A method of casting a superalloy gas turbine blade

Abstract

The application relates to the technical field of precision casting of high-temperature alloys, and discloses a high-temperature alloy casting method for a gas turbine blade, which comprises the following steps: sequentially performing lanthanum nitrate immersion coating pretreatment and ammonium carbonate solidification treatment on the inner wall of a mold shell, converting the lanthanum nitrate into a lanthanum carbonate solid interface layer in situ; sequentially immersing and coating lanthanum borate surface layer slurry and gadolinium oxide isolation layer slurry on the solidification layer to complete mold shell preparation; performing dewaxing and high-temperature sintering on the mold shell; pouring high-temperature alloy liquid into the mold shell, forming metallurgical bonding between the lanthanum borate surface layer and the surface of the casting; leaving the lanthanum borate active layer on the surface of the blade after shell removal; and performing oxalate-phosphate composite sealing treatment on the surface layer pores of the blade. The application realizes the integration of casting and the formation of a CMAS-resistant protective layer, the protective layer is metallurgically combined with the blade substrate, the combination strength is high, the surface layer micropores of the blade are effectively sealed, and the CMAS infiltration channel is blocked.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy precision casting technology, and more specifically, to a high-temperature alloy casting method for gas turbine blades. Background Technology

[0002] Gas turbine blades are exposed to high-temperature gas environments containing calcium magnesium aluminum silicate (CMAS) under high-temperature and high-pressure conditions for extended periods. CMAS melts at the blade's service temperature, penetrates the blade surface, and undergoes a chemical corrosion reaction with the blade surface material, leading to premature blade failure and severely impacting the service life and reliability of the gas turbine.

[0003] In existing high-temperature alloy blade casting processes, blade casting and the application of anti-CMAS corrosion protective coatings are two independent process chains: after the blade casting shell is removed, the protective coating is applied separately using methods such as thermal spraying. To integrate the anti-CMAS protection function into the casting process, one existing approach is to perform rare-earth nitrate activation pretreatment on the inner surface of the mold shell during mold shell preparation to enhance the chemical bonding between the subsequent functional slurry layer and the mold shell substrate, allowing the functional slurry layer to remain on the blade surface after casting. However, rare-earth nitrates are water-soluble salts, and the pretreatment layer is continuously washed away and dissolved by water-based or alcohol-based solvents during subsequent multi-stage functional slurry dipping processes, resulting in significant loss. This causes the functional slurry layer to adhere to the mold shell wall only through physical adhesion, making it difficult to achieve the goal of integrated protection. Summary of the Invention

[0004] This invention provides a high-temperature alloy casting method for gas turbine blades, solving the technical problems in related technologies such as low bonding strength between the anti-CMAS protective coating and the blade substrate, and the infiltration of CMAS due to unsealed micropores on the blade surface.

[0005] This invention provides a high-temperature alloy casting method for gas turbine blades, comprising the following steps:

[0006] The inner wall of the mold shell is pretreated by immersion coating with lanthanum nitrate solution to form a thin layer of lanthanum nitrate precursor;

[0007] The shell is immersed in ammonium carbonate solution to convert the thin layer of lanthanum nitrate precursor into an insoluble solid layer of lanthanum carbonate in situ. The byproducts are removed by rinsing and then dried.

[0008] Lanthanum borate surface layer slurry and gadolinium oxide isolation layer slurry are sequentially dipped into the lanthanum carbonate solid layer, and then the outer support shell slurry is dipped into the layer to complete the shell preparation.

[0009] After dewaxing, the shell is sintered at high temperature. Lanthanum carbonate decomposes into lanthanum oxide, and the lanthanum oxide diffuses with the lanthanum borate surface layer at high temperature to form a chemical bond.

[0010] Nickel-based high-temperature alloy molten metal is poured into the mold shell. The lanthanum borate surface layer undergoes an interfacial chemical reaction with the casting surface, forming a rare earth aluminate bonding layer on the casting surface. The lanthanum borate surface layer and the casting surface form a metallurgical bond.

[0011] During the shell removal process, the metallurgical bond strength between the lanthanum borate surface layer and the casting is higher than the interfacial bond strength between the lanthanum borate surface layer and the gadolinium oxide isolation layer. The gadolinium oxide isolation layer is peeled off with the outer support shell, while the lanthanum borate surface layer remains on the blade surface.

[0012] Preferably, the lanthanum nitrate solution has a mass fraction of 5% to 15%, the immersion time is 30 to 60 seconds, and the solution is drained for 1 to 2 minutes after removal.

[0013] Preferably, the mass fraction of the ammonium carbonate solution is 8% to 12%, and the shell is immersed in the ammonium carbonate solution for 5 to 15 minutes; rinsing is performed by rinsing with deionized water 2 to 3 times.

[0014] Preferably, the D50 particle size of the lanthanum borate powder in the lanthanum borate surface slurry is not greater than 5 μm, the binder is aluminum sol, the mass fraction of Al2O3 in the aluminum sol is 20% to 30%, and the mass ratio of lanthanum borate powder to aluminum sol is 2:1 to 3:1; the lanthanum borate surface slurry is applied in 1 to 2 coats, and after each coat, it is drained for 1 to 2 minutes.

[0015] Preferably, the D50 particle size of the gadolinium oxide powder in the gadolinium oxide isolation layer slurry is not greater than 5 μm, the binder is aluminum sol, the mass fraction of Al2O3 in the aluminum sol is 20% to 30%, and the mass ratio of gadolinium oxide powder to aluminum sol is 2:1 to 3:1; the gadolinium oxide isolation layer slurry is applied in 1 to 2 coats, and after each coat, it is drained for 1 to 2 minutes.

[0016] Preferably, the high-temperature sintering temperature is 900–1100°C, and the holding time is 1–3 hours.

[0017] Preferably, the nickel-based superalloy molten metal is poured into the molded shell using a vacuum directional solidification process or a vacuum single crystal casting process, and the molten metal pouring temperature is 1400–1500°C.

[0018] Preferably, after dehulling, the process further includes a step of sealing the pores on the leaf surface with an oxalate-phosphate composite treatment, comprising:

[0019] The blade casting was immersed in a mixed solution containing gadolinium nitrate and aluminum dihydrogen phosphate, then removed and dried at low temperature to allow the Gd... 3+ It is fixed in the pores of the blade surface with aluminum dihydrogen phosphate;

[0020] The leaves were then immersed in an ammonium oxalate solution, and the Gd in the pores... 3+The in-situ reaction with the infiltrated oxalate ions produces insoluble gadolinium oxalate, which is deposited in the pores. After removal and drying, the gadolinium oxalate and aluminum phosphate gel solidify together in the pores of the leaf surface, forming an oxalate-phosphate composite sealing film that seals the casting residual micropores on the leaf surface.

[0021] Preferably, the mass fraction of gadolinium nitrate in the mixed solution is 3%–5%, and the mass fraction of aluminum dihydrogen phosphate is 4%–6%; the immersion time of the blade casting in the mixed solution is 10–30 min; the low-temperature drying temperature is 50–80 °C, and the drying time is 0.5–1 h.

[0022] Preferably, the mass fraction of the ammonium oxalate solution is 2% to 3%; the immersion time of the leaves in the ammonium oxalate solution is 5 to 15 minutes; and after removal, they are dried at 80 to 120°C for 1 to 2 hours.

[0023] The beneficial effects of the present invention are as follows: The present invention achieves the integration of casting and the formation of the anti-CMAS protective layer by impregnating the shell surface layer with lanthanum borate functional material and forming a metallurgical bond by using high casting temperature, so that the chemically active layer of lanthanum borate is directly retained on the blade surface after the blade is deshelled. The casting process chain is shortened and the blade has anti-CMAS corrosion ability after deshelling.

[0024] The lanthanum borate functional layer remaining on the blade surface is connected to the blade substrate through a rare earth aluminate metallurgical bonding transition layer. The bonding strength is significantly higher than that of existing mechanical attachment or light sintering bonding, and the protective layer is not easy to fall off during high-temperature service thermal cycling.

[0025] The ammonium carbonate solution chemical conversion process converts soluble lanthanum nitrate into insoluble lanthanum carbonate, solving the problem of rare earth nitrate pretreatment layer being washed away by solvent. After sintering, lanthanum carbonate is converted into lanthanum oxide and forms a chemical bond with the lanthanum borate surface layer, further improving the adhesion strength of the functional layer on the shell wall.

[0026] The oxalate-phosphate composite chemical conversion sealing process deposits gadolinium oxalate and aluminum phosphate in situ within the pores of the blade surface, sealing the residual micropores from casting, eliminating the pathway for CMAS to penetrate into the blade matrix through pore channels during service, and also providing a chemical barrier function during service. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the shell layer structure of the present invention;

[0028] Figure 2 This is a schematic diagram of the transition layer between the LaBO3 functional layer and the metallurgical bonding layer on the surface of the casting according to the present invention;

[0029] Figure 3 This is a schematic diagram of the differentiated desquamation and separation interface of the present invention;

[0030] Figure 4 This is a schematic diagram of the pore filling of the oxalate-phosphate composite closed membrane of the present invention;

[0031] Figure 5 This is a bar chart comparing the bonding strength of the LaBO3 functional layer in Experiment 1 of this invention;

[0032] Figure 6 This is a comparison curve of thermal cycling stability in Experiment 1 of this invention;

[0033] Figure 7 This is a comparison curve of the lanthanum retention rate of the pretreatment layer in multiple simulated dip-coating processes in Experiment 2 of this invention;

[0034] Figure 8 This is a bar chart comparing the penetration depth after CMAS corrosion in Experiment 3 of this invention;

[0035] Figure 9 This is a bar chart comparing the mass change rate after CMAS corrosion in Experiment 3 of this invention;

[0036] Figure 10 This is a SEM image of the sample cross-section in Experiment 3 of this invention. Detailed Implementation

[0037] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0038] Example 1

[0039] This embodiment discloses a high-temperature alloy casting method for gas turbine blades, which includes the following steps:

[0040] Step 1: Immerse the shell in a 5% (w / w) solution of lanthanum nitrate (La(NO3)3) for 30 seconds, then remove and let it drain naturally for 1 minute to form a thin layer of La(NO3)3 precursor on the inner wall of the shell.

[0041] Step 2: Immerse the shell treated in Step 1 into an 8% ammonium carbonate ((NH4)2CO3) solution for 5 minutes to convert the La(NO3)3 on the inner wall of the shell into insoluble lanthanum carbonate (La2(CO3)3) in situ. After removal, rinse twice with deionized water and dry at room temperature to obtain a shell blank with a solid interface layer of La2(CO3)3 on the inner wall.

[0042] Step 3: Prepare the LaBO3 surface layer slurry. The D50 particle size of the LaBO3 powder is 2μm. Aluminum sol (20% by mass of Al2O3) is used as the binder, and the mass ratio of LaBO3 powder to aluminum sol is 2:1. Dip the shell blank into the LaBO3 surface layer slurry and drain for 1 minute. Prepare the Gd2O3 isolation layer slurry. The D50 particle size of the Gd2O3 powder is 2μm. Aluminum sol (20% by mass of Al2O3) is used as the binder, and the mass ratio of Gd2O3 powder to aluminum sol is 2:1. Dip the outer side of the LaBO3 surface layer into the Gd2O3 isolation layer slurry and drain for 1 minute. Continue to dip into the outer support shell slurry to complete the shell preparation.

[0043] Step 4: After dewaxing the shell obtained in Step 3, sinter it at 900℃ and hold it at that temperature for 1 hour to solidify the shell. La2(CO3)3 thermally decomposes into La2O3 and diffuses with the LaBO3 surface layer at high temperature to form a chemical bond.

[0044] Step 5: Using a vacuum directional solidification process, molten nickel-based superalloy metal at 1400℃ is poured into the shell obtained in Step 4. Directional solidification is completed under controlled cooling conditions to obtain the blade casting. During shell removal, the metallurgical bonding strength between the LaBO3 surface layer and the casting surface is higher than the interfacial bonding strength between the LaBO3 surface layer and the Gd2O3 isolation layer. The Gd2O3 isolation layer is peeled off along with the outer support shell, while the LaBO3 surface layer remains on the blade surface.

[0045] Step Six: Prepare a mixed solution containing Gd(NO3)3 (3% by mass) and Al(H2PO4)3 (4% by mass). Immerse the blade casting, after descaling and cleaning in Step Five, in the above solution for 10 minutes. After removal, dry it at 50°C for 0.5 hours to allow the Gd... 3+ Aluminum dihydrogen phosphate was fixed in the pores of the leaf surface; then the leaf was immersed in a 2% (w / w) ammonium oxalate ((NH4)2C2O4) solution for 5 min. 2- Gd in the pores 3+ In situ reaction generates gadolinium oxalate (Gd2(C2O4)3) which is deposited in the pores; after removal, it is dried at 80℃ for 1 h to form an oxalate-phosphate composite sealing film in the pores of the leaf surface.

[0046] Example 2

[0047] This embodiment discloses a high-temperature alloy casting method for gas turbine blades, which includes the following steps:

[0048] Step 1: Immerse the shell in a 15% (w / w) solution of lanthanum nitrate (La(NO3)3) for 60 seconds, then remove and let it drain naturally for 2 minutes to form a thin layer of La(NO3)3 precursor on the inner wall of the shell.

[0049] Step 2: Immerse the shell treated in Step 1 into a 12% ammonium carbonate ((NH4)2CO3) solution for 15 minutes to convert the La(NO3)3 on the inner wall of the shell into insoluble lanthanum carbonate (La2(CO3)3) in situ. After removal, rinse three times with deionized water and dry at 60°C to obtain a shell blank with a La2(CO3)3 solid interface layer on the inner wall.

[0050] Step 3: Prepare the LaBO3 surface layer slurry. The D50 particle size of the LaBO3 powder is 5μm. Aluminum sol (30% by mass of Al2O3) is used as the binder, and the mass ratio of LaBO3 powder to aluminum sol is 3:1. Dip the shell blank into the LaBO3 surface layer slurry twice, and then drain for 2 minutes. Prepare the Gd2O3 isolation layer slurry. The D50 particle size of the Gd2O3 powder is 5μm. Aluminum sol (30% by mass of Al2O3) is used as the binder, and the mass ratio of Gd2O3 powder to aluminum sol is 3:1. Dip the outer side of the LaBO3 surface layer into the Gd2O3 isolation layer slurry twice, and then drain for 2 minutes. Continue to dip into the outer support shell slurry to complete the shell preparation.

[0051] Step 4: After dewaxing the shell obtained in Step 3, sinter it at 1100℃ for 3 hours to solidify the shell. La2(CO3)3 thermally decomposes into La2O3 and diffuses with the LaBO3 surface layer at high temperature to form a chemical bond.

[0052] Step 5: Using a vacuum directional solidification process, molten nickel-based superalloy metal at 1500℃ is poured into the shell obtained in Step 4. Directional solidification is completed under controlled cooling conditions to obtain the blade casting. During shell removal, the metallurgical bonding strength between the LaBO3 surface layer and the casting surface is higher than the interfacial bonding strength between the LaBO3 surface layer and the Gd2O3 isolation layer. The Gd2O3 isolation layer is peeled off along with the outer support shell, while the LaBO3 surface layer remains on the blade surface.

[0053] Step Six: Prepare a mixed solution containing Gd(NO3)3 (5% by mass) and Al(H2PO4)3 (6% by mass). Immerse the blade casting, after descaling and cleaning in Step Five, in the above solution for 30 minutes. After removal, dry it at 80℃ for 1 hour to allow the Gd... 3+ Aluminum dihydrogen phosphate was fixed in the pores of the leaf surface; then the leaf was immersed in a 2% (w / w) ammonium oxalate ((NH4)2C2O4) solution for 15 min. 2- Gd in the pores 3+In situ reaction generates gadolinium oxalate (Gd2(C2O4)3) which is deposited in the pores; after removal, it is dried at 120℃ for 2 hours to form an oxalate-phosphate composite sealing film in the pores on the surface of the leaf.

[0054] Example 3

[0055] This embodiment discloses a high-temperature alloy casting method for gas turbine blades, which includes the following steps:

[0056] Step 1: Immerse the shell in a 10% (w / w) solution of lanthanum nitrate (La(NO3)3) for 45 seconds, then remove and let it drain naturally for 1.5 minutes to form a thin layer of La(NO3)3 precursor on the inner wall of the shell.

[0057] Step 2: Immerse the shell treated in Step 1 into a 10% ammonium carbonate ((NH4)2CO3) solution for 10 minutes to convert the La(NO3)3 on the inner wall of the shell into insoluble lanthanum carbonate (La2(CO3)3) in situ. After removal, rinse three times with deionized water and dry at room temperature to obtain a shell blank with a La2(CO3)3 solid interface layer on the inner wall.

[0058] Step 3: Prepare the LaBO3 surface layer slurry. The D50 particle size of the LaBO3 powder is 3μm. Aluminum sol (25% by mass of Al2O3) is used as the binder, and the mass ratio of LaBO3 powder to aluminum sol is 2.5:1. Dip the shell blank into the LaBO3 surface layer slurry twice, and then drain for 1.5 minutes. Prepare the Gd2O3 isolation layer slurry. The D50 particle size of the Gd2O3 powder is 3μm. Aluminum sol (25% by mass of Al2O3) is used as the binder, and the mass ratio of Gd2O3 powder to aluminum sol is 2.5:1. Dip the outer side of the LaBO3 surface layer into the Gd2O3 isolation layer slurry once, and then drain for 1.5 minutes. Continue to dip into the outer support shell slurry to complete the shell preparation.

[0059] Step 4: After dewaxing the shell obtained in Step 3, sinter it at 1000℃ for 2 hours to solidify the shell. La2(CO3)3 thermally decomposes into La2O3 and diffuses with the LaBO3 surface layer at high temperature to form a chemical bond.

[0060] Step 5: Using a vacuum directional solidification process, molten nickel-based superalloy metal at 1450℃ is poured into the shell obtained in Step 4. Directional solidification is completed under controlled cooling conditions to obtain the blade casting. During shell removal, the metallurgical bonding strength between the LaBO3 surface layer and the casting surface is higher than the interfacial bonding strength between the LaBO3 surface layer and the Gd2O3 isolation layer. The Gd2O3 isolation layer is peeled off along with the outer support shell, while the LaBO3 surface layer remains on the blade surface.

[0061] Step Six: Prepare a mixed solution containing Gd(NO3)3 (4% by mass) and Al(H2PO4)3 (5% by mass). Immerse the blade casting, after descaling and cleaning in Step Five, in the above solution for 20 minutes. After removal, dry it at 65°C for 1 hour to allow the Gd... 3+ Aluminum dihydrogen phosphate was fixed in the pores of the leaf surface; then the leaf was immersed in a 2% (w / w) ammonium oxalate ((NH4)2C2O4) solution for 10 min. 2- Gd in the pores 3+ In situ reaction produces gadolinium oxalate (Gd2(C2O4)3) which is deposited in the pores; after removal, it is dried at 100℃ for 1.5h to form an oxalate-phosphate composite sealing film in the pores of the leaf surface.

[0062] Example 4

[0063] This embodiment discloses a high-temperature alloy casting method for gas turbine blades, which includes the following steps:

[0064] Step 1: Immerse the shell in a 12% (w / w) solution of lanthanum nitrate (La(NO3)3) for 50 seconds, then remove and let it drain naturally for 1.5 minutes to form a thin layer of La(NO3)3 precursor on the inner wall of the shell.

[0065] Step 2: Immerse the shell treated in Step 1 into a 9% ammonium carbonate ((NH4)2CO3) solution for 12 minutes to convert the La(NO3)3 on the inner wall of the shell into insoluble lanthanum carbonate (La2(CO3)3) in situ. After removal, rinse twice with deionized water and dry at 50°C to obtain a shell blank with a La2(CO3)3 solid interface layer on the inner wall.

[0066] Step 3: Prepare the LaBO3 surface layer slurry. The D50 particle size of the LaBO3 powder is 4μm. Aluminum sol (Al2O3 mass fraction 28%) is used as the binder, and the mass ratio of LaBO3 powder to aluminum sol is 2.5:1. Dip the shell blank into the LaBO3 surface layer slurry twice, and then drain for 1.5 min. Prepare the Gd2O3 isolation layer slurry. The D50 particle size of the Gd2O3 powder is 4μm. Aluminum sol (Al2O3 mass fraction 28%) is used as the binder, and the mass ratio of Gd2O3 powder to aluminum sol is 2.5:1. Dip the outer side of the LaBO3 surface layer into the Gd2O3 isolation layer slurry once, and then drain for 1 min. Continue to dip into the outer support shell slurry to complete the shell preparation.

[0067] Step 4: After dewaxing the shell obtained in Step 3, sinter it at 1050℃ and hold it at that temperature for 1.5 hours to solidify the shell. La2(CO3)3 thermally decomposes into La2O3 and diffuses with the LaBO3 surface layer at high temperature to form a chemical bond.

[0068] Step 5: Using a vacuum directional solidification process, molten nickel-based superalloy metal at 1480℃ is poured into the shell obtained in Step 4. Directional solidification is completed under controlled cooling conditions to obtain the blade casting. During shell removal, the metallurgical bonding strength between the LaBO3 surface layer and the casting surface is higher than the interfacial bonding strength between the LaBO3 surface layer and the Gd2O3 isolation layer. The Gd2O3 isolation layer is peeled off along with the outer support shell, while the LaBO3 surface layer remains on the blade surface.

[0069] Example 5

[0070] This embodiment discloses a high-temperature alloy casting method for gas turbine blades, which includes the following steps:

[0071] Step 1: Pre-treatment by immersion coating the inner surface of the shell with lanthanum nitrate solution

[0072] This step forms a thin layer of lanthanum nitrate precursor on the inner wall of the mold shell, providing reaction raw materials for the carbonate curing treatment in step two.

[0073] Before the functional slurry dipping process in step three, the mold shell is immersed in a 10% (w / w) lanthanum nitrate (La(NO3)3) solution to ensure that all parts of the inner wall of the mold shell are in uniform contact with the solution. The dipping time is 45 seconds. After removal, the shell is allowed to drain naturally for 1.5 minutes to form a uniformly covered thin layer of La(NO3)3 precursor on the inner wall of the mold shell.

[0074] The intermediate result obtained in step one: a shell preform with a uniform thin layer of La(NO3)3 precursor attached to the inner wall of the shell. At this time, La(NO3)3 is still a water-soluble salt, which will be washed away by solvent in the multi-stage slurry dipping process in step three. It must be cured in step two before the subsequent dipping process can be carried out.

[0075] Step 2: Carbonation and curing treatment of the pretreatment layer

[0076] This step solves the problem of the rare earth nitrate pretreatment layer being washed away by solvents in the subsequent dip coating process due to its water solubility.

[0077] The shell preform processed in step one is immersed in a 10% ammonium carbonate ((NH4)2CO3) solution for 10 minutes, allowing the thin layer of La(NO3)3 precursor on the inner wall of the shell to react with the CO3 in the ammonium carbonate solution. 2- The ions undergo the following chemical reaction, whereby La(NO3)3 is converted in situ into insoluble lanthanum carbonate (La2(CO3)3) and deposited on the inner wall of the shell:

[0078]

[0079] After the conversion is completed, the shell is removed and the inner surface of the shell is rinsed three times with deionized water to remove the soluble byproduct NH4NO3. After drying at room temperature, a shell blank with a La2(CO3)3 solid interface layer on the inner wall is obtained.

[0080] The byproduct NH4NO3 is a water-soluble salt that can be completely removed by rinsing and does not affect subsequent processes.

[0081] The result obtained in step two is a shell preform with a stable La2(CO3)3 solid interface layer on its inner wall. This interface layer remains intact in the liquid solvent environment of all subsequent dip coating processes, providing a stable chemical adhesion substrate for the functional slurry layer.

[0082] Step 3: Sequential dipping of multi-material functional slurry

[0083] In this step, two functional slurries are sequentially dipped onto the surface of the La2(CO3)3 interface layer obtained in step two to form a LaBO3 chemically active surface layer and a Gd2O3 rare earth oxide isolation layer on the inner wall of the shell, thus completing the overall shell preparation.

[0084] First step: LaBO3 chemically active surface coating

[0085] The shell blank obtained in step two is immersed in a surface slurry with LaBO3 powder as the functional component, and coated twice. After each coating, it is drained for 1.5 minutes. The D50 particle size of the LaBO3 powder in the surface slurry is 3μm. Aluminum sol (Al2O3 mass fraction 25%) is used as the binder. The mass ratio of LaBO3 powder to aluminum sol is 2.5:1 to avoid the premature reaction of LaBO3 with SiO2 during the shell sintering process, which would consume its chemical activity. The LaBO3 functional slurry layer is the innermost layer of the shell (i.e. the surface layer that is in direct contact with the casting) and covers the La2(CO3)3 interface layer.

[0086] The LaBO3 surface layer performs the following two functions in this invention:

[0087] (1) CMAS chemical capture function during service: Under blade service conditions (temperature above 1200℃), the LaBO3 layer remaining on the blade surface reacts chemically with the infiltrated CMAS melt—La in LaBO3 3+ It reacts with the silicate and aluminate components in CMAS to generate chemically stable rare earth silicate phases (such as La2Si2O7) and rare earth aluminate phases, which solidify and consume the intruding CMAS components; the B2O3 component generated by the decomposition of LaBO3 forms a viscous borosilicate glass phase at high temperature, filling the pores between the reaction products and further blocking the CMAS permeation channels.

[0088] (2) Function of forming metallurgical bond with the surface of casting during casting: At the high temperature of casting (1450℃), the LaBO3 surface layer reacts with the oxide components on the surface of the nickel-based high-temperature alloy molten metal, forming a rare earth aluminate metallurgical bond transition layer on the surface of the casting, so that metallurgical bond force is generated between the LaBO3 surface layer and the surface of the casting (see step five for details).

[0089] Second step: Gd2O3 isolation layer impregnation coating

[0090] On the outer side of the LaBO3 surface layer, a functional slurry containing Gd2O3 powder (D50 particle size of 3μm) is dip-coated, with aluminum sol (Al2O3 mass fraction of 25%) as the binder. The mass ratio of Gd2O3 powder to aluminum sol is 2.5:1. One dip-coating is applied, and the material is drained for 1.5 minutes after removal. This forms a Gd2O3 isolation layer on the outer side of the LaBO3 layer to prevent direct contact between the LaBO3 surface layer and the SiO2 component in the outer support shell.

[0091] The Gd2O3 isolation layer in this invention performs the following two functions:

[0092] (1) Isolating the LaBO3 surface layer from the outer silicon-based support shell: The dense Gd2O3 isolation layer is located between the LaBO3 layer and the outer support shell, blocking the direct contact between the two, so that the LaBO3 surface layer can still maintain the chemical reaction capability with CMAS after the casting is removed from the shell.

[0093] (2) As the separation interface between the LaBO3 surface layer and the outer support shell: The Gd2O3 layer and the LaBO3 layer are bonded to each other as ceramics, and the interfacial bonding strength is lower than that formed between the LaBO3 surface layer and the casting surface in step five. During shell removal, separation occurs preferentially at the interface between the Gd2O3 layer and the LaBO3 layer: the LaBO3 surface layer remains on the casting surface with a metallurgical bond, and the Gd2O3 isolation layer is peeled off along with the outer support shell (see step five for details).

[0094] After two layers of functional slurry coating are completed, multiple layers of alumina-zirconium silicate outer support shell slurry are applied to the outside of the Gd2O3 layer using conventional shell-making processes to complete the overall shell preparation. At this point, the shell layers, from the inside out, are: La2(CO3)3 solid interface layer, LaBO3 chemically active surface layer, Gd2O3 isolation layer, and outer support shell, as follows: Figure 1 As shown.

[0095] The result obtained in step three is a complete shell with a multi-material functional layer structure. The inner wall is attached with La2(CO3)3 interface layer, LaBO3 chemically active surface layer, Gd2O3 isolation layer and outer support shell from the inside to the outside.

[0096] Step 4: Shell dewaxing and high-temperature sintering

[0097] The dewaxing and high-temperature sintering in this step are routine processes in the preparation of precision casting shells; the thermal decomposition and transformation of La2(CO3)3 that occurs during sintering is a technical feature of this invention.

[0098] The shell obtained in step three is dewaxed according to conventional processes to remove the wax mold and obtain a hollow shell. Subsequently, the shell is sintered at 1000℃ for 2 hours. The purpose of sintering is to remove the organic binder in each layer of slurry, so that the ceramic particles in each layer of the shell are sintered and solidified to obtain a shell with sufficient strength.

[0099] Thermal decomposition and transformation of La2(CO3)3 during sintering: The La2(CO3)3 solid interface layer formed in step two undergoes thermal decomposition at approximately 600–800°C, transforming into La2O3 according to the following formula:

[0100]

[0101] The decomposition temperature of La2(CO3)3 (600–800℃) is lower than the sintering temperature of the mold shell (1000℃). Therefore, by the time the sintering process is completed, the La2(CO3)3 on the inner wall of the mold shell has been completely converted into La2O3. The generated La2O3 and the LaBO3 surface layer above it are both lanthanum-containing rare earth oxides with high chemical compatibility. Under the high temperature of sintering, the two diffuse into each other and form a strong chemical bonding interface, which allows the LaBO3 surface layer to be tightly bonded to the mold shell substrate through the interface. The bonding strength is significantly higher than that of simple physical adhesion between dissimilar ceramic materials, effectively preventing the local peeling of the LaBO3 surface layer caused by the impact of high-temperature alloy molten metal pouring.

[0102] The result obtained in step four: After sintering and curing, the La2(CO3)3 on the inner wall of the multi-material functional layer shell has been transformed into La2O3. The LaBO3 surface layer is tightly connected to the shell matrix through the chemical bonding interface formed with La2O3 at high temperature. The shell structure is complete and ready for casting.

[0103] Step 5: High-temperature alloy casting and LaBO3 functional layer retention and shell removal

[0104] This step utilizes the high temperature of casting to form a metallurgical bond between the LaBO3 surface layer and the casting surface, so that the LaBO3 surface layer remains on the blade surface after descrambling. This is a key process in which casting and the formation of the anti-CMAS protective layer are completed simultaneously.

[0105] The vacuum directional solidification process is adopted. Under vacuum conditions, nickel-based superalloy molten metal at a temperature of 1450℃ is poured into the mold shell obtained in step four. After the molten metal is filled, directional solidification is completed under controlled cooling conditions to obtain the blade casting.

[0106] The metallurgical bonding process between the LaBO3 surface layer and the casting surface: During the pouring and solidification process, the innermost LaBO3 surface layer of the mold shell comes into direct contact with the molten high-temperature alloy metal. The LaBO3 surface layer reacts with the alumina formed by the oxidation of aluminum in the nickel-based high-temperature alloy at the interface, generating a rare earth aluminate bonding layer (such as LaAlO3) on the casting surface. This creates a metallurgical bond between the LaBO3 surface layer and the casting surface. Figure 2 As shown, the strength of this metallurgical bond is higher than the ceramic-ceramic interface bond strength between the LaBO3 surface layer and its outer Gd2O3 insulating layer.

[0107] After decoupling, the LaBO3 surface layer remains on the blade surface: After solidification and cooling, the casting undergoes decoupling. Under the external force of decoupling, because the strength of the LaBO3-casting interface (metallurgical bond) is higher than that of the LaBO3-Gd2O3 interface (ceramic-ceramic bond), decoupling separation occurs at the interface between LaBO3 and Gd2O3: the outer support shell and the Gd2O3 isolation layer peel off as a whole with the mold shell, and the LaBO3 chemically active surface layer, along with its bottom rare earth aluminate bonding layer, remains on the blade surface, forming a LaBO3 anti-CMAS functional layer that is metallurgically bonded to the blade matrix, such as... Figure 3 As shown.

[0108] The result obtained in step five: a high-temperature alloy blade casting with a LaBO3 anti-CMAS chemical activity functional layer on its surface. This functional layer is bonded to the blade substrate through a rare earth aluminate metallurgical bonding transition layer. The bonding method is metallurgical bonding, which makes it less prone to detachment during high-temperature service thermal cycling.

[0109] Step Six: Post-cast Oxalate-Phosphate Composite Chemical Conversion Sealing Treatment

[0110] This step seals the residual micropores formed on the blade surface during the casting process, eliminating the path for CMAS to seep into the blade matrix through the pore channels during service, and also providing a chemical barrier function during service.

[0111] This step involves two impregnation processes performed sequentially to ensure that gadolinium oxalate is deposited in situ within the pores of the leaf surface, rather than in the bulk solution—if Gd-containing... 3+ and C2O4 2- When the components are mixed in the same solution, both will pre-precipitate in large quantities in the bulk solution. The suspended particles cannot effectively penetrate into the fine pores, so they must be introduced step by step.

[0112] First impregnation: Gadolinium nitrate-aluminum dihydrogen phosphate solution impregnation

[0113] Gadolinium nitrate (Gd(NO3)3, 4% by mass) and aluminum dihydrogen phosphate (Al(H2PO4)3, 5% by mass) were dissolved in deionized water and stirred until homogeneous to prepare a Gd-containing solution.3+ And Al 3+ A mixed solution. The blade castings, after desquamation and cleaning in step five, are immersed in the above solution for 20 minutes to allow the Gd-containing material to settle. 3+ And Al 3+ The solution fully penetrates the pores of the blade surface. After removing and draining off excess liquid, the blade is dried at 65°C for 1 hour to allow the solute components to evaporate and concentrate with the solvent and be fixed in the pores; Al(H2PO4)3 undergoes dehydration and condensation during the low-temperature drying process, solidifying in the pores as an amorphous aluminum phosphate gel.

[0114] Second impregnation: Ammonium oxalate solution impregnation

[0115] Prepare a 2.5% (w / w) ammonium oxalate ((NH4)2C2O4) solution, and immerse the leaves after the first drying treatment in the solution for 10 minutes; C2O4 2- After penetrating the pores, it combines with the Gd that was retained in the pores by the first impregnation. 3+ A precipitation reaction occurs, and sparingly soluble gadolinium oxalate (Gd2(C2O4)3) is generated in situ according to the following formula and deposited in the pores:

[0116]

[0117] After being removed, the material was dried at 100℃ for 1.5h, and Al(H2PO4)3 was further dehydrated and solidified into amorphous aluminum phosphate gel. Gadolinium oxalate and aluminum phosphate gel were deposited and solidified together in the pores of the blade surface to form an oxalate-phosphate composite sealing film (in which the aluminum phosphate component was further dehydrated and transformed into crystalline AlPO4 under the high temperature of the blade during service).

[0118] The dual function of oxalate-phosphate composite blocking membranes:

[0119] (1) Pore sealing function: The composite sealing membrane fills and seals the casting residual micropores on the surface of the blade, eliminating the path of CMAS melt seeping into the blade matrix through the pore channels during the blade's service.

[0120] (2) Chemical barrier function during service: Under the high temperature service conditions of the blade (when the temperature is above 600℃, the gadolinium oxalate component in the composite sealing membrane is completely decomposed into Gd2O3). The Gd2O3 reacts chemically with the calcium and magnesium ions in the infiltrated CMAS melt at the high service temperature to generate a stable gadolinium-calcium composite oxide phase, which solidifies the CMAS intrusion component and provides additional protection for the pore sealing area of ​​the blade surface through chemical barrier.

[0121] The result obtained in step six: a high-temperature alloy blade casting with surface pores sealed by an oxalate-phosphate composite sealing film, such as... Figure 4As shown, the microporous CMAS infiltration channels on its surface are eliminated, and the blade surface simultaneously possesses dual CMAS protection from the LaBO3 chemically active layer retained in step five and the composite sealing film formed in step six.

[0122] Experimental verification

[0123] Experiment 1: Bond strength and thermal cycling stability test between LaBO3 functional layer and casting surface

[0124] 1. Experimental Objective

[0125] The bonding strength between the LaBO3 functional layer obtained by the method of this invention and the surface of the casting was verified and compared with the LaBO3 coating applied by the existing atmospheric plasma spraying (APS) process, demonstrating the advantages of the casting metallurgical bonding method in terms of bonding strength and service thermal cycle stability.

[0126] 2. Preparation of experimental samples

[0127] Both sets of comparative samples used nickel-based superalloy (DZ125) flat plate specimens (50mm×30mm×5mm) as the matrix.

[0128] Control group (sample A): After conventional casting and shell removal, a LaBO3 coating was applied to the sample surface by atmospheric plasma spraying (APS) with a spraying power of 40kW, a spraying distance of 120mm, and an Ar / H2 mixture as the carrier gas. The coating thickness was about 200μm, and it was bonded to the substrate by mechanical adhesion and light sintering.

[0129] Experimental Group (Sample B): Prepared according to the method described in Example 3 of this invention, the inner wall of the shell was subjected to the following treatments in sequence: lanthanum nitrate pretreatment (10% by mass, immersion for 45 s, draining for 1.5 min), ammonium carbonate curing (10% by mass, soaking for 10 min, rinsing 3 times, drying at room temperature), LaBO3 surface coating (LaBO3 powder D50 particle size 3 μm, aluminum sol Al2O3 mass fraction 25%, powder / sol mass ratio 2.5:1, 2 coats, draining for 1.5 min per coat), and Gd2O3 isolation layer coating (Gd2O3 powder D50 particle size 3 μm, aluminum sol Al2O3 mass fraction 25%). The LaBO3 functional layer was coated with a mixture of 25% gadolinium nitrate (mass fraction 4%) and aluminum dihydrogen phosphate (mass fraction 5%) (20 min, dried at 65℃ for 1 h) and then sintered at 1000℃ for 2 h before being vacuum-directed solidification and casting at 1450℃. After descrambling, the functional layer on the surface of the casting was sequentially subjected to two curing and sealing processes: immersion sealing in a mixture of gadolinium nitrate (mass fraction 4%) and aluminum dihydrogen phosphate (mass fraction 5%) (20 min, dried at 65℃ for 1 h) and secondary curing sealing in ammonium oxalate solution (mass fraction 2.5%) (10 min, dried at 100℃ for 1.5 h). After descrambling, the LaBO3 functional layer remained on the sample surface through metallurgical bonding, with a thickness of approximately 150–200 μm.

[0130] 3. Experimental conditions

[0131] Bond strength test: Referring to GB / T 8642-2002 Test Method for Tensile Bond Strength of Ceramic Coatings, a standard test column (25 mm in diameter) was bonded to the coating surface using epoxy resin adhesive. After curing at 23℃ for 24 hours, the coating was stretched at a rate of 1 mm / min on a universal testing machine until it detached. The maximum tensile force was recorded and the bond strength (MPa) was calculated. Three samples were tested in each group, and the average value and standard deviation were taken.

[0132] Thermal cycling stability test: Each cycle consisted of holding at 1000℃ for 30 minutes and then air-cooling to room temperature, for a total of 100 cycles; after every 25 cycles, the coating area retention rate was determined by image analysis (based on the initial coating area), and the number of cycles at which the first macroscopic peeling occurred was recorded.

[0133] 4. Experimental Procedure

[0134] Step (1): Prepare 6 samples of sample A and 6 samples of sample B respectively, of which 3 samples are used for bonding strength test and the other 3 samples are used for thermal cycling stability test.

[0135] Step (2): For the bond strength test sample, bond the test column according to GB / T 8642-2002 standard, perform tensile test on universal testing machine, record the breaking load, and calculate the bond strength (MPa).

[0136] Step (3): For the thermal cycling stability test sample, complete 100 cycles according to the above thermal cycling regime. After every 25 cycles, take a picture to record the coating state and calculate the coating retention rate.

[0137] Step (4): After the thermal cycling is completed, the sample is cut, mounted and polished along the vertical surface direction to prepare a cross-sectional sample. The micro-morphology of the coating / substrate interface is observed by SEM to confirm the interface bonding characteristics (metallurgical bonding transition layer or mechanical adhesion layer).

[0138] 5. Experimental Results

[0139] Table 1. Test results of LaBO3 functional layer bonding strength and thermal cycling stability

[0140]

[0141] Figure 5 Comparison chart of bonding strength of LaBO3 functional layers;

[0142] Figure 6 Comparison of thermal cycling stability.

[0143] 6. Analysis and Summary

[0144] Test results show that the initial bonding strength of the LaBO3 functional layer (sample B) prepared by the method of the present invention reaches 44.7 MPa, which is 3.6 times that of the APS thermal spray coating (sample A, 12.4 MPa), proving that the metallurgical bonding interface formed during the casting process has significantly higher bonding strength.

[0145] After 100 high-temperature thermal cycles, the coating retention rate of sample B remained at 95.1%, while that of sample A was only 22.7%. Furthermore, sample A showed macroscopic peeling by the 38th cycle, while sample B showed no peeling throughout the entire process. Metallurgical bonding, through the diffusion of interfacial elements to form a transition layer, effectively disperses interfacial thermal stress, fundamentally improving the service reliability of the LaBO3 functional layer and exhibiting a significant advantage in bonding strength compared to mechanical adhesion methods.

[0146] Experiment 2: Verification of the effect of ammonium carbonate curing treatment on the solvent stability of the lanthanum nitrate pretreated layer

[0147] 1. Experimental Objective

[0148] Quantitative verification was performed to determine the retention of lanthanum in the pretreatment layer during the multi-pass functional slurry sequential dipping process after the ammonium carbonate curing treatment converted soluble La(NO3)3 into insoluble La2(CO3)3, demonstrating the effectiveness of the curing treatment in eliminating solvent erosion and loss.

[0149] 2. Preparation of experimental samples

[0150] Both sets of comparative samples used the same specifications of corundum crucible-shaped shell blanks (inner diameter 80mm, wall thickness 8mm) as the base.

[0151] Control group (sample C): Only lanthanum nitrate immersion coating pretreatment was performed (mass fraction 10%, immersion coating for 45s, draining for 1.5min), and it was retained on the inner wall of the shell in the water-soluble state of La(NO3)3, without ammonium carbonate curing treatment.

[0152] Experimental group (sample D): First, lanthanum nitrate was pretreated by immersion coating (as above), then immersed in a 10% ammonium carbonate solution for 10 minutes. After removal, it was rinsed three times with deionized water and dried at room temperature. La(NO3)3 was converted in situ to La2(CO3)3 and fixed on the inner wall of the shell.

[0153] Five pieces were prepared from each of the two groups. The initial lanthanum element attachment amount was quantitatively determined by ICP-OES after complete dissolution with dilute hydrochloric acid (1:1 v / v), confirming that the initial La attachment amount of the two groups was consistent (approximately 2.8 mg / cm²).

[0154] 3. Experimental conditions

[0155] Simulated dip-coating solution: A water-based aluminum sol solution (Al2O3 mass fraction 25%, pH=4.5) was used to simulate the solvent environment of the sequential dip-coating process of the functional slurry. Four simulated dip-coating treatments were performed, with each dip lasting 3 minutes and then drained. The leachate was collected each time, and the La concentration was determined using ICP-OES. After the four dip-coatings, the inner surface of the mold shell was subjected to a final complete leaching with dilute hydrochloric acid, and the residual La content was calculated.

[0156] 4. Experimental Procedure

[0157] Step (1): Prepare 5 samples of sample C and 5 samples of sample D, and calibrate and confirm that the initial La adhesion amount of the two groups is consistent by ICP-OES.

[0158] Step (2): Perform four simulated dip-coating treatments on the two groups of samples respectively, and collect the leachate each time for later use.

[0159] Step (3): Analyze the La concentration in each leachate using ICP-OES, calculate the La loss amount in each step based on the solution volume, and calculate the La retention rate (%) in each stage based on the initial La adhesion amount.

[0160] Step (4): After four simulated dip coatings, the residual La on the inner surface of the shell was dissolved with dilute hydrochloric acid, and the final La retention rate was confirmed by ICP-OES quantification.

[0161] 5. Experimental Results

[0162] Table 2. Lanthanum retention rates of the two sample groups during the multi-stage simulated dip-coating process.

[0163]

[0164] Figure 7 Comparison curves of lanthanum retention rate in pretreatment layers during multiple simulated dip-coating processes.

[0165] 6. Analysis and Summary

[0166] Test results show that the La retention rate of the uncured La(NO3)3 pretreated layer (sample C) dropped to 43.6% after the first simulated dip coating, and only 2.4% remained after four simulated dip coatings, indicating almost complete loss. In contrast, the pretreated layer (sample D) that was cured with ammonium carbonate to convert to La2(CO3)3 retained 93.1% of the La after four simulated dip coatings, showing a significant difference between the two groups. The solubility of La2(CO3)3 is extremely low (…). Rare earth nitrates are extremely difficult to dissolve in water-based and alcohol-based slurry solvents, while La(NO3)3 is a highly soluble salt that dissolves and diffuses rapidly in solvent environments. This stark difference in solubility is the fundamental reason for the difference in retention rates. This result demonstrates that ammonium carbonate curing effectively solves the problem of rare earth nitrate pretreatment layers being washed away by solvents during multiple dip-coating processes.

[0167] Experiment 3: Barrier performance test of LaBO3 functional layer against CMAS melt penetration corrosion

[0168] 1. Experimental Objective

[0169] The high-temperature CMAS corrosion test was used to quantitatively evaluate the barrier effect of the LaBO3 functional layer prepared by the method of the present invention on the CMAS melt penetration corrosion of the blade surface. The results were compared with the bare alloy sample without the protective layer to prove the chemical barrier protection performance of the LaBO3 functional layer.

[0170] 2. Preparation of experimental samples

[0171] Both sets of comparative samples used nickel-based superalloy (DZ125) flat plate specimens (20mm×20mm×5mm) as the matrix.

[0172] Control group (sample E): Cast using conventional processes, with no protective coating on the surface after shelling, directly exposing the nickel-based superalloy matrix.

[0173] Experimental group (sample F): Prepared completely according to the method described in Example 3 of this invention, after vacuum directional solidification casting at 1450℃ and shell removal, and then subjected to two-step sealing treatment in step six (immersion in a mixture of 4% gadolinium nitrate and 5% aluminum dihydrogen phosphate for 20 min, drying at 65℃ for 1 h; then immersion in a 2.5% ammonium oxalate solution for 10 min, drying at 100℃ for 1.5 h). The sample surface is coated with a LaBO3 anti-CMAS functional layer formed by the method of this invention, with a thickness of about 180 μm, which is connected to the blade substrate in a metallurgical bonding manner.

[0174] 3. Experimental conditions

[0175] CMAS powder preparation: Weigh the corresponding oxide powders according to the nominal composition (molar fraction) CaO 33%, MgO 9%, Al2O3 13%, SiO2 45%, mix them thoroughly, and pre-melt them at 1300℃ to make CMAS glass. Grind it to D50 < 20μm for later use.

[0176] Corrosion test: Apply 5 mg / cm² corrosion coating evenly to the test surface of the sample. 2 The CMAS powder was placed in an alumina crucible and held in an atmospheric furnace at 1250°C for 10 hours. After cooling to room temperature with the furnace, it was analyzed.

[0177] 4. Experimental Procedure

[0178] Step (1): Clean the test surfaces of 5 samples from each of the two groups with anhydrous ethanol using ultrasonic cleaning and then dry them. Accurately weigh the initial mass (accuracy 0.01 mg).

[0179] Step (2): Apply 5 mg / cm² of the solution evenly to the surface of each sample. 2 The CMAS powder was heated in an atmospheric furnace at 1250℃ for 10 hours, cooled to room temperature with the furnace, and then accurately weighed again to calculate the rate of mass change (mg / cm³). 2 ).

[0180] Step (3): Cut the etched sample along the vertical surface direction, mount and polish it to prepare a cross-sectional sample. Use SEM and EDS to characterize the micro-morphology of the cross section. Use the surface scan diagram of Ca and Si elements in EDS to determine the position of the CMAS penetration front and measure the CMAS penetration depth (μm) of each sample.

[0181] Step (4): Perform EDS surface scanning on the cross section of the LaBO3 functional layer to analyze the composition distribution of the reaction products, identify the distribution location of rare earth reaction products such as La2Si2O7 and LaAlO3, and confirm the chemical barrier mechanism.

[0182] 5. Experimental Results

[0183] Table 3. CMAS corrosion (1250℃ × 10h, 5 mg / cm³) 2 The test results of each group of samples afterward

[0184]

[0185] Figure 8 Comparison of penetration depths after CMAS corrosion;

[0186] Figure 9 Comparison of mass change rates after CMAS corrosion.

[0187] Figure 10 SEM image of sample cross section.

[0188] 6. Analysis and Summary

[0189] Test results show that the LaBO3 functional layer (sample F) prepared by the method of this invention reduced the CMAS penetration depth from 162 μm in the control group to 23 μm, a reduction of 85.8%; the mass change rate decreased from +4.83 mg / cm 2 Decreased to +0.72 mg / cm 2 It has a significant barrier effect against CMAS penetration corrosion.

[0190] EDS analysis revealed that the LaBO3 functional layer reacted with the CMAS melt at 1250°C to generate rare earth reaction products such as La2Si2O7 and LaAlO3. The volume expansion effect of this dense reaction product layer blocked the channels for further CMAS penetration. The B2O3 released from the decomposition of LaBO3 formed a borosilicate glass phase at high temperature, further filling the residual pores between the reaction products. The synergistic effect of these two mechanisms reduced the CMAS penetration depth by 85.8%, strongly demonstrating the chemical barrier protection effect of the LaBO3 functional layer of this invention against CMAS corrosion.

[0191] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for high-temperature alloy casting of gas turbine blades, characterized in that, Includes the following steps: The inner wall of the mold shell is pretreated by immersion coating with lanthanum nitrate solution to form a thin layer of lanthanum nitrate precursor; The shell is immersed in ammonium carbonate solution to convert the thin layer of lanthanum nitrate precursor into an insoluble solid layer of lanthanum carbonate in situ. The byproducts are removed by rinsing and then dried. Lanthanum borate surface layer slurry and gadolinium oxide isolation layer slurry are sequentially dipped into the lanthanum carbonate solid layer, and then the outer support shell slurry is dipped into the layer to complete the shell preparation. After dewaxing, the shell is sintered at high temperature. Lanthanum carbonate decomposes into lanthanum oxide, and the lanthanum oxide diffuses with the lanthanum borate surface layer at high temperature to form a chemical bond. Nickel-based high-temperature alloy molten metal is poured into the mold shell. The lanthanum borate surface layer undergoes an interfacial chemical reaction with the casting surface, forming a rare earth aluminate bonding layer on the casting surface. The lanthanum borate surface layer and the casting surface form a metallurgical bond. During the shell removal process, the metallurgical bond strength between the lanthanum borate surface layer and the casting is higher than the interfacial bond strength between the lanthanum borate surface layer and the gadolinium oxide isolation layer. The gadolinium oxide isolation layer is peeled off with the outer support shell, while the lanthanum borate surface layer remains on the blade surface.

2. The high-temperature alloy casting method for gas turbine blades according to claim 1, characterized in that, The lanthanum nitrate solution has a mass fraction of 5% to 15%, the immersion time is 30 to 60 seconds, and it is drained for 1 to 2 minutes after removal.

3. The high-temperature alloy casting method for gas turbine blades according to claim 1, characterized in that, The ammonium carbonate solution has a mass fraction of 8% to 12%, and the shell is immersed in the ammonium carbonate solution for 5 to 15 minutes; rinsing is performed by rinsing with deionized water 2 to 3 times.

4. The high-temperature alloy casting method for gas turbine blades according to claim 1, characterized in that, The lanthanum borate surface coating slurry contains lanthanum borate powder with a D50 particle size of no more than 5 μm, and the binder is aluminum sol with an Al2O3 mass fraction of 20% to 30%. The mass ratio of lanthanum borate powder to aluminum sol is 2:1 to 3:

1. The lanthanum borate surface coating slurry is applied in 12 coats, and each coat is drained for 12 minutes after removal.

5. The high-temperature alloy casting method for gas turbine blades according to claim 1, characterized in that, The gadolinium oxide isolation layer slurry contains gadolinium oxide powder with a D50 particle size of no more than 5 μm, and the binder is aluminum sol, in which the mass fraction of Al2O3 is 20% to 30%, and the mass ratio of gadolinium oxide powder to aluminum sol is 2:1 to 3:1; the gadolinium oxide isolation layer slurry is applied in 12 coats, and after each coat, it is drained for 12 minutes.

6. The high-temperature alloy casting method for gas turbine blades according to claim 1, characterized in that, The high-temperature sintering temperature is 900–1100℃, and the holding time is 13 hours.

7. The high-temperature alloy casting method for gas turbine blades according to claim 1, characterized in that, The nickel-based superalloy molten metal is poured into the directional shell using a vacuum directional solidification process or a vacuum single crystal casting process, with the molten metal pouring temperature being 1400–1500°C.

8. The high-temperature alloy casting method for gas turbine blades according to claim 1, characterized in that, The process after dehulling also includes a step of sealing the pores on the leaf surface with an oxalate-phosphate composite treatment, including: The blade casting was immersed in a mixed solution containing gadolinium nitrate and aluminum dihydrogen phosphate, then removed and dried at low temperature to allow the Gd... 3+ It is fixed in the pores of the blade surface with aluminum dihydrogen phosphate; The leaves were then immersed in an ammonium oxalate solution, and the Gd in the pores... 3+ The in-situ reaction with the infiltrated oxalate ions produces insoluble gadolinium oxalate, which is deposited in the pores. After removal and drying, the gadolinium oxalate and aluminum phosphate gel solidify together in the pores of the leaf surface, forming an oxalate-phosphate composite sealing film that seals the casting residual micropores on the leaf surface.

9. The high-temperature alloy casting method for gas turbine blades according to claim 8, characterized in that, The mass fraction of gadolinium nitrate in the mixed solution is 3%–5%, and the mass fraction of aluminum dihydrogen phosphate is 4%–6%. The immersion time of the blade casting in the mixed solution is 10–30 min; The low-temperature drying temperature is 50-80℃, and the drying time is 0.5-1h.

10. The high-temperature alloy casting method for gas turbine blades according to claim 8, characterized in that, The ammonium oxalate solution has a mass fraction of 2% to 3%; The immersion time of the leaves in the ammonium oxalate solution is 5 to 15 minutes; After removal, dry at 80-120℃ for 12 hours.

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