Preparation method of titanium-aluminum alloy diffuser casting for engine
By optimizing the gating system and hot isostatic pressing, the problems of porosity, gas holes, shrinkage cavities, and cracking in thick areas that occur in titanium-aluminum alloy diffuser castings during centrifugal casting were solved, achieving high-quality and high-precision preparation of the castings.
Patent Information
- Application Number
- CN202511753043.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-02-24
AI Technical Summary
Existing centrifugal casting methods result in defects in titanium-aluminum alloy diffuser castings, such as porosity, air holes, shrinkage cavities, and cracking in thick areas.
The optimized gating system is designed, including a central runner and a horizontal runner, with a cross-sectional area ratio of 1:(2~2.5):(4~5). Gravity casting is adopted, and the flow rate of the molten alloy and the feeding channels are controlled through reasonable riser design and hot isostatic pressing to avoid casting defects.
It effectively avoids porosity, air holes, shrinkage cavities, and cracking in thick areas of the casting, ensuring the metallurgical quality and dimensional accuracy of the casting and meeting the high requirements of diffusers for aero-engines.
Smart Images
Figure CN121551541A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of diffuser technology, and more specifically, to a method for preparing a titanium-aluminum alloy diffuser casting for an engine. Background Technology
[0002] The diffuser for aero-engines has a thin-walled structure with a wall thickness of only 2.5~4mm. The diffuser consists of inner and outer rings, support plates, and upper and lower mounting edges, and its structure is relatively complex. In particular, the inner cavity space of the support plate is narrow. The outer wall of the inner ring, the inner wall of the outer ring, and the inner and outer surfaces of the support plate are all flow channels, which places high demands on the dimensional accuracy and metallurgical quality of the castings.
[0003] Replacing high-temperature alloys with titanium-aluminum alloys can reduce the weight of the diffuser. However, titanium-aluminum alloys are prone to reacting with the mold shell to form a loose structure or porosity, and stress concentration areas are prone to cracking during cooling. Therefore, while existing centrifugal casting can achieve rapid mold filling, it can lead to defects in the casting such as porosity, porosity, shrinkage cavities, and cracking in thick areas. Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing titanium-aluminum alloy diffuser castings for engines, which solves the technical problems of porosity, blowholes, shrinkage cavities, and cracking in thick areas caused by existing centrifugal casting. In view of this, the invention achieves this through the following solution.
[0005] This invention provides a method for preparing titanium-aluminum alloy diffuser castings for engines. During the preparation of the ceramic mold shell, the method involves real-time sensing of temperature and humidity changes near the ceramic mold shell during the drying process, and intelligent adjustment of air conditioning power to ensure the stability of temperature and humidity near the ceramic mold shell. Furthermore, it includes online intelligent analysis of real-time temperature and humidity data acquisition and control capabilities. The preparation method of this invention includes: For design of the gating system, please refer to [link / reference]. Figure 9 and Figure 10 ,as well as Figure 16 and Figure 17 The gating system includes a central gating runner and a horizontal gating runner connected to the central gating runner. The ratio of the cross-sectional areas of the central gating runner, the horizontal gating runner, and the gating gate of the gating system is 1:(2~2.5):(4~5). A wax model is prepared, comprising a system model and a product model; the product model has a shrinkage rate of 1~1.1 in the diameter direction and a shrinkage rate of 1~1.05 in the height direction; the system model is made of polymethyl methacrylate, and the product model is made of corn flour. A ceramic shell is prepared, the ceramic shell comprising a system section and a product section; the product section and the system section are composed of a surface layer, a transition layer and a back layer; The system and product parts are vitrified by firing and the wax mold is removed; after preheating the ceramic shell, the titanium-aluminum alloy is gravity-cast.
[0006] Compared with the prior art, the method for preparing titanium-aluminum alloy diffuser castings for engines of the present invention designs a gating system including a central runner and a horizontal runner, and determines the ratio of the cross-sectional areas of the central sprue, horizontal runner, and gate to be 1:(2~2.5):(4~5). After preparing the wax model and ceramic shell, the system part and the product part are vitrified by firing, and the wax model is removed. After preheating the ceramic shell, the titanium-aluminum alloy can be gravity-cast. The present invention adopts a gravity-casting method, in which the titanium-aluminum alloy enters the casting body through the central runner and horizontal runner via the gating system. Unlike the traditional TC4 and TA15 titanium alloy castings, the titanium-aluminum alloy... Titanium-aluminum alloys have low melting points and good fluidity, but their liquid-solid phase region is narrow and relatively prone to segregation. Therefore, in thick areas of the casting, shrinkage cavities can easily occur due to insufficient feeding, leading to a high risk of turbulent flow, gas entrapment, and residual porosity. Therefore, this invention slows down the flow rate of the alloy liquid through bottom-pouring, followed by diversion through horizontal runners (up to four runners), ensuring slow and stable filling of the titanium-aluminum alloy. Additionally, a fracture-prone section can be added between the gate and the casting body to buffer the shrinkage stress of the runner and prevent cracks from propagating into the casting. Simulation results show that using the optimized gating system described above can avoid the convergence of different alloy liquids, preventing turbulence and gas buildup, ultimately controlling the risk of underfilling at the top of the riser. (See [link to previous section]). Figure 5 Simultaneously, by maintaining a good feeding channel through reasonable riser design, shrinkage cavities and porosity are extracted to the riser core. Please see [link / reference]. Figure 6 Stress field analysis shows that the stress concentration area is located at the junction of the annular structure at the bottom of the casting and the gate, maintaining a distance from the casting body. (See attached image.) Figure 7 The technical solution of the present invention solves the technical problems of porosity, air holes, shrinkage cavities, and cracking in thick areas of castings caused by existing centrifugal casting.
[0007] Furthermore, in the method for preparing a titanium-aluminum alloy diffuser casting for an engine according to the present invention, the gating system further includes a riser, which is disposed in an annular region at the top of the casting or in a thick portion intersecting with the inner and outer rings.
[0008] Furthermore, in the method for preparing titanium-aluminum alloy diffuser castings for engines of the present invention, the wax model is prepared by 3D printing to form a system model and a product model, and is left to stand for 5 to 24 hours after printing; The system module has a hollow structure and is filled with wax. The polymethyl methacrylate powder has a density of 1.1~1.2 g / cm³. 3 .
[0009] Furthermore, in the method for preparing titanium-aluminum alloy diffuser castings for engines of the present invention, during the preparation of the ceramic shell, the product part consists of one surface layer, one transition layer and ten back layers. The system section is thickened by 1 to 2 layers based on the composition of the product section and wrapped with a metal mesh.
[0010] Furthermore, in the method for preparing titanium-aluminum alloy diffuser castings for engines of the present invention, during the preparation of the ceramic shell, a surface layer slurry and a transition layer slurry are prepared using silica sol and yttrium oxide powder; and a back layer slurry is prepared using silica sol and mullite powder. In the surface layer slurry or transition layer slurry, the mass ratio of silica sol to yttrium oxide powder is 1:(4~5); in the back layer slurry, the mass ratio of silica sol to mullite powder is 1:(5~6).
[0011] Furthermore, in the method for preparing a titanium-aluminum alloy diffuser casting for an engine according to the present invention, the preparation of the ceramic mold shell includes: The surface layer slurry is applied to the surface of the wax model, with a thickness of 0.2~0.3 mm; The coating layer is fixed by yttrium oxide sand, and the surface layer is obtained after the wax mold is dried; After the transition layer slurry is applied to the surface layer, and the coating layer is fixed with yttrium oxide sand, the transition layer is obtained after drying. The back layer slurry is coated onto the transition layer to fix the coating layer, and after drying, the back layer is obtained; wherein: After each layer of the backing slurry is applied, it is treated with bauxite sand; the last layer of the backing slurry, which serves as a sealing layer, is not treated with sand and is used to coat the bauxite sand.
[0012] Furthermore, in the method for preparing titanium-aluminum alloy diffuser castings for engines of the present invention, the process of vitrifying the system part and the product part by firing is achieved by two firings; The first roasting temperature is 650~800℃, and the roasting time is 8~10 hours. After the system section and product section are cooled to room temperature, they are heated to 1000~1200℃ for a second roasting. After the second roasting is 2~4 hours, the system section and product section are cooled to room temperature.
[0013] Furthermore, in the method for preparing the titanium-aluminum alloy diffuser casting for engines of the present invention, during the gravity casting process of the titanium-aluminum alloy: The smelting current is 12~20kA, and the voltage is 30~60V; Using a water-cooled copper crucible, the crucible is rotated at a speed of 5 to 15 seconds. After pouring, the ceramic shell is cooled to 780 to 820°C in the furnace, and then subjected to controlled cooling at a rate of 2 to 5°C / minute.
[0014] Furthermore, in the method for preparing the titanium-aluminum alloy diffuser casting for engines of the present invention, after the gravity casting of the titanium-aluminum alloy, the method further includes: After gravity casting of titanium-aluminum alloy, a diffuser casting is obtained. The diffuser casting is placed in a hot isostatic press and held at an argon pressure of 135-145 MPa for 2-5 hours.
[0015] Furthermore, in the method for preparing the titanium-aluminum alloy diffuser casting for engines of the present invention, after holding at argon pressure for 2-5 hours, the method further includes: The diffuser casting is subjected to vacuum annealing heat treatment; during the heat treatment process, the diffuser casting is heated to 1100°C in the furnace and held for 1 to 3 hours, and then cooled to 80°C in the furnace before being taken out of the furnace. Attached Figure Description
[0016] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the structure of a wax model according to the present invention; Figure 2 This is a schematic diagram of the structure of a ceramic shell according to the present invention; Figure 3 This is a schematic diagram of the diffuser casting in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of an X-ray film of the diffuser casting in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the simulated risk analysis of insufficient pouring in this invention; Figure 6 This is a schematic diagram of the simulated risk analysis of shrinkage cavity and porosity in this invention; Figure 7 This is a schematic diagram of the residual stress analysis simulated in this invention; Figure 8 This is a schematic diagram of the microstructure of the ceramic shell layer in Embodiment 1 of the present invention; wherein: Figure 8 (a) is a microstructure of the shell before sintering; Figure 8 (b) shows another microstructure of the shell before sintering; Figure 8 (c) shows a microstructure of the shell after sintering; Figure 8 (d) shows another microstructure after shell sintering; Figure 9This is a schematic diagram of the structure of a casting system according to the present invention; Figure 10 This is a schematic diagram of another casting system in this invention; Figure 11 This is a schematic diagram of an X-ray film of the diffuser casting in Embodiment 2 of the present invention; Figure 12 This is a schematic diagram of an X-ray film of the diffuser casting in Embodiment 3 of the present invention; Figure 13 This is a schematic diagram of the diffuser casting in Comparative Example 1 of the present invention; Figure 14 This is a schematic diagram of the photosensitive resin product mold structure of Comparative Example 2 of the present invention; Figure 15 This is a schematic diagram of the surface defects of the casting in Comparative Example 2 of the present invention; Figure 16 This is a schematic diagram of the gating system model in this invention; Figure 17 This is a schematic diagram of the riser model in this invention. Detailed Implementation
[0017] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.
[0018] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.
[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.
[0020] Replacing high-temperature alloys with titanium-aluminum alloys can reduce the weight of the diffuser. However, titanium-aluminum alloys are prone to reacting with the mold shell to form a loose structure or porosity, and stress concentration areas are prone to cracking during cooling. Therefore, while existing centrifugal casting can achieve rapid mold filling, it can lead to defects in the casting such as porosity, porosity, shrinkage cavities, and cracking in thick areas.
[0021] To address the aforementioned technical problems, this invention provides a method for preparing a titanium-aluminum alloy diffuser casting for an engine, comprising: Step 1, design the gating system, which includes a central gating runner and a horizontal gating runner connected to the central gating runner. The ratio of the cross-sectional areas of the central gating runner, the horizontal gating runner, and the gate of the gating system is 1:(2~2.5):(4~5). Step 2, prepare a wax model, which includes a system model and a product model; the product model has a shrinkage rate of 1~1.1 in the diameter direction and a shrinkage rate of 1~1.05 in the height direction; the system model is made of polymethyl methacrylate and the product model is made of corn flour; Step 3: Prepare a ceramic shell, which includes a system section and a product section; the product section and the system section are composed of a surface layer, a transition layer and a back layer; Step 4: The system and product parts are vitrified by firing and the wax mold is removed; after preheating the ceramic shell, the titanium-aluminum alloy is gravity-cast.
[0022] In the above-mentioned technical solution, the method for preparing titanium-aluminum alloy diffuser castings for engines according to the present invention designs a gating system including a central runner and a horizontal runner, and determines the ratio of the cross-sectional areas of the central sprue, the horizontal runner, and the gate to be 1:(2~2.5):(4~5). After preparing the wax model and ceramic shell, the system part and the product part are vitrified by firing, and the wax model is removed. After preheating the ceramic shell, the titanium-aluminum alloy can be gravity-cast. The present invention adopts a gravity-casting method, in which the titanium-aluminum alloy enters the casting body through the central runner and the horizontal runner via the gating system. Unlike the traditional TC4 and TA15 titanium alloy castings, the titanium-aluminum alloy... Aluminum alloys have low melting points and good fluidity, but their liquid-solid phase region is narrow and relatively prone to segregation. Therefore, in thick areas of castings, shrinkage cavities are easily formed due to insufficient feeding, and the risk of turbulent flow, gas entrapment, and residual porosity is high. Therefore, this invention slows down the flow rate of the alloy liquid through bottom-pouring, and then diverts it through horizontal runners (up to four runners), ensuring slow and stable filling of the titanium-aluminum alloy. In addition, a fracture-prone section can be added between the gate and the casting body to buffer the shrinkage stress of the runner and prevent cracks from propagating into the casting. Through simulation, the optimized gating system described above can avoid the convergence of different alloy liquids, preventing turbulence and gas buildup, and ultimately controlling the risk of underfilling at the top of the riser. Figure 5 Simultaneously, by maintaining a good feeding channel through reasonable riser design, shrinkage cavities and porosity are extracted to the riser core, see... Figure 6 Stress field analysis shows that the stress concentration area is located at the junction of the annular structure at the bottom of the casting and the gate, maintaining a distance from the casting body. (See...) Figure 7 The technical solution of the present invention solves the technical problems of porosity, air holes, shrinkage cavities, and cracking in thick areas of castings caused by existing centrifugal casting.
[0023] Please see Figure 17 As one possible implementation, in the method for preparing a titanium-aluminum alloy diffuser casting for an engine according to the present invention, the gating system further includes a riser, which is disposed in the annular region at the top of the casting or in the thick portion intersecting with the inner and outer rings. Using this technical solution simplifies the gating system, reduces heat accumulation, reduces residual stress caused by the shrinkage of the gating system, and prevents the casting from cracking.
[0024] As one possible implementation, in the method for preparing the titanium-aluminum alloy diffuser casting for engines of the present invention, the wax model is prepared by 3D printing to form a system mold and a product mold, and is left to stand for 5-24 hours after printing; the system mold is a hollow structure filled with wax; the density of the polymethyl methacrylate powder is 1.1-1.2 g / cm³. 3 Using this technical solution, PMMA (polymethyl methacrylate) powder is used to print the tree model as a whole through a powder-spreading printing method. Compared with photosensitive resin 3D printing, PMMA resin models have higher strength, lower coefficient of expansion, and less residual ash after firing, making them suitable for preparing small to medium-sized wax models with a diameter of less than 600mm. For example, the settling time can be 5 hours, 15 hours, or 24 hours; the density of the polymethyl methacrylate powder can be 1.1 g / cm³. 3 1.15g / cm 3 Or 1.2g / cm 3 .
[0025] For example, in the method for preparing a titanium-aluminum alloy diffuser casting for an engine according to the present invention, during the preparation of the ceramic shell, the product part consists of one surface layer, one transition layer and ten back layers; the system part is thickened by 1 to 2 layers based on the composition of the product part and wrapped with a metal mesh.
[0026] For example, in the method for preparing a titanium-aluminum alloy diffuser casting for an engine according to the present invention, during the preparation of the ceramic shell, a surface slurry and a transition layer slurry are prepared by using silica sol and yttrium oxide powder; a back layer slurry is prepared by using silica sol and mullite powder; in the surface layer slurry or the transition layer slurry, the mass ratio of silica sol to yttrium oxide powder is 1:(4~5); in the back layer slurry, the mass ratio of silica sol to mullite powder is 1:(5~6); in another example, in the surface layer slurry or the transition layer slurry, the mass ratio of silica sol to yttrium oxide powder can be 1:4, 1:4.5 or 1:5; in the back layer slurry, the mass ratio of silica sol to mullite powder can be 1:5, 1:5.5 or 1:6.
[0027] As one possible implementation, in the method for preparing a titanium-aluminum alloy diffuser casting for an engine according to the present invention, the preparation of the ceramic mold shell includes: The surface layer slurry is applied to the surface of the wax model, with a thickness of 0.2~0.3 mm; The coating layer is fixed by yttrium oxide sand, and the surface layer is obtained after the wax mold is dried; After the transition layer slurry is applied to the surface layer, and the coating layer is fixed with yttrium oxide sand, the transition layer is obtained after drying. The back layer slurry is coated onto the transition layer to fix the coating layer, and after drying, the back layer is obtained; wherein: After each layer of the backing slurry is applied, it is treated with bauxite sand; the last layer of the backing slurry, which serves as a sealing layer, is not treated with sand and is used to coat the bauxite sand.
[0028] Using this technical solution, a surface layer slurry composed of silica sol and yttrium oxide, along with 325-mesh yttrium oxide sand, can be used to prepare the ceramic mold shell surface layer. By rationally configuring the slurry and controlling the powder-to-liquid ratio within the aforementioned range, nano-sized yttrium oxide particles can be uniformly and diffusely distributed within the slurry. After sanding and drying, the surface layer of the mold shell forms a microstructure where nano-sized yttrium oxide powder encapsulates micron-sized yttrium oxide. Please see [link / reference]. Figure 8 The densely distributed nano-sized yttrium oxide particles significantly improve the inertness of the ceramic shell, while the micron-sized yttrium oxide sand ensures the strength of the surface layer. At the same time, the gaps form good heat dissipation channels, accelerate cooling, and avoid prolonged contact between the alloy liquid and the surface layer, which could lead to intensified reaction.
[0029] For example, in the method for preparing the titanium-aluminum alloy diffuser casting for engines of the present invention, the process of vitrifying the system part and the product part by firing is achieved through two firings; the temperature of the first firing is 650~800℃, and the firing time is 8~10 hours; after cooling the system part and the product part to room temperature, they are heated to 1000~1200℃ for a second firing, and after the second firing is 2~4 hours, the system part and the product part are cooled to room temperature. In another example, the temperature of the first firing can be 650℃, 750℃, or 800℃, and the firing time can be 8 hours, 9 hours, or 10 hours; the temperature of the second firing can be 1000℃, 1100℃, or 1200℃, and the firing time can be 2 hours, 3 hours, or 4 hours.
[0030] For example, during the gravity casting of titanium-aluminum alloy: the melting current can be 12kA, 16kA, or 20kA; the voltage can be 30V, 45V, or 60V; the crucible turning speed can be 5 seconds, 10 seconds, or 15 seconds; after casting, the ceramic shell can be cooled in the furnace to 780°C, 800°C, or 820°C; the temperature-controlled cooling rate can be 2°C / minute, 4°C / minute, or 5°C / minute.
[0031] As one possible implementation, in the method for preparing a titanium-aluminum alloy diffuser casting for an engine according to the present invention, after gravity casting of the titanium-aluminum alloy, the method further includes: obtaining a diffuser casting after gravity casting of the titanium-aluminum alloy, placing the diffuser casting in a hot isostatic press, and holding it at an argon pressure of 135-145 MPa for 2-5 hours. With this technical solution, titanium-aluminum alloys are difficult to repair by welding. During solidification, it is unavoidable that a small amount of porosity or looseness remains inside the casting. Therefore, hot isostatic pressing (HIP) is required to promote defect closure under high temperature and high pressure. When titanium-aluminum alloys are subjected to heat treatment at temperatures above 1150℃, the deformation resistance decreases from 160MPa to 100MPa, and the material softens significantly. By holding the casting at the above temperature and pressure range for 2 to 5 hours, defect closure can be ensured, while avoiding deformation of the casting due to long-term pressure holding. For example, during the HIP process, the temperature can be 1150℃, 1155℃, or 1160℃; the pressure can be 135MPa, 140MPa, or 145MPa; and the holding time can be 2 hours, 4 hours, or 5 hours.
[0032] As one possible implementation, in the method for preparing titanium-aluminum alloy diffuser castings for engines of the present invention, after holding the diffuser castings at argon pressure for 2 to 5 hours, the method further includes: performing vacuum annealing heat treatment on the diffuser castings; during the heat treatment process, the diffuser castings are heated to 1100°C in the furnace and held at that temperature for 1 to 3 hours, and then cooled to 80°C in the furnace before being removed from the furnace.
[0033] To better understand the present invention, the following specific embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.
[0034] Unless otherwise specified, all raw materials used in the following examples are commercially available.
[0035] Example 1 Please see Figures 1 to 4 ,as well as Figure 8 This embodiment provides a method for preparing a titanium-aluminum alloy diffuser casting for an engine, including: Step 1: Design the casting gating system; specifically: Based on the morphological analysis of the diffuser casting model with an outer contour of Ф600mm, the casting has an outline dimension of Ф600mm×61mm. The casting consists of an outer ring, an inner ring, and 24 blades. The maximum wall thickness of the part is 17mm, the minimum wall thickness is 2.3mm, the blade gap is small, and the widest part is 4mm. Based on this, a center bottom-pouring gravity gating system is designed. The gating system consists of a central sprue, a circular cross-shaped bottom runner, a breakable gate, and a circular riser. The cross-sectional area ratio of the central sprue, runner, and gate is 1:2.4:5. Finite element simulation was performed based on the designed gating system and casting model. Figures 5 to 7 As can be seen, the simulation analysis of the risks of incomplete casting, shrinkage cavities and porosity in the casting shows that the casting can be formed completely, and a good feeding channel is formed in the thick area and the thin-thickness junction area of the casting, with no obvious risk of incomplete casting and no obvious shrinkage cavities inside the casting. In addition, according to the stress prediction results, there is stress concentration near the gate, but it does not extend into the casting. The stress at the junction of the casting support plate and the inner and outer rings is reduced to less than 250MPa, which is far below the alloy yield strength. Step 2, prepare the wax model; specifically: The casting wax model (i.e., product mold) was printed using a PMMA (polymethyl methacrylate) powder binder jet printing process. The diameter and height shrinkage rates of the wax model were designed to be 1.01 and 1.02, respectively; the PMMA powder density was 1.1~1.2 g / cm³. 3 The printing environment temperature is controlled between 19℃ and 23℃. After printing, the wax model is left to stand for 24 hours. The wax model is then inspected using blue light scanning, and the shape and size accuracy of the wax model reaches CT4 level. The system mold is printed using cornstarch, and the cornstarch-printed casting system has a hollow structure with internal wax filling for reinforcement. Step 3, prepare the ceramic shell; specifically: The ceramic shells are manufactured using different shell-making processes depending on their function, namely the product section and the system section. Specifically, the product section is manufactured using a process of 1 top layer, 1 transition layer, and 10 back layers. The system section is manufactured using the same shell-making process as the product section, with 2 additional layers added and wire mesh wrapped around it to improve the strength of the gating system. First, the surface layer and transition layer slurry are prepared using silica sol and yttrium oxide powder. By adjusting the ratio of silica sol to yttrium oxide, the powder-to-liquid ratio of the surface layer slurry is controlled at 4.5:1. The slurry is then coated with a suitable viscosity to ensure that the coating is evenly applied to the wax model with a thickness of about 0.2~0.3mm. The coating layer is then fixed with yttrium oxide sand. Finally, the 3D printed wax model is placed in a room with constant temperature and humidity to dry. During the process, the temperature and humidity are kept stable to prepare the surface layer that comes into contact with the molten titanium-aluminum alloy. The viscosity of the surface layer slurry is then reduced to a suitable level. The coating, sanding, and drying processes are repeated on the wax model with the prepared surface layer to prepare the transition layer. Next, a backing slurry is prepared using silica sol and mullite powder, with the powder-to-liquid ratio controlled at 5.5:1. The coating, sanding, and drying processes are repeated on the wax mold with the prepared transition layer at a suitable viscosity. After each layer of backing slurry is applied, bauxite sand is used for sanding. This backing preparation process is repeated multiple times. The final layer does not undergo sanding; its main function as a sealing layer is to coat the bauxite sand, making the mold shell a smooth, unified whole and preventing sand particles from falling into the mold cavity during firing and casting. The shell is ceramicized by firing. Before firing, the smoke exhaust channel is obtained by grinding. After burying fine sand, it is placed in the firing furnace for high-temperature firing. The internal printing model is removed to obtain a hollow shell. The shell is ceramicized by high temperature to improve its strength and resist the impact of molten metal during the casting process. The firing temperature is designed to be raised to 700℃ in the furnace, held for 2 hours, and then cooled in the furnace. After cooling, the sand box is removed and the temperature is raised to 1050℃. The firing time is 2~4 hours to achieve complete burning of the printing model and ceramicization of the shell. Then it is cooled in the furnace. Furthermore, during the preparation of the ceramic shell, the temperature and humidity changes near the ceramic shell are monitored in real time during the drying process, and the air conditioning power is intelligently adjusted to ensure the stability of temperature and humidity near the ceramic shell. The process temperature and humidity real-time data acquisition and control capability online intelligent analysis were also carried out. The analysis results show that the humidity near the shell can be controlled at 30%~35% during the drying process, but there are occasional sudden changes. The online analysis system can calculate the humidity process control capability and deviation based on the real-time data. Step 4, melting and casting; specifically: The ceramic shell is preheated in a natural gas furnace. During this process, the buried sand is heated to 700℃ and held for 6 hours for preheating. After being taken out, it is quickly placed into a 150kg vacuum self-consumable melting and solidification furnace, and gravity casting is carried out under vacuum conditions. The current for melting the titanium-aluminum alloy ingot is 12kA and the voltage is 30V. A water-cooled copper crucible is used, and the crucible is turned over at a speed of 10 seconds. After casting, the ceramic shell is naturally cooled to 800±20℃ in the furnace. The vacuum is then broken and the shell is transferred to a preheated calcining furnace at 800±20℃ for controlled cooling at a rate of 2~5℃ / min. Step 5, hot isostatic pressing of castings; specifically: place the diffuser casting blank into a hot isostatic press with an inner diameter of Ф750mm, keep it at 1160℃ and 140MPa argon pressure for 4 hours, load the casting blank into a sand box, and lay a 5mm thick sponge titanium under the blank to prevent the titanium-aluminum alloy from reacting with the sand box and furnace bottom plate. Step 6, vacuum annealing heat treatment; specifically: place the diffuser casting in a vacuum annealing heat treatment furnace, use graphite pads to isolate the casting from the furnace bottom plate, load the casting into the furnace at room temperature, heat it to 1100℃ with the furnace and hold it for 2 hours, cool it with the furnace, and remove it from the furnace when it cools to 80℃.
[0036] In this embodiment, after the diffuser casting is prepared, X-ray inspection and dimensional inspection are carried out: X-ray radiographic inspection is carried out using a 450kV X-ray flaw detector in accordance with the standard method of "Radiographic Inspection" (GJB 1187A-2019). The inspection results show that the overall metallurgical quality of the casting meets the requirements of the standard of "Specification for Precision Castings of Titanium and Titanium Alloy Investment Castings" (GJB 2896A-2020).
[0037] Example 2 The preparation method of the titanium-aluminum alloy diffuser casting for engines provided in this embodiment is basically the same as that in Embodiment 1. The difference is that the outer ring feeding riser is eliminated in this embodiment to reduce the local turbulence caused by the outer ring riser. The remaining steps are the same as in Embodiment 1.
[0038] Please see Figure 11 In this embodiment, after the diffuser casting is prepared, X-ray inspection and dimensional inspection are performed. The X-ray inspection results show that the casting is completely formed, and the internal metallurgical quality reaches Grade C of GJB2896A-2020. There is local porosity in the outer ring mounting seat, which meets the Grade D requirement. The shape and size of the casting reach CT7 grade.
[0039] Example 3 The preparation method of the titanium-aluminum alloy diffuser casting for engine provided in this embodiment is basically the same as that in embodiment 1. The difference is that in this embodiment, wire mesh reinforcement is added to the bottom horizontal sprue of the circular cross intersection, and the back layer is increased from 10 layers to 11 layers. After the fifth back layer, the fifth layer process is repeated to add another layer, and the rest remains unchanged.
[0040] Please see Figure 12 In this embodiment, after the diffuser casting is prepared, X-ray inspection and dimensional inspection are performed: the X-ray inspection results show that the casting is completely formed and the overall metallurgical quality meets the C-level requirements. The shape and dimensions of the casting meet the CT7 level.
[0041] Comparative Example 1 The method for preparing diffuser castings provided in this comparative example is basically the same as that in Example 1. The difference is that this comparative example uses a center bottom pouring centrifugal casting method with a centrifugal disc rotation speed of 80 r / min.
[0042] Please see Figure 13 In this comparative example, after the diffuser casting was prepared, the casting was completed. However, due to severe cracking at the junction of the support plate and the inner and outer rings, X-ray and dimensional inspections were not performed.
[0043] Comparative Example 2 The method for preparing the diffuser casting provided in this comparative example is basically the same as that in Example 1, except that the product mold in this comparative example is made using photosensitive resin 3D printing. Please refer to [link / reference]. Figure 14 .
[0044] Please see Figure 15 In this comparative example, after the diffuser casting was prepared, the casting was completed. However, there were many internal pore defects in the casting. The main reason was that the ceramic shell expanded during the dewaxing and baking process, resulting in many surface cracks. This caused the alloy liquid to react with the shell and generate gas, forming surface pore defects.
[0045] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.
[0046] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing a titanium-aluminum alloy diffuser casting for an engine, characterized in that, include: Design a gating system, the gating system including a central gating runner and a horizontal gating runner connected to the central gating runner, the ratio of the cross-sectional areas of the central gating runner, the horizontal gating runner and the gate of the gating system being 1:(2~2.5):(4~5); A wax model is prepared, comprising a system model and a product model; the product model has a shrinkage rate of 1~1.1 in the diameter direction and a shrinkage rate of 1~1.05 in the height direction; the system model is made of polymethyl methacrylate, and the product model is made of corn flour. A ceramic shell is prepared, the ceramic shell comprising a system section and a product section; the product section and the system section are composed of a surface layer, a transition layer and a back layer; The system and product parts are vitrified by firing and the wax mold is removed; after preheating the ceramic shell, the titanium-aluminum alloy is gravity-cast.
2. The method for preparing titanium-aluminum alloy diffuser castings for engines according to claim 1, characterized in that, The gating system also includes risers, which are located in an annular area at the top of the casting or in a thick section where they intersect with the inner and outer rings.
3. The method for preparing a titanium-aluminum alloy diffuser casting for an engine according to claim 1, characterized in that, The wax molds are prepared by 3D printing to form system molds and product molds, and then left to stand for 5-24 hours after printing. The system module has a hollow structure and is filled with wax. The polymethyl methacrylate powder has a density of 1.1~1.2 g / cm³. 3 .
4. The method for preparing titanium-aluminum alloy diffuser castings for engines according to claim 1, characterized in that, In the process of preparing the ceramic shell, the product part consists of one surface layer, one transition layer and ten back layers; The system section is thickened by 1 to 2 layers based on the composition of the product section and wrapped with a metal mesh.
5. The method for preparing a titanium-aluminum alloy diffuser casting for an engine according to claim 1 or 4, characterized in that, In the process of preparing the ceramic shell, the surface layer slurry and the transition layer slurry are prepared by using silica sol and yttrium oxide powder; the back layer slurry is prepared by using silica sol and mullite powder. In the surface layer slurry or transition layer slurry, the mass ratio of silica sol to yttrium oxide powder is 1:(4~5); in the back layer slurry, the mass ratio of silica sol to mullite powder is 1:(5~6).
6. The method for preparing a titanium-aluminum alloy diffuser casting for an engine according to claim 5, characterized in that, The preparation of the ceramic shell includes: The surface layer slurry is applied to the surface of the wax model, with a thickness of 0.2~0.3 mm; The coating layer is fixed by yttrium oxide sand, and the surface layer is obtained after the wax mold is dried; After the transition layer slurry is applied to the surface layer, and the coating layer is fixed with yttrium oxide sand, the transition layer is obtained after drying. The back layer slurry is coated onto the transition layer to fix the coating layer, and after drying, the back layer is obtained; wherein: After each layer of the backing slurry is applied, it is treated with bauxite sand; the last layer of the backing slurry, which serves as a sealing layer, is not treated with sand and is used to coat the bauxite sand.
7. The method for preparing a titanium-aluminum alloy diffuser casting for an engine according to claim 1, characterized in that, The process of ceramicizing the system section and product section by firing is achieved through two firings. The first roasting temperature is 650~800℃, and the roasting time is 8~10 hours. After the system section and product section are cooled to room temperature, they are heated to 1000~1200℃ for a second roasting. After the second roasting is 2~4 hours, the system section and product section are cooled to room temperature.
8. The method for preparing a titanium-aluminum alloy diffuser casting for an engine according to claim 1, characterized in that, During the gravity casting process of titanium-aluminum alloy: The smelting current is 12~20kA, and the voltage is 30~60V; Using a water-cooled copper crucible, the crucible is rotated at a speed of 5 to 15 seconds. After pouring, the ceramic shell is cooled to 780 to 820°C in the furnace, and then subjected to controlled cooling at a rate of 2 to 5°C / minute.
9. The method for preparing a titanium-aluminum alloy diffuser casting for an engine according to claim 1, characterized in that, After gravity casting of the titanium-aluminum alloy, the process also includes: After gravity casting of titanium-aluminum alloy, a diffuser casting is obtained. The diffuser casting is placed in a hot isostatic press and held at an argon pressure of 135-145 MPa for 2-5 hours.
10. The method for preparing a titanium-aluminum alloy diffuser casting for an engine according to claim 9, characterized in that, After holding at argon pressure for 2-5 hours, the process also includes: The diffuser casting is subjected to vacuum annealing heat treatment; during the heat treatment process, the diffuser casting is heated to 1100°C in the furnace and held for 1 to 3 hours, and then cooled to 80°C in the furnace before being taken out of the furnace.