RU2625511C2 - Method of production of nanocrystal powder material for manufacture of wild-strip composite material - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method includes grinding an amorphous tape of magnetic-soft alloy in a hammer mill to particles of 3-5 mm and then grinding in a high speed disintegrator. Heat treatment of the particles obtained after grinding in the hammer mill is carried out with the provision of removing the quenching stresses. Grinding in the disintegrator is conducted to obtain a powder of 100-200 microns. From the obtained powder, 30 wt % of the powder is screened to make the first layer of the composite. The remaining powder of 100-200 mcm is heat-treated to form nanocrystal pre-precipitates, followed by grinding in a disintegrator to obtain a powder of 50-100 mcm. The 50 wt % of the obtained powder is screened to make the second layer of the composite. Heat treatment of the remaining 50-100 mm powder with the formation of a nanocrystal structure is performed, after which it is milled in a disintegrator and screened to obtain a powder of 1-50 mcm to produce the third composite layer.

EFFECT: it is possible to obtain three fractions of the powder in one process cycle and increase the efficiency of grinding.

2 cl, 1 dwg, 1 tbl, 2 ex

Description

The invention relates to powder metallurgy, and in particular to methods for producing powders intended for the manufacture of composite radar absorbing materials efficiently operating in the frequency range from 10 MHz to 40 GHz. The invention can be used in various fields of electronic technology, in particular for improving the electromagnetic compatibility of devices, for protecting biological objects from electromagnetic radiation, for improving the radiation patterns of antennas.

With the modern development and operation of microwave radio systems, electromagnetic safety problems arise. Long-term and regular exposure to microwave radiation to the human body negatively affects the brain, blood vessels, eyesight, and provokes the formation of tumors [III International Conference "Man and Electromagnetic Fields" (Sarov, May 24-27, 2010): collection of reports / Russian Federal Nuclear Center - All-Russian Scientific Research. Institute of Experimental Physics; [editorial: Lobkaeva EP and etc.]. - Sarov: RFNC-VNIIEF, 2010. - 470 p.]. That is why it is so important to comply with the established requirements of sanitary-hygienic safety standards so that such equipment does not harm human health [GN 2.1.8./2.2.4.019-94, SanPiN 2.2.4./2.1.8.055-96, GOST 12.1.006- 84]. No less important for the effective functioning of microwave technical devices is the problem of eliminating interference, including for trouble-free operation of electronic systems. In many cases, the fields created by microwave energy emitters need to be localized to some extent in order to eliminate or weaken their effect on neighboring sensitive elements of the radio equipment [Directive 2004/108 / EC]. Spurious reflections and EMF interference can also be serious sources of spurious signals and interference. [Electronic compatibility of electronic equipment: textbook. allowance / N.A. Malkov, A.P. Pudovkin. - Tambov: Publishing house of Tamb. state tech. University, 2007. - 88 p.]

An effective method that allows you to meet the requirements of electromagnetic ecology, to reduce to an acceptable level natural and artificial noise during the operation of electronic systems, is based on the use of shielding and radio-absorbing materials [Electromagnetic radiation. Methods and means of protection / V.L. Bogush, T.V. Borbotko, A.V., Gusinsky and others; Ed. L.M. Lynkova. - Mn .: Bestprint, 2003 .-- 406 p. ill .: 173].

Traditionally, composites based on alsifer, permalloy, ferrite, and also amorphous alloys of the Fe-Ni-Co system are used as radar absorbing materials. However, they do not meet modern requirements for the range of operating frequencies and operational efficiency. Practice shows that the most promising for creating effective broadband systems of electromagnetic protection are radar absorbing materials based on nanocrystalline soft magnetic powders of iron alloys [Glezer A.M., Shurygina N.A. Amorphous-crystalline alloys. - M .: FIZMATLIT, 2013. - 452 p.]. The metal composition is introduced into the dielectric matrix and thereby provides the absorption effect of the incident electromagnetic wave. The range of operating frequencies of such radar absorbing materials along with magnetic properties is decisively determined by the fractional composition of the magnetic powder. Therefore, the optimal technical solution to this problem is the creation of multilayer radar absorbing composites in which each layer is reinforced with particles of the same fractional composition and provides effective absorption in a relatively narrow frequency range, and the multilayer composition provides an integrated broadband effect. According to [K.M. Limetal. / Journal of Non-Crystalline Solids 351 (2005) 75-83] to create multilayer composites for work in the most feasible range of mega- and gigahertz frequencies, fractions from 1 to 200 microns should be used. Calculations show that for these frequency ranges, it is optimal to use three groups of the fractional composition of the powder (1-50 microns, 50-100 microns, 100-200 microns), layer-by-layer introduced into the dielectric matrix.

Ensuring the required high magnetic properties of the radar absorbing composite can be achieved through the use of powder obtained by grinding rapidly quenched (up to a million degrees per second) amorphous tape [Kuznetsov P.A. Creation of effective electromagnetic protection systems based on soft magnetic amorphous and nanocrystalline Co and Fe alloys: Dis. ... cand. tech. Sciences: 05.02.01 / FGUP TSNII KM "Prometey". - St. Petersburg, 2005]. At the same time, traditional processing methods (mills, attritors, etc.) of an amorphous tape, which, as a rule, have high hardness, do not allow one to controllably obtain the required powder fraction and do not exclude powder contamination due to grinding of rubbing working elements of the equipment.

The most effective method of processing an amorphous tape is shock disintegration processing (UDD), grinding the original amorphous tape at collision speeds of oncoming flows of the processed material in excess of ten sound speeds. However, even with such an intense exposure, it is not possible to obtain a fine fraction (less than 100 microns) with a cost-effective yield (at least 80 wt.%) From a “raw” especially hard tape.

Several methods are known for processing an amorphous ribbon in order to obtain a fine powder of a fine fraction from it. The most effective tool of influence, as practice has shown, is the thermal treatment of an amorphous tape, leading to its embrittlement due to nanocrystalline precipitates. Several analogues of such a technical solution are known, the unifying feature of which is the choice of a narrow temperature range to obtain a given narrow range of powder fractional composition, which does not cover the entire range of modern requirements.

So, in accordance with RF patent No. 2530076, to obtain a powder with a size of 15-35 microns, heat treatment of the initial amorphous tape at temperatures (0.35-0.37) T of the _{liquidus of the} alloy used is necessary. After heat treatment, grinding is carried out in a high-speed disintegrator. The specified obtained fraction (15-35 microns) operates in the resonant mode and does not provide the possibility of creating wideband electromagnetic protection systems in the entire operating frequency range (from 10 MHz to 40 GHz).

There is another method for grinding amorphous material (RF patent No. 2397024), in which a starting powder of a fraction of 80 μm is used and after heat treatment at temperatures (0.4-0.6) T of _liquidus , intensive processing is carried out in a desizer at rotor speeds of 410 m / s and a particle collision frequency of 5000-8000 bpm. This results in a nanoscale powder fraction from 3 to 100 nm, depending on the chemical composition. Such a powder is effectively used as catalysts, sorbents and activators, but it is unsuitable for creating electromagnetic protection systems.

The closest to the achieved effect to the proposed method is a method for producing nanocrystalline powder according to the patent of the Russian Federation No. 2427451 (prototype). A feature of this method is a two-stage heat treatment of an amorphous tape. Initially, the initial tape is heat treated at a temperature (0.25-0.29) T of the _{liquidus of the} alloy, after which it is crushed to a fraction of 3-5 mm. Then, the obtained particles are heat treated at a temperature (0.3-0.4) T of _liquidus to form nanocrystalline precipitates and processed in a high-speed desiterator to a fraction of 20-60 microns.

Thus, the known technical solutions make it possible to obtain nanocrystalline powders from soft magnetic alloys in the range from 15 to 60 μm, which makes it possible to obtain radar absorbing composites in the operating frequency range from 4 to 14 GHz, but do not cover the entire spectrum of the currently required operating frequencies (from 10 MHz to 40 GHz) to provide effective protection against electromagnetic radiation of technical means and biological objects. It should be emphasized that the known methods do not allow to obtain the predominant fraction with a yield of more than 40 wt.% In one cycle, which significantly increases the cost of the powder used for radio composites and makes it unprofitable in mass production.

The technical result of the invention is a method for manufacturing a powder, which allows to gradually obtain a powder material of predetermined sub-ranges of fractional composition - from 1 to 50 μm, from 50 to 100 μm, from 100 to 200 μm - by varying the heat treatment modes. With the proposed manufacturing method, the yield of the fraction is at least 80 wt.%.

To create a controlled method of heat treatment, the softening mechanisms of an amorphous tape were studied in detail, which allowed us to reasonably relate the structure obtained during heat treatment with the fractional composition of the powder after high-speed disintegration processing and to realize this effect in practice.

A feature of the proposed method is the implementation of sequential interconnected technological operations of heat treatment, in which each operation provides a given sub-range of the powder fraction, and the implementation of the full technological cycle leads to the receipt of the entire required range of fractional composition by creating a specific nanocrystalline structure in an amorphous matrix.

At the first stage, the initial amorphous tape in the delivery state (“raw”, standard thickness 20-30 microns and width 20 mm) undergoes preliminary grinding on a hammer mill to a particle size of 3-5 mm. This obtained particle size is limited by the diameter of the receiving cone of standard disintegrator plants, which are used for the subsequent processing stages.

At the second stage, obtaining the largest required fractional subrange of 100-200 μm is achieved by low-temperature annealing of particles crushed to 3-5 mm at temperatures (0.1-0.15) T of _liquidus alloy. It was experimentally established that at these temperatures and an isothermal exposure of 0.5-1.0 h, the residual quenching stresses occurring in the amorphous tape during its production during ultra-high-speed melt quenching (cooling rate up to several million degrees per second) are removed. The removal of quenching stresses embrittle the tape, but does not lead to the formation of nanocrystalline precipitates in the amorphous matrix. The embrittled tape is easily crushed in standard disintegrators to a particle size of 100-200 microns with a yield of 80-90 wt.%. The share of other fractions is insignificant and their practical use is inappropriate. From the batch of powder thus treated, the required volume is selected to create one layer of the radio composite (as a rule, 1/3 is selected).

In the third stage, the remaining 2/3 of the volume is subjected to heat treatment. Obtaining finer fractions with a cost-effective yield is achieved by controlled release of nanocrystalline phases in an amorphous matrix. The achievement of this result is based on our study on the effect of heat treatment on the structure of amorphous particles of a fraction of 100-200 μm obtained as a result of low-temperature annealing. According to our studies at temperatures (0.25–0.29) T _liquidus , the effect of nanocrystalline precipitates according to a homogeneous mechanism with the formation of Guinier-Preston zones is observed [Hono K., Ping DH Atom probe studies of nanocrystallization of amorphous alloys / Materials Characterization 44: 203 -217 (2000)], which form a kind of “grid”, along the perimeter of which (on average, the mesh size of the “weak points” of the grid is 50-100 microns) during further UDD processing, the tape is crushed. Isothermal exposure at the indicated temperatures for 100-120 min ensures after processing in the disintegrator the yield of suitable powder of a fraction of 50-100 microns is not less than 80 wt.%. The fraction of the smaller fraction of the required sub-range (1-50 μm) is very insignificant and is not of practical interest.

Of the total volume, half is selected from which the second layer of the radio composite is made. After this, the fourth, final stage of heat treatment of the remaining volume of powder is performed. Heat treatment is performed at temperatures (0.42-0.45) T of _liquidus with prolonged isothermal exposure (150-180 min) until the formation of the so-called “subnetwork” in each particle in the form of closed chains of nanocrystals of at least 40 nm in size is completed the boundaries of which are crushed to the smallest required fraction from 1 to 50 microns.

It should be specially noted that the isothermal exposure time used in the above analogues does not exceed 90 minutes, which, as tests have shown, does not lead to the full implementation of structural processes. Only an increase in the time of isothermal exposure to 150-180 minutes allows you to effectively complete the structural changes that are characteristic of the selected heat treatment temperature.

For example, our comprehensive studies of powder materials from Fe-based alloys (for Finemet type Fe-Cu-Nb-Si-B alloys) after appropriate heat treatment and crushing to a fraction of 50-100 μm showed that subsequent heating of the powder to temperatures (0 , 42-0.45) Т _liquidus and isothermal exposure for 150-180 minutes leads to the formation of nanocrystals of the type Fe ₃ Si and α- (Fe, Si) by a heterogeneous mechanism (the nuclei of these nanocrystallites are formed on the pre-precipitations of copper, which were formed during annealing at temperatures (0.25-0.29) T to _{liquid ca} ; in this case, nanocrystallites also form a “subnet” with an average size of coherent scattering regions several orders of magnitude smaller than the grid formed by copper pre-precipitates, for example, for magnetically soft iron-based alloys with an average size of coherent scattering regions of 11–20 nm. A “mesh” (similar to grain boundaries in steels) is usually 1-50 microns in size. With subsequent disintegrator grinding, the particles to be treated are destroyed by the size of the “mesh”.

Isothermal exposure at this stage of processing for 150-180 min provides a suitable powder yield of a fraction of 1-50 μm of at least 80 wt.%.

Thus, the developed scheme of sequential processing of amorphous tape for the controlled production of three subbands of fractional composition (100-200, 50-100, 1-50 μm) with a cost-effective yield of powder is the base one and provides the creation of multilayer broadband radar absorbing composites. Moreover, this scheme can be effectively implemented only subject to the established sequence of operations. The exclusion of one of the stages of the developed interconnected sequential cycle leads to a loss of controllability of the process of obtaining the required set of fractional composition of powders with a high economically viable yield.

The yield of powder of a given fraction by the proposed method is at least 80 wt.%.

The proposed method for the manufacture of powder can be illustrated by the following diagram of interrelated sequential stages of processing the material (see drawing):

The technical effect of the proposed method is the creation of a three-layer broadband radar absorbing composite material based on a powder filler of various fractions.

The technical and economic effect of the proposed method for producing powder is the absence of production waste, the possibility of reusing the powder for grinding to the desired fraction size. The economic effect is to increase the yield of expensive powder.

Example 1

An amorphous Fe – Cu – Nb – Si – B system alloy strip was selected as a starting material for obtaining a soft magnetic powder. The width of the amorphous tape is 20 mm, the thickness is 20 microns. The experimental batch was 5 kg.

At the first stage, the “raw” tape was crushed in an MD 3 × 2 hammer mill to particles with a size of 3-5 mm, which is necessary for further redistribution of the tape in a disintegrator.

At the second stage, the tape particles were heat treated at a temperature of 0.1T _liquidus for 30 minutes.

Then, the obtained particles of the tape were ground in a high-speed disintegrator DEZI-15, after grinding, the powder fraction from 100 to 200 μm was sieved, which amounted to 90 wt.% Of the initial volume of the processed material. 30 wt.% Of the screened powder from this volume (1.35 kg) went to the manufacture of the first layer of the radar absorbing composite.

In the third stage, the rest of the powder (3.65 kg) was heat treated at a temperature of 0.25T _liquidus for 100 minutes. Next, disintegration grinding was carried out. The powder fraction of 50-100 μm, 50 wt.%) (1.63 kg) of the total amount obtained was screened out and went to the manufacture of the second layer of the radar absorbing composite.

In the fourth stage, the remaining powder (2.02 kg) was heat-treated at a temperature of 0.42T _liquidus for 150 minutes and ground in a disintegrator. After grinding, a powder of a fraction of 1-50 μm (1.62 kg) was sifted out and a third layer of a radio-absorbing composite was made from it.

Then, all three layers were consolidated into a multilayer composite radar absorbing material.

Example 2

An amorphous Fe – Cu – Nb – Si – B system alloy strip was selected as a starting material for obtaining a soft magnetic powder. The width of the amorphous tape is 20 mm, the thickness is 20 microns. The experimental batch was 5 kg.

At the first stage, the “raw” tape was crushed in an MD 3 × 2 hammer mill to particles with a size of 3-5 mm, which is necessary for further redistribution of the tape in a disintegrator.

At the second stage, the tape particles were heat treated at a temperature of 0.15T _liquidus for 60 minutes.

Then, the obtained tape particles were crushed in a high-speed desi-15 disintegrator; after grinding, the powder fraction from 100 to 200 μm was sieved, which amounted to 97 wt.% Of the initial volume of the processed material. 30 wt.% Of the screened powder from this volume (1.455 kg) went to the manufacture of the first layer of the radar absorbing composite.

In the third stage, the rest of the powder (3,545 kg) was heat-treated at a temperature of 0.29T _liquidus for 120 minutes. Next, disintegration grinding was carried out. The powder fraction of 50-100 microns was weeded out, 50 wt.% (1.72 kg) of the total amount received went to the manufacture of the second layer of the radar absorbing composite.

In the fourth stage, the remaining powder (1.825 kg) was heat-treated at a temperature of 0.45T _liquidus for 180 minutes and ground in a disintegrator. After grinding, a powder of a fraction of 1-50 μm (1.65 kg) was sieved and a third layer of a radar absorbing composite was made from it.

Then, all three layers were consolidated into a multilayer composite radar absorbing material.

The results of screening for fractions are presented in table. one.

In the table. 1 shows a significant advantage of the proposed technical solution compared with the prototype.

Claims (2)

1. A method of producing a nanocrystalline soft magnetic powder material for the manufacture of a broadband radar absorbing composite, comprising grinding an amorphous tape from a soft magnetic alloy on a hammer mill to particles of 3-5 mm, grinding the resulting particles in a high-speed disintegrator, characterized in that they are heat treated after grinding on a hammer crusher particles at a temperature of (0.1-0.15) T _liquidus for 30-60 minutes to ensure removal of the quenching stresses grinding in high a high-speed disintegrator is carried out to obtain a powder with particles of 100-200 μm in size, while from the powder obtained in the disintegrator, 30 wt.% of the powder is sieved to produce the first layer of the composite, after which the remaining powder is heated with particles of 100-200 μm in size at a temperature ( 0,25-0,29) T _liquidus for 100-120 minutes to form nanocrystalline predvydeleny followed by grinding in a disintegrator to produce a powder with a particle size of 50-100 microns, screened 50 wt.% of the obtained powder to manufacture WTO th composite layer are heat treating the remaining powder with particle size of 50-100 mm at a temperature of (0,42-0,45) T _liquidus for 150-180 minutes ensuring the formation of a nanocrystalline structure, after which it was milled and screened in a disintegrator with obtaining a powder with particles of 1-50 microns in size for the manufacture of the third layer of the composite. 2. The method according to p. 1, characterized in that the powder yield of these fractions is at least 80%.

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