Amorphous and nanocrystalline soft magnetic materials

Properties of nanocrystalline ribbons

(after corresponding thermomagnetic treatment)

Properties of amorphous ribbons based on cobalt

(after corresponding thermomagnetic treatment)

Properties of amorphous ribbons based on iron-nickel

(after thermomagnetic treatment in a transverse field)

Properties of amorphous ribbons based on iron and iron-cobalt

(after thermomagnetic treatment in a transverse field)

List of metal alloyes of PC "MSTATOR"

AMAG alloys ("MSTATOR") have similar properties to materials:

Regardless of the application, when using amorphous and nanocrystalline cores in the design of inductive components, the following advantages are usually provided:

•      Reduced weight;
•      Reduced copper losses due to fewer turns;
•      Extended temperature range from -60 to 125 ºС;
•      Increased stability of properties and reliability;
•      High precision for measuring devices;
•      Improving the efficiency of the device.

Comparative characteristics of amorphous and nanocrystalline soft magnetic materials relative to traditional ones

The rapid development of modern electronics has led to the emergence of new soft magnetic materials that are widely used in matching, high-frequency and power transformers, transformer current sensors, EMI filters, measuring equipment, data transmission systems (Ethernet), etc.

The most demanded areas of application of AMAG ribbons

Cores

Advantages in a number of characteristics compared to traditionally used ferrites, electrical steel and permalloy.

Acoustomagnetic and electromagnetic labels

The detection rate of the label (transponder) is up to 90-95%. Attempts to deceive the anti-theft system are doomed to failure.

Magnetic shield

High efficiency of shielding due to the special electromagnetic properties of the material and low sensitivity to mechanical damage.

Currently, amorphous and nanocrystalline soft magnetic materials are used in various industries:

•     In telecommunication systems. Transformers and chokes ISDN, DSL, PLC.
•     In the electrical industry, replacing conventional transformer steel with an amorphous alloy provides energy savings in eddy currents.
•     In residual current devices (RCDs), controlled by differential current, designed to protect people from electric shock, including when using household electrical equipment. High permeability provides good sensitivity, low response threshold and good accuracy.
•     In solar generators.
•     In highly efficient electromagnetic shields. Low-temperature annealing makes it possible to obtain high magnetic permeability while maintaining high plasticity of the tape. They are used for shielding special rooms with sensitive equipment, shielding sensitive units of equipment, shielding cables (cables are wrapped with tape), etc.
•     In electrical engineering - current transformers, electronic electricity meters. The use of nanocrystalline materials in current transformers increases the measurement accuracy, eliminates dependence on the shape and symmetry of the load current, and provides an accuracy class of 0.2.
•     In EMC / EMI filters for switched power supplies (SMPS) and inverter drives. They have a higher interference suppression ratio in a wide frequency range.
•     In switching power supplies, inverters, in AC / DC and DC / DC converters. The new materials provide high reliability, high efficiency, small dimensions and weight, and low noise level.
•     In chokes of magnetic amplifiers. Small size, low control current, low loss.
•     In high frequency power transformers and chokes. Low losses and high operating temperatures allow for size reduction.
•     In power factor corrector chokes. Low losses and small dimensions.
•     In modern power sources for electric welding. Low weight of devices, wide temperature range, the ability to work with a stable constant current. Ease of mode regulation, versatility.
•     In battery chargers. Small dimensions, automatic shutdown, work according to the optimal program, multi-channel chargers.
•     In industrial ballasts. Reliability, low weight, tough operating conditions.
•     In audio and video equipment for the manufacture of magnetic heads for high-frequency high-density recording
•     In tube amplifiers of Hi-End audio equipment for the manufacture of output audio transformers.
•     The high radiation and corrosion resistance of amorphous materials allows them to be used as amorphous copper-based brazing alloys for joining units of nuclear and thermonuclear reactors in nuclear technology.
•     In sensors of anti-theft devices of electromagnetic and acoustomagnetic types.
•     The high resistivity of amorphous materials allows them to be used as resistive elements in efficient low-temperature (infrared) tape heaters with a surface utilization rate of up to 95%. They are used in cars (heating of seats, heating of fuel lines, batteries), in construction (underfloor heating, ceilings, new heating systems), in agriculture (local heating of premises in animal husbandry, heating of hives, greenhouses, incubators, etc.).
•     In absorbers of short voltage / current surges (interference suppression magnetic circuits). They are put on the leads of the components. Eliminate the cause of interference by changing the switching behavior.
•     Automotive applications: power supplies, flexible magnetic antennas, interference suppression chokes, etc.

Amorphous soft magnetic alloys

Amorphous alloys are a new special class of precision alloys that differ from crystalline alloys in structure, manufacturing method, region of existence on the temperature-time diagram and properties.

In the 60s, experiments on the rapid cooling of metal melts, which were carried out in order to obtain a submicroscopic metal structure, found that in some cases the crystal lattice in the metal is completely absent, and the arrangement of atoms is characteristic of a structureless, amorphous body. The structure of amorphous alloys is similar to the structure of a frozen liquid and is characterized by the absence of long-range order in the arrangement of atoms. It turned out that the amorphous metal has completely different, not similar properties to the crystalline metal. It becomes several times stronger, its resistance to corrosion increases, its electromagnetic characteristics change, and even one of the most stable constants - the modulus of elasticity. Unlike alloys with a crystalline structure, the production technology of which has serious problems associated with the antagonism of the properties of the components at the crystallization stage, in amorphous alloys all the necessary components are perfectly combined and coexist. With ultrafast cooling, the alloy solidifies before the antagonist components have time to show their antagonism. This opens up the broadest possibilities of finding the optimal combinations of components to obtain specific properties. Amorphous alloys are called metallic glasses. Interest in them is growing rapidly.

First of all, researchers were interested in the ferromagnetic properties of alloys based on iron, nickel and cobalt. The soft magnetic properties of metal glasses generally turned out to be better than the properties of permalloy, moreover, these properties are more stable. The amorphous state of the alloys is achieved by selecting the chemical composition and using a special technology for cooling from the melt at a rate higher than the critical one determined for each composition. The absence of dislocations leads to the fact that metal glasses are superior in strength to the best alloyed steels. Their high hardness results in excellent wear resistance. Another major advantage of amorphous metal alloys is their extremely high corrosion resistance. In many highly corrosive environments (sea water, acids), metal glasses do not corrode at all. For example, the corrosion rate of an amorphous alloy containing iron, nickel and chromium in a hydrochloric acid solution is practically zero. Apparently, the main reason for such a high corrosion resistance of amorphous alloys is that, having no crystal lattice, they are devoid of characteristic crystal "defects" - dislocations and, most importantly, grain boundaries. The high packing density of atoms in the crystal near these "defects" decreases so sharply that along them "enemy agents" can easily penetrate into the metal. It is important that the defect-free structure of the amorphous alloy is imparted to that thin oxide film that forms on its surface at the initial stages of the corrosion process and further protects the metal from direct contact with the "aggressor". The specificity of the technologies allows the production of amorphous alloys in the form of ribbons less than 40 microns thick.

For the manufacture of amorphous alloys in the form of strips, a cooling method is usually used, in which a jet of liquid metal is directed at a certain speed onto the surface of a rapidly rotating cylinder made of a material with high thermal conductivity. A microwire with an amorphous structure is made by melting a metal enclosed in a glass tube with a conical bottom by high-frequency currents, drawing out and cooling a thin capillary filled with metal. When heated, amorphous alloys transform into a crystalline state. For the stable operation of products made of amorphous alloys, it is necessary that their temperature does not exceed the maximum operating temperature for each alloy (T work max). Currently, the most widespread are soft magnetic amorphous alloys, which combine high magnetic and mechanical properties. Soft magnetic amorphous alloys - ferromagnetic alloys with a narrow hysteresis loop. A feature of soft magnetic amorphous alloys in comparison with crystalline ones is a large (about 20%) content of nonmagnetic elements, such as boron, silicon, carbon, phosphorus, etc., necessary to preserve the amorphous structure. The presence of these elements reduces the maximum saturation induction in amorphous alloys in comparison with crystalline ones and increases the temperature coefficient of magnetic properties. The same elements increase the electrical resistance, increase the hardness and strength of amorphous alloys, as well as their corrosion resistance. Since the beginning of the eighties, amorphous materials have been widely used in radio and electrical products, which are used instead of permalloy, ferrites, electrical steels, and magnetodielectrics.

Nanocrystalline magnetic alloys

The second representative of a new class of metastable fast-cooled alloys and an active rival of amorphous alloys are nanocrystalline alloys. Their feature is an ultrafine crystalline structure. The size of crystals (nanoparticles) in these alloys ranges from 1 to 10 nm. Nanocrystalline and amorphous alloys are the closest relatives. Their "relationship" is based on two circumstances. The first is structural similarity. As is known, the structure of amorphous alloys has a short-range order, i.e., it consists of ordered microgroups of atoms, the sizes of which are close to the sizes of nanograins of nanocrystalline alloys. Secondly, it is the production technology. Currently, the most widespread method for obtaining a nanostructure is controlled crystallization from the initial amorphous state.

Thus, the amorphous alloy is the "parent" base of the nanocrystalline alloy.

The structure of a nanocrystalline alloy is a two-phase system, one of the phases of which are nanocrystals, and the other is a residual amorphous matrix. The properties of a nanoalloy depend on the composition, size, and amount of nanocrystals, as well as their relationship to the amorphous phase. Silicon and iron are the basis of economical raw materials. Having a high saturation induction (1.2 T), good temperature stability in a wide temperature range from -60 to +180 ° C, the new nanocrystalline material has excellent characteristics in the high-frequency region at the level of amorphous cobalt-based alloys. Moreover, the new alloy is much more economical.

Precise control of the parameters of annealing of toroids wound from a ribbon allows one to regulate the required material properties (for example, the shape of the hysteresis loop, the level of magnetic permeability, the squareness coefficient, and specific losses) over a wide range. At the same time, good quality at an affordable price is becoming an increasingly important indicator of the competitiveness of nanocrystalline material in comparison with ferrites and permalloy.