A pure yttrium mold shell for titanium alloy investment casting and a preparation method thereof

Abstract

The application discloses a pure yttrium mold shell for titanium alloy investment casting and a preparation method thereof. Yttrium sol, micron-sized yttria powder, nanometer-sized yttria powder, ion yttrium source, wetting agent and defoaming agent are mixed to prepare a slurry, then the slurry is used to prepare and seal the slurry on a wax mold for eleven layers, and finally, steam dewaxing and sintering are carried out, and the pure yttrium mold shell is obtained. The application solves the problem that high-activity metals or alloys containing high-activity metals react with the material of the mold shell during the casting process, causing the surface and the interior of the workpiece to be contaminated. The pure yttrium mold shell can be used for precision casting or directional solidification of high-activity metals such as Ti and Nb or alloys containing high-activity metals.

Description

TECHNICAL FIELD

[0001] The present application relates to a pure yttrium mold shell for titanium alloy investment casting and a preparation method thereof, and belongs to the technical field of investment precision casting. BACKGROUND

[0002] Titanium alloy is an excellent structural material, which has a series of excellent performances such as small density, high specific strength, corrosion resistance, good biocompatibility, and is widely used in aerospace, ocean transportation, energy, chemical industry, medical and health industry. Titanium alloy castings have unique advantages, especially investment precision castings, which can be arbitrarily complex in shape and can be formed as a whole with little or no excess.

[0003] However, titanium is a very active chemical element, and liquid titanium has different degrees of chemical reaction with almost all molding materials. These reactions can increase the brittleness of titanium castings, increase the thickness of the oxygen-rich layer and the thickness of the alpha brittle layer, and these defects seriously affect the mechanical properties of titanium castings, bringing great difficulties to the casting of titanium alloy. Therefore, the refractory materials and binders used for titanium alloy casting need to have very high chemical stability to reduce the chemical reaction between titanium liquid and the mold shell and reduce the surface contamination layer. Therefore, the preparation process of the mold shell is the biggest difficulty in the precision casting of titanium alloy.

[0004] At present, the binder used for titanium alloy investment precision casting generally uses silica sol and zirconia sol, but these two binders will react with titanium alloy at high temperatures to varying degrees. Yttria has excellent heat resistance, corrosion resistance and high temperature stability, and is not easy to react with high-activity metals or alloys (Ti, Nb, rare earth elements, etc.) at high temperatures. Therefore, yttria has great application prospects as a mold shell material for preparing pure yttrium mold shells. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a pure yttrium mold shell for titanium alloy investment casting and a preparation method thereof, which solves the problem of contamination of the surface and internal of the workpiece caused by the reaction between high-activity metals or alloys containing high-activity metals and the materials of the mold shell during the casting process. The pure yttrium mold shell of the present application can be used for precision casting or directional solidification of high-activity metals such as Ti and Nb or alloys containing high-activity metals.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A preparation method of a pure yttrium mold shell for titanium alloy investment casting, the specific steps are as follows:

[0008] (1) first, 12-16 parts of yttrium sol, 80-82 parts of micron-sized yttria powder, 0.8-1.5 parts of nano-sized yttria powder, 0.2-0.4 parts of ionic yttrium source, 0.02-0.05 parts of wetting agent and 0.01-0.02 parts of defoaming agent are added into deionized water, the deionized water is supplemented to 100 parts, and stirring is performed to obtain a slurry;

[0009] (2) then the slurry is uniformly sprayed on the wax mold, followed by sprinkling of yttria sand and drying to complete the preparation of the first layer, followed by continuous repetition of the steps of slurry spraying and yttria sand sprinkling and drying to sequentially complete the preparation of the second to eleventh layers, after which the wax mold on which the eleventh layer is prepared is completely immersed in the slurry, taken out after being fully wetted, and finally dried when the slurry no longer continuously drips to obtain a sealing slurry wax mold;

[0010] (3) finally, the sealing slurry wax mold is subjected to steam dewaxing and normal pressure sintering to obtain the pure yttrium mold shell.

[0011] Preferably, in step (1), the micron-sized yttria powder has a particle size distribution D 90 = 40-60 μm, and the nano-sized yttria powder has a particle size distribution D 90 = 60-100 nm.

[0012] Preferably, in step (1), the micron-sized yttria powder is subjected to a modification and activation treatment before use, and the specific method is as follows: a layer of PVP (polyvinyl pyrrolidone) or PVB (polyvinyl butyral) ethanol solution is uniformly sprayed on the surface of the micron-sized yttria powder, and the mass concentration of the solution is 1-1.8%. The modification and activation treatment can increase the activity of the micron-sized yttria powder, improve the binding force of the micron-sized yttria powder with the nano-sized yttria powder and yttrium ions, and thus more easily form a firm chemical bond during high-temperature calcination, thereby increasing the strength of the mold shell.

[0013] Preferably, in step (1), the ionic yttrium source is selected from any one of yttrium nitrate, yttrium acetate, yttrium chloride or yttrium fluoride. The yttrium ions provided by the ionic yttrium source can act as a high-temperature adhesive to form a network structure with the oxygen in the yttria particles of different particle sizes at high temperature, thereby improving the high-temperature strength of the mold shell.

[0014] Preferably, in step (2), the particle size of the yttria sand is 45-100 mesh when the first layer and the second layer are prepared; the particle size of the yttria sand is 30-60 mesh when the third to sixth layers are prepared; and the particle size of the yttria sand is 10-30 mesh when the seventh to eleventh layers are prepared.

[0015] Preferably, in step (2), the drying process conditions for preparing the first layer and the second layer are: temperature 20-22 DEG C, relative humidity 60-80%, and drying time 24-48 hours; the drying process conditions for preparing the third layer to the sixth layer are: temperature 20-22 DEG C, relative humidity 60-70%, and drying time 24-48 hours; and the drying process conditions for preparing the seventh layer to the eleventh layer are: temperature 22-24 DEG C, relative humidity 50-60%, and drying time 24-48 hours.

[0016] Preferably, in step (2), the final drying process conditions are: temperature 22-24 DEG C, relative humidity 50-60%, and drying time 24-48 hours.

[0017] Preferably, in step (3), the steam dewaxing process conditions are: temperature 150-170 DEG C, steam pressure 0.4-0.6 MPa, and dewaxing time 9-15 minutes.

[0018] Preferably, in step (3), the atmospheric pressure sintering process conditions are: temperature rising rate 1-5 DEG C / min, first rising to 340-380 DEG C, holding for 1-2 hours, then rising to 700-740 DEG C, holding for 1-2 hours, then rising to 1030-1070 DEG C, holding for 1-2 hours, then rising to 1430-1470 DEG C, holding for 3-5 hours, and finally cooling down with the furnace and discharging, thereby obtaining the pure yttrium mold shell.

[0019] The beneficial effects of the present application are as follows:

[0020] In the present application, yttrium sol, micron-sized yttrium oxide powder, nano-sized yttrium oxide powder, ion yttrium source, wetting agent and defoaming agent are mixed to form a slurry, which is then used to prepare and seal the wax mold for eleven layers, and finally steam dewaxing and sintering are performed to obtain a pure yttrium mold shell for titanium alloy investment casting, thereby solving the problem that high-activity metals or alloys containing high-activity metals react with the material of the mold shell during casting, causing the surface and internal contamination of the workpiece. The pure yttrium mold shell of the present application can be used for precision casting or directional solidification of Ti, Nb and other high-activity metals or alloys containing high-activity metals.

[0021] The present application has the following advantages:

[0022] 1. The pure yttrium mold shell preparation process is simple, and can be used for precision casting or directional solidification of Ti, Nb and other high-activity metals or alloys containing high-activity metals.

[0023] 2. During the preparation of the mold shell, the micron-sized yttrium oxide powder is modified to improve its bonding force with the nano-sized yttrium oxide powder and yttrium ions. It is easier to form strong chemical bonds during high-temperature calcination. In addition, the sand-sprinkling operation increases the strength of the mold shell by grading yttrium oxide sand of different particle sizes. The resulting mold shell has high dimensional accuracy, is not easily deformed, and does not crack during directional solidification and other processes, thus meeting the requirements for thermal shock resistance.

[0024] 3. In the process of high-temperature precision casting and directional solidification casting, the pure yttrium mold shell does not react with highly reactive metals or alloys containing highly reactive metals. The surface of the casting is smooth and free of sand adhesion. Fluorescent detection shows no obvious surface defects, and the casting quality is good.

[0025] 4. In the process of high-temperature precision casting and directional solidification casting, the pure yttrium mold shell does not react with highly reactive metals or alloys containing highly reactive metals. There are no inclusions, pores, or loose shrinkage inside the casting. X-ray inspection shows no obvious internal defects, and the casting quality is good.

[0026] 5. The composition of the slurry in this application is crucial. The increase or decrease of raw materials or the formulation will affect the technical effect, as detailed below:

[0027] Yttrium sol mainly serves as an adhesive; its absence or reduction significantly affects the adhesive strength of the system (tested using the three-point bending test method, HB205352.1-2004 shell bending strength test); see Table 1 for details.

[0028] Table 1. Effect of Yttrium Sol Concentration on Bond Strength of the System

[0029] Yttrium sol parts by weight 0 5 10 12 14 16 18 20 System bonding strength 0 MPa 10 MPa 15 MPa 28 MPa 30 MPa 32 MPa 26 MPa 26 MPa

[0030] Micron-sized yttrium oxide powder primarily serves as aggregate. Modification enhances its bonding strength with nano-sized yttrium oxide powder and yttrium ions, making it easier to form strong chemical bonds during high-temperature calcination. A deficiency or reduction in this material significantly impacts the structural strength of the system (three-point bending test strength; HB205352.1-2004 shell bending strength test); see Table 2 for details.

[0031] Table 2. Effect of micron-sized yttrium oxide powder on structural strength

[0032]

[0033] Nanoscale yttrium oxide powder and ion yttrium source mainly serve to provide high-temperature binders. Their absence or reduction will have a significant impact on the high-temperature strength of the system (strength tested by the three-point bending method. HB205352.1-2004 shell bending strength test); see Tables 3 and 4 for details.

[0034] Table 3. Effect of nano-sized yttrium oxide powder on the high-temperature strength of the system

[0035]

[0036] Table 4. Effect of ion yttrium source on high temperature strength of the system

[0037] Ionic yttrium source parts by weight 0 0.05 0.1 0.2 0.3 0.4 0.5 0.6 System high temperature strength 0 MPa 5 MPa 10 MPa 32 MPa 35 MPa 35 MPa 30 MPa 29 MPa

[0038] The sanding operation increases the strength of the shell by grading the different particle sizes of the yttrium oxide sand. If the sanding particle size is too coarse or too fine, it will have a greater impact on the surface layer strength, which will decrease from 32 MPa to 22 MPa. The drying temperature, drying humidity, and drying time of the surface layer will have a greater impact on the surface quality of the shell. If the drying conditions are not sufficient, the surface quality of the shell obtained is poor, the surface is rough, and the surface layer is prone to dissolution, and the strength is insufficient (three-point bending test strength. HB205352.1-2004 shell bending strength test). See Table 5 for details.

[0039] Table 5. Effect of sanding operation on surface layer strength

[0040] BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 Figure 1 is an X-ray detection diagram of the pure yttrium shell obtained in Example 2. DETAILED DESCRIPTION

[0042] The application will be further described below in conjunction with the drawings and examples, and it should be noted that the following description is only to explain the application and does not limit its content.

[0043] Example 1:

[0044] Pure yttrium shell for precision casting of titanium alloy TC4 alloy

[0045] First step: preparing the shell slurry

[0046] The shell slurry is composed of yttrium sol, micron-sized yttrium oxide powder with a particle size distribution D 90 = 40 μm, nano-sized yttrium oxide powder with a particle size distribution D 90 = 60 nm, yttrium nitrate, and wetting agent and defoaming agent. Among them, the yttrium sol accounts for 12% of the total weight of the shell slurry, the micron-sized yttrium oxide powder accounts for 80% of the total weight of the shell slurry, the nano-sized yttrium oxide powder accounts for 0.8% of the total weight of the shell slurry, the yttrium nitrate accounts for 0.2% of the total weight of the shell slurry, the wetting agent accounts for 0.02% of the total weight of the shell slurry, and the defoaming agent accounts for 0.01% of the total weight of the shell slurry.

[0047] Among them, the micron-sized yttrium oxide powder is pre-sprayed with a 1% PVB ethanol solution before use.

[0048] Second step: preparing a pure yttrium shell

[0049] (1) The slurry prepared in the first step is sprayed on the wax mold, and after uniform control of the material, 45-mesh yttrium oxide sand is sprinkled to complete the first layer preparation; the first layer drying temperature is 22°C, the drying humidity is 70%, and the drying time is 24h.

[0050] (2) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold which has completed the first layer, and after uniform control of the material, 45-mesh yttrium oxide sand is sprinkled to complete the second layer preparation; the second layer drying temperature is 22°C, the drying humidity is 70%, and the drying time is 24h.

[0051] (3) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold which has completed the second layer, and after uniform control of the material, 30-mesh yttrium oxide sand is sprinkled to complete the third layer preparation; the third layer drying temperature is 22°C, the drying humidity is 65%, and the drying time is 24h.

[0052] (4) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold which has completed the third layer, and after uniform control of the material, 30-mesh yttrium oxide sand is sprinkled to complete the fourth layer preparation; the fourth layer drying temperature is 22°C, the drying humidity is 65%, and the drying time is 24h.

[0053] (5) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold which has completed the fourth layer, and after uniform control of the material, 30-mesh yttrium oxide sand is sprinkled to complete the fifth layer preparation; the fifth layer drying temperature is 22°C, the drying humidity is 60%, and the drying time is 36h.

[0054] (6) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold which has completed the fifth layer, and after uniform control of the material, 30-mesh yttrium oxide sand is sprinkled to complete the sixth layer preparation; the sixth layer drying temperature is 22°C, the drying humidity is 60%, and the drying time is 36h.

[0055] (7) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold which has completed the sixth layer, and after uniform control of the material, 10-mesh yttrium oxide sand is sprinkled to complete the seventh layer preparation; the seventh layer drying temperature is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0056] (8) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold which has completed the seventh layer, and after uniform control of the material, 10-mesh yttrium oxide sand is sprinkled to complete the eighth layer preparation; the eighth layer drying temperature is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0057] (9) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold on which the eighth layer has been applied, and then 10-mesh yttria sand is evenly sprinkled to complete the preparation of the ninth layer; the drying temperature of the ninth layer is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0058] (10) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold on which the ninth layer has been applied, and then 10-mesh yttria sand is evenly sprinkled to complete the preparation of the tenth layer; the drying temperature of the tenth layer is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0059] (11) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold on which the tenth layer has been applied, and then 10-mesh yttria sand is evenly sprinkled to complete the preparation of the eleventh layer; the drying temperature of the eleventh layer is 24°C, the drying humidity is 50%, and the drying time is 24h.

[0060] (12) The wax mold on which the eleventh layer has been applied is immersed in the slurry prepared in the first step, and then taken out after being fully wetted; when the slurry no longer continuously drips, the wax mold is placed in an environment with a temperature of 24°C and a relative humidity of 50% for drying for 48h, thereby completing the sealing process.

[0061] Third step: dewaxing

[0062] The wax mold on which the sealing process has been completed and which is prepared in the second step is subjected to steam dewaxing, and the dewaxing process parameters are as follows: 170°C, steam pressure 0.6MPa, and dewaxing time 9min.

[0063] Fourth step: sintering

[0064] The mold shell on which the dewaxing has been completed and which is prepared in the third step is placed in a sintering furnace for atmospheric sintering, and the setting heating rate is 1°C / min, and the sintering schedule is as follows: 360°C for 2h; 720°C for 2h; 1050°C for 2h; 1450°C for 3h; and then the mold shell is cooled in the furnace, taken out of the furnace, and a pure yttrium mold shell is obtained.

[0065] The pure yttrium mold shell prepared in Example 1 is assembled into a mold and subjected to centrifugal casting at a speed of 170r / min, and then the castings are taken out after cooling, and it is observed that the surface of the TC4 castings is smooth and there is no sand sticking phenomenon.

[0066] The surface of the castings is detected by fluorescence detection, and there is no obvious defect, and the internal part of the castings is detected by X-ray detection, and there is no defect such as slag inclusion, porosity, loose shrinkage, etc., and the quality of the castings is good.

[0067] Example 2

[0068] Pure yttrium mold shell for precision casting of titanium alloy TA15 alloy

[0069] First step: preparation of mold shell slurry

[0070] The shell slurry is composed of yttrium sol, micron-sized yttria powder with particle size distribution D 90 = 60 μm, nano-sized yttria powder with particle size distribution D 90 = 100 nm, yttrium nitrate, and wetting agent and defoaming agent. The yttrium sol accounts for 16% of the total weight of the shell slurry, the micron-sized yttria powder accounts for 82% of the total weight of the shell slurry, the nano-sized yttria powder accounts for 1.5% of the total weight of the shell slurry, the yttrium nitrate accounts for 0.4% of the total weight of the shell slurry, the wetting agent accounts for 0.05% of the total weight of the shell slurry, and the defoaming agent accounts for 0.02% of the total weight of the shell slurry.

[0071] The micron-sized yttria powder is pre-sprayed with a 1.8% PVB ethanol solution before use.

[0072] Second step: preparation of pure yttrium shell

[0073] (1) The slurry prepared in the first step is sprayed on the wax mold, and after uniform control of the material, yttria sand with a particle size of 100 mesh is sprinkled to complete the preparation of the first layer; the first layer drying temperature is 20°C, the drying humidity is 70%, and the drying time is 24h.

[0074] (2) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold on which the first layer has been coated and hung, and after uniform control of the material, yttria sand with a particle size of 100 mesh is sprinkled to complete the preparation of the second layer; the second layer drying temperature is 20°C, the drying humidity is 70%, and the drying time is 24h.

[0075] (3) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold on which the second layer has been coated and hung, and after uniform control of the material, yttria sand with a particle size of 60 mesh is sprinkled to complete the preparation of the third layer; the third layer drying temperature is 20°C, the drying humidity is 65%, and the drying time is 24h.

[0076] (4) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold on which the third layer has been coated and hung, and after uniform control of the material, yttria sand with a particle size of 60 mesh is sprinkled to complete the preparation of the fourth layer; the fourth layer drying temperature is 22°C, the drying humidity is 65%, and the drying time is 24h.

[0077] (5) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold on which the fourth layer has been coated and hung, and after uniform control of the material, yttria sand with a particle size of 60 mesh is sprinkled to complete the preparation of the fifth layer; the fifth layer drying temperature is 22°C, the drying humidity is 60%, and the drying time is 36h.

[0078] (6) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold on which the fifth layer has been coated and hung, and after uniform control of the material, yttria sand with a particle size of 60 mesh is sprinkled to complete the preparation of the sixth layer; the sixth layer drying temperature is 22°C, the drying humidity is 60%, and the drying time is 36h.

[0079] (7) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the sixth layer, and then the 30 mesh yttria sand is evenly sprinkled to complete the preparation of the seventh layer; the drying temperature of the seventh layer is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0080] (8) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the seventh layer, and then the 30 mesh yttria sand is evenly sprinkled to complete the preparation of the eighth layer; the drying temperature of the eighth layer is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0081] (9) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the eighth layer, and then the 30 mesh yttria sand is evenly sprinkled to complete the preparation of the ninth layer; the drying temperature of the ninth layer is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0082] (10) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the ninth layer, and then the 30 mesh yttria sand is evenly sprinkled to complete the preparation of the tenth layer; the drying temperature of the tenth layer is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0083] (11) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the tenth layer, and then the 30 mesh yttria sand is evenly sprinkled to complete the preparation of the eleventh layer; the drying temperature of the eleventh layer is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0084] (12) The wax mold coated with the eleventh layer is immersed in the slurry prepared in the first step, and then taken out after being fully wetted. When the slurry no longer continuously drips, it is placed in an environment with a temperature of 24°C and a relative humidity of 50% for drying for 48h, completing the sealing process.

[0085] Third step: dewaxing

[0086] The wax mold which has completed the sealing process prepared in the second step is subjected to steam dewaxing, and the dewaxing process parameters are: 160°C, steam pressure 0.5MPa, and dewaxing time 12min.

[0087] Fourth step: sintering

[0088] The mold shell which has completed dewaxing prepared in the third step is placed in a sintering furnace for atmospheric sintering, and the setting heating rate is 1°C / min. The sintering schedule is 360°C for 2h; 720°C for 2h; 1050°C for 2h; 1440°C for 3.5h; and then the furnace is cooled down, and the mold shell is taken out of the furnace to obtain a pure yttrium mold shell.

[0089] The pure yttrium shell prepared in Example 2 was used to make a mold, and centrifugal casting was performed at a speed of 170 r / min. After casting was completed, the TA15 casting was removed after cooling, and the surface of the casting was smooth and free of sand sticking.

[0090] The surface of the casting was free of obvious defects, and the internal part of the casting was free of slag inclusion, porosity, loose shrinkage, and other defects, and the casting quality was good. Figure 1 )

[0091] Example 3

[0092] Pure yttrium shell for directional solidification of Ti-45Al-6Nb

[0093] First step: preparation of mold shell slurry

[0094] The mold shell slurry is composed of yttrium sol, micron-sized yttria powder with a particle size distribution D 90 = 50 μm, nano-sized yttria powder with a particle size distribution D 90 = 80 nm, yttrium nitrate, and wetting agent and defoaming agent. The yttrium sol accounts for 14% of the total weight of the mold shell slurry, the micron-sized yttria powder accounts for 81% of the total weight of the mold shell slurry, the nano-sized yttria powder accounts for 1.15% of the total weight of the mold shell slurry, the yttrium nitrate accounts for 0.3% of the total weight of the mold shell slurry, the wetting agent accounts for 0.035% of the total weight of the mold shell slurry, and the defoaming agent accounts for 0.015% of the total weight of the mold shell slurry.

[0095] The micron-sized yttria powder is pre-sprayed with a 1.4% PVB ethanol solution before use.

[0096] Second step: preparation of pure yttrium shell

[0097] (1) The slurry prepared in the first step is sprayed on the wax mold, and after uniform control of the material, yttria sand with a particle size of 70 mesh is sprinkled to complete the preparation of the first layer; the first layer is dried at a temperature of 20°C, a humidity of 75%, and for a time of 24 h.

[0098] (2) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold on which the first layer has been applied, and after uniform control of the material, yttria sand with a particle size of 70 mesh is sprinkled to complete the preparation of the second layer; the second layer is dried at a temperature of 20°C, a humidity of 75%, and for a time of 24 h.

[0099] (3) Repeat the above steps, and the slurry prepared in the first step is sprayed on the wax mold on which the second layer has been applied, and after uniform control of the material, yttria sand with a particle size of 45 mesh is sprinkled to complete the preparation of the third layer; the third layer is dried at a temperature of 20°C, a humidity of 70%, and for a time of 24 h.

[0100] (4) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the third layer, and then the 45 mesh yttrium oxide sand is evenly sprinkled to complete the fourth layer preparation; the fourth layer drying temperature is 22°C, the drying humidity is 70%, and the drying time is 24h.

[0101] (5) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the fourth layer, and then the 45 mesh yttrium oxide sand is evenly sprinkled to complete the fifth layer preparation; the fifth layer drying temperature is 22°C, the drying humidity is 65%, and the drying time is 36h.

[0102] (6) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the fifth layer, and then the 45 mesh yttrium oxide sand is evenly sprinkled to complete the sixth layer preparation; the sixth layer drying temperature is 22°C, the drying humidity is 65%, and the drying time is 36h.

[0103] (7) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the sixth layer, and then the 45 mesh yttrium oxide sand is evenly sprinkled to complete the seventh layer preparation; the seventh layer drying temperature is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0104] (8) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the seventh layer, and then the 45 mesh yttrium oxide sand is evenly sprinkled to complete the eighth layer preparation; the eighth layer drying temperature is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0105] (9) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the eighth layer, and then the 45 mesh yttrium oxide sand is evenly sprinkled to complete the ninth layer preparation; the ninth layer drying temperature is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0106] (10) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the ninth layer, and then the 45 mesh yttrium oxide sand is evenly sprinkled to complete the tenth layer preparation; the tenth layer drying temperature is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0107] (11) Repeat the above steps, the slurry prepared in the first step is sprayed on the wax mold which has been coated with the tenth layer, and then the 45 mesh yttrium oxide sand is evenly sprinkled to complete the eleventh layer preparation; the eleventh layer drying temperature is 24°C, the drying humidity is 50%, and the drying time is 36h.

[0108] (12) The wax mold which has been coated with the eleventh layer is immersed in the slurry prepared in the first step, and then taken out after being fully wetted. When the slurry no longer continuously drips, it is placed in an environment with a temperature of 24°C and a relative humidity of 50% for drying for 48h, completing the sealing process.

[0109] Third step: dewaxing

[0110] The wax mold after the sealing process is obtained in the second step is subjected to steam dewaxing, and the dewaxing process parameters are as follows: 170℃, steam pressure 0.6MPa, and dewaxing time 10min.

[0111] Fourth step: sintering

[0112] The mold shell after the dewaxing in the third step is put into a sintering furnace for atmospheric sintering, and the setting heating rate is 1℃ / min, and the sintering system is as follows: 360℃ for 2h; 720℃ for 2h; 1050℃ for 2h; 1460℃ for 4h; and then the furnace is cooled down, and the furnace is discharged to obtain a pure yttrium mold shell.

[0113] The pure yttrium mold shell obtained in Example 3 is assembled and subjected to centrifugal casting at a speed of 170r / min, and after the casting is completed, the casting is cooled down and taken out, and the Ti-45Al-6Nb casting is observed to have a smooth surface and no sand sticking phenomenon.

[0114] The casting is subjected to fluorescence detection, and no obvious defects are found on the surface, and the X-ray detection shows that there are no slag inclusion, pores, loose shrinkage porosity and other defects in the inside, and the casting quality is good.

[0115] Although the specific embodiments of the present application are described above with reference to the accompanying drawings, the description is not a limitation on the protection scope of the present application, and various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the protection scope of the present application.

Claims

1. A method for producing a pure yttrium mold shell for a titanium alloy investment casting, characterized by, The specific steps are as follows: (1) 12-16 parts of yttrium sol, 80-82 parts of micron-sized yttria powder, 0.8-1.5 parts of nano-sized yttria powder, 0.2-0.4 parts of ionic yttrium source, 0.02-0.05 parts of wetting agent and 0.01-0.02 parts of defoaming agent are added into deionized water in terms of weight parts, and the deionized water is supplemented to 100 parts, and then stirred and mixed uniformly to obtain a slurry; (2) then the slurry is uniformly sprayed on the wax mold, followed by sprinkling yttria sand and drying to complete the preparation of the first layer, and then the steps of slurry spraying and yttria sand sprinkling and drying are continuously repeated to sequentially complete the preparation of the second layer to the eleventh layer, after which the wax mold with the eleventh layer prepared is completely immersed in the slurry, taken out after being fully wetted, and finally dried when the slurry no longer continuously drips, to obtain a sealing slurry wax mold; (3) finally, the sealing slurry wax mold is subjected to steam dewaxing and normal pressure sintering, and the pure yttrium mold shell is obtained.

2. The production method according to claim 1, characterized by, In step (1), the micrometer-sized yttria powder has a particle size distribution D 90 = 40 to 60 μm, and the nanometer-sized yttria powder has a particle size distribution D 90 = 60 to 100 nm.

3. The preparation method according to claim 1, characterized in that, In step (1), the micron-sized yttria powder is subjected to modification and activation treatment before use, and the specific method is: a layer of PVP or PVB ethanol solution is uniformly sprayed on the surface of the micron-sized yttria powder, and the mass concentration of the solution is 1-1.8%; the modification and activation treatment can increase the activity of the micron-sized yttria powder, improve its bonding force with the nano-sized yttria powder and yttrium ions, so that it is easier to form a firm chemical bond during high-temperature calcination, thereby increasing the strength of the mold shell.

4. The method of claim 1, wherein, In step (1), the ionic yttrium source is selected from any one of yttrium nitrate, yttrium acetate, yttrium chloride or yttrium fluoride.

5. The preparation method according to claim 1, characterized in that, In step (2), the particle size of the yttria sand is 45-100 mesh when the first layer and the second layer are prepared; the particle size of the yttria sand is 30-60 mesh when the third layer to the sixth layer are prepared; and the particle size of the yttria sand is 10-30 mesh when the seventh layer to the eleventh layer are prepared.

6. The method of claim 1, wherein, In step (2), the drying process conditions are: temperature 20-22℃, relative humidity 60-80%, and drying time 24-48 hours when the first layer and the second layer are prepared; the drying process conditions are: temperature 20-22℃, relative humidity 60-70%, and drying time 24-48 hours when the third layer to the sixth layer are prepared; and the drying process conditions are: temperature 22-24℃, relative humidity 50-60%, and drying time 24-48 hours when the seventh layer to the eleventh layer are prepared.

7. The preparation method according to claim 1, characterized in that, In step (2), the final drying process conditions are: temperature 22-24℃, relative humidity 50-60%, and drying time 24-48 hours.

8. The method of claim 1, wherein, In step (3), the process conditions for steam dewaxing are: temperature 150-170℃, steam pressure 0.4-0.6 MPa, and dewaxing time 9-15 minutes.

9. The method of claim 1, wherein, In step (3), the process conditions for normal pressure sintering are: the heating rate is 1-5℃ / min, first heated to 340-380℃, kept for 1-2 hours, then heated to 700-740℃, kept for 1-2 hours, then heated to 1030-1070℃, kept for 1-2 hours, then continuously heated to 1430-1470℃, kept for 3-5 hours, and finally cooled with the furnace, and then taken out of the furnace to obtain the pure yttrium mold shell.

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