inert gas through the central vent hole of the lower forming mold to maintain the pressure in the lower mold cavity at 2MPa to 15MPa; 3. Under the conditions of a pressure of 2MPa to 15MPa in the lower die cavity and a primary reaction temperature, a primary reaction of Ni foil and Al foil is carried out to obtain a Ni2Al3 / Ni composite structure; 4. After the primary reaction is completed, the temperature is raised to the bulging temperature. During the heating process, the vacuum is evacuated through the central vent hole of the forming lower mold to a vacuum degree of ≤1Pa, and inert gas is filled through the central vent hole of the forming upper mold until the pressure in the upper mold cavity is 5MPa~30MPa. Then, under the conditions of bulging temperature, vacuum degree in the lower mold cavity of ≤1Pa and pressure in the upper mold cavity of 5MPa~30MPa, the pressure difference between the upper and lower molds is used to drive the Ni2Al3 / Ni composite structure to undergo plastic deformation and expand to fill the entire special-shaped mold cavity, thereby obtaining a Ni2Al3 / Ni composite structure after gas pressure forming; 5. After gas pressure forming, the pressure difference between the upper and lower molds is maintained and the temperature is raised to the secondary reaction temperature. Under the conditions of the secondary reaction temperature, the vacuum degree in the lower mold cavity ≤1Pa and the pressure in the upper mold cavity of 5MPa~30MPa, the Ni2Al3 / Ni composite structure after gas pressure forming is subjected to secondary reaction to obtain a NiAl / Ni3Al gradient structure special-shaped shell part.

2. The method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming according to claim 1, characterized in that The Ni foil and Al foil described in step 1 are pretreated Ni foil and pretreated Al foil, and the pretreatment is specifically carried out according to the following steps: ① Heat-treating the Ni foil at a temperature of 500° C. to 700° C. for 0.5 h to 1 h to obtain a heat-treated Ni foil; ② heat-treating the Al foil at a temperature of 300° C. to 400° C. for 0.5 h to 1 h to obtain a heat-treated Al foil; ③ The surfaces of the heat-treated Ni foil and the heat-treated Al foil were shot peened to remove the surface oxide layer, and finally ultrasonically cleaned with anhydrous ethanol for 5 minutes to 15 minutes under an ultrasonic power of 100W to 300W, and finally dried to obtain the pretreated Ni foil and the pretreated Al foil.

3. The method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming according to claim 1, characterized in that The thickness of the Ni foil in step 1 is 50 μm to 100 μm; the thickness of the Al foil in step 1 is 25 μm to 115 μm.

4. The method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming according to claim 1, characterized in that The laminated structure in step 1 consists of two outer composite unit layers and one central composite unit layer, and the thickness of the two outer composite unit layers is ≥0.45 mm; the thickness of the central composite unit layer is ≥0.5 mm.

5. A method for preparing a NiAl / Ni3Al gradient structured special-shaped shell member by integrating in-situ reaction and gas pressure forming according to claim 4, characterized in that The thickness ratio of the Ni foil to the Al foil in the outer composite unit layer is 1:1.

5.

6. The method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming according to claim 4, characterized in that The thickness ratio of the Ni foil to the Al foil in the central composite unit layer is 2:

1.

7. The method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming according to claim 1, characterized in that The primary reaction temperature in step 3 is 630°C to 650°C.

8. The method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming according to claim 1, characterized in that The primary reaction time in step 3 is 2 h to 4 h.

9. The method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming according to claim 1, characterized in that The bulging temperature in step 4 is 750°C to 850°C.

10. The method for preparing NiAl / Ni3Al gradient structure special-shaped shell parts by integrating in-situ reaction and gas pressure forming according to claim 1, characterized in that The secondary reaction temperature in step 5 is 1050° C. to 1150° C.; the secondary reaction time in step 5 is 2 h to 4 h.

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