With the continuous advancement of electronic technology and the progress of active components, the size and weight of electronic products have been significantly reduced, driving electronic components—including electronic transformers—toward lighter, thinner, and smaller designs. The manufacturing processes for electronic transformers are now undergoing a profound transformation. It is an inevitable trend for electronic transformers to evolve toward higher frequencies, lower losses, lighter weights, and smaller sizes. As the core component of electronic transformers, soft magnetic cores will play a pivotal role in this transformative shift. Therefore, promoting the widespread use of amorphous and nanocrystalline soft magnetic alloy materials—with high saturation magnetization, high initial permeability, and low losses at high frequencies—as magnetic cores for electronic transformers will greatly facilitate the miniaturization of these transformers and meet the growing demands of the electronics industry.

Currently, with the advancement of nanotechnology and rapid quenching techniques, a variety of new nanomaterials—such as nanocrystalline powders, nanofilm materials, and nanoparticle film materials—are continuously being developed. Once these novel nanomaterials are industrialized, they will greatly accelerate the development of electronic transformers toward higher frequencies, miniaturization, and surface-mount technology.

Production and Properties of Amorphous and Nanocrystalline Soft Magnetic Alloy Materials

Amorphous alloys are a new type of alloy material that emerged in the 1970s. They are produced by employing an internationally advanced ultra-rapid quenching technique, which cools liquid metal at a cooling rate of 1 × 10⁶ °C per second directly into solid ribbons with thicknesses ranging from 0.02 mm to 0.04 mm. This process results in an amorphous alloy microstructure characterized by short-range order and long-range disorder in atomic arrangement—a structure that lacks the crystalline lattice typical of conventional metallic materials. Consequently, amorphous alloys exhibit unique properties that differ from those of traditional materials, including excellent soft magnetic properties, corrosion resistance, wear resistance, high hardness, high strength, and high electrical resistivity. Due to their outstanding performance and simple manufacturing process, amorphous alloys have become a focus of research, development, and application in both domestic and international materials science communities since the 1980s. Not only have they been used to develop soft magnetic materials for the electronics industry, but also other alloy materials with diverse applications, such as brazing materials, catalysts, and structural materials. In the late 1980s, materials scientists further developed nanocrystalline soft magnetic alloys based on the amorphous structure, which display even superior soft magnetic properties. Currently, the family of amorphous-nanocrystalline soft magnetic alloys mainly comprises four major categories: iron-based amorphous alloys, iron-nickel-based amorphous alloys, cobalt-based amorphous alloys, and iron-based nanocrystalline alloys.

Amorphous and nanocrystalline alloy materials, when used as magnetic cores for electronic transformers, can effectively facilitate miniaturization and offer distinct advantages over traditional soft magnetic materials. Cold-rolled silicon steel boasts a high saturation magnetization; however, due to its low effective permeability and high high-frequency losses, it cannot operate at frequencies reaching the kHz range. Even when using thinner silicon steel sheets, the loss levels still fail to match those of iron-based amorphous alloys. Ferrite materials are inexpensive, but their Curie temperature is low—above 100°C, their saturation magnetization already drops significantly, thus limiting their operating temperature. Moreover, their saturation magnetization is below 0.5 T, necessitating larger volumes when manufacturing high-power magnetic cores. As for permalloy, although its magnetic properties are excellent and comparable to those of amorphous and nanocrystalline materials, it contains more than 50% nickel, resulting in high costs and complex processing techniques. Consequently, obtaining thin strips suitable for high-frequency applications is extremely expensive. The performance-to-price ratio of these two materials is simply incomparable.

Currently, domestic enterprises are constrained by the limitations of equipment and technology used in the manufacturing of amorphous and nanocrystalline alloy materials. These alloy ribbons still face challenges related to stamping, shearing processes, and pricing. However, with the advancement of rapid quenching technology, the expanding application of these products, and efforts through technology introduction and technological upgrades, these issues will be resolved in the not-too-distant future.

Application of Amorphous and Nanocrystalline Alloy Materials in Electronic Transformers

Generally speaking, the primary requirements for core materials used in electronic transformers are as follows: (1) high saturation magnetic flux density; (2) as low high-frequency losses as possible; (3) high initial permeability; (4) high Curie temperature and excellent thermal stability; (5) good environmental stability and insensitivity to mechanical stress; (6) for certain applications, such as pulse transformers, a high rectangularity ratio or low remanence (Br) is also required. Due to factors such as their thin ribbon thickness and resistivity, amorphous and nanocrystalline soft magnetic alloys can meet these performance requirements within the frequency range of 50 kHz to 1 MHz (typically below several hundred kilohertz). As a result, the development and application of amorphous and nanocrystalline alloys in this frequency band have become remarkably active. A wide variety of core components have been developed using these materials and are extensively employed in the power industry, the electronics industry, and the field of power electronic devices—for instance, as transformers, reactors, filters, and EMI suppression components in current transformers, switch-mode power supplies, inverter power supplies, and programmable exchange power supplies.

I believe that there are still opportunities for wider market adoption in the following areas:

(1) As a substitute for thinner silicon steel products, market demand data from the Shanghai Institute of Steel Research indicate that thinner silicon steel (thickness < 0.1 mm) was extensively used in the 1970s for various electronic components operating at frequencies above 400 Hz, such as high-frequency transformers, reactors, and magnetic shields. Currently, there is significant market demand in this area; however, suppliers are struggling to meet the demand. Replacing these silicon steel products with amorphous and nanocrystalline alloy materials not only enhances product performance and quality and facilitates miniaturization but also offers attractive pricing advantages.

(2) High-permeability and high-power magnetic core components—due to limitations in domestic ferrite production equipment and technological conditions—have made it difficult for high-permeability, high-performance, and high-power ferrites to meet domestic market demands. If amorphous and nanocrystalline materials are used instead, this could facilitate the localization and miniaturization of certain electronic devices.

(3) For certain electronic products used in harsh environments with high operating temperatures and adverse conditions—such as those employed in oilfield drilling and marine exploration—various magnetic components can be fabricated using amorphous and nanocrystalline alloy materials. This approach ensures optimal material utilization and eliminates the challenges associated with material selection.

(4) Various magnetic components used in military products such as aviation and aerospace equipment need to be small and lightweight, exhibit excellent temperature stability, and meet stringent magnetic performance requirements. Using amorphous nanocrystalline alloy materials is far superior to other soft magnetic materials in this regard.

(5) The miniaturization of high-frequency, high-current, high-power power transformers, reactors, filters, and other components is currently largely achieved using ferrite or cold-rolled silicon steel, with operating frequencies f ranging from 20 kHz and magnetic flux densities B ranging from 0.2 T to 0.3 T. However, by adopting amorphous and nanocrystalline alloy cores, the operating frequency can be increased to 40 kHz to 50 kHz, while the magnetic flux density B can be raised to 0.5 T to 0.6 T. This approach can significantly reduce the volume and size of magnetic-core components.

(6) Various EMI-resistant components.

Several Issues Worth Noting in the Application of Amorphous and Nanocrystalline Alloys

Although amorphous and nanocrystalline alloys have been used in China for nearly 20 years, many users still harbor some doubts about the application of these materials. I believe it is necessary to clarify this point.

Ageing Stability of Amorphous Nanocrystalline Alloys Amorphous alloys are formed by rapid quenching of liquid metals and exist in a thermodynamically metastable state, with a tendency to transform into the crystalline phase. Once severe crystallization occurs, the alloy’s magnetic properties will be lost entirely. Consequently, some people have expressed concern that the magnetic cores made from amorphous nanocrystalline alloys might experience performance degradation due to ageing during service. However, this concern is actually unwarranted. On the one hand, crystallization typically occurs at temperatures above the amorphous-to-crystalline transition temperature (>350℃), whereas in practical applications, the operating temperatures of electronic devices rarely exceed 200℃. On the other hand, before being put into use, amorphous nanocrystalline alloy cores undergo annealing treatments at 300℃ for more than one hour, resulting in a highly stable microstructure. Moreover, the over 20-year track record of such cores both domestically and internationally demonstrates that they do not suffer from ageing-induced performance changes.

Temperature Stability of Amorphous Nanocrystalline Alloys The Curie temperature of amorphous nanocrystalline alloys ranges from 300°C to 560°C, significantly higher than that of soft magnetic materials such as ferrites. Practical temperature tests conducted on military and defense products have also shown that within the temperature range of -55°C to 150°C, the variation in magnetic properties of amorphous nanocrystalline alloys is between 5% and 10%, meeting their performance requirements. Moreover, this variation is completely reversible with temperature changes. Therefore, these alloy materials exhibit excellent temperature stability.

Impact and Vibration Resistance of Amorphous Nanocrystalline Alloys Magnetic devices made from amorphous nanocrystalline alloys exhibit highly reliable impact and vibration resistance. Early products made from amorphous nanocrystalline alloys were primarily used in military applications, where electronic components are subjected to rigorous impact and vibration tests—some as high as 30g to 50g. Typically, these tests were conducted either individually after the iron cores had been encapsulated and boxed, or together with the complete device; in all cases, no degradation in performance was observed. As for civilian products, there is absolutely no issue whatsoever regarding impact and vibration resistance.

Standardization of Specifications for Amorphous and Nanocrystalline Alloy Cores Currently, in most cases, amorphous and nanocrystalline alloy cores are used to replace other soft magnetic materials such as silicon steel, permalloy, and ferrites. This preconceived notion dictates that the specification standards for amorphous and nanocrystalline alloy cores can only be derived from and adapted to existing core specification standards, thereby meeting users’ application requirements. Fortunately, most of these cores are fabricated by winding thin alloy strips, a process that is simple and flexible, allowing for great adaptability in core dimensions and enabling manufacturing tailored precisely to the dimensions and specifications requested by users. Of course, since the magnetic properties of amorphous and nanocrystalline alloy cores differ from those of other materials, it is not possible to simply copy the specification standards of cores made from other materials; sometimes, minor adjustments are necessary.

Development of Amorphous and Nanocrystalline Soft Magnetic Alloy Materials

With the rapid advancement of nanotechnology and rapid quenching techniques, amorphous nanocrystalline soft magnetic alloy materials are continuously improving. Not only have the performance and quality of currently industrialized thin-strip products been significantly enhanced, but research and development efforts are also underway to create amorphous nanocrystalline alloy powders and powder-based products, thin-film materials, and composite materials. The development and industrialization of these novel nanomaterials will have a substantial potential impact on the electronic transformer industry. The author believes that the following aspects deserve particular attention from colleagues in the electronic transformer industry.

The brittleness of amorphous nanocrystalline alloy ribbons has been significantly improved. In recent years, foreign manufacturers of amorphous ribbons have fully overcome the key technical challenges in producing amorphous ribbons, successfully developing high-performance, high-quality alloy ribbons that are now suitable for shearing and processing. Domestic enterprises have also actively undertaken technological upgrades and have largely resolved the key technical challenges in amorphous ribbon production. Once industrial-scale production is achieved, the punching and shearing issues that colleagues in the electronic transformer industry have been concerned about will no longer be a problem.

Development and Application of Amorphous and Nanocrystalline Alloy Powders and Powder Products The research and development of amorphous and nanocrystalline alloy powders and powder products have broadened the application scope of these alloy materials in the field of electronic technology. Magnetic core products made from these alloys—used as filtering inductors, energy-storage inductors, and inductor components in PFC technologies for various high-frequency power supplies—have now been industrialized and standardized. Their permeability μe is within 100, essentially meeting the requirements for high-frequency inductor components.

Currently, most amorphous nanocrystalline alloy powders are produced by crushing amorphous ribbons into powder, which poses certain challenges in both powder preparation and nanocrystallization processes. These challenges make it difficult to address them using conventional powder metallurgy techniques—for instance, amorphous powder particles tend to be hard and flat, making them difficult to shape and process. However, by leveraging nanotechnology and rapid solidification techniques, it may be possible to obtain spherical or near-spherical amorphous nanocrystalline powder particles. This approach offers significant advantages for the preparation of powder-based products and can greatly enhance the magnetic core performance of such powders. The research and development of these materials hold at least the following potential application markets in the electronic transformer industry: (1) Powder magnetic cores for electronic transformers—abroad, there have already been reports of powder iron cores with permeability μe as high as 6,000. If such powder iron cores were used as magnetic cores in electronic transformers, they could be fabricated in a manner similar to current ferrite core production. Yet their performance would far surpass that of ferrite materials, and the implications would be profound. (2) Magnetic media for nanomagnetic fluids—research and development efforts on using nanomagnetic fluids as magnetic cores for electronic transformers are attracting increasing attention. Amorphous nanocrystalline alloys possess excellent soft-magnetic properties, and processing them into powder does not alter their intrinsic magnetic characteristics. Therefore, amorphous nanocrystalline alloys have become an ideal choice for this purpose.

Amorphous Nanocrystalline Thin-Film Materials The production method for amorphous nanocrystalline thin-film materials differs from the rapid-quenching technology currently in use. However, as a new type of nanocrystalline material with profound implications for future electronic transformers, it deserves attention from our colleagues.

With the rapid advancement of surface-mount technology, device integration technology, and microfabrication techniques, electronic devices have made significant strides toward miniaturization, lightweight design, thinning, and micro-sizing. An important approach to achieving these goals is to increase the operating frequency of such devices. Traditional soft magnetic ferrite materials have high resistivity but too low saturation magnetization, limiting their operating frequency to only 5 MHz to 10 MHz. Beyond this frequency range, partial “short circuits” occur at grain boundaries, causing a sharp rise in core losses and a consequent decline in magnetic performance. Therefore, after exceeding the above-mentioned frequency limits, metal thin-film materials are typically employed instead. Consequently, there has emerged an application market for research into new thin-film magnetic core materials that exhibit both high resistivity and high saturation magnetization. This development also opens up opportunities for the exploration and application of amorphous and nanocrystalline thin films as well as granular films. Moreover, since the high-resistivity and high-saturation-magnetization thin-film magnetic core materials currently under development are predominantly fabricated using processes such as sputtering or electroplating—techniques and equipment that have long been established in large-scale manufacturing—this will greatly facilitate the industrial production of amorphous and nanocrystalline thin films, granular films, and other similar materials.