CN118389872A - A method for preparing Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment - Google Patents

Abstract

A preparation method of Ni-Fe-Ga-Co shape memory alloy monocrystal based on melt purification treatment belongs to the field of shape memory alloy. The method specifically comprises the following steps: (1) Preparing a polycrystalline bar stock by an arc melting and suction casting technology; (2) Placing the polycrystalline bar stock into a quartz mold with a tip, and filling glass purifying agent powder into gaps around the polycrystalline bar stock; (3) melting the bar stock by induction heating for purification treatment; (4) regulating and controlling the temperature of the tip region; (5) Flowing the superheated alloy liquid into the tip of the die to form a pre-crystallization nucleus at the front edge of the tip; (6) And controlling the lifting rod to drive the overheated alloy liquid to be cooled slowly and directionally, so as to obtain the shape memory alloy monocrystal. The invention utilizes the glass purifying agent to purify the alloy, so that the alloy liquid has large thermodynamic supercooling degree, but is in a overheat state; the crystal nucleus prefabricated by the tip is utilized to gradually invade the superheated liquid for growth, so that the melt is in low dynamic supercooling, thereby ensuring the unidirectional stable growth of the single crystal nucleus and realizing the low-cost preparation of the shape memory alloy monocrystal.

Description

A method for preparing Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment

Technical Field

The invention belongs to the field of shape memory alloys, and in particular relates to a method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment.

Background technique

Shape memory alloy is a smart metal material that can sense, drive and respond to external field (stress field, temperature field) stimulation. Under stress stimulation, shape memory alloy can produce huge elasticity far exceeding that of traditional metals. This unique property makes it widely used in biomedicine, aerospace, smart manufacturing and other fields, such as in the manufacture of dental archwires, vascular stents and spacecraft landing cushioning devices.

The superelasticity of Ni-Fe-Ga-Co shape memory alloy single crystal is greater than 12%, far exceeding that of traditional metal materials, and it also has the advantages of small stress hysteresis and good cyclic stability. However, for polycrystalline materials, the superelasticity is only about 6%, and it also has disadvantages such as large stress hysteresis and poor cyclic stability. Brittle fracture can occur under low stress cycles far below the yield strength of the alloy. The key to the practical application of Ni-Fe-Ga-Co shape memory alloy is to develop new technologies and methods for low-cost preparation of bulk single crystals.

The existing technologies for preparing single crystal alloys mainly include seed crystal method and crystal selection method. The seed crystal method usually requires the pre-preparation of single crystals of a certain size as seed crystals to guide crystal growth. It has high requirements for the shape and size of the seed crystals, and the preparation is difficult, the success rate is low, and the cost is high. The crystal selection method uses the geometric constraints of the spiral channel to prepare single crystals. The mold preparation process is complicated, and the mold cannot be reused. The preparation cost is high and the efficiency is low. In the prior art, technicians have proposed a method for preparing single crystals based on deep supercooling technology. For example, patent number CN111020704B discloses a TiNbVZr single crystal alloy growth method under electrostatic suspension conditions, that is, using the deep supercooling technology characteristics based on the electrostatic suspension of the melt, it instantly solidifies into a spherical single crystal under cooling to avoid the generation of impurities, but the metal can only prepare spherical single crystals of smaller size (about 2mm in diameter); patent number CN117070785A discloses a Cu-Mn-Ga-Ni single crystal superelastic alloy microwire and its preparation method, which realizes the deep supercooling of the melt through molten glass purification and cyclic superheating technology, and realizes the preparation of single crystal wires by combining glass coating method, but the diameter of the wire prepared by this technology is only in the micrometer level. The above-mentioned single crystal preparation method based on deep supercooling technology cannot realize the preparation of large-size bulk single crystal alloys. Patent numbers CN101935791A and CN1552544A disclose a method for preparing directional alloy materials by combining deep supercooling treatment with directional solidification technology, which realizes the preparation of ferromagnetic shape memory alloy polycrystals with preferential orientation.

In summary, the alloy has a large thermodynamic undercooling after deep supercooling treatment. After the micro-sample is stimulated to form nuclei, it can be grown at a high speed under a large kinetic undercooling to obtain a single crystal. However, for large-sized bulk samples, the large kinetic undercooling will lead to the inability to effectively release the latent heat of crystallization, thus failing to form a single crystal. Therefore, under the existing conditions and the accumulation of technology, how to achieve the simple, efficient and low-cost preparation of shape memory alloy bulk single crystals is a technical problem that needs to be solved urgently in this field.

Summary of the invention

The present invention is based on the inventor's discovery and understanding of the following facts and problems: the alloy has a large thermodynamic supercooling after deep supercooling treatment, and the micro-sized sample can achieve the preparation of single crystals through the extremely rapid growth of the crystal nucleus. However, due to the large kinetic supercooling limit, the crystallization latent heat of large-sized alloys cannot be effectively released, so this method cannot be further extended to the preparation of large-sized bulk single crystal samples. To this end, the inventor aims to achieve simple, efficient and low-cost preparation of shape memory alloy bulk single crystals. Through a large number of experiments and process explorations, it is found that: the alloy is purified by glass purifier, so that the alloy liquid has a large thermodynamic supercooling, but is in an overheated state; then the crystal nucleus prefabricated at the tip is used to gradually invade the superheated liquid to grow, so that the melt is in a low kinetic supercooling, thereby ensuring the unidirectional stable growth of a single crystal nucleus.

In order to achieve the above object, the technical solution adopted by the present invention is as follows:

A method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment, wherein the alloy is purified by using a glass purifier so that it has a large thermodynamic undercooling, but the alloy liquid is in an overheated state; a crystal nucleus prefabricated at the tip of a quartz mold is gradually invaded into the overheated liquid for growth, so that the melt is in a low kinetic undercooling, thereby ensuring the unidirectional stable growth of a single crystal nucleus, and realizing low-cost preparation of a Ni-Fe-Ga-Co shape memory alloy single crystal, and specifically comprising the following steps:

(1) Mixing metal raw materials according to the component ratio for preparing single crystals, and preparing polycrystalline rods through arc melting and suction casting technology;

(2) placing the polycrystalline rod into a quartz mold, wherein the mold is composed of a round tube, a perforated disc and a conical tip from top to bottom, and the gap around the rod and the quartz mold is filled with glass purifier powder, and then the mold is placed on a lifting rod;

(3) By controlling the heating power of the induction power supply, the rod material in the mold is induction heated and fused with the purifier, and the temperature of the melting area of the alloy rod is controlled to be above the melting point _Tm , and the temperature is kept for purification;

(4) Adjust the lifting rod to control the temperature zone at the tip of the quartz mold to ensure that the temperature at the front edge of the tip is lower than the melting point T _m and the temperature at the end of the tip is close to the melting point T _m ;

(5) Control the heating power of the induction power supply to increase the temperature of the melting area of the alloy rod. The superheated alloy liquid flows into the tip of the mold through the perforated disc by gravity, forming a prefabricated crystal nucleus at the front edge of the tip;

(6) Control the lifting rod to drive the superheated alloy liquid to slowly and directionally cool to obtain a Ni-Fe-Ga-Co shape memory alloy single crystal.

Preferably, in step (1), the arc melting process is performed by flipping and remelting for no less than 5 times to ensure that the alloy composition obtained is uniform, and the diameter of the polycrystalline rod obtained after copper mold suction casting is in the range of 5 to 20 mm.

Preferably, in step (2), the quartz mold is composed of a round tube, a perforated disc and a conical tip welded from top to bottom, the wall thickness of the round tube and the tip area is less than 2 mm, the tip area is conical, the bottom diameter is equal to the outer diameter of the round tube, the cone angle is 10 to 60°, and the tip length L ≥ 15 mm, so as to ensure that there is a large temperature difference between the tip front and the tip end when the tip temperature can be controlled by adjusting the position later; the inner diameter _D1 of the round tube and the diameter _d1 of the polycrystalline bar satisfy: _d1 + 1 mm ≤ _D1 ≤ _d1 + 2 mm; the outer diameter of the perforated disc is equal to the outer diameter _D2 of the round tube, the disc thickness ranges from 1 to 3 mm, and the inner diameter _d2 should satisfy: 2 mm ≤ _d2 ≤ _D1 - 2 mm. It is worth noting that if the inner diameter of the perforated disc is too large, the alloy liquid will flow directly into the tip during the purification process, and if the inner diameter is too small, the alloy liquid cannot flow into the tip through subsequent heating.

Preferably, in step (2), the chemical composition of the purifier includes SiO ₂ , B ₂ O ₃ , K ₂ O and Al ₂ O ₃ , and the mass ratio thereof is 0.6-0.8: 0.05-0.2: 0.02-0.06: 0.01-0.04.

Preferably, in step (3), the induction heating power is controlled so that the relationship between the melting area temperature _T1 of the alloy rod and the melting point _Tm satisfies the following conditions: _Tm +100℃ _≤T1≤Tm +200℃, the heating rate is 10-30℃/min, _and the heat preservation purification time is 5-40min, so as to achieve the best purification effect.

Preferably, in step (4), the relationship between the temperature of the mold tip area and the melting point T _m is: the temperature T ₂ at the front edge of the tip satisfies, T ₂ ≤ T _m - 400 ° C; the temperature T ₃ at the rear end of the tip satisfies, T _m - 50 ° C ≤ T ₃ ≤ T _m + 50 ° C, to ensure that in the subsequent heating process, the temperature at the front edge of the tip is still lower than the melting point, and the temperature at the rear end of the tip is higher than the melting point, thereby forming a prefabricated crystal nucleus at the front edge of the tip.

Preferably, in step (5), the temperature of the melting area of the alloy rod is increased to T _{4 by controlling the power of the induction heating power supply, and the relationship between T 4 and} the melting point T _m satisfies: T _m + 300 ℃ ≤ T ₄ ≤ T _m + 400 ℃, and the heating rate is 10 to 30 ℃/min, so that the alloy liquid flows into the tip through the perforated disc under the action of gravity.

Preferably, in step (5), the superheated alloy liquid flows into the mold tip through the perforated disc due to gravity and solidifies at the front edge of the tip to form a prefabricated crystal nucleus, and the entire tip is not completely solidified.

Preferably, in step (6), the pulling rod pulls the alloy into the Ga-In-Sn coolant at a pulling speed of 0.01 to 0.05 mm/s to ensure stable and unidirectional growth of the tip crystal nucleus.

Compared with the prior art, the present invention has the following significant advantages:

1. Compared with the seed crystal method for preparing single crystals, the present invention does not need to prepare large seed crystals through a complicated process; compared with the spiral crystal selection method for preparing single crystals, the quartz mold used in the present invention has a simple structure, while the spiral crystal selection method requires the preparation of a spiral crystal selector, and the process includes wax mold preparation, multiple slurry coating, roasting and other processes, which are complicated and have a low success rate. The single crystal preparation technology of the present invention involves a simple mold, and the process flow used can be carried out in traditional directional solidification, so the preparation process is simple and the cost is low.

2. The present invention uses a glass purifier to purify the alloy, so that the alloy liquid has a large thermodynamic undercooling, but is in an overheated state; the crystal nuclei prefabricated at the tip gradually invade the superheated liquid to grow, so that the melt is in a low dynamic undercooling, ensuring the unidirectional stable growth of a single crystal nucleus, and realizing the low-cost preparation of shape memory alloy single crystals. The present invention cleverly utilizes dynamic undercooling and thermodynamic undercooling treatment, reduces the growth technology threshold of bulk single crystal alloys and the dependence on expensive single crystal preparation equipment, and the single crystal preparation principle has universality and practical engineering value.

3. The Ni-Fe-Ga-Co shape memory alloy single crystal prepared by the present invention has no defects, and the preparation process is pollution-free, low-cost, and easy to be applied in engineering.

The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

FIG1 is a simplified structural diagram of a directional solidification system used in a method for preparing a Ni—Fe—Ga—Co shape memory alloy single crystal based on melt purification provided by the present invention.

2 is a crystal orientation diagram of a cross section of a Ni—Fe—Ga—Co shape memory alloy single crystal prepared in Example 1 of the present invention along the growth direction.

3 is a {100} pole figure of the cross section of the Ni—Fe—Ga—Co shape memory alloy single crystal prepared in Example 1 of the present invention along the growth direction.

4 is an inverse pole figure of a cross section of a Ni—Fe—Ga—Co shape memory alloy single crystal prepared in Example 1 of the present invention along the growth direction.

5 is a {100} pole figure of a cross section of a Ni—Fe—Ga—Co shape memory alloy single crystal prepared in Example 2 of the present invention along the growth direction.

6 is an inverse pole figure of a cross section of a Ni—Fe—Ga—Co shape memory alloy single crystal prepared in Example 2 of the present invention along the growth direction.

7 is a {100} pole figure of the cross section of the Ni—Fe—Ga—Co shape memory alloy single crystal prepared in Example 3 of the present invention along the growth direction.

8 is an inverse pole figure of a cross section of a Ni—Fe—Ga—Co shape memory alloy single crystal prepared in Example 3 of the present invention along the growth direction.

9 is a crystal orientation diagram of a cross section of a Ni—Fe—Ga—Co shape memory alloy bulk polycrystalline prepared in Comparative Example 1 of the present invention along the growth direction.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings, and the technical solutions in the embodiments of the present invention will be described clearly and completely. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. Instead, they are only examples of devices and methods consistent with some aspects of the present disclosure as detailed in the attached claims.

The terms "first", "second", etc. in the specification and claims of the present disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so that the embodiments of the present disclosure described herein can be implemented in an order other than those illustrated or described herein, for example.

In addition, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or elements is not necessarily limited to those steps or elements explicitly listed, but may include other steps or elements not explicitly listed or inherent to such process, method, product, or apparatus.

Multiple includes two or more.

It should be understood that the term "and/or" used in this disclosure is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and/or B can represent: A exists alone, A and B exist at the same time, and B exists alone.

Example 1

This embodiment provides a method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment. The chemical formula of the prepared single crystal is: Ni ₃₅ Fe ₁₈ Ga ₂₇ Co ₂₀ (at.%), and the melting point is 1250 °C. The method specifically includes the following steps:

(1) According to the above composition ratio, metal elements Ni, Fe, Ga and Co with a purity greater than 99.99% were weighed, and Ni ₃₅ Fe ₁₈ Ga ₂₇ Co ₂₀ shape memory alloy ingots were prepared by arc melting technology. During the melting process, the ingots were repeatedly turned over and melted at least 5 times to make the composition uniform, and then the ingots were sucked into polycrystalline rods with a diameter of 4 mm by copper mold suction casting method;

(2) The structural diagram of the directional solidification system used in the present invention is shown in FIG1. The polycrystalline rod is placed in a quartz mold, wherein the mold is composed of a round tube, a perforated disc and a conical tip from top to bottom, and the gap around the polycrystalline rod and the quartz tube is filled with glass purifier powder. The quartz mold is placed vertically and firmly on the mold base of the directional solidification furnace, and the furnace chamber is evacuated to below 5×10 ^-3 Pa, and then filled with 0.05 Pa of high-purity argon as a protective gas;

(3) The temperature is raised to 1400 °C at a rate of 30 °C/min by controlling the heating power of the induction power supply and then kept at this temperature for 15 min for purification. At this time, the bar material and the purifier in the mold are heated and fused. Due to the limitation of the perforated disc, the alloy liquid does not flow into the tip of the mold.

(4) Adjust the lifting rod to control the temperature zone of the quartz mold tip so that the temperature at the front edge of the tip is 750 °C and the temperature at the end of the tip is 1250 °C;

(5) The heating power of the induction power supply is controlled to raise the temperature of the melting area of the alloy rod to 1650 °C. The superheated alloy liquid flows into the tip of the mold through the perforated disc under the action of gravity. Since the temperature at the front of the tip is lower than the melting point of the alloy, the alloy liquid with deep supercooling ability will form a tiny single crystal core after entering the tip. The temperature at the very end of the tip is higher than the melting point of the alloy. Therefore, the entire tip is not completely solidified, and only a prefabricated crystal nucleus is formed at the front of the tip.

(6) The lifting rod is controlled to move downward at a speed of 0.03 mm/s, driving the superheated alloy liquid into the Ga-In-Sn liquid metal coolant and slowly cooling it directionally. The prefabricated crystal nucleus at the tip can grow stably and unidirectionally, and is always in a low kinetic supercooling state during the growth process, thereby obtaining _{a Ni35Fe18Ga27Co20} shape memory alloy single crystal with a diameter of _{5 mm} .

Figures 2, 3 and 4 are respectively the crystal orientation diagram, pole figure and anti-pole figure of the cross section of the Ni-Fe-Ga-Co shape memory alloy single crystal prepared in this embodiment along the growth direction. It can be seen that the crystal orientation diagram of the cross section of the Ni-Fe-Ga-Co shape memory alloy single crystal prepared in this embodiment along the growth direction has uniform color, and the pole figure only has four <100> crystal direction projections corresponding to the single crystal, and the crystal direction projections of the anti-pole figure are all concentrated near the <001>orientation; indicating that the Ni ₃₅ Fe ₁₈ Ga ₂₇ Co ₂₀ shape memory alloy prepared in this embodiment is a single crystal with a near <001> orientation along the growth direction.

Example 2

This embodiment provides a method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment. The chemical formula of the prepared single crystal is: Ni ₄₅ Fe ₁₉ Ga ₂₇ Co ₉ (at.%), and the melting point is 1150 °C. The method specifically includes the following steps:

(1) According to the above composition ratio, metal elements Ni, Fe, Ga and Co with a purity greater than 99.99% were weighed, and Ni ₄₅ Fe ₁₉ Ga ₂₇ Co ₉ shape memory alloy ingots were prepared by arc melting technology. During the melting process, the ingots were repeatedly turned over and melted at least 5 times to make the composition uniform, and then the ingots were sucked into polycrystalline rods with a diameter of 4 mm by copper mold suction casting method;

(2) Place the polycrystalline rod into a quartz mold, where the mold consists of a round tube, a perforated disc and a conical tip from top to bottom, and fill the gap around the polycrystalline rod and the quartz tube with glass purifier powder. Place the quartz mold vertically and firmly on the mold base of the directional solidification furnace, evacuate the furnace chamber to below 5×10 ^-3 Pa, and then fill it with 0.05 Pa of high-purity argon as a protective gas;

(3) The temperature is raised to 1350 °C at a rate of 30 °C/min by controlling the heating power of the induction power supply and then kept at this temperature for 20 min for purification. At this time, the bar material and the purifier in the mold are heated and fused. Due to the limitation of the perforated disc, the alloy liquid does not flow into the tip of the mold.

(4) Adjust the lifting rod to control the temperature zone of the quartz mold tip so that the temperature at the front edge of the tip is 700 °C and the temperature at the end of the tip is 1200 °C;

(5) The heating power of the induction power supply is controlled to raise the temperature of the melting area of the alloy rod to 1550 °C. The superheated alloy liquid flows into the tip of the mold through the perforated disc under the action of gravity. Since the temperature at the front of the tip is lower than the melting point of the alloy, the alloy liquid with deep supercooling ability will form a tiny single crystal core after entering the tip. The temperature at the very end of the tip is higher than the melting point of the alloy. Therefore, the entire tip is not completely solidified, and only a prefabricated crystal nucleus is formed at the front of the tip.

(6) The lifting rod is controlled to move downward at a speed of 0.05 mm/s, driving the superheated alloy liquid into the Ga-In-Sn liquid metal coolant and slowly cooling it directionally. The prefabricated crystal nucleus at the tip can grow stably and unidirectionally, and is always in a low kinetic supercooling state during the growth process, thereby obtaining a Ni ₄₅ Fe ₁₉ Ga ₂₇ Co ₉ shape memory alloy single crystal with a diameter of 7 mm.

FIG5 and FIG6 are the pole figures and anti-pole figures of the cross section of the Ni-Fe-Ga-Co shape memory alloy single crystal prepared in this embodiment along the growth direction, respectively. It can be seen that in the pole figures of the cross section of the shape memory alloy single crystal prepared in this embodiment along the growth direction, there are only four <100> crystal direction projections corresponding to the single crystal, and the crystal direction projections of the anti-pole figures of the cross section along the growth direction are all concentrated near the <001> orientation, indicating that the Ni ₄₅ Fe ₁₉ Ga ₂₇ Co ₉ shape memory alloy prepared in this embodiment is a single crystal with a near <001> orientation along the growth direction.

Example 3

This embodiment provides a method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment. The chemical formula of the prepared single crystal is: Ni ₄₀ Fe ₁₈ Ga ₂₇ Co ₁₅ (at.%), and the melting point is 1100 °C. The method specifically includes the following steps:

(1) According to the above composition ratio, metal elements Ni, Fe, Ga and Co with a purity greater than 99.99% were weighed, and Ni ₄₀ Fe ₁₈ Ga ₂₇ Co ₁₅ shape memory alloy ingots were prepared by arc melting technology. During the melting process, the ingots were repeatedly turned over and melted at least 5 times to make the composition uniform, and then the ingots were sucked into polycrystalline rods with a diameter of 4 mm by copper mold suction casting method;

(2) Place the polycrystalline rod into a quartz mold, where the mold consists of a round tube, a perforated disc and a conical tip from top to bottom, and fill the gap around the polycrystalline rod and the quartz tube with glass purifier powder. Place the quartz mold vertically and firmly on the mold base of the directional solidification furnace, evacuate the furnace chamber to below 5×10 ^-3 Pa, and then fill it with 0.05 Pa of high-purity argon as a protective gas;

(3) The temperature is raised to 1300 °C at a rate of 30 °C/min by controlling the heating power of the induction power supply and then kept at this temperature for 10 min for purification. At this time, the bar material and the purifier in the mold are heated and fused. Due to the limitation of the perforated disc, the alloy liquid does not flow into the tip of the mold.

(4) Adjust the lifting rod to control the temperature zone of the quartz mold tip so that the temperature at the front edge of the tip is 650 °C and the temperature at the end of the tip is 1100 °C;

(5) The heating power of the induction power supply is controlled to raise the temperature of the melting area of the alloy rod to 1500 °C. The superheated alloy liquid flows into the tip of the mold through the perforated disc under the action of gravity. Since the temperature at the front of the tip is lower than the melting point of the alloy, the alloy liquid with deep supercooling ability will form a tiny single crystal core after entering the tip. The temperature at the very end of the tip is higher than the melting point of the alloy. Therefore, the entire tip is not completely solidified, and only a prefabricated crystal nucleus is formed at the front of the tip.

(6) The lifting rod is controlled to move downward at a speed of 0.02 mm/s, driving the superheated alloy liquid into the Ga-In-Sn liquid metal coolant and slowly cooling it directionally. The prefabricated crystal nucleus at the tip can grow stably and unidirectionally, and is always in a low kinetic supercooling state during the growth process, thereby obtaining a Ni ₄₀ Fe ₁₈ Ga ₂₇ Co ₁₅ shape memory alloy single crystal with a diameter of 12 mm.

FIG7 and FIG8 are respectively the pole figures and the anti-pole figures of the cross section of the Ni—Fe—Ga—Co shape memory alloy single crystal prepared in this embodiment along the growth direction. It can be seen that in the pole figures of the cross section of the shape memory alloy single crystal prepared in this embodiment along the growth direction, there are only four <100> crystal direction projections corresponding to the single crystal, and the crystal direction projections of the anti-pole figures of the cross section along the growth direction are all concentrated near the <001> orientation, indicating that the Ni ₄₀ Fe ₁₈ Ga ₂₇ Co ₁₅ shape memory alloy prepared in this embodiment is a single crystal with a near <001> orientation along the growth direction.

Comparative Example 1

This embodiment provides a shape memory alloy prepared by ordinary directional solidification as a comparison. The chemical formula of the prepared shape memory alloy is: Ni ₃₅ Fe ₁₈ Ga ₂₇ Co ₂₀ (at.%), and specifically includes the following steps:

(1) According to the above composition ratio, metal elements Ni, Fe, Ga and Co with a purity greater than 99.99% were weighed, and Ni ₃₅ Fe ₁₈ Ga ₂₇ Co ₂₀ shape memory alloy ingots were prepared by arc melting technology. During the melting process, the ingots were repeatedly turned over and melted at least 5 times to make the composition uniform, and then the ingots were sucked into polycrystalline rods with a diameter of 4 mm by copper mold suction casting method;

(2) A quartz tube with both ends open is placed vertically and firmly on the mold base of a directional solidification furnace, and the polycrystalline rod is placed in the quartz tube. The furnace chamber of the directional solidification furnace is evacuated to below 5×10 ^-3 Pa, and then filled with 0.05 Pa of high-purity argon as a protective gas;

(3) By controlling the heating power of the induction power supply, the temperature is raised to 1400 °C at a rate of 30 °C/min and kept at this temperature for 10 min to completely melt the polycrystalline rod;

(4) The lifting rod is controlled to move downward at a speed of 0.03 mm/s, driving the superheated alloy liquid into the Ga-In-Sn liquid metal coolant, and slowly cooling it in a direction to obtain the Ni ₃₅ Fe ₁₈ Ga ₂₇ Co ₂₀ shape memory alloy.

FIG9 is a crystal orientation diagram of a cross section of a Ni—Fe—Ga—Co shape memory alloy block polycrystalline prepared in this comparative example along the growth direction. It can be seen that the orientation diagram of the entire cross section along the growth direction is not uniform in color, indicating that the Ni ₃₅ Fe ₁₈ Ga ₂₇ Co ₂₀ shape memory alloy prepared in this example is polycrystalline.

Finally, it should be noted that the above embodiments are only used to illustrate the implementation process and features of the present invention, rather than to limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, ordinary technicians in this field should understand that any modifications and partial replacements made without departing from the spirit and scope of the present invention should be covered by the protection scope of the present invention.

Claims (9)

1. A method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment, characterized in that: a glass purifier purifies the alloy so that it has a large thermodynamic undercooling, but the alloy liquid is in an overheated state; a crystal nucleus prefabricated at the tip of a quartz mold is gradually invaded into the overheated liquid to grow, so that the melt is in a low dynamic undercooling, thereby ensuring the unidirectional stable growth of a single crystal nucleus, and realizing the low-cost preparation of a Ni-Fe-Ga-Co shape memory alloy single crystal, which specifically includes the following steps: (1) Mixing metal raw materials according to the component ratio for preparing single crystals, and preparing polycrystalline rods through arc melting and suction casting technology; (2) placing the polycrystalline rod into a quartz mold, wherein the mold is composed of a round tube, a perforated disc and a conical tip from top to bottom, and the gap around the rod and the quartz mold is filled with glass purifier powder, and then the mold is placed on a lifting rod; (3) By controlling the heating power of the induction power supply, the rod material in the mold is induction heated and fused with the purifier, and the temperature of the melting area of the alloy rod is controlled to be above the melting point _Tm , and the temperature is kept for purification; (4) Adjust the lifting rod to control the temperature zone at the tip of the quartz mold to ensure that the temperature at the front edge of the tip is lower than the melting point T _m and the temperature at the end of the tip is close to the melting point T _m ; (5) Control the heating power of the induction power supply to increase the temperature of the melting area of the alloy rod. The superheated alloy liquid flows into the tip of the mold through the perforated disc by gravity, forming a prefabricated crystal nucleus at the front edge of the tip; (6) Control the lifting rod to drive the superheated alloy liquid to slowly and directionally cool to obtain a Ni-Fe-Ga-Co shape memory alloy single crystal. 2. The method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment according to claim 1, characterized in that: in step (1), the arc melting process is flipped and remelted for no less than 5 times, and the diameter of the polycrystalline rod obtained after copper mold suction casting is in the range of 5 to 20 mm. 3. The method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment according to claim 1, characterized in that: in step (2), the quartz mold is composed of a round tube, a perforated disc and a conical tip welded from top to bottom, the wall thickness of the round tube and the tip area is less than 2 mm, the tip area is conical, the bottom diameter is equal to the outer diameter of the round tube, the cone angle is 10 to 60°, and the tip length L ≥ 15 mm; the inner diameter _D1 of the round tube and the diameter _d1 of the polycrystalline rod satisfy: _d1 + 1 mm ≤ _D1 ≤ _d1 + 2 mm; the outer diameter of the perforated disc is equal to the outer diameter _D2 of the round tube, the disc thickness ranges from 1 to 3 mm, and the inner diameter _d2 satisfies: 2 mm ≤ _d2 ≤ _D1 - 2 mm. 4. The method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment according to claim ₁ , characterized in that: in step (2), the chemical composition of the purifier includes _SiO2 , _B2O3 , _K2O and _Al2O3 , _and the mass ratio thereof is 0.6-0.8: 0.05-0.2: 0.02-0.06: 0.01-0.04. 5. The method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment according to claim 1, characterized in that: in step (3), the power of the induction heating power supply is controlled so that the relationship between the melting area temperature _T1 of the alloy rod and the melting point _Tm satisfies: _Tm +100℃ _≤T1≤Tm + ₂₀₀ ℃, the heating rate is 10～30℃/min, and the heat preservation purification time is 5～40min. 6. The method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment according to claim 1, characterized in that: in step (4), the relationship between the temperature of the mold tip area and the melting _{point Tm} is: the tip front temperature _T2 satisfies, _T2 ≤ _Tm -400℃; the tip end temperature _T3 satisfies, _Tm -50℃ _≤T3≤Tm +50℃. 7. The method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment according to claim 1, characterized in that: in step (5), the temperature of the melting area of the alloy rod is increased to _T4 by controlling the power of the induction heating power supply, and the relationship between _T4 and the melting point _Tm satisfies: _Tm +300℃ _≤T4≤Tm +400℃, _and the heating rate is 10～30℃/min. 8. The method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment as described in claim 1 is characterized in that: in step (5), the superheated alloy liquid flows into the mold tip through the perforated disc due to gravity, solidifies at the front of the tip to form a prefabricated crystal nucleus, and the entire tip is not completely solidified. 9. The method for preparing a Ni-Fe-Ga-Co shape memory alloy single crystal based on melt purification treatment according to claim 1, characterized in that: in step (6), the pulling rod pulls the alloy into the Ga-In-Sn coolant at a pulling speed of 0.01 to 0.05 mm/s.