A method for 3D printing a multi-layered heterogeneous ceramic shell for titanium alloy casting

Abstract

The application provides a method for 3D printing of a multi-layer heterogeneous ceramic mold shell for titanium alloy casting, which comprises the following steps: dividing a three-dimensional model of the ceramic mold shell into a surface layer, an adjacent surface layer and a back layer, and connecting the surface layer and the back layer through the adjacent surface layer; according to the three-dimensional model, simultaneously extruding and forming the surface layer, the back layer and the adjacent surface layer by using multiple barrels respectively filled with yttrium oxide slurry, aluminum oxide slurry and mixed slurry of yttrium oxide and zirconium oxide, so as to obtain an integrated mold shell; and drying, degreasing, sintering and post-processing the mold shell, so as to obtain a ceramic mold shell for titanium alloy casting. In conclusion, the ceramic mold shell is divided into the surface layer, the adjacent surface layer and the back layer, multiple barrels are used for synchronous cooperation, and multiple modeling materials with different particle sizes are extruded layer by layer to print different areas of the ceramic mold shell, so that an integrated multi-layer composite ceramic mold shell with high surface precision, high surface inertness and high strength is obtained.

Description

Technical Field

[0001] This invention relates to the field of rapid casting technology, and more particularly to a method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting. Background Technology

[0002] Titanium alloys possess excellent properties, including low density, high strength, and corrosion resistance, and are widely used in aerospace, shipbuilding, and automotive industries. Current titanium alloy casting production primarily utilizes precision casting. However, due to titanium's high chemical reactivity, it undergoes a violent chemical reaction with molding materials such as quartz sand and corundum during pouring, resulting in severe casting defects. This necessitates the use of expensive molding materials like yttrium oxide and zirconium oxide. Traditional processes for preparing titanium alloy molds for investment casting are extremely complex, have long production cycles, and are costly, failing to meet the modern demands for short-process, rapid, low-cost, and low-energy-consumption production.

[0003] Layered extrusion 3D printing (additive manufacturing) technology can be combined with investment casting technology to directly print titanium alloy shells through layered extrusion, replacing the traditional wax pattern shell making process. This can effectively shorten the production cycle and reduce production costs, and is suitable for the production of complex, small-batch, and multi-variety castings.

[0004] Patent document CN111940683A discloses a method and apparatus for preparing ceramic shell cores for precision casting, using a multi-head 3D printer extrusion device to rapidly form complex ceramic shell cores for precision casting, but it does not apply this to the printing of mold shells. Patent document CN110227797B discloses a process and equipment for preparing 3D printed ceramic mold shells for titanium alloy casting, using inkjet bonding 3D printing to directly print mold shells for titanium alloy casting, but the surface mold shell still needs to be coated, and the coating preparation process is complex, costly, and time-consuming.

[0005] Traditionally, materials used to prepare ceramic molds for titanium alloy casting include yttrium oxide and zirconium oxide. These materials prevent violent chemical reactions between the ceramic mold and the highly reactive titanium alloy during casting, thus avoiding impacts on casting accuracy and performance. However, yttrium oxide and zirconium oxide are expensive, significantly increasing production costs. While the aforementioned methods can produce molds for titanium alloy casting, they are costly and complex. Therefore, there is an urgent need to develop a method for preparing multilayer ceramic molds suitable for titanium alloy casting, addressing the problems associated with the aforementioned preparation techniques and ceramic mold materials, and meeting the demands of industrial production. Summary of the Invention

[0006] In view of this, the present invention proposes a method for 3D printing multi-layer heterogeneous ceramic shells for titanium alloy casting. The method divides the ceramic shell into three parts: a face layer, a face layer, and a back layer. The face layer and the back layer are connected by the face layer. For the above three-layer structure, multiple barrels are used to extrude different molding materials of different particle sizes in layers to print different areas of the ceramic shell, resulting in an integrated multi-layer composite ceramic shell with high surface precision, high surface inertia, and high strength. Combined with vacuum precision casting technology, it is possible to achieve precision casting of integrated titanium alloys, achieving the goals of short process, high-efficiency production, and cost reduction.

[0007] The technical solution of this invention is implemented as follows:

[0008] This invention provides a method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting, comprising the following steps:

[0009] S1 performs a three-dimensional modeling of the ceramic shell based on the structure of the titanium alloy casting and divides the area into three parts: the face layer, the adjacent layer, and the back layer. The face layer and the back layer are connected to each other through the adjacent layer.

[0010] In the above steps, according to the strength and precision requirements of the ceramic shell to be prepared, the three-dimensional model is divided into regions, namely a surface layer and a back layer structure. There is also an adjacent layer between the surface layer and the back layer, forming an integrated three-dimensional model. The ceramic shell is a casting shell used for casting.

[0011] S2 uses multiple barrels containing yttrium oxide slurry, alumina slurry, and a mixture of yttrium oxide and zirconium oxide slurry to simultaneously extrude and form a shell with an integrated surface layer, back layer, and adjacent surface layer, based on a three-dimensional model.

[0012] The above process enables the integral forming of shells with different materials, different particle sizes, and multiple gradients.

[0013] S3 performs drying, degreasing, sintering and post-treatment of the mold shell to obtain a ceramic mold shell for titanium alloy casting.

[0014] More preferably, in step S2, the yttrium oxide slurry is prepared as follows: using 500-2000 mesh yttrium oxide powder as the main material, 1.5-2.5% methylcellulose as a binder, 25-35% ammonium polyacrylate aqueous solution as a dispersant, 8-12% ammonia as a pH adjuster, and 700-1000 mesh calcium oxide as a sintering aid, the slurry is ball-milled at 200 r / min at 20-25℃ for 8-10 hours, and then allowed to stand for at least 30 minutes to obtain the yttrium oxide slurry; the yttrium oxide slurry is used for printing the surface shell. The mass ratio of yttrium oxide powder, ammonium polyacrylate aqueous solution, methylcellulose, ammonia, and calcium oxide powder is (75-80):(1-3):(15-20):(1-3):(1-3).

[0015] More preferably, in step S2, the alumina slurry is prepared by using 200-400 mesh alumina powder as the main material, 1.5-2.5% methylcellulose by mass concentration as a binder, and 8-12% acetic acid solution by volume concentration as a dispersant. The slurry is ball-milled at 200 r / min at 20-25℃ for 8-10 hours, and then allowed to stand for at least 30 minutes to obtain the alumina slurry. The alumina slurry is used for printing the back shell. The mass ratio of alumina powder, acetic acid solution, and methylcellulose is (72-80):(2-5):(17-25).

[0016] More preferably, the preparation method of the yttrium oxide and zirconium oxide mixed slurry is as follows: using a mixture of 500-2000 mesh yttrium oxide and zirconium oxide powder as the main material, 1.5-2.5% methylcellulose by mass concentration as a binder, 25-35% ammonium polyacrylate aqueous solution by mass concentration as a dispersant, 8-12% ammonia water by volume concentration as a pH adjuster, and 700-1000 mesh calcium oxide as a sintering aid, the slurry is ball-milled at 200 r / min at 20-25℃ for 8-10 hours, and then allowed to stand for more than 30 minutes to obtain the yttrium oxide and zirconium oxide mixed slurry. The yttrium oxide and zirconium oxide mixed slurry is used for printing the surface layer.

[0017] More preferably, in the yttrium oxide and zirconium oxide slurry, yttrium oxide powder, zirconium oxide powder, ammonium polyacrylate aqueous solution, methylcellulose, and ammonia are mixed uniformly in a mass ratio of (35-45):(35-45):(1-3):(15-25):(1-3); the amount of calcium oxide is 1-5% of the total weight of other raw materials (yttrium oxide powder, zirconium oxide powder, ammonium polyacrylate aqueous solution, methylcellulose, and ammonia).

[0018] Yttrium oxide and zirconium oxide possess excellent high-temperature inertness, preventing reactions between the ceramic shell and the titanium alloy at high temperatures. Using other ceramic shells, such as alumina or calcium oxide shells, would cause the titanium alloy to react with the ceramic shell, making it difficult to form high-quality titanium alloys. Furthermore, a mixture of these two materials is chosen as the facing layer to ensure a stable and robust interface with both the face and back layers.

[0019] The binder can bond ceramic powder together, ensuring the accurate shape and size of the shell; it can also slow down the flow of ceramic powder, making it easier to control during the extrusion process; at the same time, it can improve the bonding force between ceramic powder and substrate, improving the strength and durability of the shell. Through the above actions, the ceramic powder and substrate are bonded together to form a complete shell.

[0020] Dispersants can reduce the viscosity of ceramic particles, making them easier to disperse evenly in slurry. They can also increase the surface area of ​​ceramic particles, making them easier to be adsorbed and dispersed by another liquid or solid. Furthermore, they can reduce particle agglomeration, making them more dispersed and stable.

[0021] Proper pH adjustment can improve the smoothness and precision of the shell surface, thereby improving product quality and production efficiency. The pH value needs to be adjusted according to factors such as specific materials, extrusion equipment, and process conditions.

[0022] Ball milling can reduce the agglomeration of particulate powders in slurry systems.

[0023] More preferably, the thickness of the surface layer is 1-2 mm. If the surface layer is too thin, it can easily lead to insufficient strength and high-temperature stability of the ceramic shell. The porosity of the surface layer is 40%-50%. The thickness of the adjacent layer is 1.5-2.5 mm, and the porosity is 20%-40%. The thickness of the back layer is 2-3 mm, and the porosity is 5%-20%.

[0024] More preferably, the needle diameter of the barrel containing yttrium oxide slurry is 0.05-0.3 mm; the needle diameter of the barrel containing alumina slurry is 0.3-0.4 mm; and the needle diameter of the barrel containing a mixed slurry of yttrium oxide and zirconium oxide is 0.3-0.4 mm. A smaller needle diameter allows for the formation of molded shells with higher precision, but if the diameter is too small, it can easily lead to low production efficiency or needle clogging. This invention improves the precision of ceramic molded shells by selecting appropriate needles for the face layer, back layer, and adjacent layer molded shells.

[0025] More preferably, the extrusion speed of the layered extrusion molding is 5-9 mm / s.

[0026] More preferably, the height of the top layer is 0.08-0.13 mm, the height of the back layer is 0.17-0.23 mm, and the height of the adjacent layer is 0.1-0.2 mm.

[0027] More preferably, in step S3, the printed ceramic shell is placed in a drying oven, and the drying conditions are a temperature of 47-53°C, a humidity of <5%, and a drying time of 24 hours.

[0028] More preferably, in step S3, the dried ceramic shell is placed in a calcining furnace for high-temperature calcination. First, it is calcined at 300℃ for 0.8-1.3h to remove the binder, and then calcined at 1400℃-1500℃ for 4h to obtain a multilayer composite ceramic shell with high surface precision, high surface inertness, high strength and low cost.

[0029] In this invention, the wall thickness of the ceramic shell is generally less than 8-12 mm.

[0030] The working principle of this invention is as follows:

[0031] A 3D model of the ceramic shell to be prepared was created based on the structure of the titanium alloy casting. According to the different precision and strength requirements of the multi-layered ceramic shell, the 3D model was divided into a surface layer and a back layer. Between the surface layer and the back layer is an adjacent layer. The surface layer, adjacent layer, and back layer constitute an integrated 3D model. This 3D model has a complex 3D structure, including internal channels.

[0032] For the three-layer structure, multiple barrels are used simultaneously and collaboratively to extrude different areas of the ceramic shell using various molding materials of different particle sizes. Simultaneously, the extrusion molding process parameters for the corresponding areas of the multi-layer ceramic shell to be prepared are determined according to actual production needs, including the diameter of the extruder head, extrusion speed, and layer height. Then, each area is sliced ​​according to the required precision.

[0033] In ceramic shell casting, the forming accuracy of the surface ceramic shell directly affects the forming accuracy of the casting surface, and the material used for the surface ceramic shell directly determines the quality of the casting surface. Due to the performance requirements of multi-layer ceramic shells for titanium alloy casting, yttrium oxide and zirconium oxide, which have good stability, are selected as the surface shell materials, while high-strength alumina is selected as the back shell material. Furthermore, due to precision requirements, the powder particles used for printing the surface shell are finer, resulting in a smaller extruder diameter, a smaller layer height, and a suitable extrusion molding rate. Conversely, the powder particles used for printing the back shell are coarser, resulting in a larger extruder diameter, a larger layer height, and a suitable extrusion molding rate, thus reducing production costs while increasing shell strength.

[0034] Finally, the fired ceramic shell is finished to improve its surface precision and meet the requirements of precision casting of titanium alloy.

[0035] Multi-layer ceramic shells can be precisely adjusted in terms of shell material and thickness according to actual production needs, so that there is a good interface bond between each layer of ceramic shell, realizing the precise and rapid forming of multi-layer ceramic shells for precision casting of titanium alloys.

[0036] The method for 3D printing ceramic shells of the present invention has the following advantages over the prior art:

[0037] 1. This invention divides the ceramic mold shell for titanium alloy casting into three parts: a face layer, a back layer, and an adjacent layer. Different printing pastes are used for different parts of the ceramic mold shell. At the same time, through the function of the adjacent layer, the transition between different materials can be further realized, so that each layer of mold shell made of different materials can give full play to its function, and at the same time improve the interface bonding between each layer of mold shell.

[0038] 2. The main material of the surface layer is yttrium oxide or zirconium oxide, which has good chemical inertness and fine particle size, but is expensive; the main material of the back layer is alumina, which has high refractoriness but is inexpensive; by selecting the surface layer and back layer materials, the multi-layer composite ceramic shell can have high surface precision, high surface inertness and high strength, while reducing costs.

[0039] 3. The facing layer material consists of yttrium oxide, zirconium oxide, ammonium polyacrylate aqueous solution, methylcellulose, and ammonia. The facing layer slurry is ball-milled after sintering. This combination of materials ensures a stable and robust interface between the facing and back layers, guaranteeing accurate shape and dimensions of the shell, increasing the dispersion of the slurry across the three layers, and controlling the smoothness and precision of the shell surface. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of the ceramic shell formed by multi-head layered extrusion in Example 1.

[0042] Figure 2 These are optical microscope images of the interfaces of the face layer, adjacent layer, and back layer of the ceramic shell prepared in Example 1. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] (1) Based on the structure of the 2-meter-long titanium alloy intake pipe casting, a three-dimensional model of the corresponding shell to be prepared is established, and it is divided into three parts: surface layer 1, adjacent layer 2, and back layer 3. An adjacent layer 2 is set between surface layer 1 and back layer 3 (e.g., Figure 1 As shown, the thickness of the top layer 1 is 1.5 mm, the thickness of the front layer 2 is 2 mm, and the thickness of the back layer 3 is 2.5 mm.

[0046] (2) Import the 3D model into the layer extrusion printer, and use slicing software to perform Z-axis layer slicing on the 3D model to obtain the layer processing instructions.

[0047] (3) Mix 1500 mesh yttrium oxide powder, 20% ammonium polyacrylate aqueous solution, 2% methylcellulose, 10% ammonia water and 850 mesh calcium oxide powder in a mass ratio of 78:2:18:2:2. Then, ball mill the slurry at 200 r / min at 22°C for 8 hours and let it stand for 30 minutes to obtain yttrium oxide slurry. Load the yttrium oxide slurry into the barrel 4 of the layered extrusion molding equipment for molding the surface shell.

[0048] (4) Mix 300 mesh alumina powder, 10% acetic acid solution and 2% methylcellulose in a mass ratio of 76:3:21. Then, ball mill the slurry at 150 r / min at 22°C for 9 hours and let it stand for 30 minutes to obtain alumina slurry. Load the alumina slurry into the barrel 6 of the layered extrusion molding equipment for molding the back shell.

[0049] (5) Mix 1500 mesh yttrium oxide, 1500 mesh zirconium oxide powder, 30% ammonium polyacrylate aqueous solution, 2% methylcellulose and 10% ammonia water in a mass ratio of 40:38:2:20:2 until uniform. Then add 3% calcium oxide of the total weight of the above raw materials and ball mill the slurry at 200 r / min at 22°C for 8 hours. Let it stand for 30 minutes to obtain the printing slurry for the face layer. Load the printing slurry for the face layer into the barrel 5 of the layer extrusion molding equipment for molding the face layer shell.

[0050] (6) Using the above slurry as raw material, a titanium alloy shell is formed by layered extrusion molding. The needle diameter of the barrel containing yttrium oxide slurry is 0.2 mm; the needle diameter of the barrel containing alumina slurry is 0.35 mm; and the needle diameter of the barrel containing a mixed slurry of yttrium oxide and zirconium oxide is 0.35 mm. The extrusion speed of the layered extrusion molding is 8 mm / s. The layer height of the face layer is 0.1 mm, the layer height of the back layer is 0.2 mm, and the layer height of the adjacent layer is 0.15 mm.

[0051] (7) Finally, the printed ceramic shell is placed in a drying oven under the following conditions: temperature 51℃, humidity 3%, and drying time 24 hours. The dried ceramic shell is then placed in a firing furnace for high-temperature firing. First, it is fired at 300℃ for 1.0 h to remove the binder, and then at 1450℃ for 4 h to obtain a high-strength shell. The porosity of the surface layer is 45%; the porosity of the adjacent surface layer is 30%; and the porosity of the back layer is 10%.

[0052] The optical micrograph at the interface between the surface shell and the back shell is as follows: Figure 2 As shown, the surface shell and the back shell are well bonded, realizing the layered extrusion molding of multi-layer, multi-particle-size ceramic shells.

[0053] Example 2

[0054] (1) Based on the structure of the titanium alloy impeller casting, a three-dimensional model of the corresponding shell to be prepared is established, and it is divided into three parts: surface layer, adjacent layer and back layer. An adjacent layer is set between the surface layer and the back layer. The surface layer has a thickness of 1 mm, the adjacent layer has a thickness of 2 mm, and the back layer has a thickness of 2 mm.

[0055] (2) Import the 3D model into the layer extrusion printer, and use slicing software to perform Z-axis layer slicing on the 3D model to obtain the layer processing instructions.

[0056] (3) Mix 500 mesh zirconia powder, 25% ammonium polyacrylate aqueous solution, 1.5% methylcellulose, 8% ammonia water and 700 mesh calcium oxide powder in a mass ratio of 75:1:15:1:1. Then, ball mill the slurry at 200 r / min at 20℃ for 8 hours and let it stand for 30 minutes to obtain zirconia slurry.

[0057] (4) Mix 200 mesh alumina powder, 8% acetic acid solution and 1.5% methylcellulose in a mass ratio of 72:2:17. Then, ball mill the slurry at 20°C and a speed of 150 r / min for 8 hours. After standing for 30 minutes, the alumina slurry is obtained.

[0058] (5) Mix 500 mesh yttrium oxide, 800 mesh zirconium oxide powder, 25% ammonium polyacrylate aqueous solution, 1.5% methylcellulose and 8% ammonia water in a mass ratio of 35:35:1:15:1. Then, ball mill the slurry at 200 r / min at 20°C for 8 hours and let it stand for 30 minutes to obtain yttrium oxide and zirconium oxide slurry.

[0059] (6) Using the above slurry as raw material, a titanium alloy shell is formed by layered extrusion molding. The needle diameter of the barrel containing yttrium oxide slurry is 0.05 mm; the needle diameter of the barrel containing alumina slurry is 0.3 mm; and the needle diameter of the barrel containing a mixed slurry of yttrium oxide and zirconium oxide is 0.3 mm. The extrusion speed of the layered extrusion molding is 5 mm / s. The layer height of the face layer is 0.08 mm, the layer height of the back layer is 0.17 mm, and the layer height of the adjacent layer is 0.1 mm.

[0060] (7) Finally, the printed ceramic shell is placed in a drying oven under the following conditions: temperature 47℃, humidity 4%, and drying time 24 hours. The dried ceramic shell is then placed in a firing furnace for high-temperature firing. First, it is fired at 300℃ for 0.8 hours to remove the binder, and then at 1400℃ for 4 hours to obtain a high-strength shell. The porosity of the surface layer is 40%; the porosity of the adjacent surface layer is 20%; and the porosity of the back layer is 5%.

[0061] Example 3

[0062] (1) Based on the structure of the titanium alloy impeller casting, a three-dimensional model of the corresponding shell to be prepared is established and it is divided into three parts: surface layer, adjacent layer and back layer. An adjacent layer is set between the surface layer and the back layer. The surface layer has a thickness of 2mm, the adjacent layer has a thickness of 2mm, and the back layer has a thickness of 3mm.

[0063] (2) Import the 3D model into the layer extrusion printer, and use slicing software to perform Z-axis layer slicing on the 3D model to obtain the layer processing instructions.

[0064] (3) Mix 2000 mesh zirconia powder, 35% ammonium polyacrylate aqueous solution, 2.5% methylcellulose, 12% ammonia water and 1000 mesh calcium oxide powder in a mass ratio of 80:3:20:3:3. Then, ball mill the slurry at 200 r / min at 25°C for 12 h and let it stand for 30 min to obtain zirconia slurry.

[0065] (4) Mix 400 mesh alumina powder, 12% acetic acid solution and 2.5% methylcellulose in a mass ratio of 80:5:25. Then, ball mill the slurry at 150 r / min at 25°C for 12 h and let it stand for 30 min to obtain alumina slurry.

[0066] (5) Mix 2000 mesh yttrium oxide, 800 mesh zirconium oxide powder, 35% ammonium polyacrylate aqueous solution, 2.5% methylcellulose and 12% ammonia water in a mass ratio of 45:45:3:25:3. Then, ball mill the slurry at 200 r / min at 25°C for 12 h and let it stand for 30 min to obtain yttrium oxide and zirconium oxide slurry.

[0067] (6) Using the above slurry as raw material, a titanium alloy shell is formed by layered extrusion molding. The needle diameter of the barrel containing yttrium oxide slurry is 0.3 mm; the needle diameter of the barrel containing alumina slurry is 0.4 mm; and the needle diameter of the barrel containing a mixed slurry of yttrium oxide and zirconium oxide is 0.4 mm. The extrusion speed of the layered extrusion molding is 9 mm / s. The layer height of the face layer is 0.13 mm, the layer height of the back layer is 0.23 mm, and the layer height of the adjacent layer is 0.2 mm.

[0068] (7) Finally, the printed ceramic shell is placed in a drying oven under the following conditions: temperature 53℃, humidity 4%, and drying time 24 hours. The dried ceramic shell is then placed in a firing furnace for high-temperature firing. First, it is fired at 300℃ for 1.3 hours to remove the binder, and then at 1500℃ for 4 hours to obtain a high-strength shell. The porosity of the surface layer is 50%; the porosity of the adjacent surface layer is 40%; and the porosity of the back layer is 20%.

[0069] Comparative Example 1 only has a surface layer and a back layer, but no adjacent layer.

[0070] The ceramic shell was printed according to the preparation method in Example 1. The difference was that the three-dimensional model of the shell to be prepared did not include the apical layer, and no shell containing the apical layer was prepared. Otherwise, it was consistent with Example 1.

[0071] Comparative Example 2 only has the surface layer, without the adjacent and back layers.

[0072] The ceramic shell was printed according to the preparation method in Example 1. The difference was that the three-dimensional model of the shell to be prepared only had the surface layer and did not include the face layer and the back layer. The shell containing the face layer and the back layer was not prepared. Everything else was consistent with Example 1.

[0073] Comparative Example 3: The slurry composition of both the top and back layers is entirely alumina, with no adjacent layers.

[0074] The ceramic shell was printed according to the preparation method in Example 1, except that the yttrium oxide powder in the surface shell was replaced with alumina powder. Also, the three-dimensional model of the shell to be prepared did not include the apical layer, and no shell containing the apical layer was prepared. Everything else was the same as in Example 1.

[0075] Comparative Example 4: The slurry composition of the surface layer is alumina, without an adjacent layer or a back layer.

[0076] The ceramic shell was printed according to the preparation method in Example 1, except that the yttrium oxide powder in the surface shell was replaced with alumina powder. Also, the three-dimensional model of the shell to be prepared did not include the face layer and the back layer, and no shell containing the face layer and the back layer was prepared. Everything else was the same as in Example 1.

[0077] Comparative Example 5: The slurry composition of both the face and back layers is entirely yttrium oxide, with no adjacent layer.

[0078] The ceramic shell was printed according to the preparation method in Example 1, except that the alumina powder in the back shell was replaced with yttrium oxide powder. Also, the three-dimensional model of the shell to be prepared did not include the apical layer, and no shell containing the apical layer was prepared. Everything else was the same as in Example 1.

[0079] Comparative Example 6: Different Surface Layer Slurry

[0080] The ceramic shell was printed according to the preparation method in Example 1, except that the printing paste for the face layer contained only yttrium oxide and zirconium oxide powder in a mass ratio of 40:38; all other aspects were consistent with Example 1.

[0081] In this comparative example, since the printing paste of the adjacent layer only contains yttrium oxide and zirconium oxide powder, it cannot be shaped and cannot form a paste. It can be used for coating methods, but cannot be used for the 3D printing method in this application.

[0082] Comparative Example 7: Different Surface Layer Slurry

[0083] The ceramic shell was printed according to the preparation method in Example 1, except that the printing paste for the face layer only included yttrium oxide powder, zirconium oxide powder and ammonium polyacrylate aqueous solution, with a mass ratio of 40:38:2; all other aspects were consistent with Example 1.

[0084] In this comparative example, since the printing slurry for the face layer only contains yttrium oxide powder, zirconium oxide powder, and an aqueous solution of ammonium polyacrylate, the slurry viscosity is too low to form a paste. It can be used for coating methods, but not for the 3D printing method in this application.

[0085] Comparative Example 8: Different Surface Layer Slurry

[0086] The ceramic shell was printed according to the preparation method in Example 1, except that the printing paste for the face layer only included yttrium oxide powder, zirconium oxide powder and methylcellulose, with a mass ratio of 40:38:20; all other aspects were consistent with Example 1.

[0087] In this comparative example, since the printing slurry for the face layer only includes yttrium oxide powder, zirconium oxide powder and methylcellulose, the slurry cannot achieve a uniform state when mixed, and cannot be formed. It is prone to clogging the needle during the extrusion process. It can be used for coating methods, but cannot be used for the 3D printing method in this application.

[0088] Comparative Example 9: Different surface layer slurry

[0089] The ceramic shell was printed according to the preparation method in Example 1, except that the printing paste for the face layer only included yttrium oxide powder, zirconium oxide powder and ammonia water, with a mass ratio of 40:38:2; all other aspects were consistent with Example 1.

[0090] In this comparative example, since the printing slurry for the adjacent layer only contains yttrium oxide powder, zirconium oxide powder, and ammonia, the slurry viscosity is too low to form a paste. It can be used for coating methods, but not for the 3D printing method in this application.

[0091] Comparative Example 10: Different Approach Layer Slurries

[0092] The ceramic shell was printed according to the preparation method in Example 1, except that the printing paste for the face layer only included yttrium oxide powder, zirconium oxide powder, ammonium polyacrylate aqueous solution and methylcellulose in a mass ratio of 40:38:2:20; all other aspects were consistent with Example 1.

[0093] In this comparative example, since the printing paste for the face layer only includes yttrium oxide powder, zirconium oxide powder, ammonium polyacrylate aqueous solution and methylcellulose, the paste viscosity is too high to be extruded smoothly. It can be used for coating methods, but not for the 3D printing method in this application.

[0094] Comparative Example 11: Different surface layer slurry materials

[0095] The ceramic shell was printed according to the preparation method in Example 1, except that the printing paste for the face layer only included yttrium oxide powder, zirconium oxide powder, ammonium polyacrylate aqueous solution and ammonia water in a mass ratio of 40:38:2:2; all other aspects were consistent with Example 1.

[0096] In this comparative example, since the printing paste for the face layer only includes yttrium oxide powder, zirconium oxide powder, ammonium polyacrylate aqueous solution and ammonia, the paste viscosity is too low to form a paste. It can be used for coating methods, but not for the 3D printing method in this application.

[0097] The ceramic shells prepared in the above embodiments and comparative examples 1-5 were subjected to surface roughness, shrinkage rate and bending strength tests. The specific test results are shown in Table 1 below.

[0098] Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-5 of the present invention

[0099]

[0100] The performance test results in Table 1 show that:

[0101] Because the shell prepared in Comparative Example 1 does not have a face shell connecting the face shell and the back shell, and the shrinkage rate of the face shell differs too much from that of the back shell, the shell is prone to cracking when pouring titanium alloy molten metal, and it is impossible to obtain a ceramic shell suitable for titanium alloy casting.

[0102] Comparative Example 2, due to having only a surface layer, resulted in a shell thickness that was too thin, leading to a bending strength of only 10.3 MPa, which could not meet the requirements. During the casting of large titanium alloy components, this could easily cause the shell to deform or crack, resulting in cracks in the castings. It was impossible to obtain a ceramic shell suitable for titanium alloy casting.

[0103] The alumina-based mold shell prepared in Comparative Example 3 had too high a surface roughness, resulting in low surface precision and poor quality of the obtained titanium alloy castings. During the casting of large titanium alloy components, the mold shell is prone to reacting with the molten titanium alloy at high temperatures, leading to the presence of molten titanium alloy inside the mold shell and affecting the quality of the castings.

[0104] Comparative Example 4 only has a surface layer, and the surface layer slurry is composed of alumina. The shell thickness is too thin, and the bending strength is too low, only 12.1 MPa, which cannot meet the requirements. In the casting process of large titanium alloy components, it is easy to cause the shell to deform or crack, resulting in cracks in the casting. It is impossible to obtain a ceramic shell suitable for titanium alloy casting. At the same time, the shell is prone to reacting with the titanium alloy molten material at high temperatures, resulting in the presence of titanium alloy molten material inside the shell, which affects the quality of the casting.

[0105] The shell prepared in Comparative Example 5 has too low bending strength, with only 12.4 MPa for the surface layer and 13.4 MPa for the back layer, which cannot meet the requirements. In the casting process of large titanium alloy components, it is easy to cause the shell to deform or crack, resulting in cracks in the casting. It is impossible to obtain a ceramic shell suitable for titanium alloy casting.

[0106] In addition, in Comparative Examples 6-11, due to the different slurry in the face layer, the viscosity of the slurry in the face layer was too low or too high, which prevented the formation of slurry or blocked the needle, and therefore could not be used in the 3D printing method of this application.

[0107] The multilayer titanium alloy composite shell prepared by the method provided in this invention has good surface roughness, suitable sintering shrinkage rate and sufficient bending strength, which can meet the requirements of high-quality precision casting of titanium alloy.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting, characterized in that, Includes the following steps: S1 performs a three-dimensional modeling of the ceramic shell based on the structure of the titanium alloy casting, and divides the three-dimensional model into three parts: the face layer, the adjacent layer, and the back layer. The face layer and the back layer are connected to each other through the adjacent layer. S2 uses multiple cylinders containing yttrium oxide slurry, alumina slurry, and a mixed slurry of yttrium oxide and zirconium oxide respectively to simultaneously extrude and form a shell integrating the surface layer, back layer, and adjacent layer, based on the three-dimensional model. S3 involves drying, degreasing, sintering, and post-treatment of the mold shell to obtain a ceramic mold shell for titanium alloy casting.

2. The method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting as described in claim 1, characterized in that: In step S2, the yttrium oxide slurry is prepared as follows: using 500-2000 mesh yttrium oxide powder as the main material, 1.5-2.5% methylcellulose as a binder, 25-35% ammonium polyacrylate aqueous solution as a dispersant, 8-12% ammonia water as a pH adjuster, and 700-1000 mesh calcium oxide as a sintering aid, the mixture is ball-milled at 20-25°C for 8-10 hours, and then allowed to stand to obtain the yttrium oxide slurry. The yttrium oxide slurry is used for printing the surface shell.

3. The method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting as described in claim 2, characterized in that: The mass ratio of yttrium oxide powder, ammonium polyacrylate aqueous solution, methylcellulose, ammonia water, and calcium oxide powder is (75-80):(1-3):(15-20):(1-3):(1-3).

4. The method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting as described in claim 1, characterized in that: In step S2, the alumina slurry is prepared by using 200-400 mesh alumina powder as the main material, methyl cellulose with a mass concentration of 1.5-2.5% as the binder, and acetic acid solution with a volume concentration of 8-12% as the dispersant. The mixture is ball-milled at 20-25°C for 8-10 hours and then allowed to stand to obtain the alumina slurry. The alumina slurry is used for printing the back shell.

5. The method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting as described in claim 4, characterized in that: The mass ratio of alumina powder, acetic acid solution, and methylcellulose is (72-80):(2-5):(17-25).

6. The method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting as described in claim 1, characterized in that: In step S2, the preparation method of the yttrium oxide and zirconium oxide mixed slurry is as follows: using a mixture of 500-2000 mesh yttrium oxide and zirconium oxide powder as the main material, 1.5-2.5% methylcellulose by mass concentration as a binder, 25-35% ammonium polyacrylate aqueous solution by mass concentration as a dispersant, 8-12% ammonia water by volume concentration as a pH adjuster, and 700-1000 mesh calcium oxide as a sintering aid, ball milling is performed at 20-25℃ for 8-10 hours. After standing, the yttrium oxide and zirconium oxide mixed slurry is obtained. The yttrium oxide and zirconium oxide mixed slurry is used for printing the surface layer.

7. The method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting as described in claim 6, characterized in that: In the yttrium oxide and zirconium oxide mixed slurry, the mass ratio of yttrium oxide powder, zirconium oxide powder, ammonium polyacrylate aqueous solution, methylcellulose, and ammonia is (35-45):(35-45):(1-3):(15-25):(1-3); the amount of calcium oxide is 1-5% of the total weight of yttrium oxide powder, zirconium oxide powder, ammonium polyacrylate aqueous solution, methylcellulose, and ammonia.

8. The method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting as described in claim 1, characterized in that: In step S2, the needle diameter of the cylinder containing yttrium oxide slurry is 0.05-0.3 mm; the needle diameter of the cylinder containing alumina slurry is 0.3-0.4 mm; and the needle diameter of the cylinder containing a mixed slurry of yttrium oxide and zirconium oxide is 0.3-0.4 mm.

9. The method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting as described in claim 1, characterized in that: The thickness of the surface layer is 1-2 mm, and the porosity of the surface layer is 40%-50%; the thickness of the adjacent layer is 1.5-2.5 mm, and the porosity of the adjacent layer is 20%-40%; the thickness of the back layer is 2-3 mm, and the porosity of the back layer is 5%-20%.

10. The method for 3D printing multilayer heterogeneous ceramic shells for titanium alloy casting as described in claim 1, characterized in that: The height of the top layer is 0.08-0.13mm, the height of the back layer is 0.17-0.23mm, and the height of the adjacent layer is 0.1-0.2mm.

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