CN103658575B - A kind of internal roller type single roller rapid quenching prepares the method for amorphous thin ribbon - Google Patents

Abstract

The invention discloses a method for preparing an amorphous thin strip by rapid quenching of an inner roller type single roller, which belongs to the technical field of preparation of the amorphous thin strip. The inner roller is adopted, and the inner roller is a hollow straight cylinder structure. The melt is sprayed on the inner surface of the inner roller rotating around the central axis. The inner surface of the inner roller is straight, The direction of the centrifugal force on the melt is changed from perpendicular to the contact surface up to perpendicular to the contact surface and pointing inward. The thin strip prepared by the method of the invention has thinner size, higher surface finish and better performance.

Description

A method for preparing amorphous thin strips by inner-roll single-roll rapid quenching

technical field

The invention belongs to the technical field of preparation of amorphous thin strips, and relates to a novel single-roll strip stripping method to solve the problems of liquid droplets splashing and difficult strip formation during the strip stripping process, specifically a concave single-roll quick quenching method .

technical background

Single roll quick quenching method, also known as melt cooling roll spin coagulation method, continuous casting thin strip method. The method of producing amorphous ribbons invented by Bedell is shown in Figures 1 and 2. The molten metal sprays on the surface of the cooling roll rotating at high speed and spreads under the action of gravity and wetting to form a molten pool; the interface layer between the molten pool and the cooling roll is quenched and solidified, and rotates with the cooling roll to continue cooling to form a thin metal strip; Thin metal strip detaches from the rim surface of the roller under the action of self-shrinkage and centrifugal force [Xian Chunchun, Li Derong. Characteristics of the melting pool of planar flow casting technology [J]. Journal of Harbin Institute of Technology, 2000, 24 (4): 273-274] .

F _Friction : The contact surface between the roller and the melt forms a thin solidified layer and adheres to the surface of the roller and is accelerated by the rotating roller. There is a velocity gradient in the melt. Small, the force on the mutual movement inside the melt is expressed as F _{friction force} .

F _Adhesion : Refers to the ability of a certain material to adhere to the surface of another material, specifically the ability of the melt to adhere to the surface of the roller.

F _{Centrifugal force} : The molten metal is accelerated by the roller and rotates with the roller, resulting in a centrifugal force away from the center of rotation.

In the single-roll quick quenching process, the melt is subjected to centrifugal force F _{centrifugal force} , adhesion force F _{adhesion force} , and tangential stress F _{friction force} .

Melting pool: It refers to the liquid-solid metal expansion area where the molten metal comes out of the nozzle and forms a certain shape on the surface of the roller, and the molten metal is spread and solidified in this area.

The high-speed rotation of the roller provides a tangential stress F _friction to the molten pool and drives the molten pool to move in the same direction. Figure 3 shows the initial melt pool morphology (solid line) and the melt pool morphology (dotted line) during the process of preparing amorphous wire from the melt. It can be seen from the figure that the molten master alloy and the There is a clear difference between wetting and static wetting between rollers [Yu Shengsheng, Sun Jianfei. Research on CoFeSiB alloy melt drawn wire characteristics [D]. Harbin Institute of Technology (Harbin), 2011: 5‐6]. During the melt pulling process, the shape of the molten pool changes drastically along the direction of roller rotation; at the same time, the wetting angle changes from the static wetting angle θ _e to the upstream contact angle θ _u and the downstream contact angle θ _d , where the Reflecting the dynamic wettability of the molten master alloy on the roll is θ _d . The smaller θ _d is, the better the dynamic wettability is, and the more the molten pool changes in the direction of the wheel rotation. [M.Allahverdi, RobinA.L.Drew, Strom _‐ Olsen.WettingandmeltextractioncharacteristicsofZrO2 _{‐ Al2O3basedmaterials} [J].JournalofAmericanCeramicSociety.1997,80:2910‐2916] found that although the static wettability is poor ( The wetting angle reaches 140°-160°), but the presence of tangential stress results in a small dynamic wetting angle and improved wetting ability. M.Allahverdi et al [Huang Shiying. The dynamic equations and verification of the formation of amorphous thin strips by the single-roll quenching method Ⅲ[J]. Instrument Materials., 1985,18(4):160-164] Obtained by high-speed photography technology The dynamic wetting of molten metal droplets and the morphology of the molten pool, the length L and thickness δ of the molten metal droplet under different wheel speeds are analyzed; as the wheel speed V increases, the tangential stress F _friction increases, and the melt spread area increases .

In the prior art, the melt is subjected to centrifugal force perpendicular to the contact surface of the roller, and the centrifugal force makes the melt tend to fall off the surface of the roller instead of spreading on the surface of the roller. When the centrifugal force is greater than the adhesion force, the molten metal falls off the roller before it is fully cooled. On the surface of the wheel, a droplet splash phenomenon is formed. For example, the rotational speed is 40m/s, the diameter of the roller is 0.4m, and the centrifugal acceleration of the liquid metal is as high as 816g, which is prone to splashing of droplets.

In the prior art, in order to enable the melt to spread effectively on the surface of the roller and improve the wettability of the roller and the melt, it is necessary to consider viscosity (μ), surface tension (γ), wettability, surface roughness (Ra), Temperature (T), phase change factors, adjusting multiple parameters such as melt injection speed, angle, distance, roller speed, roller material wettability, etc., increase the complexity of the process, for some molten metals with high viscosity, and rollers For molten metal materials with poor wetting, it is difficult to form strips no matter how the process parameters are adjusted, and a smooth and uniform rapid solidification material cannot be obtained [Mao Zhonghan. Manufacturing method of amorphous alloys [J]. Rare metal alloy processing, 1980, 01:11-15].

Amorphous or metastable phase, with superior mechanical, optical, magnetic and other properties, in order to obtain the required amorphous or metastable phase microcrystalline ribbon, a cooling rate above 10 ⁶ ~ 10 ⁸ K/s is required . It is known that the overall heat transfer method in the rapid quenching process is mainly Newtonian cooling:

${<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; dT</span>}}{\mathrm{<span\; class="notranslate">\; d\&tau;</span>}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; pl</span>}}\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

ρ _l is the density of the metal liquid, С _pl is the specific heat of the metal liquid at constant pressure, and the heat transfer coefficient of the α alloy liquid and the cooling roll. h is the thickness of the metal strip. It can be seen that the cooling rate is inversely proportional to the thickness of the alloy strip and directly proportional to the rotational speed of the roller.

The existing technology adopts increasing the rotational speed of the roller to increase the cooling rate. When the rotation speed of the wheel disc increases to a certain level, the thickness of the strip does not decrease much, but the pulling marks on the surface of the strip are too large, the surface roughness increases, and meshes and cavities appear, which affect the quality of the thin strip. At the same time, the centrifugal force increases, Under the action of centrifugal force, the melt is likely to cause droplet splashing, which affects production safety. Therefore, the speed of the cooling roll should generally not be too large, and the line speed should be less than 35m/s.

The existing technology is to reduce the size of the nozzle to reduce the thickness of the strip and increase the cooling speed. However, due to the influence of the purity of the molten metal, the nozzle is easily blocked by impurities in the molten metal and the spray strip is stopped. At the same time, it flows through the nozzle per unit time. The flow rate of molten metal is too small, and the molten metal at the nozzle will block the nozzle due to continuous cooling and solidification, so the diameter of the nozzle should not be too small, generally 0.6-0.12 mm, and the molten metal must maintain a certain degree of superheat to ensure continuous flow spray tape. In the existing technical conditions, due to the limitations of technology and methods, only 30-60 micron amorphous alloy strips can be prepared by spraying.

The existing technology is to use the roller material with high thermal conductivity, but with the increase of the thermal conductivity of the wheel, after the melt is pulled for a unit time, the remaining temperature of the melt inside the molten pool will gradually decrease, and the time required for solidification will be shorter. The smaller the spread area of the melt on the roller, the worse the wettability and the worse the belt forming performance. When choosing a metal roulette, the cooling speed and the stripping performance cannot be taken into consideration.

Rayleigh wave: refers to the regular periodic ripples of liquid column or unsolidified metal under the combined action of surface tension and gravity

Rayleigh wave defects and entrained gas holes are easily formed on the surface of the amorphous strip prepared by the prior art. When the rotation speed of the roller is low, eddy currents are formed around the free surface of the strip to cause the disturbance of the melt pulling layer, and Rayleigh waves are easily formed on the surface of the amorphous strip. The formation process of the entire Rayleigh wave can be divided into three stages: (1) The melt is in contact with the roller; (2) The melt pulling layer moves together with the roller; (3) The melt pulling layer is separated from the roller . When the roller is in contact with the melt, a very thin solidification layer is formed due to the chilling effect of the tip of the roller, which can be regarded as the thermal boundary layer δ _T . The momentum boundary layer δ _V is much larger than the thermal boundary layer δ _T , and the entire momentum boundary layer δ _V is in the liquid state except the thermal boundary layer δ _T . formed in. When the semi-solid boundary layer is flying in the protective gas, since it has separated from the rim at this time, the solidification process mainly conducts heat through convection and radiation, and the cooling rate decreases rapidly, causing the size of the Rayleigh wave to further expand, forming a Rayleigh wave defect. When the rotating speed of the wheel is high, the entrainment of protective gas causes the melt drawing layer to break before it is completely solidified.

The patent (200810247383.7) proposes a method to obtain a smooth and uniform rapid solidification material by increasing the injection speed of the liquid metal alloy, but it can only determine the problem of stripping of some materials. The body can't solve it well

Therefore, how to solve the strip forming performance of the single-roll quick quenching method, it is necessary to develop new equipment and new processes.

Contents of the invention

The purpose of the present invention is to provide a new method of throwing strips, which overcomes the problems in the prior art, that is, solves the splashing of the melt droplets of the fast-setting thin strips in the single-roller fast-setting thin strip method, the difficulty of forming strips, and the existence of thin strips. To solve problems such as defects, bubbles, etc., a rapidly quenched amorphous alloy thin strip with thinner size, higher surface finish and better performance is prepared.

In order to solve the above problems, the core solution of the present invention is to change the structure of the roller, adopt the inner roller roller, adopt the inner roller roller as a hollow straight cylinder structure, and spray the melt on the inner roller roller that rotates around the central axis. On the inner surface of the wheel, the inner surface of the inner roller type roller is a straight cylinder (as shown in Figure 4), so that the direction of the centrifugal force on the melt changes from perpendicular to the contact surface upwards to perpendicular to the contact surface and pointing into the contact surface. The amorphous ribbon at the edge of the inner surface shrinks itself upon cooling, and the ribbon is peeled off by a gas nozzle or collected by a coiling device. On the one hand, the invention can reduce the upward centrifugal force of the vertical contact surface and solve the problem of melt splashing.

The present invention exemplifies the disc-type single-roller stripping method, which is characterized in that:

(1) Cooling water passes through the interlayer of the roller, and the inner surface of the roller is used as the contact surface and is perpendicular to the central axis (as shown in Figure 4).

(2) The molten material is melted in the furnace and sprayed on the inner surface of the roller through the nozzle.

(3) The melt forms a molten pool on the inner surface and cools to form a thin and smooth amorphous ribbon.

(4) The amorphous thin strip at the edge of the inner surface is cooled and shrinks by itself, and the thin strip is peeled off by a gas nozzle or collected by a coiling device.

(5) The belt throwing method of the present invention can adjust the parameters of the tethering process according to specific needs.

Compared with prior art, the beneficial effect of the present invention is

1. In the prior art, the metal is sprayed on the outer surface of the roller, and the metal melt is subjected to centrifugal force perpendicular to the contact surface of the roller (Figure 1), and the melt cannot be effectively spread on the surface of the roller. When the centrifugal force is greater than the adhesion force, The molten metal falls off the surface of the roller before it is fully cooled, forming a droplet splashing phenomenon. In the present invention, the roller type is changed to a disc type so that the direction of the centrifugal force is changed from upward to downward perpendicular to the contact surface. On the one hand, the centrifugal force on the vertical contact surface can be reduced, and the problem of splashing by the melt can be solved. At the same time, the centrifugal force is strong (up to 400 ~ 800G) to promote the spread of the melt on the inner surface of the roller, so that the melt with high viscosity and poor wettability can spread on the surface of the roller, and at the same time, the melt spreads thinner and faster, so that the melt has sufficient cooling rate.

2. The existing technology is necessary to ensure the stability of the melt and prevent the nozzle from clogging. The temperature of the molten pool is kept at a certain degree of superheat. Roller materials with high thermal conductivity (such as copper rollers and molybdenum rollers) are used, although the melt can be guaranteed Cooling speed, but after the melt is pulled for a unit time, the remaining temperature of the melt inside the molten pool is low, and the time required for solidification is too short, and the melt solidifies before it can spread on the rollers, which is not conducive to the spread of the melt and the formation of belts The performance is poor; the melt of the present invention spreads thinner and faster under the action of F _{centrifugal force} , the area is larger, and the belt forming performance is better.

3. The existing technology uses high speed to obtain sufficient supercooling degree. High speed is easy to make the protective gas around the molten pool get involved in the molten pool. At the same time, the melt deflects with the rotation of the roller. Too high speed is easy to This leads to the fracture of the melt-drawing layer. On the other hand, in the present invention, due to the _{centrifugal force} of the melt F, the rapid spreading of the melt is promoted, and sufficient cooling speed and thin strip spreading area can be obtained at a low roller speed without excessively high speed.

4. In the existing technology, the method of reducing the diameter of the nozzle can only obtain an amorphous ribbon with a thickness greater than 20 microns, and the phenomenon of nozzle clogging, interrupted spraying or broken ribbon often occurs, and the production efficiency is not high. In the present invention, under the _{centrifugal force} of F, the residual temperature of the molten pool rises after the melt is pulled for a unit time, and the spreading area of the melt on the rollers increases, and the thickness is small, so that very thin non-woven fabrics can be obtained without using too small nozzles. Crystal tape, there will be no nozzle clogging, and at the same time, the width of the amorphous tape and the efficiency of the spray tape will be improved.

5. In the prior art, Rayleigh wave defects are easily formed during the stripping process. Under the action of the _{centrifugal force} of the melt F, the present invention promotes the rapid spreading of the melt into thin sheets and rapid condensation into a solid state. Rayleigh waves can only be formed in a liquid state, thereby reducing the generation of Rayleigh wave defects and obtaining thin strips with smooth surfaces.

Description of drawings

Figure 1 Schematic diagram of the cylindrical single-roller fast-setting thin-belt method

1. Cooling roll 2. Nozzle 3. Metal liquid 4. Fast-setting thin strip;

Fig. 2 Schematic diagram of cylindrical single-roll fast-setting thin-belt melt pool

1. Cooling roll 2. Melt metal injection 3. Metal liquid 4. Fast-setting thin strip;

Figure 3 Dynamic wettability under shear stress

1. Liquid metal 2. Roller surface, θ _e static contact angle, θ _u upstream contact angle, θ _d downstream contact angle. Solid line - static shape of molten pool, dotted line - dynamic shape of molten pool;

Figure 4 Sectional view of inner roller type single roller belt throwing method

1. Inner roller type single roller 2. Nozzle 3. Melting pool 4. Amorphous ribbon 5. Gas nozzle;

Figure 5 Schematic diagram of inner roller single roller stripping method

1. Cooling roll 2. Nozzle 3. Melting pool 4. Amorphous ribbon 5. Gas nozzle.

detailed description

The specific embodiments of the present invention are described in detail below in conjunction with the examples, but the specific embodiments of the present invention are not limited to the following examples.

Example 1:

A method for preparing a fast-quenched amorphous alloy thin strip, including batching, smelting, secondary smelting, strip spraying, and harvesting. The mass percentage of its chemical composition is: 21.57%Sm, 72.84%Fe, 1.66%Zr, 3.93%Co.

Using 99.5% metal samarium, industrial pure iron, metal cobalt, and metal zirconium as raw materials, it is melted in an intermediate frequency vacuum induction melting furnace. Before melting, the vacuum chamber is first vacuumed, and then high-purity argon is used as a protective gas to avoid alloy oxidation. . The melting temperature is 1600°C. Secondary melting is carried out in the induction ladle, and the spray belt pressure is established in the nozzle package, and the spray belt pressure is 0.10Mpa. The protective atmosphere pressure is 0.05Mpa.

The inner roller is made of molybdenum, and the inside of the roller is cooled by circulating water. The inner diameter of the cooling roll is 400 mm, and the linear speed of the roll edge is 24 m/s. In-place finish turning of cooling rolls: Guarantee rolling surface roughness Ra<0.2μm.

The nozzle aperture is 0.5mm, the nozzle is close to the edge of the roller, and 20mm away from the edge of the roller.

The molten metal is sprayed onto the inner surface of the roller and cooled rapidly to form a fast solidified thin strip. A stripping gas nozzle is added at the end of the cooling roller to peel off the amorphous strip on the surface of the roller through the air flow. The diameter of the nitrogen gas nozzle is 2mm, and the air pressure is 0.5 Mpa, collected after falling off the amorphous strip.

Obtain thin strips with a uniform thickness of 8-9 microns, and Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 fast-solidified thin strips with a surface roughness of less than 0.24 μm. There is no splashing during the process, and there is no α-Fe soft magnetic phase in the alloy. After grinding and nitriding to form Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 N _x , after making bonded magnets, the magnetic properties are B _r =1.09T, (BH) _max =23.8MGOe.

In Comparative Example 1, the composition, roller diameter, roller speed, nozzle size and other factors are the same, and the cylindrical roller type stripping method is adopted (Fig. 1). The shape uniformity of the obtained thin strip is poor, there are many alloys with different shapes and sizes, and sometimes even droplet splashing occurs, and spherical particles appear. There are a large number of α-Fe and SmFe ₃ phases, and the magnetic energy product is small.

Table 1, embodiment and comparative example contrast

Example 2:

The conical fast-setting thin strip method adopted in embodiment 2, the difference of other parameters in embodiment 1 is that the rotational speed of the roller is 16 m/s. A thin strip of Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 with a thickness of 9-12 microns and a surface roughness of less than 0.22 μm was obtained. There was no splashing during the process, and there was no α-Fe soft magnetic phase in the alloy. After grinding, Nitriding forms Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 N _x , and after being made into a bonded magnet, the magnetic properties are B _r =1.07T, (BH) _max =23.2MGOe. Comparing Example 1 and Example 2, the rotating speed of the roller decreases, the thickness of the strip increases slightly, and the magnetic energy product of the bonded magnet decreases slightly.

For comparative example 2, the roll-type quick-setting thin-belt method was adopted, and other parameters were as in embodiment 2. Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 thin strip fast-setting flakes, although there is no melt splashing phenomenon, the thickness of the obtained fast-setting flakes is 30-50 microns, and the XRD diffraction peak of the α-Fe phase is relatively high. , Nitrided, and bonded Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 N _x magnets have a small magnetic energy product.

Table 1, embodiment and comparative example contrast

Claims (1)

1. a preparation method for fast quenching amorphous alloy ribbon, comprise batching, melting, secondary smelting, spray band, collect, its chemical composition mass percent is: 21.57%Sm, 72.84%Fe, 1.66%Zr, 3.93%Co;

Use 99.5% samarium metal, ingot iron, metallic cobalt, metal zirconium are raw material, adopt the melting of intermediate frequency vacuum induction melting furnace, first vacuumize before melting at vacuum cavity, then adopt high-purity argon gas to be protective gas, avoid alloy oxidation; Smelting temperature is 1600 DEG C; Secondary fusion in inductionization ladle, sets up spray band pressure in nozzle bag, and spray band pressure is 0.10Mpa; Protective atmosphere pressure is 0.05Mpa;

Internal roller type running roller is prepared into, the logical circulating water in internal roller type running roller inside with molybdenum; Internal roller type running roller internal diameter is 400mm, and internal roller type running roller edge line speed is 24m/s; Internal roller type running roller finish turning in place, ensures roll surface roughness Ra <0.2 μm;

Nozzle bore 0.5mm, nozzle near internal roller type running roller edge, from internal roller type running roller edge 20mm;

Molten metal cools after being ejected into internal roller type running roller inner surface fast, forms fast solidifying strip, adds strip gas nozzle at internal roller type running roller end, by air-flow, internal roller type roller surface amorphous ribbon is peeled away, nitrogen gas nozzle diameter is 2mm, and air pressure is 0.5Mpa, collects after the amorphous band that comes off;

Obtaining thickness is 8 ~ 9 microns of uniform strips, the Sm that surface roughness is less than 0.24 μm _1.0zr _0.3fe _8.1co _0.6, not there is splash phenomena in process, not occurring α-Fe soft magnetism phase in alloy in fast solidifying strip, forms Sm through grinding, nitrogenize _1.0zr _0.3fe _8.1co _0.6n _x, after making bonded permanent magnet, magnetic property is B _r=1.09T, (BH) _max=23.8MGOe.