MgO-y2o3-based crucible for smelting ni-tial alloy in ultra-high vacuum and preparation method thereof

Abstract

The application discloses a MgO-Y2O3-based crucible for ultra-vacuum smelting of Ni-TiAl alloy and a preparation method thereof. The technical scheme is as follows: the chemical components of the application are as follows: MgO-Y2O3-based light-weight refractory raw material with core-shell structure (MgO-Y2O3 for short) is used as raw material (three kinds of particle levels are aggregates and one kind of fine powder is matrix), pure calcium aluminate is used as binder and CaF2 is used as additive. The preparation method of the application is as follows: the aggregates are placed in a stirrer, mixed uniformly, the matrix and the binder are added and stirred; then, CaF2 suspension is added at a uniform speed, mixed uniformly, vacuum casting is performed, drying is carried out, the product is obtained by keeping the temperature at 1100 DEG C to 1300 DEG C for 2 to 5 hours and keeping the temperature at 1650 DEG C to 1780 DEG C for 4 to 8 hours. The MgO-Y2O3-based crucible for ultra-vacuum smelting of Ni-TiAl alloy is obtained. The product prepared by the application has the advantages of low vacuum evaporation rate, long service life, no pollution to smelting melt, intermittent use, good thermal shock stability and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of MgO-Y2O3-based crucibles. Specifically, it relates to a MgO-Y2O3-based crucible for ultra-high vacuum melting of Ni-TiAl alloy and a preparation method thereof. BACKGROUND

[0002] Ni-TiAl high-temperature alloy is a key lightweight material for the next generation of high-performance, high-thrust-to-weight ratio engines. Induction furnace vacuum crucible melting is the most effective method for large-scale production of Ni-TiAl high-temperature alloy at low cost. Compared with the existing melting process of heavy nickel-based high-temperature alloy, Ni-TiAl high-temperature alloy requires higher melting temperature, and the chemical erosion of the crucible is more serious with the increase of Ti and Al active elements in the alloy, not only affecting the control of alloy composition, but also adversely affecting the quality of the Ni-TiAl alloy. At the same time, there is a problem of poor thermal shock resistance of alkaline crucible, which is difficult to adapt to the intermittent operation characteristics of alloy production.

[0003] Currently, there has been progress in related research: "A crucible for melting alloys containing active elements and a preparation method thereof" (CN202111034475.9) patent technology, which uses spraying and smearing double processes to coat yttria on an alumina-based crucible in a nitrogen environment, reducing the reactivity of the active element alloy at the contact interface with the crucible, although it improves the service life of the crucible, but the technology not only has high preparation cost, and the bonding strength of the yttria coating and the alumina matrix is difficult to remain unchanged during the recycling process of the crucible, once it peels off and melts into the alloy melt, it will form an external inclusion, which is difficult to ensure production stability and safety.

[0004] For example, "Electric melting yttria ceramic crucible for titanium alloy melting and casting and preparation method thereof" (CN201610593898.7) patent technology, which uses yttria and zirconia as raw materials, and prepares high-purity crystalline raw materials by high-frequency heating and shell melting method for magnetic stirring of yttria melt. The yttria ceramic crucible prepared after a series of steps. The yttria ceramic crucible prepared by this technology has the characteristics of not sticking and not infiltrating, and the purity of the Ti alloy melted is improved, but this technology does not improve the problems of low mechanical strength, intermittent use and poor thermal shock stability of the yttria ceramic crucible.

[0005] For example, "a method for sintering yttrium oxide ceramic crucible at low temperature" (CN202110388155.7) patent technology, this technology selects yttrium oxide powder as raw material, magnesium oxide powder and titanium oxide powder as sintering aid, mixes and presses into shape to obtain yttrium oxide ceramic crucible. The technology uses sintering aid to reduce the sintering temperature of yttrium oxide ceramic, and the addition of sintering aid also improves the density, but magnesium oxide will volatilize Mg and O vapor under high temperature vacuum condition, which not only reduces the service life of the crucible, but also pollutes the smelting melt.

[0006] MgO crucible has been applied to heavy Ni-based vacuum smelting due to its mature technology and excellent hydration resistance compared with CaO. However, MgO begins to decompose and produce Mg and O gas under high temperature vacuum environment above 1680℃ due to its own volatility, which has a great adverse effect on the quality of smelting melt, so its application in Ni-TiAl alloy ultra-vacuum ultra-high temperature smelting is limited. SUMMARY

[0007] The present application aims to overcome the defects of the prior art, and the purpose is to provide a preparation method of MgO-Y2O3-based crucible for ultra-vacuum smelting of Ni-TiAl alloy, which has simple preparation process and low cost. The MgO-Y2O3-based crucible for ultra-vacuum smelting of Ni-TiAl alloy prepared by the method has low vacuum evaporation rate, long service life, does not pollute the smelting melt, can be used intermittently and has good thermal shock stability.

[0008] To achieve the above purpose, the technical solution adopted by the present application is as follows:

[0009] Step 1, the chemical composition and content of the MgO-Y2O3-based crucible for ultra-vacuum smelting of Ni-TiAl alloy are as follows:

[0010] 20-26wt% of MgO-Y2O3 particles with particle size less than 5mm and greater than or equal to 3mm, 25-30wt% of MgO-Y2O3 particles with particle size less than 3mm and greater than or equal to 1mm, and 15-25wt% of MgO-Y2O3 particles with particle size less than 1mm and greater than or equal to 0.088mm are used as aggregates.

[0011] 20-30wt% of MgO-Y2O3 fine powder with particle size less than 74μm is used as matrix.

[0012] 2.5-3wt% of pure calcium aluminate cement is used as binder.

[0013] 1-1.5wt% of CaF2 suspension turbidity liquid with concentration of 200-1000ppm is added as additive.

[0014] Step 2, according to the chemical components and their contents described in Step 1, first put the aggregate into a stirrer, mix uniformly, then add the matrix and the binding agent, stir uniformly; then under stirring conditions, add the CaF2 suspension turbidity at a uniform speed, mix uniformly, and use vacuum pouring to form.

[0015] Step 3, dry the formed body at 110℃-220℃ for 16-24 hours, keep it at 1100℃-1300℃ for 2-5 hours, and keep it at 1650℃-1780℃ for 4-8 hours to obtain the MgO-Y2O3-based crucible for ultra-vacuum smelting of Ni-TiAl alloy.

[0016] The matrix microstructure of the MgO-Y2O3-based crucible for ultra-vacuum smelting of Ni-TiAl alloy is needle-like CA6, and the aggregate is MgO-Y2O3-based crucible with continuous grain boundary core-shell structure.

[0017] The MgO-Y2O3 is a short name for "MgO-Y2O3-based light-weight refractory raw material with core-shell structure"; and the preparation method of the MgO-Y2O3-based light-weight refractory raw material with core-shell structure is:

[0018] Take 45-64wt% porous light-burned magnesium oxide, 34-52wt% magnesium hydroxide and 2-5wt% yttrium metal as raw materials, plus 1-1.5wt% nano calcium carbonate solution with a concentration of 500-4000ppm, ball mill for 1-3 hours, and machine press into a green body under the condition of 150-200MPa; first heat the green body to 700℃-900℃ and keep it for 2-4 hours; then heat it to 1520℃-1550℃ and keep it for 1-3 hours; then heat it to 1700℃-1800℃ and keep it for 3-6 hours; and cool it naturally in the furnace to obtain the MgO-Y2O3-based light-weight refractory raw material with core-shell structure.

[0019] Crush and sieve the MgO-Y2O3-based light-weight refractory raw material with core-shell structure to obtain aggregate and matrix material of three particle sizes, wherein the three particle sizes are: less than 5mm and greater than or equal to 3mm, less than 3mm and greater than or equal to 1mm, and less than 1mm and greater than or equal to 0.088mm; and the particle size of the matrix material is <74μm.

[0020] The MgO-Y2O3-based light-weight refractory raw material with core-shell structure has an apparent porosity of 5.6-11.2% and a bulk density of 3.25-3.45g / cm 3The MgO content is 95-97wt%; the Y2O3 content is 2-5wt%; the high-temperature vacuum evaporation rate is 0.75-1.22% under the conditions of a temperature of 1700 DEG C and a pressure of 10Pa, and the strength retention rate is 55-68% after three times of water cooling at 1100-120 DEG C.

[0021] The pure calcium aluminate cement has an Al2O3 content of < 82% and a CaO content of > 19%, and the particle size of the pure calcium aluminate cement is < 74mu.

[0022] The preparation method of the CaF2 suspension turbidity liquid with a concentration of 200-1000ppm is as follows: the CaF2 is added into purified water in a mass ratio of CaF2: purified water of 1-5:4997.5, and stirring is performed to obtain the CaF2 suspension turbidity liquid with a concentration of 200-1000ppm; the CaF2 content is greater than 99.5wt%, and the particle size is less than 10mu.

[0023] The MgO content in the porous light-burned magnesium oxide is > 99.6wt%; and the micro-nano closed pores account for 45-55% of the total pores.

[0024] The Mg(OH)2 content in the magnesium hydroxide is > 99.7wt%, and the SiO2 content is < 0.05wt%.

[0025] The Y content in the metallic yttrium is > 99.9wt%.

[0026] The preparation method of the nano calcium carbonate solution with a concentration of 500-4000ppm is as follows: the nano calcium carbonate is added into purified water in a mass ratio of nano calcium carbonate: purified water of 1-8:1999, and stirring is performed to obtain the nano calcium carbonate solution with a concentration of 500-4000ppm.

[0027] The CaCO3 content in the nano calcium carbonate is > 99.9wt%.

[0028] The mass ratio of the corundum ball to the raw material is 2-3:1.

[0029] Compared with the prior art, the present application has the following positive effects:

[0030] The application adopts MgO-Y2O3-based light-weight refractory raw material with core-shell structure (referred to as MgO-Y2O3) as main raw material, which is first decomposed at 700-900 DEG C to generate nanoscale internal pores, and then in the process of temperature rise, yttrium begins to melt and completely wet the surface of MgO grains, and Y-MgO coating structure is formed at high temperature, and then the binary system of MgO-Y2O3 does not generate intermediate compounds, so that Y2O3 is mainly distributed on the surface and grain boundary of the material at high temperature, and no intermediate phase is generated; meanwhile, the H2O molecules discharged in the decomposition process of magnesium hydroxide raw material provide effective channel pores, which provide channels and power for the rearrangement of Y2O3 on the MgO grains and the penetration into the material, and finally the MgO-Y2O3 material with core-shell grain structure characteristics is formed after high-temperature sintering, Y2O3 can be uniformly distributed on the surface of MgO grains, and no surface segregation and enrichment occurs, and a certain amount of nanoscale pores exist in the MgO grains, which can effectively improve the thermal shock resistance of the material. Meanwhile, the MgO-Y2O3 material with core-shell grain structure characteristics can improve the hydration resistance of the MgO-Y2O3-based MgO-Y2O3-based crucible for super vacuum smelting Ni-TiAl alloy by uniformly distributing stable Y2O3 shell on the grain boundary, and reduce the volatilization rate of MgO at high temperature under vacuum.

[0031] The MgO-Y2O3 adopted in the application has excellent hydration resistance; the vacuum casting forming process can solve the problem of large-scale production of large vacuum induction furnaces (0.5 tons or more) by limiting the high-difficulty and high-waste-rate isostatic pressing forming technology. Meanwhile, the MgO-Y2O3 light-weight refractory raw material with core-shell grain structure characteristics is used as the crucible material, which solves the problem of high vacuum volatilization rate of the existing magnesium crucible under vacuum and alloy pollution. Compared with the existing Y2O3 directly coated MgO crucible, the Y2O3 distributed on the grain boundary of the application greatly reduces the risk of Y2O3 coating peeling, and improves the thermal shock resistance of the overall MgO-Y2O3-based crucible. Moreover, in the high-temperature sintering process, Al2O3 and CaO in the matrix will combine in situ to generate micro-nano needle-shaped CA6, which can first improve the bonding strength between the matrix and the aggregate, so that the high-temperature strength of the MgO-Y2O3-based crucible for super vacuum smelting Ni-TiAl alloy is improved, and secondly, the micro-nano needle-shaped CA6 phase has good hydration resistance, which can further improve the hydration resistance of the MgO-Y2O3-based crucible. Meanwhile, after high-temperature sintering, the MgO-Y2O3-based crucible for super vacuum smelting Ni-TiAl alloy is also sintered and densified, thereby improving the strength and hydration resistance of the product.

[0032] The MgO-Y2O3-based crucible for super-vacuum smelting Ni-TiAl alloy prepared by the method has the advantages of excellent thermal shock resistance, repeated use under intermittent smelting conditions, strong corrosion resistance to Ni-TiAl alloy, low vacuum evaporation rate, no introduction of foreign inclusions, and can be used in the construction of large-scale vacuum induction furnace lining.

[0033] The MgO-Y2O3-based crucible for super-vacuum smelting Ni-TiAl alloy has the following properties: the apparent porosity is 4.10-7.86%; the bulk density is 3.10-3.60 g / cm 3 ; the high-temperature bending strength at 1400°C is 12-18 MPa, and no cracks are generated after 8 times of wind cooling cycles at 1100°C-20°C.

[0034] Therefore, the method has the characteristics of simple preparation process and low cost, and the prepared MgO-Y2O3-based crucible for super-vacuum smelting Ni-TiAl alloy has the advantages of low vacuum evaporation rate, long service life, no pollution to smelting melt, intermittent use, and good thermal shock stability. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The microstructure of the MgO-Y2O3-based crucible for super-vacuum smelting Ni-TiAl alloy prepared by the method after heat treatment.

[0036] Figure 2 The cross-sectional view of the MgO-Y2O3-based crucible for super-vacuum smelting Ni-TiAl alloy prepared by the method after intermittent smelting K417G (Ti, Al>10wt%) for six times. DETAILED DESCRIPTION

[0037] The application will be further described below in combination with the drawings and specific embodiments, which are not limitations to the protection scope of the application.

[0038] A MgO-Y2O3-based crucible for super-vacuum smelting Ni-TiAl alloy and a preparation method thereof. The preparation method of the specific embodiment is as follows:

[0039] Step 1, the chemical components and contents of the MgO-Y2O3-based crucible for super-vacuum smelting Ni-TiAl alloy are as follows:

[0040] 20-26wt% of MgO-Y2O3 particles with a particle size of less than 5mm and greater than or equal to 3mm, 25-30wt% of MgO-Y2O3 particles with a particle size of less than 3mm and greater than or equal to 1mm, and 15-25wt% of MgO-Y2O3 particles with a particle size of less than 1mm and greater than or equal to 0.088mm are used as aggregates;

[0041] The MgO-Y2O3 base material is 20-30wt% of MgO-Y2O3 fine powder with particle size <74μm;

[0042] The binding agent is 2.5-3wt% of pure calcium aluminate cement.

[0043] The additive is 1-1.5wt% of CaF2 suspension turbidity liquid with concentration of 200-1000ppm.

[0044] Step 2, according to the chemical components and their contents in step 1, first put the aggregate into a stirrer, mix uniformly, then add the base material and the binding agent, stir uniformly; then under stirring condition, add the CaF2 suspension turbidity liquid at a uniform speed, mix uniformly, and use vacuum pouring method to form.

[0045] Step 3, dry the formed body at 110-220℃ for 16-24 hours, keep at 1100-1300℃ for 2-5 hours, and keep at 1650-1780℃ for 4-8 hours, to obtain the MgO-Y2O3 base crucible for super vacuum smelting of Ni-TiAl alloy.

[0046] The MgO-Y2O3 base crucible for super vacuum smelting of Ni-TiAl alloy is detected: the apparent porosity is 4.10-7.86%; the bulk density is 3.10-3.60g / cm 3 ; the 1400℃ high temperature bending strength is 12-18MPa, and there is no crack after 8 times of 1100-20℃ air cooling cycle.

[0047] The preparation method of the MgO-Y2O3 base light weight refractory raw material with core-shell structure is:

[0048] Take 45-64wt% of porous light burned magnesium oxide, 34-52wt% of magnesium hydroxide and 2-5wt% of metallic yttrium as raw materials, plus 1-1.5wt% of nano calcium carbonate solution with concentration of 500-4000ppm to the raw materials, ball mill for 1-3 hours, machine press into green body under 150-200MPa; first heat the green body to 700-900℃, keep for 2-4 hours; then heat to 1520-1550℃, keep for 1-3 hours; then heat to 1700-1800℃, keep for 3-6 hours; naturally cool down in the furnace, to obtain the MgO-Y2O3 base light weight refractory raw material with core-shell structure.

[0049] The MgO-Y2O3 base light weight refractory raw material with core-shell structure: the apparent porosity is 5.6-11.2%; the bulk density is 3.25-3.45g / cm 3The MgO content is 95-97wt%, the Y2O3 content is 2-5wt%, the high-temperature vacuum evaporation rate is 0.75-1.22% under the conditions of temperature 1700 DEG C and pressure 10Pa, and the strength retention rate is 55-68% after three times of water cooling at 1100-200 DEG C.

[0050] The preparation method of the CaF2 suspension turbidity liquid with the concentration of 200-1000ppm is as follows: the CaF2 is added into purified water according to the mass ratio of CaF2: purified water 1-5:4997.5, and then stirring is conducted to obtain the CaF2 suspension turbidity liquid with the concentration of 200-1000ppm.

[0051] The preparation method of the nano calcium carbonate solution with the concentration of 500-4000ppm is as follows: the nano calcium carbonate is added into purified water according to the mass ratio of nano calcium carbonate: purified water 1-8:1999, and then stirring is conducted to obtain the nano calcium carbonate solution with the concentration of 500-4000ppm.

[0052] The ball milling is as follows: the corundum ball is used as the ball milling medium, and the mass ratio of the corundum ball: raw material is 2-3:1.

[0053] In the embodiment, the MgO-Y2O3 is the same as the MgO-Y2O3 base lightweight refractory raw material with core-shell structure;

[0054] The substrate microstructure of the MgO-Y2O3 base crucible for the ultra-vacuum smelting of Ni-TiAl alloy is a needle-shaped CA6, and the MgO-Y2O3 base crucible is a continuous crystal boundary core-shell structure.

[0055] The MgO-Y2O3 is the abbreviation of the patent technology of the MgO-Y2O3 base lightweight refractory raw material with core-shell structure;

[0056] The MgO-Y2O3 base lightweight refractory raw material with core-shell structure is crushed and sieved to obtain three kinds of particle levels of aggregate and one kind of substrate material, wherein the three kinds of particle levels are: less than 5mm and greater than or equal to 3mm, less than 3mm and greater than or equal to 1mm, less than 1mm and greater than or equal to 0.088mm; and the particle size of the substrate material is less than 74μm.

[0057] The microstructure of the MgO-Y2O3 base lightweight refractory raw material with core-shell structure has a full-crystal boundary MgO-Y2O3 core-shell structure, and the Y2O3 shell structure is continuously dense on the crystal boundary.

[0058] The pure calcium aluminate cement has an Al2O3 content less than 82% and a CaO content greater than 19%; and the particle size of the pure calcium aluminate cement is less than 74μm.

[0059] The CaF2 content is greater than 99.5wt%, and the particle size is less than 10μm.

[0060] The MgO content in the porous light-burned magnesium oxide is >99.6wt%; the micro-nano closed pores account for 45-55% of the total pores.

[0061] The Mg(OH)2 content in the magnesium hydroxide is >99.7wt%, and the SiO2 content is <0.05wt%.

[0062] The Y content in the metallic yttrium is >99.9wt%.

[0063] The CaCO3 content in the nano calcium carbonate is >99.9wt%.

[0064] The embodiments are not described again.

[0065] Embodiment 1

[0066] A MgO-Y2O3-based crucible for super-vacuum smelting of Ni-TiAl alloy and a preparation method thereof. The preparation method of the specific embodiment is as follows:

[0067] Step 1, the chemical components and contents of the MgO-Y2O3-based crucible for super-vacuum smelting of Ni-TiAl alloy are as follows:

[0068] 20wt% of MgO-Y2O3 particles with a particle size of less than 5mm and greater than or equal to 3mm, 30wt% of MgO-Y2O3 particles with a particle size of less than 3mm and greater than or equal to 1mm, and 21wt% of MgO-Y2O3 particles with a particle size of less than 1mm and greater than or equal to 0.088mm are used as aggregates;

[0069] 26.5wt% of MgO-Y2O3 fine powder with a particle size of <74μm is used as a matrix;

[0070] 2.5wt% of pure calcium aluminate cement is used as a binding agent.

[0071] A CaF2 suspension turbidity solution with a concentration of 200ppm at a concentration of 1wt% of the chemical components is used as an additive.

[0072] Step 2, the aggregates are placed in a stirrer, mixed uniformly, and then the matrix and the binding agent are added and stirred uniformly; then the CaF2 suspension turbidity solution is added at a uniform speed under stirring conditions, mixed uniformly, and formed by vacuum pouring.

[0073] Step 3, the formed green body is dried at 110℃ for 16 hours, kept at 1100℃ for 2 hours, and kept at 1650℃ for 4 hours to obtain the MgO-Y2O3-based crucible for super-vacuum smelting of Ni-TiAl alloy.

[0074] The preparation method of the CaF2 suspension turbidity solution with the concentration of 200 ppm is as follows: according to the mass ratio of CaF2 to pure water of 1:4997.5, the CaF2 is added into the pure water and stirred to obtain the CaF2 suspension turbidity solution with the concentration of 200 ppm.

[0075] The MgO-Y2O3-based crucible prepared in the embodiment is detected as follows: the apparent porosity is 4.10%; the bulk density is 3.10 g / cm 3 ; the high-temperature bending strength at 1400 ℃ is 12 MPa; and no cracks are found after 8 times of wind cooling cycle from 1100 ℃ to 20 ℃.

[0076] The MgO-Y2O3-based crucible prepared in the embodiment is used as the crucible for vacuum smelting of Ni-TiAl alloy, and 20 wt% of Ti and 60 wt% of high-purity Ni and 20 wt% of Al after refining are added into the MgO-Y2O3-based crucible as raw materials. The raw materials are inductively heated to be completely melted at 1700 ℃ in a vacuum environment of <5 Pa, and the composition homogenization is completed after 20 min of holding. The melted melt is poured into a CuO metal mold, and the alloy composition is analyzed after cooling, wherein O is 9 ppm, and Mg is 0.0002 wt%.

[0077] The MgO-Y2O3-based crucible after smelting has no cracks and no obvious reaction layer on the inner and outer surfaces.

[0078] In the embodiment, the MgO-Y2O3-based light-weight refractory raw material with the core-shell structure is prepared by using 45 wt% of porous light-burned magnesium oxide, 52 wt% of magnesium hydroxide and 3 wt% of yttrium metal as raw materials, and adding 1.5 wt% of a nano calcium carbonate solution with a concentration of 500 ppm to the raw materials, ball milling for 3 hours, and machine pressing into a green body under the condition of 180 MPa.

[0079] The preparation method of the MgO-Y2O3-based light-weight refractory raw material with the core-shell structure is as follows:

[0080] The MgO-Y2O3-based light-weight refractory raw material with the core-shell structure is prepared by using 45 wt% of porous light-burned magnesium oxide, 52 wt% of magnesium hydroxide and 3 wt% of yttrium metal as raw materials, and adding 1.5 wt% of a nano calcium carbonate solution with a concentration of 500 ppm to the raw materials, ball milling for 3 hours, and machine pressing into a green body under the condition of 180 MPa.

[0081] The MgO-Y2O3-based light-weight refractory raw material with the core-shell structure is detected as follows: the apparent porosity is 9.80%; the bulk density is 3.36 g / cm 3 ; the MgO content is 97 wt%; the Y2O3 content is 3 wt%; the high-temperature vacuum volatilization rate is 1.04% (the high-temperature vacuum volatilization rate of a comparative sample 97 fused magnesite is 2.54%) under the condition of holding and pressure for 1 h at 1700 ℃ and 10 Pa in a vacuum induction smelting furnace; and the strength retention rate is 56% after three times of water cooling from 1100 ℃ to 20 ℃.

[0082] The preparation method of the nano calcium carbonate solution with a concentration of 500 ppm is as follows: according to the mass ratio of nano calcium carbonate to purified water of 1:1999, the nano calcium carbonate is added to the purified water, and stirred to obtain the nano calcium carbonate solution with a concentration of 500 ppm.

[0083] The ball milling is as follows: corundum balls are used as the ball milling medium, and the mass ratio of the corundum balls to the raw material is 2:1.

[0084] Example 2

[0085] An MgO-Y2O3-based crucible for super-vacuum smelting of Ni-TiAl alloy and a preparation method thereof. The preparation method of the embodiment is as follows:

[0086] Step 1, the chemical components and contents of the MgO-Y2O3-based crucible for super-vacuum smelting of Ni-TiAl alloy are as follows:

[0087] The MgO-Y2O3 particles with a particle size of less than 5 mm and greater than or equal to 3 mm account for 26 wt%, the MgO-Y2O3 particles with a particle size of less than 3 mm and greater than or equal to 1 mm account for 25 wt%, and the MgO-Y2O3 particles with a particle size of less than 1 mm and greater than or equal to 0.088 mm account for 15 wt%.

[0088] The MgO-Y2O3 fine powder with a particle size of less than 74 μm accounts for 30.0 wt%.

[0089] The pure calcium aluminate cement accounts for 4.0 wt%.

[0090] The CaF2 suspension turbidity liquid with a concentration of 600 ppm accounts for 1.5 wt% of the chemical components.

[0091] Step 2, the aggregate is placed in a stirrer, mixed uniformly, then the matrix and the binder are added and stirred uniformly, then the CaF2 suspension turbidity liquid is added at a constant speed under stirring, mixed uniformly, and formed by vacuum pouring.

[0092] Step 3, the formed body is dried at 150 ℃ for 20 hours, kept at 1220 ℃ for 4 hours, and kept at 1700 ℃ for 6 hours to obtain the MgO-Y2O3-based crucible for super-vacuum smelting of Ni-TiAl alloy.

[0093] The preparation method of the CaF2 suspension turbidity liquid with a concentration of 600 ppm is as follows: according to the mass ratio of CaF2 to purified water of 3:4997.5, the CaF2 is added to the purified water, and stirred to obtain the CaF2 suspension turbidity liquid with a concentration of 600 ppm.

[0094] The MgO-Y2O3 based crucible prepared in the embodiment is used as a crucible for vacuum smelting Ni-TiAl alloy. 20wt% of Ti and 60wt% of high-purity Ni and 20wt% of Al after refining are added as raw materials into the MgO-Y2O3 crucible. The raw materials are fully melted at 1700°C in a vacuum environment of <5Pa by induction heating, and the composition homogenization is completed after holding for 20min. The melted melt is poured into a CuO metal mold, and the alloy composition is analyzed after cooling, wherein O is 4ppm, and Mg is 0.0002wt%. 3 The high-temperature bending strength at 1400°C is 16MPa, and there is no crack after 8 times of wind cooling cycle from 1100°C to 20°C.

[0095] The MgO-Y2O3 based crucible prepared in the embodiment is used as a crucible for vacuum smelting Ni-TiAl alloy. 20wt% of Ti and 60wt% of high-purity Ni and 20wt% of Al after refining are added as raw materials into the MgO-Y2O3 crucible. The raw materials are fully melted at 1700°C in a vacuum environment of <5Pa by induction heating, and the composition homogenization is completed after holding for 20min. The melted melt is poured into a CuO metal mold, and the alloy composition is analyzed after cooling, wherein O is 4ppm, and Mg is 0.0002wt%.

[0096] The inner and outer surfaces of the MgO-Y2O3 based crucible after smelting are intact without cracks and obvious reaction layers.

[0097] In the embodiment, the MgO-Y2O3 based light-weight refractory raw material with core-shell structure is prepared by the following method:

[0098] The preparation method of the MgO-Y2O3 based light-weight refractory raw material with core-shell structure is as follows:

[0099] 47wt% of porous light-burned magnesium oxide, 48wt% of magnesium hydroxide and 5wt% of metallic yttrium are used as raw materials, and 1.5wt% of a nano calcium carbonate solution with a concentration of 4000ppm is additionally added. The raw materials are ball milled for 3 hours and are mechanically pressed into a green body under the condition of 200MPa. The green body is first heated to 800°C and held for 3 hours, then heated to 1550°C and held for 3 hours, and then heated to 1800°C and held for 3 hours. The MgO-Y2O3 based light-weight refractory raw material with core-shell structure is prepared by natural cooling in the furnace.

[0100] The MgO-Y2O3 based light-weight refractory raw material with core-shell structure is detected as follows: the apparent porosity is 5.60%; the bulk density is 3.45g / cm 3 ; the MgO content is 95wt%; the Y2O3 content is 5wt%; the high-temperature vacuum volatilization rate is 0.75% under the condition of holding and pressure for 1h at 1700°C and 10Pa in a vacuum induction smelting furnace (2.54% for a comparative sample 97 electro-fused magnesite); and the strength retention rate is 68% after three times of water cooling from 1100°C to 20°C.

[0101] The preparation method of the nano calcium carbonate solution with the concentration of 4000 ppm is as follows: according to the mass ratio of nano calcium carbonate to purified water of 8:1999, the nano calcium carbonate is added into the purified water, and stirred to obtain the nano calcium carbonate solution with the concentration of 4000 ppm.

[0102] The ball milling is as follows: corundum balls are used as the ball milling medium, and the mass ratio of the corundum balls to the raw material is 3:1.

[0103] Example 3

[0104] An MgO-Y2O3-based crucible for super-vacuum smelting of Ni-TiAl alloy and a preparation method thereof.

[0105] Step 1, the chemical components and contents of the MgO-Y2O3-based crucible for super-vacuum smelting of Ni-TiAl alloy are as follows:

[0106] 22wt% of MgO-Y2O3 particles with a particle size of less than 5 mm and greater than or equal to 3 mm, 30wt% of MgO-Y2O3 particles with a particle size of less than 3 mm and greater than or equal to 1 mm, and 25wt% of MgO-Y2O3 particles with a particle size of less than 1 mm and greater than or equal to 0.088 mm are used as aggregates;

[0107] 20.0wt% of MgO-Y2O3 fine powder with a particle size of less than 74 μm is used as a matrix;

[0108] 3.0wt% of pure calcium aluminate cement is used as a binding agent.

[0109] A CaF2 suspension turbidity liquid with a concentration of 1000 ppm is additionally used as an additive, and the content of the chemical component is 1.5wt%.

[0110] Step 2, the aggregates are placed in a stirrer, mixed uniformly, and then the matrix and the binding agent are added and stirred uniformly; then the CaF2 suspension turbidity liquid is added at a constant speed under stirring conditions, mixed uniformly, and formed by a vacuum pouring method.

[0111] Step 3, the formed green body is dried at 220℃ for 24 hours, kept at 1300℃ for 5 hours, and kept at 1780℃ for 8 hours to obtain the MgO-Y2O3-based crucible for super-vacuum smelting of Ni-TiAl alloy.

[0112] The preparation method of the CaF2 suspension turbidity liquid with the concentration of 1000 ppm is as follows: according to the mass ratio of CaF2 to purified water of 5:4997.5, the CaF2 is added into the purified water, and stirred to obtain the CaF2 suspension turbidity liquid with the concentration of 1000 ppm.

[0113] The MgO-Y2O3 based crucible prepared in the embodiment is used as a crucible for vacuum smelting Ni-TiAl alloy. 20wt% of Ti and 60wt% of high-purity Ni and 20wt% of Al after refining are added into the MgO-Y2O3 based crucible as raw materials. The raw materials are fully melted at 1700°C in a vacuum environment of <5Pa by induction heating, and the composition homogenization is completed after holding for 20min. The melted melt is poured into a CuO metal mold, and the alloy composition is analyzed after cooling, wherein O is 0.7ppm, and Mg is 0.0004wt%. 3 The high-temperature bending strength at 1400°C is 18MPa, and there is no crack after 8 times of air cooling cycle from 1100°C to 20°C.

[0114] The MgO-Y2O3 based crucible prepared in the embodiment is used as a crucible for vacuum smelting Ni-TiAl alloy. 20wt% of Ti and 60wt% of high-purity Ni and 20wt% of Al after refining are added into the MgO-Y2O3 based crucible as raw materials. The raw materials are fully melted at 1700°C in a vacuum environment of <5Pa by induction heating, and the composition homogenization is completed after holding for 20min. The melted melt is poured into a CuO metal mold, and the alloy composition is analyzed after cooling, wherein O is 0.7ppm, and Mg is 0.0004wt%.

[0115] The MgO-Y2O3 based crucible prepared in the embodiment is used as a crucible for vacuum smelting Ni-TiAl alloy. 20wt% of Ti and 60wt% of high-purity Ni and 20wt% of Al after refining are added into the MgO-Y2O3 based crucible as raw materials. The raw materials are fully melted at 1700°C in a vacuum environment of <5Pa by induction heating, and the composition homogenization is completed after holding for 20min. The melted melt is poured into a CuO metal mold, and the alloy composition is analyzed after cooling, wherein O is 0.7ppm, and Mg is 0.0004wt%.

[0116] In the embodiment, the MgO-Y2O3 based light-weight refractory raw material with core-shell structure is prepared by the following method:

[0117] The preparation method of the MgO-Y2O3 based light-weight refractory raw material with core-shell structure is as follows:

[0118] The MgO-Y2O3 based light-weight refractory raw material with core-shell structure is prepared by using 64wt% of porous light-burned magnesium oxide, 34wt% of magnesium hydroxide and 2wt% of yttrium metal as raw materials, and adding 1.0wt% of a nano calcium carbonate solution with a concentration of 2000ppm to the raw materials, ball milling for 1 hour, and then machine pressing the green body under the condition of 150MPa. The green body is first heated to 700°C and held for 2 hours, then heated to 1520°C and held for 1 hour, and then heated to 1700°C and held for 5 hours. The MgO-Y2O3 based light-weight refractory raw material with core-shell structure is prepared by natural cooling in the furnace.

[0119] The MgO-Y2O3 based light-weight refractory raw material with core-shell structure is prepared by using 64wt% of porous light-burned magnesium oxide, 34wt% of magnesium hydroxide and 2wt% of yttrium metal as raw materials, and adding 1.0wt% of a nano calcium carbonate solution with a concentration of 2000ppm to the raw materials, ball milling for 1 hour, and then machine pressing the green body under the condition of 150MPa. The green body is first heated to 700°C and held for 2 hours, then heated to 1520°C and held for 1 hour, and then heated to 1700°C and held for 5 hours. The MgO-Y2O3 based light-weight refractory raw material with core-shell structure is prepared by natural cooling in the furnace. 3 The MgO-Y2O3 based light-weight refractory raw material with core-shell structure is prepared by using 64wt% of porous light-burned magnesium oxide, 34wt% of magnesium hydroxide and 2wt% of yttrium metal as raw materials, and adding 1.0wt% of a nano calcium carbonate solution with a concentration of 2000ppm to the raw materials, ball milling for 1 hour, and then machine pressing the green body under the condition of 150MPa. The green body is first heated to 700°C and held for 2 hours, then heated to 1520°C and held for 1 hour, and then heated to 1700°C and held for 5 hours. The MgO-Y2O3 based light-weight refractory raw material with core-shell structure is prepared by natural cooling in the furnace.

[0120] The preparation method of the 2000 ppm nano calcium carbonate solution is as follows: nano calcium carbonate is added into purified water in a mass ratio of 4:1999, and stirred to obtain a 2000 ppm nano calcium carbonate solution.

[0121] The ball milling is as follows: corundum balls are used as the ball milling medium, and the mass ratio of the corundum balls to the raw material is 2.5:1.

[0122] Compared with the prior art, the embodiment has the following positive effects:

[0123] The embodiment uses MgO-Y2O3-based light-weight refractory raw material with core-shell structure (referred to as MgO-Y2O3) as the main raw material. The raw material is first decomposed at 700-900°C to generate nano-sized internal pores, and then during the temperature rising process, a large amount of metal yttrium begins to melt and completely wets the surface of MgO grains, and a Y-MgO coating structure is formed at high temperature. The MgO-Y2O3 binary system does not generate intermediate compounds, so that Y2O3 is mainly distributed on the surface and grain boundaries of the material at high temperature, and no intermediate phase is generated. At the same time, the H2O molecules discharged during the decomposition of magnesium hydroxide raw material provide effective channel pores, which provide channels and power for the rearrangement of Y2O3 on the MgO grains and the penetration of Y2O3 into the material. After high-temperature sintering, MgO-Y2O3 material with core-shell grain structure characteristics is formed, Y2O3 can be uniformly distributed on the surface of MgO grains, and will not segregate and enrich on the surface, and a certain amount of nano-sized pores exist in the MgO grains. This nano-pore structure can effectively improve the thermal shock resistance of the material. At the same time, the MgO-Y2O3 material with core-shell grain structure characteristics can improve the hydration resistance of the MgO-Y2O3-based crucible for smelting Ni-TiAl alloy in ultra-high vacuum by using the uniformly distributed Y2O3 shell on the grain boundaries, and reduce the volatilization rate of MgO at high temperature in vacuum.

[0124] The MgO-Y2O3 used in the specific embodiment has excellent hydration resistance; compared with the isostatic pressing forming technology which is difficult and has a high waste rate, the vacuum casting forming process can solve the problem of large-scale production of large vacuum induction furnaces (more than 0.5 tons) in a limited way. At the same time, the MgO-Y2O3 light refractory raw material with the core-shell grain structure is used as the crucible material, which solves the problem of high vacuum volatilization rate of the existing magnesium crucible under vacuum conditions and pollution of the alloy. Compared with the existing Y2O3 directly coated with MgO crucible, the Y2O3 grain boundary distribution of the specific embodiment greatly reduces the risk of Y2O3 coating peeling, and improves the thermal shock resistance of the overall MgO-Y2O3-based crucible. Moreover, during high-temperature sintering, Al2O3 and CaO in the matrix will combine in situ to form micro-nano needle-shaped CA6. First, the micro-nano needle-shaped CA6 can improve the bonding strength between the matrix and the aggregate, thereby improving the high-temperature strength of the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloy, and second, the micro-nano needle-shaped CA6 phase has good hydration resistance, which can further improve the hydration resistance of the MgO-Y2O3-based crucible. At the same time, after high-temperature sintering, the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloy is sintered and densified, thereby improving the strength and hydration resistance of the product.

[0125] The MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloy prepared in the specific embodiment is shown in the accompanying drawings, Figure 1 The microstructure of the MgO-Y2O3-based crucible for vacuum melting of Ni-TiAl alloy prepared in Example 1 after heat treatment; Figure 2 The cross-sectional view of the MgO-Y2O3-based crucible for vacuum melting of Ni-TiAl alloy prepared in Example 2 after intermittent melting of K417G (Ti, Al > 10wt%) six times. From Figure 1 It can be seen that, during high-temperature treatment, Al2O3 and CaO in the matrix will combine in situ to form micro-nano needle-shaped CA6; from Figure 2 It can be seen that, after intermittent melting of K417G (Ti, Al > 10wt%) six times, the surface of the crucible does not appear to peel off and crack. The MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloy prepared in the specific embodiment has excellent thermal shock resistance and can be repeatedly used under intermittent melting conditions, has strong resistance to Ni-TiAl alloy corrosion, low vacuum volatilization rate and no introduction of foreign inclusions, and can be used in the construction of large vacuum induction furnace linings.

[0126] The MgO-Y2O3-based crucible for super vacuum melting Ni-TiAl alloy is detected to have an apparent porosity of 4.10-7.86%, a bulk density of 3.10-3.60 g / cm 3 , a high-temperature bending strength at 1400℃ of 12-18 MPa, and no cracks after 8 times of wind cooling cycle at 1100℃-20℃.

[0127] Therefore, the embodiment has the characteristics of simple preparation process and low cost, and the prepared MgO-Y2O3-based crucible for super vacuum melting Ni-TiAl alloy has low vacuum evaporation rate, long service life, no pollution to smelting melt, intermittent use, and good thermal shock stability.

Claims

1. A method for preparing a MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys, characterized in that... The preparation method is as follows: Step 1: The chemical composition and content of the MgO-Y2O3-based crucible are as follows: The aggregate consists of 20–26 wt% MgO-Y2O3 particles with a particle size of less than 5 mm and greater than or equal to 3 mm, 25–30 wt% MgO-Y2O3 particles with a particle size of less than 3 mm and greater than or equal to 1 mm, and 15–25 wt% MgO-Y2O3 particles with a particle size of less than 1 mm and greater than or equal to 0.088 mm. The matrix consists of 20–30 wt% of MgO-Y2O3 fine powder with a particle size <74 μm; Using 2.5–3 wt% pure calcium aluminate cement as a binder; An additive is a CaF2 suspension with a concentration of 200-1000 ppm, comprising 1-1.5 wt% of the aforementioned chemical components. Step 2: According to the chemical components and their contents described in Step 1, first place the aggregate in a mixer and mix evenly, then add the matrix and the binder and mix evenly; then add the CaF2 suspension turbid liquid at a uniform speed under stirring conditions, mix evenly, and mold by vacuum casting. Step 3: Dry the formed blank at 110℃~220℃ for 16~24 hours, keep it at 1100℃~1300℃ for 2~5 hours, and keep it at 1650℃~1780℃ for 4~8 hours to obtain a MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloy. The MgO-Y2O3 is an abbreviation for "MgO-Y2O3-based lightweight refractory material with a core-shell structure"; the preparation method of the MgO-Y2O3-based lightweight refractory material with a core-shell structure is as follows: Using 45–64 wt% porous lightly calcined magnesia, 34–52 wt% magnesia hydroxide, and 2–5 wt% metallic yttrium as raw materials, and adding 1–1.5 wt% of the raw materials to a nano-calcium carbonate solution with a concentration of 500–4000 ppm, the mixture is ball-milled for 1–3 hours and machine-pressed into green blanks under 150–200 MPa conditions. The green blanks are first heated to 700–900°C and held for 2–4 hours; then heated to 1520–1550°C and held for 1–3 hours; then heated to 1700–1800°C and held for 3–6 hours; and then naturally cooled in the furnace to obtain a MgO-Y2O3-based lightweight refractory material with a core-shell structure. The MgO-Y2O3-based lightweight refractory raw material with a core-shell structure was crushed and sieved to obtain three particle sizes of aggregate and matrix material. The three particle sizes are: less than 5 mm and greater than or equal to 3 mm, less than 3 mm and greater than or equal to 1 mm, and less than 1 mm and greater than or equal to 0.088 mm. The particle size of the matrix material is <74 μm.

2. The method for preparing the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys according to claim 1, characterized in that: The core-shell structured MgO-Y2O3-based lightweight refractory material has an apparent porosity of 5.6–11.2% and a bulk density of 3.25–3.45 g / cm³. 3 The MgO content is 95-97 wt%; the Y2O3 content is 2-5 wt%; under the conditions of 1700℃ and 10Pa, after holding at the temperature and pressure for 1 hour, the high-temperature vacuum volatilization rate is 0.75-1.22%; after three water coolings at 1100-20℃, the strength retention rate is 55-68%.

3. The method for preparing the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys according to claim 1, characterized in that: The pure calcium aluminate cement has an Al2O3 content of <82% and a CaO content of >19%; the particle size of the pure calcium aluminate cement is <74μm.

4. The method for preparing the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys according to claim 1, characterized in that: The method for preparing the CaF2 suspension with a concentration of 200-1000 ppm is as follows: CaF2 is added to pure water at a mass ratio of CaF2 to pure water of 1-5:4997.5, and stirred to obtain the CaF2 suspension with a concentration of 200-1000 ppm; the CaF2 content is greater than 99.5 wt%, and the particle size is less than 10 μm.

5. The method for preparing the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys according to claim 1, characterized in that: The porous lightly calcined magnesium oxide contains >99.6 wt% MgO; the ratio of micro- and nano-closed pores to total pores is 45-55%.

6. The method for preparing the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys according to claim 1, characterized in that: The magnesium hydroxide contains Mg(OH)2 content > 99.7 wt% and SiO2 content < 0.05 wt%.

7. The method for preparing the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys according to claim 1, characterized in that: The Y content of the yttrium metal is >99.9 wt%.

8. The method for preparing the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys according to claim 1, characterized in that: The method for preparing the nano-calcium carbonate solution with a concentration of 500-4000 ppm is as follows: according to the mass ratio of nano-calcium carbonate to pure water of 1-8:1999, the nano-calcium carbonate is added to the pure water and stirred to obtain a nano-calcium carbonate solution with a concentration of 500-4000 ppm. The CaCO3 content of the nano-calcium carbonate is >99.9 wt%.

9. The method for preparing the MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys according to claim 1, characterized in that: The ball milling process involves using corundum balls as the milling medium, with the mass ratio of corundum balls to raw materials being 2 to 3:

1.

10. A MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloys, characterized in that... The MgO-Y2O3-based crucible for ultra-vacuum melting of Ni-TiAl alloy is prepared by the method described in any one of claims 1 to 9. The matrix microstructure of the MgO-Y2O3-based crucible used for ultra-vacuum melting of Ni-TiAl alloy is needle-shaped CA6, and the aggregate is a MgO-Y2O3-based crucible with a continuous grain boundary core-shell structure.

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