CN1440848A

CN1440848A - Prepn process of TbDyFe-base directionally solidified alloy crystal

Info

Publication number: CN1440848A
Application number: CN 02110945
Authority: CN
Inventors: 李碚
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-02-28
Filing date: 2002-02-28
Publication date: 2003-09-10
Anticipated expiration: 2022-02-28
Also published as: CN1184036C

Abstract

The present invention provides preparation process of TbDyFe-base magnetostrictive alloy. The technological process includes preparing mother alloy in a cold crucible inducing furnace with high efficiency and high mother bar quality; and several heater structure are designed for directional solidification with resistive heater. By means of preparing crystals of different diameters, several times of directional solidification and simultaneous directional solidification of several mother rods, the present invention has high crystal preparing efficiency and quality and develops high efficiency magnetic field heat treating method.

Description

Method for preparing TbDyFe-based alloy directionally solidified crystal

The technical field is as follows:

the invention belongs to a technology for preparing directionally solidified TbDyFe-based magnetostrictive alloy.

Background art:

the rare earth giant magnetostrictive alloy is an Rfe2 compound (R refers to rare earth element) capable of generating large strain in a magnetic field, mainly comprises two types of (TbDy) Fe2 alloy and SmFe2 alloy, and most commonly adopts tb0.3dy0.7fe1.95 alloy (Terfenol-D). TbDyFe alloy is generally produced by melting a master alloy in a vacuum non-consumable arc furnace, treating the master alloy in a vacuum directional solidification apparatus to form the master alloy into a directionally crystallized structure having a<112>orientation, and then heat treating the master alloy.

For directional solidification processing of Terfenol-D, single crystals were prepared early on using the Czochralski technique. In 1981 Savage et al used the Bridgeman technique in U.S. patent No. 4308474: the master rod in the tubular crucible is melted by the induction coil, and the crucible is lowered at a certain speed. U.S. patent No.4609402 issued to o.d. mcmasters in 1986 uses a floating zone float technique: the mother rod is positioned at the axis of the vertical tubular quartz chamber, the mother rod forms a melting zone by the induction coil, and the melting zone moves upwards along with the movement of the inductor from bottom to top. In 1988 e.d. gibson et al published an improved Bridgman technique in us patent No. 4770704. In the technology, a plurality of ingots are placed in a crucible at the upper part of a furnace body, furnace burden is melted uniformly by a medium-frequency induction power supply, and alloy liquid is injected into a quartz mould tube through a hole at the bottom of the crucible. On this basis, the american etremma Crystal Growth technology was established by etremma corporation from 1995 for mass production.

Other techniques for producing large-diameter crystals by the MB method include a method in which K.Murakami melts a charge material by an electric resistance furnace and then moves a crucible downward (U.S. Pat. No.5067551, 1991), a method in which Murakami zone-melts a mother rod by a high-frequency induction coil, andboth the crucible and the charge material move downward (U.S. Pat. No.5063986,1991), a method in which S.Okatomo moves a high-frequency zone-melting induction coil outside a quartz cell upward and directional solidification conditions are improved by an insulating member (see int.Symp.on GMSM and their appl., Tokyo, 1992, 175-180), and a continuous method in which E.Nakamura et al melts the charge material in a copper crucible by an ion arc water cooling, the bottom of the crucible is opened with a water cooling elongated mold, a carriage in the mold is continuously pulled down, and alloy liquid gradually enters the mold to solidify (see U.S. Pat. No.5114467, 1992), and the like.

The above review shows that the directional solidification treatment of Terfenol-D mostly uses a high-frequency induction coil as a heater, and the zone-melting type directional solidification treatment by resistance heating has not been reported yet.

The invention content is as follows:

the invention aims to provide a technical method for preparing high-performance TbDyFe-based directionally solidified alloy, which has higher preparation efficiency, lower production cost and is suitable for production scale.

1. The invention provides a method for preparing TbDyFe-based alloy directionally solidified crystals, which comprises the following steps of mother alloy preparation, directional solidification, heat treatment and magnetic field heat treatment, and is characterized in that:

a. the preparation process of the master alloy comprises the following steps: before smelting, the stopper rod head blocks the crucible injection hole; when the material is erected in the heating process, the stopper rod head is moved up and down to loosen the furnace burden; rotating and moving the stopper rod head up and down in the material melting process, and stirring the alloy melt; after smelting, lifting the stopper rod head, lifting the alloy ingot solidified in the crucible, operating the holding head to turn over the alloy ingot, returning the turned-over alloy ingot to the crucible for remelting, and then enabling the alloy melt to enter a mold to be solidified into a master alloy rod;

b. the directional solidification process comprises the following steps: firstly, putting seed crystal and mother rod into a crucible whose inner diameter is slightly larger than that of mother rod, then vacuumizing furnace body, and making vacuum degree be higher than 10^-1After Pa, inert gas with the pressure of-0.09 to +0.2MPa is quickly filled; then, forming a melting zone at the upper end of the seed crystal and the lower end of the mother rod by using a pressure melting type resistance heater surrounding the mother rod, pulling down and rotating the melting zone to move towards the direction of a cooler away from a high-temperature zone, solidifying the melting zone from bottom to top in the moving process, moving a new melting zone upwards along the mother rod, and continuously performing the process until the zone melting-solidification process is finished at the top of the mother rod;in the process, the temperature of the melting zone is controlled within 1260-1380 ℃, the width of the melting zone is controlled to be approximately the same as the diameter of the mother rod, the moving speed of the melting zone is within 0.5-30 mm/min, the rotating speed is 0.5-30 rpm, and the alloy rod has a directional crystallization organization and a twinned single crystal organization.

c. The heat treatment and magnetic field heat treatment process comprises the following steps:

and (3) carrying out dynamic heat treatment on the directionally solidified alloy rod, namely, the treatment temperature fluctuates around the eutectic temperature of 800-1100 ℃, and slowly cooling after 1-5 hours. And then placing the alloy rod into a quartz tube with the tube axis vertical to the direction of the magnetic field, vacuumizing the quartz tube, filling inert gas into the quartz tube, starting a heating furnace surrounding the quartz tube to heat the alloy rod within the range of 380-580 ℃ for 0.5-3 hours, then starting the magnetic field when the temperature is reduced to 280-340 ℃ to enable the temperature of the magnetic field to reach 240-960 KA/m, simultaneously enabling the quartz tube to rotate around the axis at the rotating speed of 0.2-10 rpm, keeping the rotating speed for 0.5-3 hours, and then slowly cooling.

In the above process, the top of the plug rod head controlled by the driving device is provided with a blade, so that the plug rod head can reciprocate up and down during the rotating and stirring process. The resistance heating is composed of 2-3 heating sections, the uppermost layer is a preheating section, the middle layer is a high-temperature section, and a heat preservation section is preferably arranged on the lower layer, so that a temperature gradient is formed up and down in the high-temperature section. The process of moving the molten zone along the mother rod can be repeated for a plurality of times. The temperature of the melting zone is preferably 1280-1330 ℃, the moving speed of the melting zone is preferably 2-15 mm/min, and the rotating speed is preferably 2-15 rpm. The heat treatment temperature of the alloy bar is preferably fluctuated within 900-1000 ℃. In the magnetic field heat treatment process, the alloy rod in the quartz tube is preferably heated for 1-2 hours at the temperature of 400-500 ℃, then the magnetic field with the magnetic field intensity of 400-640 KA/m is started when the temperature is preferably reduced to 310-330 ℃, meanwhile, the quartz tube rotates at the rotating speed of 0.5-2 rpm, and then the temperature is slowly reduced after the heating for 1-2 hours under the condition of keeping the operation of the magnetic field and the quartz tube.

The invention provides a relatively complete technology for preparing directionally solidified TbDyFe-based magnetostrictive alloy, is suitable for efficiently preparing high-performance products under production conditions, and provides a reasonable preparation process for crystals of various specifications including fine crystals, coarse crystals and the like.

In the aspect of mother alloy preparation, the technology mainly adopts a cold crucible vacuum induction furnace as smelting and casting equipment. Compared with a vacuum non-consumable electric arc furnace, the preparation method has much higher preparation efficiency and is suitable for the production requirement. Compared with a common vacuum induction furnace, the alloy can be remelted for many times, the components can be adjusted to ideal accuracy and uniformity, and the residual materials generated in the smelting-casting process can be returned to the furnace, so that the preparation cost is reduced. The cold crucible vacuum melting furnace with the stirring-ingot turning-casting operation system is used for smelting and casting, so that the preparation efficiency, the quality of the mother rod and the yield are further improved.

Compared with an induction heater, the resistance heater has the advantages of low equipment cost, easy temperature measurement and control, large heat penetration depth, favorability for preparing coarse crystals and the like. The method provided by the invention solves the difficulty of zone-melting type directional solidification by using a resistance heater, and reduces the pollution of crucible materials to the alloy; the disturbance to a molten pool when the mother rod is zone-melted is eliminated by utilizing the technology of controlling the feeding of the mother rod; theheat preservation section is arranged on the heater, so that heat flow is prevented from being transmitted along the radial direction of the alloy rod, and the axial transmission of the heat flow is ensured; several directional solidification can be realized in one operation period by arranging several melting zones in one heater; by utilizing the technology of the invention, the directional solidification treatment can be simultaneously carried out on a plurality of mother rods in one operation period. These techniques provide guarantees for improved directional solidification and improved processing efficiency. In addition, the present invention is designed for the preparation of fine crystals, making it possible to achieve float zone melting using a resistance heater.

In the aspect of heat treatment, the invention adopts a dynamic treatment technology to shorten the treatment time. In the aspect of magnetic field heat treatment, the technology provided by the invention enables the directional solidification crystal of a non-twin single crystal to be subjected to the treatment, and the magnetic field heat treatment can be used for the production process without metallographic observation.

Description of the drawings:

FIG. 1 shows a schematic view of a master alloy rod preparation system, in which

1-induction power supply, 2-vacuum smelting furnace, 3-vacuum-inert gas system, 4-electric control system, 5-crucible, 6-plug rod injection mechanism (6-1-plug rod head, 6-2-driving rod, 6-3-power-transmission mechanism, 6-4-blade), 7-ingot-turning mechanism (7-1-holding head, 7-2-operating rod), 8-casting mechanism (8-1-mould, 8-2-mould frame, 8-3-mould heating-heat-preservation device).

FIG. 2 shows a schematic view of a directional solidification system, in which

9-master alloy rod, 10-furnace body, 11-vacuum-inert gas system, 12-power supply-heater system (12-1-power supply, 12-2-resistance heater, 12-3-temperature measuring probe, 12-4-temperature control device), 13-furnace charge processing system (13-1-crystal pulling rod, 13-2-crystallizer, 13-3-crucible, 13-4-cooler, 13-5-heat insulation pad, 13-6-feeding rod), 14-driving system and 15-seed crystal.

FIG. 3 is a schematic view of several zone-melting resistance heating methods, in which

A-simple heater (12-2-heater),

b-multi-section heater (12-2 ' -1-preheating section, 12-2 ' -2-high temperature section, 12-2 ' -3-heat preservation section),

a C-multiple melting zone heater (12-2 '-1-preheating section, 12-2' -2-high temperature section, 12-2 '-3-holding section, 12-2' -4-middle section),

d-double layer heater (12-2 '-1-auxiliary heater, 12-2' -2-main heater). 9-master alloy rod, 9-1-melting zone.

FIG. 4 is a schematic view showing a driving mode of the vacuum directional solidification apparatus, in which

The a-heater moves upwards (12-2-heater),

B-No moving mother rod and heaters (12-2-a, -B, -c, -d, -e heaters bottom up segments). 9-master alloy rod, 13-1-crystal pulling rod, 13-2-crystallizer, 13-3-crucible, 13-4-cooler, 13-5-heat insulation pad, 13-6-feeding rod and 15-seed crystal.

FIG. 5 shows a schematic view of a different type of directional solidification mode of a mother rod, in which

A-medium diameter thicker rods, B-medium diameter finer rods, C-large diameter rods, D-small diameter rods, E-multi-rods.

9-master alloy rod, 12-2-heater, 13-1-crystal pulling rod, 13-2-crystallizer, 13-3-crucible, 13-4-cooler, 13-5-heat insulation pad, 13-6-feeding rod and 15-seed crystal.

FIG. 6 is a schematic diagram of a magnetic field heat treatment technique

9-mother alloy bar, 16-quartz furnace tube, 17-electromagnet, 18-rotatable vacuum seal, 19-vacuum-inert gas system, and 20-heating furnace.

The specific implementation mode is as follows:

the present invention specifically proposes the use of the apparatus set forth in my prior patent application (01274217.1) to produce master alloys, as shown in FIG. 1. The equipment is provided with a stirring-ingot-turning-casting operation system which comprises a plug injection rod mechanism (6), an ingot turning mechanism (7) and a casting mechanism (8). The plug rod injection mechanism consists of a plug rod head (6-1), a driving rod (6-2) and a power-transmission mechanism (6-3). The stopper rod head is an element which can be inserted into and block a nozzle (5-1) at the bottom of the crucible, the upper surface of the stopper rod head can be provided with a short blade (6-4), and the lower end of the stopper rod head is connected with a driving rod. The axis of the driving rod is superposed with the axis of the crucible injection hole, and the driving rod downwards extends out of the furnace body (2) through vacuum sealing and is combined with the power-transmission mechanism. The power-transmission mechanism enables the plug rod head to move up and down and rotate around the axis of the crucible through the driving rod. The drive shaft also has the use of circulating water connected to the stopper rod head to cool it. The ingot tilting mechanism (7) is positioned above the crucible, consists of a holding head (7-1) for holding the alloy ingot and an operating rod (7-2) for operating the holding head, and has the function of tilting the alloy ingot. The casting mechanism (8) is arranged above the crucible and surrounds a driving rod (6-2), and mainly comprises a mould (8-1) and a mould frame (8-2). The mold includes a single tube mold and a multi-tube mold. The mechanism also generally requires the provision of heating or/and heat-retaining means (8-3) for the mould.

The system has multiple functions of loosening furnace burden, stirring feed liquid, ingot turning and remelting, direct casting and the like. Before smelting, the stopper rod head (6-1) is used for blocking a crucible injection hole (5-1); when the material is erected in the heating process, the furnace burden can be loosened by moving the stopper rod head up and down; in the material melting process, the stopper rod head is rotated and moved up and down to stir the alloy liquid; and after smelting, lifting the stopper rod head, lifting the alloy ingot solidified in the crucible, operating the ingot overturning mechanism to overturn the alloy ingot, and then returning the overturned alloy ingot to the crucible for remelting. After the smelting process is finished, the stopper rod head (6-1) is pulled down, so that the stopper rod head moves from the crucible injection hole (5-1) to the mold (8-1), and the alloy liquid enters the mold along with the stopper rod head and is solidified. The system enables the alloying, homogenizing, casting and other processes to be completed in one furnace, improves the preparation efficiency, improves the product quality and reduces the production cost. The casting mechanism of the system can be used for casting a plurality of master alloy rods at one time, the compactness of the master rods can be improved through pressure casting or centrifugal casting technology, the metallurgical defect is reduced, and the yield is improved.

The master alloy rod (9) is in a directional solidification apparatus, as shown in fig. 2. The directional solidification treatment is carried out by using a zone-melting resistance heater, and the equipment mainly comprises the following parts:

(1) a furnace body system (10). Vertical metal furnaces are generally used, but quartz furnaces are also used. They should have good vacuum tightness.

(2) A vacuum-inert gas system (11). The function is to provide vacuum condition for the furnace body and fill protective inert gas (such as Ar gas). The inert gas is preferably a high-purity gas.

(3) A heater-power supply system (12). The power supply (12-1) supplies a stable alternating or direct current to the annular resistance heater (12-2). The heater is generally arranged inside the furnace body and surrounds the mother rod (9). When a quartz furnace body is used, the heater may also be located outside the furnace body, surrounding the furnace body. The system also comprises a temperature measuring probe (12-3) and a control device (2-4) which are arranged near the melting zone. The electrothermal material of the heater can be high-quality NiCr alloy or high-quality FeCrAl alloy and other common electrothermal alloys, and can also be Pt, W, Mo, Ta, graphite, SiC or MoSi₂And a high melting point material. The outside of the electric heating material is provided with a heat-insulating layer.

(4) A charge handling system (13). Mainly comprises a water-cooled metal crystal pulling rod (13-1), a water-cooled crystallizer (13-2) at the head part of the crystal pulling rod and a tubular crucible (13-3) arranged on the crystallizer, wherein a master alloy rod is placed in the crucible. The crystal pulling rod is vertically downward, and the crucible is generally made of high-quality heat-resistant ceramic materials, and the axes of the crystal pulling rod and the crucible are superposed. A seed crystal (15) is preferably provided between the lower end of the mother rod and the mold,a cooler (13-4) surrounding the mother rod and the pull rod is preferably provided below the heater (12-2), and an annular heat insulating pad (13-5) surrounding the pull rod of the mother rod is preferably provided between the heater and the cooler and is made of a heat-resistant ceramic material.

(5) A drive system (14). Acting to drive the pulling rod to move along the axial direction of the mother rod. The system preferably simultaneously drives the crystal puller to rotate about the axis of the parent rod to provide a uniform temperature profile across the same cross-section of the parent rod.

Firstly, seed crystal (15) and mother rod (9) are put into a crucible with the inner diameter slightly larger than the diameter of the mother rod(13-3), then the furnace body (10) is vacuumized, and the vacuum degree is higher than 10^-1Pa (is preferably higher than 10^-2Pa), and then rapidly charging inert gas with the pressure of-0.09 to +0.2Mpa (preferably-0.06 to +0.1 MPa). For protection ofThe operation of vacuumizing and inflating can be run for several times to ensure the atmosphere is clean. If a perfect vacuum system is not provided, the furnace body can be flushed by inert gas without vacuum pumping or only primary vacuum pumping until the atmosphere in the furnace body is clean.

In the directional solidification process, the upper end of a seed crystal (15) and the lower end of a mother rod (9) are melted by a heater (12-2) to form a molten zone (9-1), then a pulling rod (13-1) is pulled downwards (preferably simultaneously rotated), the formed molten zone is solidified from bottom to top in the process of moving to a cooler (13-4) from a high-temperature zone away from the heater, and a new molten zone moves upwards along the mother rod. This process continues until the zone-melting, solidification process is completed at the top of the parent rod. To ensure the effect, the directional solidification process can be repeated 1 or several times. In the process, the temperature of the melting zone is controlled to be 1260-1380 ℃, preferably 1280-1330 ℃, and the width of the melting zone is controlled to be approximately the same as the diameter of the mother rod; the moving speed of the crystal pulling rod can be 0.5-30 mm/min, preferably 2-15 mm/min; the rotation speed is 0.5 to.0 rpm, preferably 2 to 15 rpm. The alloy rod subjected to the directional solidification treatment has a directionally crystallized structure or a twin single crystal structure.

In order to shorten the contact time of the molten alloy and the crucible wall (13-3), a resistance heater (12-2) for generating zone melting heating effect is used. In order to avoid the impact and disturbance of the mother rod on the molten pool (9-1) during zone melting, a feeding rod (13-6) is preferably arranged above the mother rod (9) and clamps the upper end of the mother rod, and the axis of the feeding rod is coincident with the axis of the pulling rod (13-1). And a feeding rod is moved downwards by using another driving system (14'), and the mother rod is fed into the melting zone (13-3) in time in the process that the melting zone moves upwards along the mother rod, so that the stability of the melting zone is ensured. The technique using the feed rod is also applicable to the process of directional solidification by an induction heater.

The moving speed (V) of the feeding rod (13-6)₂) Should be matched with the moving speed (V) of the crystal pulling rod (3-1)₁) Matching: if the inner diameter of the crucible (13-3) is D₁The diameter of the mother rod (9) is D2, then V₁×D＝＝V₂×D₂I.e. V₂＝V₁×D₁/D₂. The feed rod preferably rotates around the curve of the mother rod during the downward movementPreferably, the direction of rotationis the same as the direction of rotation of the crystal pullerConversely, the rotational speeds are similar.

In order to realize zone-melting type directional solidification, the invention provides the following design schemes (figure 3) for the resistance heater (12-2):

(1) simple heater (12-2) (fig. 3-A)

The height of this heater is small, and the width of the melting zone (9-1) is limited by the height of the heater itself. The difficulty of creating localized melt zones in the parent rod is greater with small heaters, so such heaters are preferably made of high melting point materials.

(2) Multi-section heater (12-2') (FIG. 3-B)

The heater has a large height and consists of a plurality of heating sections, and the temperature of each section is detected and controlled respectively. The simplest case is a two-stage heater, with a wider upper section (12-2 '-1) set at a temperature below the alloy's freezing point for preheating the parent rod (9); the lower section (12-2' -2) is narrower and is set at a temperature above the melting point of the alloy, which causes the parent rod to create a melt zone (9-1). As the high-temperature section is used for locally heating the preheated mother rod, a melting zone is easier to form, the function of the high-temperature section is to prevent radial heat flow of the alloy liquid in the solidification process, promote the heat flow to be intensively transmitted downwards along the axial direction of the crystal (9) through the crystal pulling rod (13-1) and the cooler (13-4) and ensure the directional solidification effect. In addition, preheating section and heat preservation section can also contain several sections respectively, and the temperature that makes to be close to the high temperature section is higher, and the temperature of keeping away from the high temperature section is lower, slows down the heating and the cooling rate of mother's stick, prevents that the mother's stick fracture.

The electric heating materials of all the sections of the heater can be the same or different, but the high-temperature section is preferably made of high-melting-point materials.

(3) Multiple melting zone heater (12-2') (FIG. 3-C)

This is also a multi-stage heater, but with several high temperature stages (12-2 "-2) that can perform several zone-melting directional solidification processes on the parent rod during one run. The heater has a preheating section (12-2 ' -1) at the uppermost, preferably a heat-retaining section (12-2 ' -3) at the lowermost, and an intermediate section (12-2 ' -4) between the high-temperature sections. The most common is a dual zone heater. The set temperature of the high temperature section is higher than the melting point of the alloy, and the set temperatures of the preheating section, the heat preservation section and the middle section are lower than the solidifying point of the alloy. Like the previous multi-stage heater, the preheat, soak, and intermediate stages may also each include several heating stages. The material selection principle of each section of the heater is the same as that of the multi-section heater.

(4) Double layer heater (12-2') (FIG. 3-C)

Such heaters include two layers, the temperature of each layer being separately sensed and controlled. The outer layer uses an auxiliary heater (12-2' -1) with larger height, the temperature is set to be lower than the solidifying point of the alloy, the preheating and heat preservation effects are generated, and the auxiliary heater can be made of common electric heating materials; the inner layer uses a relatively narrow main heater (12-2' -2) set at a temperature above the melting point of the alloy for creatinga molten zone, preferably made of a high melting point material. In the auxiliary heater, the main heater is preferably located at a position lower than the middle thereof, and two or more main heaters are preferably arranged along the axis of the mother rod (9) and spaced from each other. When two main heaters are arranged, two zone-melting directional treatments can be realized in one operation process. The auxiliary heater can be of one-stage type or of multi-stage type.

4. Drive mode for directional solidification

The directional solidification technology is designed according to the driving mode of moving the mother rod downwards. In addition to this, the following driving modes can be used:

(1) drive heater to move upwards (fig. 4-A)

The heater (12-2) is driven to move upwards by a driving system (14'), the heat insulation pad (13-5) and the cooler (13-4) are required to follow the movement, and the crystal pulling rod (13-1) is not moved. If the feed rod (13-6) is used for feeding the mother rod (9), the downward moving speed of the feed rod is matched with the moving speed of the heater. The heater and other parts of the apparatus in this mode are constructed in the same manner as the downward motion of the mother rod, and the processes of zone melting and directional solidification are similar, including the rotation of the pull rod and the feed rod about the axis.

(2) Non-moving mother rod and heater (fig. 4-B)

When the driving mode is adopted, the zone melting and directional solidification processes are realized by adjusting the temperature of the heater (12-2) along the axial direction of the mother rod (9). The crystal pulling rod (13-1) and the heater (12-2) do not move. The heater is similar in construction to the multi-section heater (12-2'), but the height should be greater than the length of the parent rod, so that the entire parent rod is within the height of the heater. The mode of adjusting the temperature of each section is as follows: firstly, enabling a mother rod to form a melting zone (9-1) at the bottom section (12-2-a) of a heater; then moving the molten zone to an upward section (12-2-b) to solidify the alloy of the bottom section; thereafter, the molten zone is moved to the further upper stage (12-2-c) to solidify the alloy of the lower stage (12-2-b). This was done in sequence until the uppermost section of the master rod was zone melted and solidified. Above the zone melting section, the set temperature of each section should be below the solidifying point of the alloy. They may be the same or may be set to rise section by section toward the zone-melting section; below the zone melting section, the set temperature of each section should also be below the alloy freezing point, which may be the same or may be set to decrease from section to section away from the zone melting section. The more the number of the heater sections is, the better the directional solidification effect is. If the feed rods (13-6) are used to feed the mother rods, the feed rods are moved downward at a speed matched to the temperature regulation process of the heater, and the crystal pulling rods and the feed rods are preferably capable of rotating around a shaft.

5. Selection of modes of directional solidification techniques

In principle, the above apparatus configurations and techniques of items 2 to 4 are applicable to various conditions (diameter, length and number) of the mother rod (9), but different technical modes can be selected according to actual conditions to obtain better directional solidification effect and higher preparation efficiency. For example:

(1) preparation of medium diameter single master rod

When the diameter of the mother rod (9) islarger, it is better to use a multi-stage heater (12-2 '), particularly a multi-zone heater (12-2') (FIG. 5-A); since it is difficult to realize a narrow melting zone by the single layer resistance heater, it is preferable to use a double layer heater (12-2 ') when the diameter of the mother rod is small, and it is preferable to provide two main heaters (12-2' -2) in order to enhance the effect of directional solidification (FIG. 5B).

Although the feeding rods (13-6) can produce better directional solidification effect, the feeding rods can be omitted under the condition because the impact on a molten pool caused by melting is small when the diameter of the mother rod is small and the control difficulty of the feeding rods is large.

(2) Preparation of Large diameter Single mother stick (FIG. 5-C)

When processing a large diameter mother rod (9), the mother rod may generate a large impact on the molten pool (9-1) during zone melting, so the feed rod (13-6) is preferable to hold and feed the mother rod. In operation, a seed crystal (15) is placed at the bottom of a crucible (13-3), a mother rod or the crucible is moved to contact the seed crystal, and a melting zone is formed at the contact zone of the mother rod and the seed crystal by a heater (12-2). The feed rod is then moved synchronously with the crystal puller (13-1) or heater at precisely matched speeds to move the melt zone upwardly.

The large diameter parent rod requires a wide melting zone, so a multi-stage heater can be used for heating (12-2'). Although a simple heater can be used, the heater has no heat preservation effect on the alloy below a melting zone, cannot prevent radial heat flow, and the solidified alloy is easy to crack; although a dual layer heater (12-2') may also be used, it is more complex and difficult to control.

(3) Small diameter Single motherstick preparation (FIG. 5-D)

The small diameter mother rod (9) can adopt the same directional solidification technology as the medium diameter mother rod, but because the specific surface area of the fine crucible is large, the surface reaction and the surface defect are seriously generated, and therefore, the directional solidification is preferably carried out by using the floating zone melting technology. At this time, the feed rod (13-6) must be installed, but the crucible (13-3) is not used, and the upper and lower ends of the mother rod are respectively clamped by the crystal pulling rod (13-1) and the feed rod (13-6). The heater (12-2) firstly generates a melting zone (9-1) at the lower part of the mother rod, and the melting zone is kept stable by the surface tension of the alloy liquid. The crystal puller and the feed rod are then moved downwardly at the same speed, or only the heater is moved, to move the melt zone upwardly. The crystal puller and the feed pin are also preferably rotated about the axis at the same speed and direction.

When the seed crystal (15) is used, the lower end of the seed crystal is respectively held by the pulling rod (13-1), the upper end of the mother rod is held by the feeding rod (13-6), and the pulling rod or the feeding rod is moved to make the upper end of the seed crystal contact with the lower end of the mother rod. Then, a fusion zone is formed at the contact region of the mother rod and the seed crystal by a heater (12-2), and the other operations are the same as above.

In this mode, the molten zone must be narrow, so it is preferable to heat it with a double heater (12-2').

(4) Medium diameter/Multi-mother Bar preparation (FIG. 5-E)

The mode is used for carrying out directional solidification treatment on a plurality of mother rods in one operation process so as to improve thepreparation efficiency and reduce the energy consumption. The structure and technique of this mode is substantially the same as that of the medium diameter/single rod mode except that the heater (12-2), cooler (12-4), insulation blanket (12-5) and crystallizer (12-2) should all have a larger diameter. A plurality of tubular crucibles (13-3) are vertically arranged on the crystallizer, and seed crystals (15) and mother rods (9) are arranged in each crucible. The directional solidification operation is then carried out according to the technique of medium diameter/single rod mode. This mode can use heaters of various structures, but the double layer heater (12-2') is preferable. When a double-layered heater is used, the temperature of one main heater (12-2 '-2) or two main heaters spaced apart from each other in the direction of the mother rod, the temperature of the auxiliary heater (12-2' -1) and the main heaters are preferably measured and controlled. The cooler preferably uses a liquid metal (e.g., In-Ga alloy, etc.) as the cooling medium (13-4-1), so that similar cooling conditions can be obtained for each crucible after entering the cooler.

In this mode, the use of a feed rod will also give better directional solidification, but for multi-rod processing the control is more difficult.

6. Heat treatment and magnetic field heat treatment

In directionally solidified crystals, except for the main phase Rfe₂In addition, there is the formation of Rfe during the solidification process₃And R (R means Tb and Dy) and the like. By heat treatment near the eutectic temperature, Rfe in the alloy₃Same R phase reaction to form Rfe₂The non-equilibrium phase can be eliminated, and the performance can be improved.

The heat treatment is carried out under the condition of filling inert gas (such as Ar gas) after vacuumizing, wherein the inert gas has high purity, and the temperature is controlled to be 800-1100 ℃ (preferably 900-1000 ℃). Due to the fact that The reaction is slow and the heat treatment generally takes a long time, e.g., 10 hours or more. The dynamic treatment technology provided by the invention enables the treatment temperature to fluctuate within the required temperature range, thus accelerating the reaction process and shortening the treatment time. By using the technology, the reaction can be completed only by carrying out heat treatment for 1-5 hours, and ideal performance is obtained. After the treatment, the alloy needs to be cooled slowly to prevent the alloy from forming cracks.

In the form of rod (TbDy) Fe₂In the twin single crystal, a group of parallel {111} twin crystal planes are parallelIn the case of a rod shaft, the rod shaft,<112>the direction is also parallel to the rod axis. Below the curie temperature (about 350 ℃), along a plane perpendicular to the twin plane<111>The magnetic field is applied in a direction (easy magnetization direction) so that the magnetic domains are aligned in a direction perpendicular to the rod axis. The magnetostriction performance of the crystal subjected to the magnetic field heat treatment can be greatly improved. The difficulty of magnetic field heat treatment is that it requires metallographic observation of each crystal to determine its vertical axis<111>Directionally, and only twinned single crystals are possible for this observation. In general directionally solidified (TbDy) Fe₂In the alloy bar, though<112>The direction also being close to the parallel axes but perpendicular to the axes<111>The directions are randomly distributed.

The processed alloy can be twin single crystal or not, and has high processing efficiency without metallographic observation. The basis for this treatment is: in alloy rods with better directional solidification quality, the<112>direction of most of the grains is parallel to the rod axis, and the<111>direction in these grains is perpendicular to the rod axis. Therefore, if the directionally solidified alloy rod is made perpendicular to the magnetic field and slowly rotated about the rod axis, the grains have the opportunity to orient their<111>direction parallel to the direction of the magnetic field and their magnetic domains in a direction perpendicular to the rod axis. After treatment, most of the magnetic domains in the alloy rod are oriented in a direction perpendicular to the rod axis.

The treatment process comprises the following steps: subjecting the directionally solidified and heat treated (TbDy) Fe₂The alloy rod (9) is placed in a quartz tube (16), andwith the rod axis parallel to the tube axis. The quartz tube is placed in a direct current magnetic field (17) with the axial direction perpendicular to the magnetic field direction and is connected with a vacuum-inert gas filling system (19) through a rotatable vacuum sealing interface (18), and a heating furnace (20) is placed around the quartz tube. After vacuuming and filling inert gas (such as Ar gas), the alloy rod is heated for 0.5 to 3 hours (preferably 1 to 2 hours) at 380 to 580 ℃ (preferably 400 to 500 ℃). Then, the temperature is reduced to 280-340 ℃ (preferably 310-330 ℃) and the magnetic field is started. The magnetic field intensity is 240-960 kA/m (preferably 400-640 kA/m), and the quartz tube is rotated around the shaft at a rotation speed of 0.2 to 10rpm (preferably 0.5 to 2 rpm). When the alloy rod is long, the quartz tube should be moved in the tube axis direction so that each part of the rod can uniformly receive the action of the magnetic field. Heating for 0.5-3 hr (preferably 1-2 hr), maintaining the magnetic field, and driving the quartz tubeSlowly cooling the mixture under the condition (1). Figure 6 shows a schematic view of magnetic field heat treatment.

Another method for providing vacuum or inert gas conditions is to place the alloy rod (9) into a sealed quartz tube (16) and seal the other end of the quartz tube under vacuum or inert gas filling after vacuum. Then, the quartz tube was placed in a magnetic field (17), and magnetic field heat treatment was performed in a similar manner to the foregoing.

Example (b):

example 1

The alloy was melted in a cold crucible vacuum induction furnace with stirring-ingot-casting operation (fig. 1), with a power supply of 200kw and a frequency of 8 kH. The crucible (5) is a split water-cooled red copper crucible with a bottom sprue, the inner diameter is 80mm, the height is 180mm, and the sprue diameter is 25 mm. The middle injection pipe of the casting mechanism (8) is screwed into the injection port, the mould pipes with different diameters are communicated with the middle injection pipe through the bottom injection plate, and the heater (8-3) surrounds the mould.

3.5kg of furnace charge is prepared according to the proportion of Tb0.29Dy0.71Fe1.95. After charging, vacuum pumping and charging high-purity argon with the pressure of-0.02 Mpa, and then starting a power supply to heat the furnace burden. After furnace burden is melted down, the plug rod head (6-1) is rotated to stir the feed liquid, and the smelting power supply is turned off after 2-3 minutes. And lifting the stopper rod head to lift the alloy ingot after the alloy is solidified. Then, the ingot is turned over by an ingot turning mechanism (7), and the stopper rod head is lowered to feed the ingot into the crucible. The alloy was remelted twice in this way. Preferably, after remelting for 1 minute, the stopper rod is pulled down at a rate of 80 mm/minute without stopping the heating until all the liquid alloy enters the die tube (8-1).

After discharge, 1 piece of cast rod with the diameter of 20mm, 10 pieces of cast rod with the diameter of 10mm and 8 pieces of cast rod with the diameter of 8mm are obtained, the lengths of the cast rods are all about 200mm, the total weight of the cast rods is about 2.9kg, and the quality of the cast rods is good. The composition of the alloy was analyzed by sampling from each of the three gauge bars, and the results showed that the alloy had a uniform and correct composition (Table 1) and very low impurity content (Table 2). The cast rod was surface ground and used as a master rod for directional crystallization.

TABLE 1 results of analysis of alloy elements of the alloy of example 1%

	Tb	Dy	Fe
	Tb	Dy	Fe	Required ingredients	17.71	42.25	40.04
Analysis of components	17.74±0.03	42.18±0.08	40.08±0.05	Required ingredients	17.71	42.25	40.04

Table 2, results of analysis of impurities of the alloy of example 1%

	O	N	F	C	S	Al	Si
	O	N	F	C	S	Al	Si	Required ingredients	≤0.03	≤0.01	≤0.02	≤0.02	≤0.01	≤0.01	≤0.02
Analysis of components	0.012	0.005	0.010	0.008	0.002	0.008	0.013	Required ingredients	≤0.03	≤0.01	≤0.02	≤0.02	≤0.01	≤0.01	≤0.02

Example 2

Using the directional solidification apparatus shown in FIG. 2, master rods (9) having a diameter of 20mm and a length of 195mm prepared in example 1 were treated in a large-diameter single-rod mode, and the upper ends of the rods were held by feed bars (13-6) (FIGS. 5-3). A quartz crucible (13-3) having an inner diameter of 21mm and a length of 250mm is held above the crystallizer (13-2), and a seed crystal (15) having a height of 15mm and a diameter of 18mm is placed in the crucible. The crucible was surrounded by a 3-stage heater (12-2) with an inner diameter of 30mm and a total power of 20 kw. The upper section (12-2' -1) of the heater is 100mm high, the lower section (12-2-3) is 50mm high, the heaters are all prepared by using high-temperature FeCrAl alloy, and the set temperature is 1000 ℃. The middle section (12-2' -2) of the heater was made of Pt wire with a height of 30mm and a set temperature of 1290 ℃. The heater is arranged on an annular corundum heat insulation pad (13-5) with the thickness of 20mm, and a red copper water-cooling annular cooler (13-4) is fixed below the annular corundum heat insulation pad, and has the inner diameter of 30mm and the height of 50 mm.

And (3) lifting the crystal pulling rod (13-1), positioning the upper end face of the seed crystal at the center of the middle section of the heater, and then lowering the feeding rod (13-6) to enable the mother rod (9) to enter the crucible (13-3) and the lower end to just contact with the seed crystal (15). The directional furnace (10) is vacuumized to 5 x 10^-3After Pa, high-purity Ar with the pressure of 0.01Mpa is filled, and then a heater power supply (12-1) is started. When the temperature of the middle section reaches the set temperature and keeps the temperature for 2 minutes, the up-and-down driving systems (14, 14') are simultaneously started, so that the crystal pulling rod descends at the speed of 6mm/min, rotates clockwise at the speed of 3rpm, descends at the speed of 6.3mm/min and rotates anticlockwise at the speed of 3 rpm. When the upper end of the mother rod moves out of the lower end of the heater and approaches to enter the cooler (13-4), the heating and driving process is stopped.

After discharging, the finished rod with the diameter of about 20.5mm and the length of about 200mm is obtained, and the finished rod has no cracks and holes. Detection indicated that, at 40kAm^-1Under the axial magnetic field of (2), the axial strain of the rod is 520X 10^-6。Example 3

The alloy rod (9) obtained in example 2 was placed in a vacuum heat treatment furnace, and vacuum was applied to 5X 10^-3And introducing high-purity Ar with the pressure of 0.01Mpa into the reactor after Pa. The temperature in the treatment process fluctuates at 850-950 ℃, the fluctuation period is 20min, the temperature is reduced after the treatment is accumulated for 2 hours, and the alloy is cooled along with the furnace. The results of the tests carried out on the tapped alloy bars show that they are at 40kAm^-1Under the axial magnetic field of (2), the axial strain of the rod is 610X 10^-6(ii) a Axial compressive stress at 6MPa and 40kAm^-1Under the magnetic field of (2), the strain reaches 1230 multiplied by 10^-6。

Placing the heat-treated rod (9) into a quartz tube (16) with a length of 250mm and an inner diameter of 30mm, sealing one end, connecting the quartz tube with a vacuum system (19), and vacuumizing to 2 × 10^-1Heating and sealing with quartz lamp at PaThe unsealed end of the quartz tube is sealed. The quartz tube holder was placed in a heating furnace (20) having a length of 400mm and an inner diameter of 40mm, and the heating furnace was placed between the pole heads of the electromagnets (17) so that the tube axis was parallel to the pole head faces (see FIG. 6). The quartz tube was heated to 480 ℃ and then kept warm for 1 hour. Then, the temperature is reduced to 320 ℃, and the magnetic field is started to enable the magnetic field intensity to reach 480 kA/m. At the same time, the quartz tube was driven at a rotational speed of 1rpm and a reciprocating speed of 50mm/min, so that a magnetic field was applied to each portion of the alloy rod having a length of 200 mm. After the temperature is kept for 0.5 hour,the temperature is slowly reduced under the conditions of keeping the magnetic field and driving the quartz tube. After tapping, the results of the tests on the alloy bars showed that the alloy bars had a value of 40kAm^-1Strain 880X 10 under axial magnetic field^-6(ii) a Axial compressive stress at 2MPa and 40kAm^-1Under the magnetic field of (2), the strain reaches 1260X 10^-6。

Claims

1. A method for preparing TbDyFe-based alloy directionally solidified crystals comprises the following steps of mother alloy preparation, directional solidification, heat treatment and magnetic field heat treatment, and is characterized in that:

a. the preparation process of the master alloy comprises the following steps: before smelting, a stopper rod head (6-1) is used for blocking a crucible injection hole (5-1); when the material is erected in the heating process, the stopper rod head is moved up and down to loosen the furnace burden; rotating and moving the stopper rod head up and down in the material melting process, and stirring the alloy melt; after smelting, the stopper rod head is lifted, the alloy ingot solidified in the crucible is lifted, the holding head (7-1) is operated to overturn the alloy ingot, the overturned alloy ingot is sent back to the crucible for remelting, and then the alloy melt enters a die (8-1) to be solidified into a master alloy rod (9);

b. the directional solidification process comprises the following steps: firstly, seed crystals (15) and a mother rod (9) are put into a crucible (13-3) with the inner diameter slightly larger than that of the mother rod, then a furnace body (10) is vacuumized, and inert gas with the pressure of-0.09 to +0.2MPa is quickly filled after the vacuum degree is higher than 10-1 Pa; then, a melting zone is formed at the upper end of the seed crystal and the lower end of the mother rod by a pressure melting type resistance heater (12-2) surrounding the mother rod, then the melting zone is pulled down and rotated to leave a high-temperature zone and move towards a cooler (13-4), the melting zone is solidified from bottom to top in the process, a new melting zone moves upwards along the mother rod, and the process is continuously carried out until the zone melting-solidification process is finished at the top of the mother rod; in the process, the temperature of the melting zone is controlled within 1260-1380 ℃, the width of the melting zone is controlled to be approximately the same as the diameter of the mother rod, the moving speed of the melting zone is within 0.5-30 mm/miu, the rotating speed is 0.5-30 rpm, and the alloy rod after the process has a directional crystallization organization and a twinned single crystal organization;

c. heat treatment and magnetic field heat treatment

And (3) carrying out dynamic heat treatment on the directionally solidified alloy rod, namely, the treatment temperature fluctuates around the eutectic temperature of 800-1100 ℃, and slowly cooling after 1-5 hours. Then placing the alloy rod (9) into a quartz tube (16) with the tube axis vertical to the direction of the magnetic field, vacuumizing the quartz tube, filling inert gas into the quartz tube, starting a heating furnace (20) surrounding the quartz tube to heat the alloy rod within the range of 380-580 ℃ for 0.5-3 hours, starting the magnetic field when the temperature is reduced to 280-340 ℃ to enable the temperature of the magnetic field to reach 240-960 KA/m, rotating the quartz tube around the axis at the rotating speed of 0.2-10 rpm, keeping the rotating speed for 0.5-3 hours, and then slowly reducing the temperature.

2. The method for preparing TbDyFe-based alloydirectionally solidified crystals as claimed in claim 1, wherein the tip of the stopper rod head (6-1) controlled by the driving means is equipped with a blade (6-4) to reciprocate up and down while rotating and stirring.

3. The method for preparing a TbDyFe-based alloy directionally solidified crystal according to claim 1, wherein the resistance heating is comprised of 2 to 3 heating sections, the uppermost layer is a preheating section, the middle layer is a high temperature section, and preferably, a heat retaining section is provided on the lower layer so that a temperature gradient is formed above and below the high temperature section.

4. The method for producing TbDyFe-based alloy directionally solidified crystals as claimed in claim 1, wherein the moving process of the melt zone along the mother rod (9) is repeated a plurality of times.

5. The method for preparing TbDyFe-based alloy directionally solidified crystals according to claim 4, wherein the temperature of the melt zone is preferably in the range of 1280 to 1330 ℃, the moving speed of the melt zone is preferably 2 to 15mm/min, and the rotating speed is preferably 2 to 15 rpm.

6. The method for preparing TbDyFe-based alloy directionally solidified crystals as claimed in claim 1, wherein the heat treatment temperature of the alloy rod is preferably fluctuated within 900 to 1000 ℃.

7. The method for preparing TbDyFe-based alloy directionally solidified crystals according to claim 1, wherein the alloy rod (9) in the quartz tube (16) is heated at a temperature of 400 to 500 ℃ for 1 to 2 hours during the magnetic heat treatment, and then the magnetic field with a magnetic field strength of 400 to 640KA/m is started when the temperature is preferably lowered to 310 to 330 ℃, and the quartz tube is rotated at a speed of 0.5 to 2rpm, and then the temperature is slowly lowered after heating for 1 to 2 hours while keeping the magnetic field and the quartz tube in operation.