Silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting and preparation method of silica sol-yttrium oxide composite mold shell surface layer
By using a method for preparing a silica sol-yttrium oxide composite mold shell surface layer, the problems of hydration sensitivity and insufficient sintering density of yttrium oxide mold shells are solved, achieving high strength, thermal shock resistance, and low-cost casting effects for the mold shell, which is suitable for high-precision castings of TiAl alloys.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-05
- Publication Date
- 2026-04-03
Abstract
Description
Technical Field
[0001] This invention relates to the field of metal smelting technology, and in particular to a silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting and its preparation method. Background Technology
[0002] Thrust-to-weight ratio is a core indicator for evaluating aero-engine performance, and reducing engine weight is one of the key paths to improving it. Traditional high-temperature structural materials are mainly nickel-based superalloys with densities as high as 7.9-9.5 g / cm³. While they possess excellent mechanical properties at high temperatures, their large weight becomes a bottleneck restricting further improvements in engine efficiency. TiAl alloys, with a density of only 3.8-4.2 g / cm³, offer a more competitive advantage. 3 (Approximately half the strength of nickel-based alloys), while maintaining good strength, creep resistance, and oxidation resistance in the 600-800℃ temperature range, it has become an important choice for the new generation of lightweight high-temperature structural materials and is widely used in key parts such as turbine blades and compressor components.
[0003] Investment casting technology, with its advantages of strong controllability of the "mold-melt" interface and the ability to achieve near-net-shape forming of complex components, is considered the mainstream process for precision forming of TiAl alloys. Among these, the preparation of the mold shell, especially the design and control of the surface layer material, directly determines the surface quality and yield of the casting. Because TiAl alloys are extremely chemically reactive in the molten state and readily react violently with conventional refractory materials, extremely stringent requirements are placed on the chemical inertness of the mold shell surface layer.
[0004] Currently, the main surface refractory materials suitable for titanium alloy investment casting include graphite, refractory metals, and oxide ceramics. Among various oxides, based on their bonding free energy with titanium, their chemical stability from highest to lowest is: Y₂O₃ > ThO₂ > CaO > ZrO₂ > Al₂O₃ > MgO > SiO₂. Among these, yttrium oxide (Y₂O₃), due to its high melting point of 2410℃, excellent high-temperature structural stability, and a contact angle of up to 153° with molten titanium, exhibits the lowest interfacial reactivity. Its corrosion rate is two orders of magnitude lower than that of ZrO₂, making it widely recognized as the most ideal mold shell material for TiAl alloy casting.
[0005] However, yttrium oxide has long been hampered by its significant "water-based weakness" in practical applications. Y₂O₃ readily reacts with water to form Y(OH)₃ hydrates, accompanied by volume expansion, leading to a sharp increase in slurry viscosity. It typically gels within 6 hours of standing, losing its workability and becoming difficult to reuse. During drying, the dehydration and decomposition of the hydrates triggers a microcrack network, causing the mold shell to peel and shed powder during firing or casting, and in severe cases, resulting in "pitting" defects on the casting surface. Furthermore, the surface charge of Y₂O₃ particles is highly sensitive to the pH of the system. Once the pH drops below 10 due to CO₂ absorption or dilution, the particle zeta potential decreases rapidly, inducing irreversible agglomeration and sedimentation, further limiting the slurry's processing window. These problems collectively result in the engineering bottleneck of "short lifespan, poor stability, and high cost" for yttrium oxide water-based slurries, severely restricting the stable mass production of large, high-precision TiAl alloy components.
[0006] To improve slurry stability, silica sol has become a preferred binder for preparing yttrium oxide slurries due to its advantages such as adjustable pH, high sintering activity, and low cost. Studies have shown that by adding inorganic or organic strong bases (such as tetramethylammonium hydroxide) to adjust the pH of silica sol to above 11.2, Y₂O₃ hydration can be effectively inhibited, extending the slurry's service life. Simultaneously, the SiO₂ particles in the silica sol help improve the mechanical strength and resistance to molten metal erosion of the mold shell. However, existing silica sol / yttrium oxide mold shells still face two major problems: Firstly, Y2O3 itself has low sintering activity, and even under high-temperature calcination conditions, it is difficult to fully densify, resulting in insufficient overall strength of the mold shell and limited thermal shock resistance and anti-stripping performance. Secondly, while the highly active SiO2 particles introduced by silica sol are beneficial for sintering, they damage the chemical inertness of the mold shell. In the localized SiO2 enrichment areas, it is easy to become a "breakthrough point" for TiAl melt erosion, inducing severe interfacial reactions. The thickness of the contamination layer on some castings even exceeds 500μm, which is far from meeting the quality requirements of high-performance aerospace components.
[0007] In summary, there is an urgent need for a novel shell surface layer technology that can fully utilize the chemical inertness of yttrium oxide, effectively overcome its hydration sensitivity, improve sintering density, and simultaneously suppress the negative effects of SiO2.
[0008] In view of this, the present invention is proposed. Summary of the Invention
[0009] The purpose of this invention is to provide a silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting and its preparation method, so as to solve the problems existing in the prior art.
[0010] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is to provide a silica sol-yttrium oxide composite mold shell surface layer slurry for TiAl alloy investment casting, wherein the raw materials include the following components by weight: 1100-1350 parts of first zirconia stabilized fused yttrium oxide powder, 120-150 parts of second zirconia stabilized fused yttrium oxide powder, 12-15 parts of calcium carbonate, 11-14 parts of tetramethylammonium hydroxide, 150-180 parts of silica sol, 100-160 parts of water, 1 part of wetting agent and 1 part of defoamer; The particle size of the first zirconium oxide stabilized fused yttrium oxide powder is 300-400 mesh; The particle size of the second zirconium oxide stabilized fused yttrium oxide powder is 1000-1250 mesh.
[0011] Furthermore, the zirconium oxide content in both the first and second zirconium oxide stabilized fused yttrium oxide powders is 4-7 wt%, and the purity is ≥99%.
[0012] Furthermore, the calcium carbonate has a particle size of 1000-1250 mesh and a purity of ≥99.5%.
[0013] Furthermore, the silica sol has a mass concentration of 29%-31% and a particle size of 8-15 nm.
[0014] In this invention, the viscosity of the silica sol-yttrium oxide composite mold shell surface slurry is 20-25 seconds (Ford-4 cup method).
[0015] The second technical solution of the present invention provides a method for preparing the above-mentioned silica sol-yttrium oxide composite mold shell surface layer slurry, comprising the following steps: The raw materials are mixed according to the weight ratio to obtain the silica sol-yttrium oxide composite mold shell surface slurry for TiAl alloy investment casting.
[0016] The third technical solution of the present invention provides a method for preparing a silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting, comprising the following steps: (1) Immerse the mold shell in the above-mentioned silica sol-yttrium oxide composite mold shell surface slurry, control the slurry, sprinkle zirconium oxide stabilized fused yttrium oxide sand on the surface, and then dry it; preferably, dry it for 5-7 hours at a temperature of 20-23℃, relative humidity of 45%-65%, and wind speed of 0.3-0.6 m / s.
[0017] (2) Immerse the dried mold shell from step (1) into the yttrium sol and then dry it to obtain the silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting.
[0018] Preferably, the soaking time in step (2) is 40-60 min.
[0019] Furthermore, the zirconium oxide content in the zirconium oxide stabilized fused yttrium oxide sand is 4-7 wt%, and the purity is ≥99.9%.
[0020] Furthermore, the particle size of the zirconium oxide stabilized fused yttrium oxide sand is 70-120 mesh.
[0021] Furthermore, the mass concentration of the yttrium sol is 12%-16%, and the particle size is 2-3 nm.
[0022] This invention addresses the core defects of traditional yttrium oxide water-based slurries through precise optimization of the raw material system, significantly improving the basic performance of the mold shell surface layer. On one hand, using zirconia-stabilized fused yttrium oxide powder as the core refractory aggregate not only fully preserves the inherent advantages of yttrium oxide's high-temperature resistance and strong chemical inertness, but also significantly improves its hydration resistance through the stabilizing effect of zirconia, effectively avoiding problems such as slurry gelation and mold shell cracking caused by the formation of Y(OH)3 hydrates upon contact between the powder and water. On the other hand, the optimized particle size distribution of 325-mesh coarse particles and 1000-mesh fine particles improves the powder bulk density, significantly increasing the powder-to-liquid ratio of the slurry and the density of the mold shell. Combined with calcium carbonate as a mineralizer, this further enhances the sintering activity of the mold shell, fundamentally overcoming the shortcomings of low chemical activity and insufficient sintering of traditional yttrium oxide powder, thus substantially improving the structural stability of the mold shell.
[0023] This invention achieves synergistic optimization of the mechanical properties and interfacial reaction resistance of the mold shell. Through yttrium sol impregnation treatment, nano-yttrium oxide particles with a particle size of only 2-3 nm can deeply penetrate the pores of the mold shell. This not only effectively reduces the pore size and improves the density of the mold shell, but also uniformly coats the highly active SiO2 particles on the surface of the mold shell, blocking the reaction path between the TiAl alloy melt and SiO2 at the source. This completely solves the problem of severe interfacial reaction and excessively thick reaction layer caused by traditional processes. At the same time, it ensures that the mold shell will not develop microcracks due to fluctuations in external conditions during the preparation process, thus comprehensively strengthening the mechanical properties of the mold shell. Ultimately, it achieves excellent performance with a billet strength >7 MPa and a high-temperature strength of >15 MPa at 1500℃, and its thermal shock resistance is significantly improved compared to traditional mold shells.
[0024] The technical solution of this invention achieves a balanced optimization of the overall performance, stability, and production cost of the mold shell, possessing significant engineering application value. The surface roughness of the prepared mold shell surface layer is <1.2μm, providing high-precision forming assurance for TiAl alloy castings. The thickness of the interface reaction layer between the casting and the mold shell is controlled below 150μm, effectively avoiding casting contamination and significantly improving product qualification rate. Simultaneously, through precise control of the pH value of the silica sol using tetramethylammonium hydroxide, the service life of the slurry is extended to more than two months, solving the technical problem of "short service life and narrow window" of traditional slurries. Combined with the high cost-effectiveness of the silica sol binder, this significantly reduces the production and quality control costs of the mold shell.
[0025] The performance indicators of the mold shell surface layer of this invention can meet the stringent requirements of TiAl alloy investment casting, successfully breaking through the technical bottleneck that restricts the development of TiAl alloy investment casting towards higher precision and larger size, and providing reliable technical support for the widespread application of TiAl alloy in high-end equipment fields such as aero-engines.
[0026] The present invention discloses the following technical effects: This invention effectively solves the key technical problems in investment casting of TiAl alloys, such as the hydration sensitivity of the yttrium oxide mold shell, insufficient sintering density, and severe interfacial reactions.
[0027] This invention utilizes zirconia-stabilized fused yttrium oxide powder to significantly enhance the powder's resistance to hydration. Through a rational gradation of coarse and fine yttrium oxide powder and the introduction of calcium carbonate mineralizer, the particle packing structure is optimized, promoting high-temperature sintering and substantially improving the density and mechanical strength of the mold shell. After surface drying, this invention introduces yttrium sol impregnation treatment, allowing nano-yttrium oxide to deeply penetrate and encapsulate the active SiO2 particles in the silica sol, inhibiting the interfacial reaction between the TiAl melt and the mold shell at its source. The resulting mold shell surface layer possesses excellent chemical inertness, structural integrity, and process reliability, exhibiting a smooth surface, high strength, and good thermal shock resistance, providing a practical technical solution for high-precision, high-quality investment casting of TiAl alloys. Detailed Implementation
[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.
[0029] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.
[0031] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.
[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.
[0033] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.
[0034] In the following embodiments of the present invention, the two types of zirconia-stabilized yttrium oxide powder and zirconia-stabilized yttrium oxide sand with different particle sizes were purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd. They were made by electro-melting, cooling, crushing, grinding and sieving of zirconia and yttrium oxide mixed powder at a temperature of 2400℃-2700℃.
[0035] Example 1 This embodiment provides a method for preparing a silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting, the specific steps of which are as follows: (1) Preparation of silica sol-yttrium oxide composite mold shell surface layer slurry Take 3.8 kg of tetramethylammonium hydroxide and 34.2 kg of distilled water (purity ≥99.9%, conductivity ≤0.10 mS / m) to prepare a 10% tetramethylammonium hydroxide solution, totaling 38 kg. Slowly add this solution to 50 kg of silica sol (SiO2 content 30wt%, particle size 8-15 nm, pH 9.7) while stirring slowly for 10 minutes to ensure uniform mixing. Then, under vigorous stirring to form a stable vortex, add the following powders in sequence: Zirconia stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 325 mesh; containing 5 wt% ZrO2, purity ≥99%) 369 kg; 41 kg of zirconia-stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 1000 mesh; containing 5 wt% ZrO2, purity ≥99%); Calcium carbonate powder (particle size 1250 mesh, purity ≥99.5%) 4.1 kg.
[0036] During the powder addition process, distilled water was added in small, repeated additions, totaling 12 kg, to maintain suitable fluidity of the slurry. The entire powder addition process was controlled within 25 minutes. After the powder was added, 0.3 kg each of polyoxyethylene fatty alcohol ether wetting agent and silicone defoamer were added, and high-speed stirring was continued for 15 minutes to fully wet and evenly disperse the powder in the slurry. Subsequently, the stirring speed was reduced to 60 rpm, and low-speed stirring was carried out for 2 hours. After that, the mixture was transferred to a slurry dipping machine and allowed to stand and mature for 24 hours before use. The viscosity was 22 seconds (measured using the Forecast-4 cup method).
[0037] (2) Preparation of the mold shell surface layer Immerse the wax model in a special wax model cleaning solution for 30 seconds, then rinse it thoroughly with clean water and let it air dry.
[0038] After cleaning and drying, slowly immerse the wax model into the surface slurry prepared in step (1), rotate it for 5 seconds, and then pull it out at a uniform speed, controlling the slurry until the excess slurry flows away naturally. Then, use 70-120 mesh zirconia stabilized yttrium oxide sand (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, containing 5 wt% ZrO2, purity ≥99%) to evenly and thoroughly sprinkle sand on the surface of the wax model to ensure complete surface coverage.
[0039] (3) Drying and Yttrium Sol Impregnation Treatment of Mold Shell Surface Layer The sand-sprayed mold shell was placed in a drying room at an ambient temperature of 22℃, relative humidity of 55%, and wind speed of 0.3 m / s for 6 hours. Then, the dried mold shell was completely immersed in a container containing yttrium sol (an aqueous colloidal solution with a Y₂O₃ mass fraction of 15% and a particle size of 2-3 nm), ensuring the liquid level was above the top of the mold, for 50 minutes. After removal, it was dried again under the same conditions to obtain the final mold shell surface layer.
[0040] The slurry was stored for two months, and a rheometer was used to measure its properties at 2.5 seconds. -1 The viscosity measured at the shear rate was only 700 mPa·s, and the slurry viscosity remained stable, indicating that the hydration of yttrium oxide powder was not obvious and the slurry did not show obvious signs of aging. The blank strength of the mold shell surface layer measured by three-point bending strength test was 7.5 MPa, the high temperature strength at 1500℃ was 18.5 MPa, and the residual strength loss rate at 1200℃ was 45%. The surface roughness of the mold shell measured by optical profilometer was 1.2 μm. The sintering shrinkage rate of the mold shell after firing at 1000℃ was 0.52%. The TiAl alloy castings obtained at a mold shell preheating temperature of 1000℃ and a casting temperature of 1700℃ were analyzed by scanning electron microscopy. The results showed that the thickness of the reaction layer at the interface between the casting and the mold shell was 120 μm, which meets the casting requirements of high-performance aerospace components.
[0041] Example 2 This embodiment provides a method for preparing a silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting, the specific steps of which are as follows: (1) Preparation of silica sol-yttrium oxide composite mold shell surface layer slurry Mix 3.4 kg of tetramethylammonium hydroxide with 30.6 kg of distilled water (purity ≥99.9%, conductivity ≤0.10 mS / m) to prepare a 10% tetramethylammonium hydroxide solution, totaling 34 kg. Slowly add this alkaline solution to 56 kg of silica sol (SiO2 content 29 wt%, particle size 8-15 nm, pH = 9.8) while stirring slowly for 10 minutes to ensure uniform mixing. Then, under vigorous stirring to form a stable vortex, add the following powders in sequence: Zirconia stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 325 mesh, containing 5 wt% ZrO2, purity ≥99%) 360 kg; 40 kg of zirconia-stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 1000 mesh, containing 5 wt% ZrO2, purity ≥99%); Calcium carbonate powder (particle size 1250 mesh, purity ≥99.5%) 3.5 kg.
[0042] During the powder addition process, distilled water was added in small, repeated additions, totaling 10 kg, to maintain suitable slurry flowability. The entire powder addition process was controlled within 20 minutes. After the powder was added, 0.3 kg each of polyoxyethylene fatty alcohol ether wetting agent and silicone defoamer were added, and high-speed stirring was continued for 15 minutes to fully wet and evenly disperse the powder in the slurry. Subsequently, the stirring speed was reduced to 60 rpm, and low-speed stirring was carried out for 2 hours. Then, the slurry was transferred to a dip coater and allowed to stand for 24 hours to mature. The viscosity of the slurry was measured to be 25 seconds before use (using the Forecast-4 cup method).
[0043] (2) Preparation of the mold shell surface layer Immerse the wax model in a special wax model cleaning solution for 25 seconds, then rinse it thoroughly with clean water and let it air dry.
[0044] Slowly immerse the dried wax model into the prepared surface slurry, rotate it for about 5 seconds, and then lift it out at a uniform speed, controlling the slurry until excess slurry flows off naturally. Then, evenly and thoroughly sprinkle 70-120 mesh zirconia-stabilized yttrium oxide sand (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, containing 5 wt% ZrO2, purity ≥99%) onto the surface of the wax model to ensure complete and thorough surface coverage.
[0045] (3) Drying and Yttrium Sol Impregnation Treatment of Mold Shell Surface Layer The sand-sprayed mold shell was placed in a dry environment at 21℃, 58% relative humidity, and 0.4 m / s for 7 hours. Then, the dried mold shell was completely immersed in yttrium sol (an aqueous colloidal solution with 15% Y₂O₃ mass fraction and 2-3 nm particle size), with the liquid level above the top of the mold, for 45 minutes. After removal, it was dried again under the same conditions to obtain the final silica sol-yttrium oxide composite mold shell surface layer.
[0046] The slurry was stored for two months, and a rheometer was used to measure its properties at 2.5 seconds. -1 The viscosity measured at the shear rate was only 750 mPa·s, and the slurry viscosity remained stable, indicating that the hydration of yttrium oxide powder was not obvious and the slurry did not show obvious signs of aging. The blank strength of the mold shell surface layer measured by three-point bending strength test was 7.8 MPa, the high temperature strength at 1500℃ was 17.2 MPa, and the residual strength loss rate at 1200℃ was 48%. The surface roughness of the mold shell measured by optical profilometer was 1.3 μm. The sintering shrinkage rate of the mold shell after firing at 1000℃ was 0.58%. The TiAl alloy castings obtained at a mold shell preheating temperature of 1000℃ and a casting temperature of 1700℃ were analyzed by scanning electron microscopy. The results showed that the thickness of the reaction layer at the interface between the casting and the mold shell was 150 μm, which meets the casting requirements of high-performance aerospace components.
[0047] Example 3 This embodiment provides a method for preparing a silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting, the specific steps of which are as follows: (1) Preparation of silica sol-yttrium oxide composite mold shell surface layer slurry Mix 4.0 kg of tetramethylammonium hydroxide with 36.0 kg of distilled water (purity ≥99.9%, conductivity ≤0.10 mS / m) to prepare a 10% tetramethylammonium hydroxide solution, totaling 40 kg. Slowly add this alkaline solution to 47 kg of silica sol (SiO2 content 31 wt%, particle size 8-15 nm, pH = 10.0) while stirring slowly for 10 minutes to ensure uniform mixing.
[0048] Subsequently, a stable vortex is formed under vigorous stirring, and the following powders are added in sequence: Zirconia stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 325 mesh, containing 5 wt% ZrO2, purity ≥99%) 378 kg; 42 kg of zirconia-stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 1000 mesh, containing 5 wt% ZrO2, purity ≥99%); Calcium carbonate powder (particle size 1250 mesh, purity ≥99.5%) 4.3 kg.
[0049] During the powder addition process, distilled water was added in small, repeated additions, totaling 13 kg, to maintain suitable slurry flowability. The entire powder addition process was controlled within 30 minutes. After the powder was added, 0.3 kg each of polyoxyethylene fatty alcohol ether wetting agent and silicone defoamer were added, and high-speed stirring was continued for 15 minutes to fully wet and evenly disperse the powder in the slurry. Subsequently, the stirring speed was reduced to 60 rpm, and low-speed stirring was carried out for 2 hours. Then, the slurry was transferred to a dip coater and allowed to stand for 24 hours to mature. The viscosity of the slurry was measured to be 23 seconds before use (using the Forecast-4 cup method).
[0050] (2) Preparation of the mold shell surface layer Immerse the wax model in a special wax model cleaning solution for 30 seconds, then rinse it thoroughly with clean water and let it air dry.
[0051] Slowly immerse the dried wax model into the prepared surface slurry, rotate it for about 5 seconds, and then lift it out at a uniform speed, controlling the slurry until excess slurry flows off naturally. Then, evenly and thoroughly sprinkle 70-120 mesh zirconia-stabilized yttrium oxide sand (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, containing 5 wt% ZrO2, purity ≥99%) onto the surface of the wax model to ensure complete and thorough surface coverage.
[0052] (3) Drying and Yttrium Sol Impregnation Treatment of Mold Shell Surface Layer The sand-sprayed mold shell was placed in a dry environment at 20℃, 60% relative humidity, and 0.5 m / s for 6 hours. Then, the dried mold shell was completely immersed in yttrium sol (an aqueous colloidal solution with 15% Y₂O₃ mass fraction and 2-3 nm particle size), with the liquid level above the top of the mold, for 60 minutes. After removal, it was dried again under the same conditions to obtain the final silica sol-yttrium oxide composite mold shell surface layer.
[0053] The slurry was stored for two months, and a rheometer was used to measure its properties at 2.5 seconds. -1 The viscosity measured at the shear rate was only 680 mPa·s, and the slurry viscosity remained stable, indicating that the hydration of yttrium oxide powder was not obvious and the slurry did not show obvious signs of aging. The blank strength of the mold shell surface layer measured by three-point bending strength was 8.2 MPa, the high-temperature strength at 1500℃ was 19.5 MPa, and the residual strength loss rate at 1200℃ was 42%. The surface roughness of the mold shell measured by optical profilometer was 1.1 μm. The sintering shrinkage rate of the mold shell after firing at 1000℃ was 0.54%. The TiAl alloy castings obtained at a mold shell preheating temperature of 1000℃ and a casting temperature of 1700℃ were analyzed by scanning electron microscopy. The results showed that the thickness of the reaction layer at the interface between the casting and the mold shell was 100 μm, which meets the casting requirements of high-performance aerospace components.
[0054] Comparative Example 1 This comparative example provides a method for preparing a silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting. The difference between this comparative example and the previous example is that it uses single-particle-size zirconium oxide stabilized yttrium oxide as the refractory material for slurry preparation. The specific steps are as follows: (1) Preparation of silica sol-yttrium oxide composite mold shell surface layer slurry Take 3.8 kg of tetramethylammonium hydroxide and 34.2 kg of distilled water (purity ≥99.9%, conductivity ≤0.10 mS / m) to prepare a 10% tetramethylammonium hydroxide solution, totaling 38 kg. Slowly add this solution to 50 kg of silica sol (SiO2 content 30 wt%, pH 9.7) while stirring slowly for 10 minutes to ensure uniform mixing. Then, under vigorous stirring to form a stable vortex, add the following powders in sequence: Zirconia stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 325 mesh; containing 5 wt% ZrO2, purity ≥99%) 410 kg; Calcium carbonate powder (particle size 1250 mesh, purity ≥99.5%) 4.1 kg.
[0055] During the powder addition process, distilled water was added in small, repeated additions, totaling 12 kg, to maintain suitable fluidity of the slurry. The entire powder addition process was controlled within 25 minutes. After the powder was added, 0.3 kg each of polyoxyethylene fatty alcohol ether wetting agent and silicone defoamer were added, and high-speed stirring was continued for 15 minutes to fully wet and evenly disperse the powder in the slurry. Subsequently, the stirring speed was reduced to 60 rpm, and low-speed stirring was carried out for 2 hours. After that, the mixture was transferred to a slurry dipping machine and allowed to stand and mature for 24 hours before use. The viscosity was 22 seconds (measured using the Forecast-4 cup method).
[0056] (2) Preparation of the mold shell surface layer Immerse the wax model in a special wax model cleaning solution for 30 seconds, then rinse it thoroughly with clean water and let it air dry.
[0057] After cleaning and drying, slowly immerse the wax model into the surface slurry prepared in step (1), rotate it for 5 seconds, and then pull it out at a uniform speed, controlling the slurry until the excess slurry flows away naturally. Then, use 70-120 mesh zirconia stabilized yttrium oxide sand (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, containing 5 wt% ZrO2, purity ≥99%) to evenly and thoroughly sprinkle sand on the surface of the wax model to ensure complete surface coverage.
[0058] (3) Drying and Yttrium Sol Impregnation Treatment of Mold Shell Surface Layer The sand-sprayed mold shell was placed in a drying room at an ambient temperature of 22℃, relative humidity of 55%, and wind speed of 0.3 m / s for 6 hours. Then, the dried mold shell was completely immersed in a container containing yttrium sol (an aqueous colloidal solution with a Y₂O₃ mass fraction of 15% and a particle size of 2-3 nm), ensuring the liquid level was above the top of the mold, for 50 minutes. After removal, it was dried again under the same conditions to obtain the final mold shell surface layer.
[0059] The slurry was stored for two months, and a rheometer was used to measure its properties at 2.5 seconds. -1 The viscosity measured at the shear rate was only 710 mPa·s, and the slurry viscosity remained stable, indicating that the hydration of yttrium oxide powder was not obvious and the slurry did not show obvious signs of aging. The blank strength of the mold shell surface layer was 6.5 MPa, the high temperature strength at 1500℃ was 11.5 MPa, and the residual strength loss rate at 1200℃ was 53% by three-point bending test. The surface roughness of the mold shell was 1.5 μm measured by optical profilometer. The sintering shrinkage rate of the mold shell after firing at 1000℃ was 0.42%. The TiAl alloy castings obtained at a mold shell preheating temperature of 1000℃ and a casting temperature of 1700℃ were analyzed by scanning electron microscopy. The results showed that the thickness of the reaction layer at the interface between the casting and the mold shell was 220 μm.
[0060] Comparative Example 2 This comparative example provides a method for preparing a silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting. The difference between this comparative example and the previous example is that calcium carbonate powder is not added. The specific steps are as follows: (1) Preparation of silica sol-yttrium oxide composite mold shell surface layer slurry Take 3.8 kg of tetramethylammonium hydroxide and 34.2 kg of distilled water (purity ≥99.9%, conductivity ≤0.10 mS / m) to prepare a 10% tetramethylammonium hydroxide solution, totaling 38 kg. Slowly add this solution to 50 kg of silica sol (SiO2 content 30 wt%, pH 9.7) while stirring slowly for 10 minutes to ensure uniform mixing. Then, under vigorous stirring to form a stable vortex, add the following powders in sequence: Zirconia stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 325 mesh, containing 5 wt% ZrO2, purity ≥99%) 378 kg; 42 kg of zirconia-stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 1000 mesh, containing 5 wt% ZrO2, purity ≥99%); During the powder addition process, distilled water was added in small, repeated additions, totaling 12 kg, to maintain suitable fluidity of the slurry. The entire powder addition process was controlled within 25 minutes. After the powder was added, 0.3 kg each of polyoxyethylene fatty alcohol ether wetting agent and silicone defoamer were added, and high-speed stirring was continued for 15 minutes to fully wet and evenly disperse the powder in the slurry. Subsequently, the stirring speed was reduced to 60 rpm, and low-speed stirring was carried out for 2 hours. After that, the mixture was transferred to a slurry dipping machine and allowed to stand and mature for 24 hours before use. The viscosity was 22 seconds (measured using the Forecast-4 cup method).
[0061] (2) Preparation of the mold shell surface layer Immerse the wax model in a special wax model cleaning solution for 30 seconds, then rinse it thoroughly with clean water and let it air dry.
[0062] After cleaning and drying, slowly immerse the wax model into the surface slurry prepared in step (1), rotate it for 5 seconds, and then pull it out at a uniform speed, controlling the slurry until the excess slurry flows away naturally. Then, use 70-120 mesh zirconia stabilized yttrium oxide sand (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, containing 5 wt% ZrO2, purity ≥99%) to evenly and thoroughly sprinkle sand on the surface of the wax model to ensure complete surface coverage.
[0063] (3) Drying and Yttrium Sol Impregnation Treatment of Mold Shell Surface Layer The sand-sprayed mold shell was placed in a drying room at an ambient temperature of 22℃, relative humidity of 55%, and wind speed of 0.3 m / s for 6 hours. Then, the dried mold shell was completely immersed in a container containing yttrium sol (an aqueous colloidal solution with a Y₂O₃ mass fraction of 15% and a particle size of 2-3 nm), ensuring the liquid level was above the top of the mold, for 50 minutes. After removal, it was dried again under the same conditions to obtain the final mold shell surface layer.
[0064] The slurry was stored for two months, and a rheometer was used to measure its properties at 2.5 seconds. -1 The viscosity measured at the shear rate was only 690 mPa·s, and the slurry viscosity remained stable, indicating that the hydration of yttrium oxide powder was not obvious and the slurry did not show obvious signs of aging. The blank strength of the mold shell surface layer measured by three-point bending strength test was 6.8 MPa, the high temperature strength at 1500℃ was 9.5 MPa, and the residual strength loss rate at 1200℃ was 56%. The surface roughness of the mold shell measured by optical profilometer was 1.6 μm. The sintering shrinkage rate of the mold shell after firing at 1000℃ was 0.48%. The TiAl alloy castings obtained at a mold shell preheating temperature of 1000℃ and a casting temperature of 1700℃ were analyzed by scanning electron microscopy. The results showed that the thickness of the reaction layer at the interface between the casting and the mold shell was 200 μm.
[0065] Comparative Example 3 This comparative example provides a method for preparing a silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting. The difference between this comparative example and the previous example is that the yttrium sol impregnation treatment was not performed. The specific steps are as follows: (1) Preparation of silica sol-yttrium oxide composite mold shell surface layer slurry Take 3.8 kg of tetramethylammonium hydroxide and 34.2 kg of distilled water (purity ≥99.9%, conductivity ≤0.10 mS / m) to prepare a 10% tetramethylammonium hydroxide solution, totaling 38 kg. Slowly add this solution to 50 kg of silica sol (SiO2 content 30 wt%, pH 9.7) while stirring slowly for 10 minutes to ensure uniform mixing. Then, under vigorous stirring to form a stable vortex, add the following powders in sequence: Zirconia stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 325 mesh, containing 5 wt% ZrO2, purity ≥99%) 378 kg; 42 kg of zirconia-stabilized yttrium oxide powder (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, particle size 1000 mesh, containing 5 wt% ZrO2, purity ≥99%); Calcium carbonate powder (particle size 1250 mesh, purity ≥99.5%) 4.1 kg.
[0066] During the powder addition process, distilled water was added in small, repeated additions, totaling 12 kg, to maintain suitable fluidity of the slurry. The entire powder addition process was controlled within 25 minutes. After the powder was added, 0.3 kg each of polyoxyethylene fatty alcohol ether wetting agent and silicone defoamer were added, and high-speed stirring was continued for 15 minutes to fully wet and evenly disperse the powder in the slurry. Subsequently, the stirring speed was reduced to 60 rpm, and low-speed stirring was carried out for 2 hours. After that, the mixture was transferred to a slurry dipping machine and allowed to stand and mature for 24 hours before use. The viscosity was 22 seconds (measured using the Forecast-4 cup method).
[0067] (2) Preparation of the mold shell surface layer Immerse the wax model in a special wax model cleaning solution for 30 seconds, then rinse it thoroughly with clean water and let it air dry.
[0068] After cleaning and drying, slowly immerse the wax model into the surface slurry prepared in step (1), rotate it for 5 seconds, and then pull it out at a uniform speed, controlling the slurry until the excess slurry flows away naturally. Then, use 70-120 mesh zirconia stabilized yttrium oxide sand (purchased from Zhengzhou Zhenzhong Electrofused New Materials Co., Ltd., model DY-60, containing 5 wt% ZrO2, purity ≥99%) to evenly and thoroughly sprinkle sand on the surface of the wax model to ensure complete surface coverage.
[0069] (3) Drying of the mold shell surface layer The sand-spread mold shell is placed in a drying room with an ambient temperature of 22℃, relative humidity of 55%, and wind speed of 0.3 m / s for 6 hours to obtain the final mold shell surface layer.
[0070] The slurry was stored for two months, and a rheometer was used to measure its properties at 2.5 seconds. -1 The viscosity measured at the shear rate was only 700 mPa·s, and the slurry viscosity remained stable, indicating that the hydration of yttrium oxide powder was not obvious and the slurry did not show obvious signs of aging. The blank strength of the mold shell surface layer was 5.5 MPa, the high temperature strength at 1500℃ was 8.5 MPa, and the residual strength loss rate at 1200℃ was 59% by three-point bending test. The surface roughness of the mold shell was 1.7 μm measured by optical profilometer. The sintering shrinkage rate of the mold shell after firing at 1000℃ was 0.39%. The TiAl alloy castings obtained at a mold shell preheating temperature of 1000℃ and a casting temperature of 1700℃ were analyzed by scanning electron microscopy. The results showed that the thickness of the reaction layer at the interface between the casting and the mold shell was 320 μm.
[0071] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A silica sol-yttrium oxide composite mold shell surface layer slurry for investment casting of TiAl alloys, characterized in that, The raw materials comprise the following components by weight: 1100-1350 parts of first zirconia stabilized fused yttrium oxide powder, 120-150 parts of second zirconia stabilized fused yttrium oxide powder, 12-15 parts of calcium carbonate, 11-14 parts of tetramethylammonium hydroxide, 150-180 parts of silica sol, 100-160 parts of water, 1 part of wetting agent and 1 part of defoamer; The particle size of the first zirconium oxide stabilized fused yttrium oxide powder is 300-400 mesh; The particle size of the second zirconium oxide stabilized fused yttrium oxide powder is 1000-1250 mesh; The first and second zirconium oxide stabilized fused yttrium oxide powders are both obtained by electro-melting, cooling, crushing, grinding and sieving of a mixture of zirconium oxide and yttrium oxide powders at a temperature of 2400℃-2700℃.
2. The silica sol-yttrium oxide composite mold shell surface layer slurry according to claim 1, characterized in that, The zirconium oxide content in the first and second zirconium oxide stabilized fused yttrium oxide powders is independently 4-7 wt%.
3. The silica sol-yttrium oxide composite mold shell surface slurry according to claim 1, characterized in that, The calcium carbonate has a particle size of 1000-1250 mesh.
4. The silica sol-yttrium oxide composite mold shell surface slurry according to claim 1, characterized in that, The silica sol has a mass concentration of 29%-31% and a particle size of 8-15 nm.
5. The method for preparing the silica sol-yttrium oxide composite mold shell surface layer slurry according to any one of claims 1-4, characterized in that, Includes the following steps: The raw materials are mixed according to the weight ratio to obtain the silica sol-yttrium oxide composite mold shell surface slurry for TiAl alloy investment casting.
6. A method for preparing a silica sol-yttrium oxide composite mold shell surface layer for investment casting of TiAl alloys, characterized in that, Includes the following steps: (1) Immerse the mold shell in the silica sol-yttrium oxide composite mold shell surface slurry according to any one of claims 1-4, control the slurry, sprinkle zirconium oxide stabilized fused yttrium oxide sand on the surface, and then dry it; (2) Immerse the dried mold shell from step (1) into yttrium sol and then dry it to obtain the silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting.
7. The method for preparing the silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting according to claim 6, characterized in that, The zirconium oxide content in the zirconium oxide stabilized fused yttrium oxide sand is 4-7 wt%; the zirconium oxide stabilized fused yttrium oxide sand is made by electro-melting, cooling, crushing, grinding and sieving a mixture of zirconium oxide and yttrium oxide powder at a temperature of 2400℃-2700℃.
8. The method for preparing the silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting according to claim 6, characterized in that, The particle size of the zirconium oxide stabilized fused yttrium oxide sand is 70-120 mesh.
9. The method for preparing the silica sol-yttrium oxide composite mold shell surface layer for TiAl alloy investment casting according to claim 6, characterized in that, The yttrium sol has a mass concentration of 12%-16% and a particle size of 2-3 nm.