Giant magnetostrictive alloy directional solidification shell and preparation method thereof

Abstract

The invention provides a giant magnetostrictive alloy directional solidification shell and a preparation method thereof, the shell comprises composite powder and silica sol, and the composite powder comprises white corundum powder, bentonite and floating beads. The preparation method comprises the following steps: firstly, mixing prepared composite powder with silica sol to prepare a wet material, injecting the wet material into a mold to obtain a shell, and then sequentially drying and sintering the shell to obtain the giant magnetostrictive alloy directional solidification shell. According to the invention, the shell is prepared from the powder in a specific ratio, so that the problem that the performance of the giant magnetostrictive alloy is reduced due to poor heat conductivity and air permeability of the side surface of the material and poor directional solidification effect in the traditional directional solidification process is solved. The shell is composed of a refractory material and silica sol and is pressed and sintered in cooperation with different molds, so that the shell has the advantages of being controllable in thickness, high in strength, resistant to high temperature and suitable for the large-size giant magnetostrictive alloy, and the requirement for directional solidification and stable preparation of the giant magnetostrictive alloy is met.

Description

Technical Field

[0001] This invention relates to the field of directional solidification casting, and more specifically to a directional solidification mold shell for preparing super magnetostrictive alloys and its preparation method. Background Technology

[0002] Directional solidification is an advanced casting process that controls the direction of crystal growth, particularly suitable for preparing crystals or single-crystal alloys with specific oriented textures. The materials used in castings primarily focus on high-temperature resistant systems, such as nickel-based, cobalt-based, and iron-based high-temperature alloys, as well as rare-earth iron, iron-gallium, and iron-aluminum magnetostrictive alloys. The main process involves placing a pre-fabricated mold shell in a specialized directional solidification furnace. By precisely controlling the temperature gradient, the molten metal solidifies layer by layer from the bottom in a predetermined direction. Specifically, the bottom of the mold shell contacts a water-cooled crystallizer, while the upper part of the shell is kept at a high temperature by a heater, forming a stable temperature gradient field. As the mold shell moves downwards at a constant speed (or the heating zone moves upwards), the molten metal solidifies sequentially from bottom to top under the influence of this temperature gradient, with grains growing directionally along the heat flow direction. After solidification, slow cooling, and shell removal, high-performance castings with columnar or single-crystal structures are obtained.

[0003] The production of high-performance castings using the directional solidification process of supermagnetostrictive alloys typically employs traditional ceramic crucibles or quartz tubes, both of which have inherent limitations. While traditional ceramic shells offer the advantage of mature manufacturing processes, their poor lateral thermal conductivity and permeability make it difficult to establish an ideal unidirectional temperature gradient during directional solidification. Uneven heat dissipation from the shell sidewalls leads to grain growth deviating from the intended direction, and the shell thickness is difficult to control precisely, resulting in poor quality consistency between different batches of castings. The insufficient thermal conductivity and permeability of traditional shells directly contribute to a significant decrease in directional solidification efficiency, leading to reduced crystal orientation and unstable magnetostrictive properties in the resulting supermagnetostrictive alloy. These problems severely restrict the application scope and product quality stability of the directional solidification process for supermagnetostrictive alloys.

[0004] Giant magnetostrictive alloys, especially rare-earth-iron (such as TbDyFe) giant magnetostrictive alloys, have broad application prospects in sensors, actuators, and transducers due to their excellent magnetostrictive properties. To obtain high-performance giant magnetostrictive alloys, it is necessary to prepare single-crystal or oriented columnar structures with specific crystal orientations through directional solidification processes.

[0005] Currently, the main casting containers used in the directional solidification process of supermagnetostrictive alloys include ceramic crucibles and quartz tubes.

[0006] Although traditional ceramic crucibles have mature manufacturing processes, good high-temperature resistance, and high chemical stability, they have the following technical drawbacks:

[0007] (1) Insufficient temperature control performance: It is difficult to establish a uniform temperature field distribution between the crucible sidewall and the melt in traditional ceramic crucibles. During the directional solidification process, an ideal unidirectional temperature gradient cannot be formed. The isotherms at the solid-liquid interface are prone to bending and twisting, causing the grain growth direction to deviate from the predetermined axial direction, which easily leads to defects such as impurities and off-axis grains.

[0008] (2) Poor permeability: Traditional dense ceramic crucibles have low permeability. During the directional solidification process, the gas released from the melt cannot be discharged in time, which easily forms casting defects such as porosity and shrinkage cavities inside the casting, seriously affecting the density and mechanical properties of the casting.

[0009] Although quartz tubes have good transparency and low risk of melt contamination, they are not strong enough to withstand the gravity and thermal stress during the directional solidification process of large-size super magnetostrictive alloys.

[0010] The shortcomings of traditional ceramic crucibles in terms of thermal conductivity and permeability directly lead to the following problems: a significant decrease in directional solidification effect, difficulty in controlling the solid-liquid interface morphology, and low crystal orientation in the prepared supermagnetostrictive alloys. This results in reduced low-field magnetostrictive properties or decreased consistency and stability of magnetostrictive properties, severely impacting the practical applications of the materials. Furthermore, poor batch-to-batch casting quality consistency leads to low product qualification rates and persistently high production costs.

[0011] The existence of these problems severely restricts the industrial application of the directional solidification process for supermagnetostrictive alloys and the stability of product quality. There is an urgent need to develop new casting containers to improve the temperature field control accuracy and casting quality consistency during the directional solidification process. Summary of the Invention

[0012] To overcome the aforementioned technical problems, this invention provides a shell for the directional solidification of a supermagnetostrictive alloy. This shell is composed of refractory materials and silica sol in a specific ratio, pressed into shape using molds of different specifications, and then prepared through low-temperature drying and high-temperature sintering. This preparation method endows the shell with significantly controllable thickness, high strength, and high-temperature resistance, while also greatly improving the thermal conductivity and permeability of the shell's sides, creating more ideal process conditions for the directional solidification of the supermagnetostrictive alloy.

[0013] To achieve this objective, the present invention adopts the following technical solution:

[0014] In a first aspect, the present invention provides a shell for directional solidification of a super magnetostrictive alloy, wherein the raw material composition of the shell includes: composite powder and silica sol; wherein the composite powder includes: white corundum powder, bentonite and bleaching beads.

[0015] The shell of this invention comprises composite powder and silica sol. The composite powder includes white corundum powder, bentonite, and silicide flocculation beads, which work synergistically to form a composite material system with excellent high-temperature performance. The shell can withstand the high-temperature environment during the directional solidification process of the supermagnetostrictive alloy while maintaining good dimensional stability and structural integrity.

[0016] As a preferred technical solution of the present invention, the white fused alumina powder includes any one or a combination of at least two of #24 white fused alumina powder, #46 white fused alumina powder, #150 white fused alumina powder, or W20 white fused alumina powder. Typical but non-limiting combinations include combinations of #24 white fused alumina powder and #46 white fused alumina powder, combinations of #24 white fused alumina powder and #150 white fused alumina powder, combinations of #24 white fused alumina powder and W20 white fused alumina powder, combinations of #24 white fused alumina powder, #46 white fused alumina powder and #150 white fused alumina powder, and combinations of #24 white fused alumina powder, #46 white fused alumina powder, #150 white fused alumina powder and W20 white fused alumina powder, etc.

[0017] Preferably, the white fused alumina powder further includes #220 white fused alumina powder and / or #320 white fused alumina powder.

[0018] As a preferred technical solution of the present invention, the mass ratio of white corundum powder to ash bleaching beads is 1:(0.02-0.05), such as 1:0.02, 1:0.03, 1:0.04 or 1:0.05, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] In this invention, silicide cenospheres serve as a lightweight filler in the mold shell, reducing density and improving thermal shock resistance. When the amount of silicide cenospheres added is too small, the lightweighting effect is not significant, resulting in a high overall density of the mold shell. This not only increases material costs but also easily leads to stress concentration and cracking defects, while failing to fully utilize the thermal shock resistance improvement effect of the silicide cenospheres. Conversely, when the amount of silicide cenospheres added is too large, although the mold shell density decreases, the effective contact area between aggregate particles such as white corundum is reduced, weakening the overall structural strength of the mold shell. This leads to a significant decrease in bending and compressive strength, making the mold shell prone to breakage during handling and casting. Furthermore, excessive silicide cenospheres may also undergo excessive deformation at high temperatures due to their low strength, affecting the dimensional accuracy of the casting.

[0020] As a preferred technical solution of the present invention, the mass ratio of white corundum powder to bentonite is 1:(0.04-0.08), such as 1:0.04, 1:0.05, 1:0.06, 1:0.07 or 1:0.08, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] In this invention, bentonite plays a crucial bonding role as a binder in the mold shell. Insufficient bentonite leads to weak bonding between white fused alumina powder particles, reducing the overall strength and density of the mold shell and making it prone to cracking or detachment, thus affecting the surface quality of the casting. Conversely, excessive bentonite, while enhancing bonding performance, significantly reduces the permeability of the mold shell. Furthermore, excessive binder may cause excessive shrinkage during high-temperature sintering, reducing the dimensional stability and thermal shock resistance of the mold shell and potentially increasing the risk of sand adhesion defects on the casting surface.

[0022] In this invention, white fused alumina powder is used as the main refractory aggregate, bentonite is used as a suspending agent and plasticizer, and bleaching perlite is used as a lightweight filler. The above raw materials are thoroughly mixed in a mixing device to ensure uniform dispersion of each component, thereby preparing a composite powder with stable performance.

[0023] As a preferred technical solution of the present invention, the particle size range of the #24 white corundum powder is 700-850μm, such as 700μm, 710μm, 720μm, 730μm, 740μm, 750μm, 760μm, 770μm, 780μm, 790μm, 800μm, 810μm, 820μm, 830μm, 840μm or 850μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] As a preferred technical solution of the present invention, the particle size range of the #46 white corundum powder is 355-425μm, such as 355μm, 360μm, 365μm, 370μm, 375μm, 380μm, 385μm, 390μm, 395μm, 400μm, 405μm, 410μm, 415μm, 420μm or 425μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] As a preferred technical solution of the present invention, the particle size range of the #150 white corundum powder is 76-106μm, such as 76μm, 78μm, 80μm, 82μm, 84μm, 86μm, 88μm, 90μm, 92μm, 94μm, 96μm, 98μm, 100μm, 102μm, 104μm or 106μm, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] As a preferred technical solution of the present invention, the particle size range of the #220 white fused alumina powder is 63-75μm, such as 63μm, 64μm, 65μm, 66μm, 67μm, 68μm, 69μm, 70μm, 71μm, 72μm, 73μm, 74μm or 75μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] As a preferred technical solution of the present invention, the particle size range of the #320 white corundum powder is 46-58μm, such as 46μm, 47μm, 48μm, 49μm, 50μm, 51μm, 52μm, 53μm, 54μm, 55μm, 56μm, 57μm or 58μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] As a preferred technical solution of the present invention, the particle size range of the W20 white corundum powder is 14-20μm, such as 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] As a preferred technical solution of the present invention, the white fused alumina powder includes: #24 white fused alumina powder, #46 white fused alumina powder, #150 white fused alumina powder, #220 white fused alumina powder, #320 white fused alumina powder, and W20 white fused alumina powder; the #24 white fused alumina powder, #46 white fused alumina powder, #150 white fused alumina powder, #220 white fused alumina powder, #320 white fused alumina powder, and W20 white fused alumina powder are arranged sequentially, and the mass ratio of each adjacent component is 1:(0.8-1.2), such as 1:0.8, 1:0.9, 1:1.0, 1:1.1, or 1:1.2, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] In this invention, the ratio between adjacent white fused alumina powder particles is 1:(0.8-1.2), and this particle size distribution design follows the principle of close packing. The coarser white fused alumina powder acts as a skeleton material, providing basic strength and rigid support for the shell; the finer white fused alumina powder fills the gaps between the coarser particles, forming a denser packing structure. The two work together to achieve the best filling effect.

[0031] When the proportion of coarse-grained white corundum powder is too high, although a stable skeletal structure can be formed, the gaps between the particles are large and cannot be effectively filled, leading to increased shell porosity and decreased density. This loose structure not only reduces the mechanical strength of the shell but also causes sand adhesion defects during the pouring process due to the penetration of molten metal, severely affecting the surface finish of the casting. In addition, too many large particles can easily form stress concentration areas inside the shell.

[0032] Conversely, when the proportion of fine-grained white corundum powder is too high, the large surface area of ​​the fine particles requires more binder to achieve effective coating. This not only increases the amount of silica sol used but also leads to increased drying shrinkage of the mold shell, making it prone to cracking. Excessive fine particles significantly reduce the permeability of the mold shell, making it difficult for gas in the mold cavity to escape in time during high-temperature pouring, which may cause defects such as porosity and inclusions in the casting.

[0033] Therefore, by controlling the ratio of white corundum powder of different particle sizes within the range of 1:(0.8-1.2), the advantages of coarse and fine particles can be complemented, ensuring that the shell has sufficient strength while obtaining suitable density, porosity and air permeability, thus ensuring that the shell exhibits excellent comprehensive performance during the directional solidification process of the super magnetostrictive alloy.

[0034] As a preferred technical solution of the present invention, the weight ratio of the composite powder to the silica sol is (6-8):1, such as 6:1, 7:1 or 8:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Secondly, the present invention provides a method for preparing a directional solidification shell of a supermagnetic-strictive alloy, the method comprising the following steps:

[0036] (1) Mix the prepared composite powder with silica sol to form a wet material;

[0037] (2) Pour the wet material into the mold and compact it layer by layer to obtain the shell;

[0038] (3) Transfer the shell and mold to an oven for primary drying, then remove the mold and continue secondary drying to obtain a pre-cured shell;

[0039] (4) The pre-cured shell is transferred to a high-temperature furnace for sintering to obtain a shell with directional solidification of super magnetostrictive alloy.

[0040] As a preferred technical solution of the present invention, the mold in step (2) includes a 3D printed core and / or a stainless steel mold.

[0041] The mold for preparing the shell according to this invention includes a 3D-printed core and a stainless steel mold, which are used together to form shells of different thicknesses and sizes. The stainless steel mold provides external support during the shell drying and shaping process and can be removed from the shell after drying and shaping. The 3D-printed core provides internal support during shell preparation and is naturally ablated and removed during the subsequent high-temperature sintering process in a muffle furnace. This mold structure design makes the shell preparation process both flexible and economical.

[0042] After the shell is pressed and formed, it needs to undergo a multi-stage drying and curing process to ensure that the shell has sufficient strength and dimensional stability, specifically including three stages.

[0043] Phase 1: Preliminary drying and curing treatment.

[0044] The pressed shell, along with the outer stainless steel mold, is placed in a constant temperature drying oven and pre-dried at a temperature range of 40-60℃ for 6-8 hours.

[0045] As a preferred technical solution of the present invention, the temperatures of the first drying and the second drying in step (3) are independently 40-60℃, such as 40℃, 42℃, 44℃, 46℃, 48℃, 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, etc., but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] In this invention, within this temperature range, the moisture in the mold shell can evaporate slowly and evenly, preventing cracking or deformation of the mold shell due to excessively rapid heating. The main purpose of this stage is to allow the outer surface of the mold shell to initially solidify and form an outer shell layer with a certain strength, providing the necessary structural support for subsequent demolding operations.

[0047] As a preferred technical solution of the present invention, the drying time for one drying cycle is 6-8 hours, such as 6 hours, 6.2 hours, 6.4 hours, 6.6 hours, 6.8 hours, 7.0 hours, 7.2 hours, 7.4 hours, 7.6 hours, 7.8 hours, 8.0 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Second stage: Demolding and deep drying treatment.

[0049] After the outer surface of the shell has initially solidified, the outer stainless steel shell mold is disassembled. At this point, the shell has acquired preliminary self-supporting ability. The demolded shell continues to undergo deep drying at 40-60℃ under the same temperature conditions for 12-16 hours. This extended drying time ensures that residual moisture inside the shell is fully removed, achieving a thoroughly dry state from the surface to the interior. This prevents the shell from cracking or developing internal defects due to rapid moisture vaporization during subsequent high-temperature sintering.

[0050] As a preferred technical solution of the present invention, the secondary drying time is 12-16 hours, such as 12 hours, 12.5 hours, 13.0 hours, 13.5 hours, 14.0 hours, 14.5 hours, 15.0 hours, 15.5 hours or 16.0 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Third stage: High-temperature sintering strengthening treatment.

[0052] After complete drying, the shell is transferred to a muffle furnace for high-temperature sintering. A programmed temperature control method is used, raising the furnace temperature from room temperature to 1300℃-1400℃ at a rate of 5-10℃ / min. After reaching the set temperature, it is held for 2 hours to allow the inorganic binder in the shell material to fully react, forming strong sintered necks between particles, thus significantly improving the mechanical strength and high-temperature stability of the shell. After holding, the heating system is turned off, allowing the shell to cool naturally to room temperature with the furnace, preventing cracking caused by thermal stress from rapid cooling.

[0053] As a preferred technical solution of the present invention, the sintering temperature in step (4) is 1300-1400℃, such as 1300℃, 1310℃, 1320℃, 1330℃, 1340℃, 1350℃, 1360℃, 1370℃, 1380℃, 1390℃ or 1400℃, etc., and the sintering time is 1-2h, such as 1.0h, 1.2h, 1.4h, 1.6h, 1.8h or 2.0h, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0054] As a preferred embodiment of the present invention, the heating rate of the sintering process is 5-10℃ / min, such as 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. If the heating rate is too fast, thermal stress will be generated in the shell, leading to cracking; if the heating rate is too slow, it will greatly increase the time cost.

[0055] Through the gradient temperature treatment process described above, the prepared shell has excellent dimensional accuracy, mechanical strength and thermal stability, meeting the technical requirements for subsequent high-temperature molten metal casting.

[0056] As a preferred technical solution of the present invention, the method further includes the following steps:

[0057] (1) White fused alumina powder, bentonite and bleaching beads are prepared into a composite powder, wherein the mass ratio of white fused alumina powder to bentonite is 1:(0.04-0.08) and the mass ratio of white fused alumina powder to bleaching beads is 1:(0.02-0.05). The prepared composite powder is mixed with silica sol at a weight ratio of (6-8):1 to prepare a wet material.

[0058] (2) Pour the wet material into the mold and compact it layer by layer to obtain the shell;

[0059] (3) Transfer the shell and mold to an oven for primary drying at a temperature of 40-60℃ for 6-8 hours. Then remove the mold and continue secondary drying at a temperature of 40-60℃ for 12-16 hours to obtain a pre-cured shell.

[0060] (4) The pre-cured shell is transferred to a high-temperature furnace for sintering. The sintering temperature is 1300-1400℃ and the sintering time is 1-2h. The sintered shell is a directional solidified shell of super magnetostrictive alloy.

[0061] Compared with the prior art, the present invention has at least the following beneficial effects:

[0062] (1) The present invention provides a directional solidification shell of a super magnetostrictive alloy, which improves the comprehensive performance of the shell through the optimized combination of several materials. The shell has the significant characteristics of precise and controllable thickness, high strength, and high temperature resistance, and greatly improves the directional thermal conductivity and air permeability of the shell. At the same time, due to the controllable thickness, the shell can meet the directional solidification of large-sized materials, avoiding the problems of cracking and steel leakage of traditional shells;

[0063] (2) The powder formulation uses white fused alumina of various particle sizes as the main aggregate component, including white fused alumina powders of different particle sizes such as #24, #46, #150, #320 and W20. This multi-grade ratio can achieve a reasonable aggregate gradation, so that coarse and fine particles fill each other and improve the strength of the mold shell. The combination of white fused alumina of different particle sizes, with coarse particles providing support as a skeleton and fine particles filling the gaps, can ensure that the mold shell has sufficient mechanical strength and obtain good surface quality, avoiding the problems of cracking and steel leakage caused by uneven thermal stress in traditional mold shells. Bentonite plays a role in enhancing the adhesion in the formulation and can reduce the tendency of the mold shell to crack during the drying process. Ash flocculation can reduce the overall weight of the mold shell, help the mold shell to be breathable, allow gas to escape smoothly during the casting process, reduce the risk of porosity defects and improve the thermal shock resistance performance. In the wet material formulation, the refractory material and silica sol are prepared in a ratio of (6-8):1. Silica sol, as a binder, can firmly bond refractory material particles together at room temperature to form a wet material with a certain strength.

[0064] (3) During the technical development process, it was discovered that the thickness of the shell determines the thermal conductivity and strength of the entire shell. Based on this discovery, shells of different thicknesses are prepared using different molds, which is completely different from the traditional design concept of coating-type shells with uncontrollable thickness. This greatly improves the controllability of the shell's influence on the directional solidification process, which can meet the directional solidification requirements of small-sized materials and also change the thickness to adapt to the strength requirements of large-sized materials. The combination of white corundum powder and silica sol with different mesh sizes ensures that the shell has sufficient strength and air permeability, as well as the flatness of the contact surface. Attached Figure Description

[0065] Figure 1 This is a diagram of the shell molding structure provided in Embodiment 1 of the present invention;

[0066] Among them, 1-stainless steel mold; 2-shell blank; 3-3D printed core;

[0067] Figure 2 Metallographic diagram of a TbDyFe sample prepared using the directional solidification shell of the supermagnetostrictive alloy provided in Example 1. Detailed Implementation

[0068] To better explain the present invention, it will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0069] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are all available from commercial sources.

[0070] Example 1

[0071] This embodiment provides a shell for directional solidification of a supermagnetostrictive alloy. The raw material composition of the shell includes composite powder and silica sol. The composite powder and HS-30 silica sol are mixed according to the following weight components: 6.4 parts by weight.

[0072] The composite powder is mixed according to the following weight components: 2 parts of #24 white fused alumina powder, 2 parts of #46 white fused alumina powder, 2 parts of #150 white fused alumina powder, 1.6 parts of #220 white fused alumina powder, 0.5 parts of bentonite, and 0.2 parts of bleaching powder.

[0073] This embodiment also provides a method for preparing the shell of the above-mentioned supermagnetostrictive alloy through directional solidification, the method comprising the following steps:

[0074] (1) Prepare a composite powder by mixing white corundum powder, bentonite and ash bleaching beads in the above proportions. Mix the prepared composite powder with HS-30 silica sol in a weight ratio of 6.4:1 to form a wet material.

[0075] (2) Pour the wet material into the mold and compact it layer by layer to obtain the shell;

[0076] (3) Transfer the shell and mold to an oven for a first drying at 50°C for 6 hours. Then remove the mold and continue the second drying at 50°C for 12 hours to obtain a pre-cured shell.

[0077] (4) The pre-cured shell is transferred to a high-temperature furnace for sintering. The sintering temperature is 1350℃, the heating rate of the sintering process is 5℃ / min, and the sintering time is 2h. The sintering yields a super magnetostrictive alloy directional solidified shell.

[0078] Example 2

[0079] This embodiment provides a shell for directional solidification of a supermagnetostrictive alloy. The raw material composition of the shell includes composite powder and silica sol. The composite powder and HS-30 silica sol are mixed according to their weight components: 7 parts composite powder and 1 part HS-30 silica sol.

[0080] The composite powder is mixed according to the following weight components: 3 parts of #24 white fused alumina, 3 parts of #46 white fused alumina powder, 3 parts of #150 white fused alumina powder, 3 parts of #320 white fused alumina powder, 3 parts of W20 white fused alumina powder, 1 part of bentonite, and 0.3 parts of bleaching beads.

[0081] This embodiment also provides a method for preparing the shell of the above-mentioned supermagnetostrictive alloy through directional solidification, the method comprising the following steps:

[0082] (1) Prepare a composite powder by mixing white corundum powder, bentonite and ash bleaching beads in the above proportions. Mix the prepared composite powder with HS-30 silica sol in a weight ratio of 7:1 to form a wet material.

[0083] (2) Pour the wet material into the mold and compact it layer by layer to obtain the shell;

[0084] (3) Transfer the shell and mold to an oven for primary drying at 45°C for 7 hours. Then remove the mold and continue secondary drying at 40°C for 14 hours to obtain a pre-cured shell.

[0085] (4) The pre-cured shell is transferred to a high-temperature furnace for sintering. The sintering temperature is 1350℃, the heating rate of the sintering process is 7℃ / min, and the sintering time is 2h. The sintering yields a super magnetostrictive alloy directional solidified shell.

[0086] Example 3

[0087] This embodiment provides a shell for directional solidification of a supermagnetostrictive alloy. The raw material composition of the shell includes composite powder and silica sol. The composite powder and HS-30 silica sol are mixed according to the following weight components: 7.3 parts by weight.

[0088] The composite powder is mixed according to the following weight components: 15 parts of #24 white fused alumina, 15 parts of #46 white fused alumina powder, 15 parts of #150 white fused alumina powder, 15 parts of #320 white fused alumina powder, 15 parts of W20 white fused alumina powder, 5 parts of bentonite, and 3 parts of bleaching beads.

[0089] This embodiment also provides a method for preparing the shell of the above-mentioned supermagnetostrictive alloy through directional solidification, the method comprising the following steps:

[0090] (1) Prepare a composite powder by mixing white corundum powder, bentonite and ash bleaching beads in the above proportions. Mix the prepared composite powder with HS-30 silica sol in a weight ratio of 7.3:1 to form a wet material.

[0091] (2) Pour the wet material into the mold and compact it layer by layer to obtain the shell;

[0092] (3) Transfer the shell and mold to an oven for primary drying at 45°C for 8 hours. Then remove the mold and continue secondary drying at 60°C for 16 hours to obtain a pre-cured shell.

[0093] (4) The pre-cured shell is transferred to a high-temperature furnace for sintering. The sintering temperature is 1350℃, the heating rate of the sintering process is 10℃ / min, and the sintering time is 2h. The sintering yields a super magnetostrictive alloy directional solidified shell.

[0094] Example 4

[0095] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Embodiment 1, except that the composite powder is mixed according to the following weight components: 7.6 parts of #24 white corundum, 0.5 parts of bentonite, and 0.2 parts of bleaching beads.

[0096] Example 5

[0097] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Embodiment 1, except that the composite powder is mixed according to the following weight components: 7.6 parts of #320 white corundum powder, 0.5 parts of bentonite, and 0.2 parts of bleaching beads.

[0098] Example 6

[0099] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Embodiment 1, except that the composite powder is mixed according to the following weight components: 3 parts of #24 white fused alumina, 4.6 parts of #320 white fused alumina powder, 0.5 parts of bentonite, and 0.2 parts of bleaching beads.

[0100] Example 7

[0101] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Embodiment 1, except that the content of ash flocculation beads is adjusted to 0.1 parts.

[0102] Example 8

[0103] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Embodiment 1, except that the content of ash flocculation beads is adjusted to 0.5 parts.

[0104] Example 9

[0105] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Embodiment 1, except that the bentonite content is adjusted to 0.2 parts.

[0106] Example 10

[0107] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Embodiment 1, except that the bentonite content is adjusted to 0.7 parts.

[0108] Example 11

[0109] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Embodiment 1, except that the content of #46 white corundum powder is adjusted to 1.4 parts.

[0110] Example 12

[0111] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Example 1, except that the content of #46 white corundum powder is adjusted to 2.6 parts.

[0112] Example 13

[0113] This embodiment provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Embodiment 1, except that the heating rate of the sintering process is adjusted to 12℃ / min.

[0114] Comparative Example 1

[0115] This comparative example provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Example 1, except that white corundum powder is replaced with brown corundum powder.

[0116] Comparative Example 2

[0117] This comparative example provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Example 1, except that the composite powder does not include white corundum powder, bentonite is adjusted to 4.3 parts, and ash bleaching beads are adjusted to 4.0 parts.

[0118] Comparative Example 3

[0119] This comparative example provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Example 1, except that the composite powder does not include bentonite, #220 white corundum powder is adjusted to 1.9 parts, and ash bleaching beads are adjusted to 0.4 parts.

[0120] Comparative Example 4

[0121] This comparative example provides a shell for directional solidification of a super magnetostrictive alloy and its preparation method. The raw materials and methods are the same as in Example 1, except that the composite powder does not include ash bleaching beads, #220 white corundum powder is adjusted to 1.7 parts, and bentonite is adjusted to 0.6 parts.

[0122] Performance testing

[0123] The shells obtained by directional solidification of the supermagnetostrictive alloys provided in Examples 1-13 and Comparative Examples 1-4 were subjected to performance tests. The test results are shown in Table 1.

[0124] Table 1

[0125] Density% Flexural strength weight Example 1 92 34 5 Example 2 94 30 5.02 Example 3 93 31 4.93 Example 4 78 20 4.7 Example 5 85 24 4.85 Example 6 83 25 4.8 Example 7 93 29 5.05 Example 8 89 27 4.85 Example 9 90 25 4.95 Example 10 91 31 4.98 Example 11 90 27 4.93 Example 12 91 28 5.01 Example 13 88 26 4.92 Comparative Example 1 85 22 5.1 Comparative Example 2 55 8 3.5 Comparative Example 3 75 15 4.9 Comparative Example 4 95 31 5.2

[0126] From Table 1 and Figure 1-2 As can be seen, the directional solidification shell of the super magnetostrictive alloy provided by this invention follows the principle of close packing in the particle size distribution design between white fused alumina powders. Coarse-grained white fused alumina powder serves as a skeleton material, providing basic strength and rigid support for the shell. Fine-grained white fused alumina powder fills the gaps between the coarse particles, forming a denser packing structure. In addition, bentonite is added as a binder, and ash celery is added as a lightweight filler to reduce density and improve thermal shock resistance in the shell. This results in a shell with sufficient strength, high density, and good air permeability.

[0127] A comprehensive comparison of Examples 1 and 4-6, 11-12 shows that the ratio of white fused alumina powder of different particle sizes is 1:0.8-1.2, and this particle size distribution design follows the principle of close packing. Coarse-grained white fused alumina powder acts as a skeleton material, providing basic strength and rigidity support for the mold shell; fine-grained white fused alumina powder fills the gaps between the coarse particles, forming a denser packing structure. The two work synergistically to achieve the best filling effect. When the proportion of coarse-grained white fused alumina powder is too high, although a stable skeleton structure can be formed, the gaps between the particles are large and cannot be effectively filled, leading to increased porosity and decreased density of the mold shell. This loose structure not only reduces the mechanical strength of the mold shell but also causes sand adhesion defects during the pouring process due to the penetration of molten metal, severely affecting the surface finish of the casting. Furthermore, excessive large particles can easily create stress concentration areas inside the mold shell. Conversely, when the proportion of fine-grained white fused alumina powder is too high, the large surface area of ​​the fine particles requires more binder to achieve effective coating. This not only increases the amount of silica sol used but also leads to increased drying shrinkage of the mold shell, making it prone to cracking. Excessive fine particles significantly reduce the permeability of the mold shell, making it difficult for gas in the mold cavity to escape in time during high-temperature casting, which may cause defects such as porosity and inclusions in the casting. Therefore, controlling the ratio of white fused alumina powder of different particle sizes within the range of 1:0.8-1.2 can achieve the complementary advantages of coarse and fine particles, ensuring sufficient strength of the mold shell while obtaining suitable density, porosity, and permeability, ensuring that the mold shell exhibits excellent comprehensive performance during the directional solidification process of the supermagnetostrictive alloy.

[0128] A comprehensive comparison of Examples 1 and 7-8 shows that when the amount of ash cenospheres added is too small, the lightweighting effect is not obvious, and the overall density of the shell is too high. This not only increases material costs but also easily leads to stress concentration and crack defects. At the same time, it cannot fully exert the effect of ash cenospheres in improving the thermal shock resistance of the shell. Conversely, when the amount of ash cenospheres added is too large, although the shell density is reduced, the effective contact area between aggregate particles such as white corundum is reduced, weakening the overall structural strength of the shell. This results in a significant decrease in bending strength and compressive strength, making the shell prone to breakage during handling and casting. In addition, excessive ash cenospheres may also deform excessively at high temperatures due to their low strength, affecting the dimensional accuracy of the casting.

[0129] A comprehensive comparison of Examples 1 and 9-10 shows that when the amount of bentonite added is too small, insufficient binder will result in weak bonding between white corundum powder particles, reducing the overall strength and density of the shell, making it prone to cracking or detachment, and affecting the surface quality of the casting. Conversely, when the amount of bentonite added is too large, although the bonding performance is enhanced, the permeability of the shell will be significantly reduced. At the same time, excessive binder may cause excessive shrinkage during high-temperature sintering, which will reduce the dimensional stability and thermal shock resistance of the shell, and may also increase the risk of sand adhesion defects on the surface of the casting.

[0130] A comprehensive comparison of Examples 1 and 13 shows that if the heating rate exceeds the preferred range set in this application, the inorganic binder in the shell material is not fully reacted, and a strong sintering neck cannot be formed between the particles, thereby reducing the mechanical strength and high-temperature stability of the shell.

[0131] A comprehensive comparison of Example 1 and Comparative Example 1 shows that if the white corundum powder is replaced with a framework material, the strength and density of the prepared shell will decrease significantly, and a stable framework structure cannot be formed.

[0132] A comprehensive comparison of Example 1 and Comparative Examples 2-4 shows that the composite powder comprises white fused alumina powder, bentonite, and bleached silica, wherein the white fused alumina powder serves as the main refractory aggregate; bentonite acts as a suspending agent and plasticizer; and bleached silica serves as a lightweight filler. Thorough mixing of the above raw materials in a mixing device is essential to ensure uniform dispersion of each component, thus obtaining a composite powder with stable performance. Reducing any one of the components will prevent the achievement of a synergistic effect.

[0133] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A shell for directional solidification of a supermagnetostrictive alloy, characterized in that, The raw material composition of the shell includes: composite powder and silica sol; The composite powder includes: white corundum powder, bentonite, and bleaching beads.

2. The shell according to claim 1, characterized in that, The white fused alumina powder includes any one or a combination of at least two of the following: #24 white fused alumina powder, #46 white fused alumina powder, #150 white fused alumina powder, or W20 white fused alumina powder. Preferably, the white fused alumina powder further includes #220 white fused alumina powder and / or #320 white fused alumina powder.

3. The shell according to claim 1 or 2, characterized in that, The mass ratio of white corundum powder to ash bleaching beads is 1:(0.02-0.05); Preferably, the mass ratio of white corundum powder to bentonite is 1:(0.04-0.08).

4. The shell according to claim 2 or 3, characterized in that, The white fused alumina powder includes: #24 white fused alumina powder, #46 white fused alumina powder, #150 white fused alumina powder, #220 white fused alumina powder, #320 white fused alumina powder and W20 white fused alumina powder; Preferably, the #24 white fused alumina powder, #46 white fused alumina powder, #150 white fused alumina powder, #220 white fused alumina powder, #320 white fused alumina powder, and W20 white fused alumina powder are arranged in sequence, and the mass ratio of each adjacent pair of components is 1:(0.8-1.2).

5. The shell according to any one of claims 1-4, characterized in that, The weight ratio of the composite powder to the silica sol is (6-8):

1.

6. A method for preparing a shell formed by directional solidification of a supermagnetostrictive alloy as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) Mix the prepared composite powder with silica sol to form a wet material; (2) Pour the wet material into the mold and compact it layer by layer to obtain the shell; (3) Transfer the shell and mold to an oven for primary drying, then remove the mold and continue secondary drying to obtain a pre-cured shell; (4) The pre-cured shell is transferred to a high-temperature furnace for sintering to obtain a shell with directional solidification of super magnetostrictive alloy.

7. The preparation method according to claim 6, characterized in that, The mold described in step (2) includes a 3D printed core and a stainless steel mold.

8. The preparation method according to claim 6 or 7, characterized in that, The temperatures for the primary and secondary drying processes in step (3) are independently 40-60℃; Preferably, the drying time for one drying cycle is 6-8 hours; Preferably, the secondary drying time is 12-16 hours.

9. The preparation method according to any one of claims 6-8, characterized in that, The sintering temperature in step (4) is 1300-1400℃; Preferably, the sintering time is 1-2 hours; Preferably, the heating rate of the sintering process is 5-10℃ / min.

10. The preparation method according to any one of claims 6-9, characterized in that, The method includes the following steps: (1) White fused alumina powder, bentonite and bleaching beads are prepared into a composite powder, wherein the mass ratio of white fused alumina powder to bentonite is 1:(0.04-0.08) and the mass ratio of white fused alumina powder to bleaching beads is 1:(0.02-0.05). The prepared composite powder is mixed with silica sol at a weight ratio of (6-8):1 to prepare a wet material. (2) Pour the wet material into the mold and compact it layer by layer to obtain the shell; (3) Transfer the shell and mold to an oven for primary drying at a temperature of 40-60℃ for 6-8 hours. Then remove the mold and continue secondary drying at a temperature of 40-60℃ for 12-16 hours to obtain a pre-cured shell. (4) The pre-cured shell is transferred to a high-temperature furnace for sintering. The sintering temperature is 1300-1400℃, the heating rate of the sintering process is 5-10℃ / min, and the sintering time is 1-2h. The shell is obtained by sintering a super magnetostrictive alloy directional solidification shell.

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