Concept
Permalloy often refers to iron-nickel alloys with a nickel content in the range of 30~90%. It is a very widely used soft magnetic alloy. Through appropriate technology, magnetic properties can be effectively controlled, such as initial permeability exceeding 105, maximum permeability exceeding 106, and as low as 2‰ Austria Permalloy with a coercive force close to 1 or close to 0 and a rectangular coefficient close to 1 or close to 0, the permalloy with a face-centered cubic crystal structure has good plasticity and can be processed into 1μm ultra-thin ribbons and various usage forms. Commonly used alloys are 1J50, 1J79, 1J85 and so on.
The saturation magnetic induction of 1J50 is slightly lower than that of silicon steel, but its magnetic permeability is dozens of times higher than that of silicon steel, and its iron loss is also 2 to 3 times lower than that of silicon steel. It is made into a transformer with a higher frequency (400~8000Hz), and the no-load current is small. It is suitable for making small high-frequency transformers below 100W. 1J79 has good comprehensive performance and is suitable for high frequency and low voltage transformers, leakage protection switch cores, common mode inductance cores and current transformer cores. The initial permeability of 1J85 can reach more than one hundred thousand (105), which is suitable for low-frequency or high-frequency input and output transformers, common mode inductors and high-precision current transformers with weak signals.
A brief history
In 1913, American GWElmen discovered that Ni-Fe alloys containing 30% to 90% nickel were exposed to weak and medium magnetic fields. It has good soft magnetic properties. Among them, the initial permeability μi of the nickel-iron alloy with 78% nickel is the highest, so it was named permalloy, which means magnetically permeable alloy. He also discovered a special heat treatment process to further increase the initial permeability of the Ni-Fe alloy by 50% to 90%, called "permalloy heat treatment". In 1921, 78% Ni-Fe alloy was used in telephone relays. In 1924, the British Smith (Smith) and others invented a 76% Ni-Fe alloy with copper and chromium added, called "Mumetal" (produced by the British Telcon company). In 1931, the American T.D. Yensen invented the process of vacuum melting and hydrogen high temperature annealing to purify the alloy, and developed the super nickel-iron alloy under the brand name Hipernik. In 1934, American GA Kelsall discovered that magnetic field heat treatment can significantly increase the maximum permeability of iron-nickel alloys. After 65% Ni-Fe (65 permalloy) heat treatment in a magnetic field, μmax sub>increased by about 10 times. In 1947, American R.M.Bozorth and others invented the highest alloy of μi and μm, called superpermalloy. In the early 1960s, the China Iron and Steel Research Institute invented a method of treating with a transverse magnetic field and adding an appropriate amount of oxygen, and obtained Br and Hc close to zero. Very constant 65% Ni-Fe alloy (Chinese brand 1J66). After the 1970s, in order to meet the needs of the development of high-frequency switching power supplies and magnetic recording technology, various elements such as niobium, tantalum, vanadium, tungsten, titanium, silicon, and aluminum were added to nickel-iron alloys containing high nickel to obtain high hardness and high hardness. The resistivity, low loss, high permeability alloy has become the most representative alloy in soft magnetic alloys with the most types of properties, the widest variety and applications.
Structural magnetism
Permalloy is an iron-nickel alloy with higher magnetic permeability in a weaker magnetic field, and a nickel-iron alloy with a nickel content of more than 30%. Both have a single-phase face-centered cubic (γ) structure at room temperature, but the single-phase structure near 30% Ni is very unstable. Therefore, practical iron-nickel soft magnetic alloys have a nickel content of more than 36%. The iron-nickel alloy contains nickel near 75% (atomic fraction), and the Ni3Fe long-range order transformation occurs in this single-phase alloy. At this time, the lattice constant and physical properties of the alloy, such as electrical resistance The rate and magnetism will change. Therefore, it is necessary to consider the impact of orderly transitions on performance. A small amount of additional elements such as Mo or Cu are usually added to the Ni3Fe alloy to suppress the formation of long-range order.
Mutual relationship
Figure 1 shows the saturation magnetization Js and Curie temperature Tc of the binary nickel-iron alloy , The relationship between magnetocrystalline anisotropy K1 and magnetostriction constant λ and nickel content. Figure 2 shows the relationship between K1 and λ of Ni-(Fe+Cu)-Mo alloy, composition and cooling rate of heat treatment. Figure 3 shows the uniaxial anisotropy constants Ku1, Ku2 obtained by the rolling and magnetic annealing process Varies with nickel content. It can be seen from the figure that K1 is not only dependent on the composition, but also related to the short-range order of Ni3Fe (controlled by the cooling rate of heat treatment). λ is basically determined by the composition. Only at the composition of Ni3Fe, the cooling rate has a little effect on λ111 and λ100. The Ku2 produced by the magnetic field heat treatment at a temperature below Tc is one less than the Ku1 produced by the slip deformation (during cold rolling) Orders of magnitude. Both Ku1 and Ku2 are uniaxial anisotropy, so when magnetized in the preferred direction, a rectangular hysteresis loop can be obtained, and magnetization in the vertical direction can be obtained Flat loop with low Br. For alloys with a nickel content of 70%~80%, the K1≤0, the easy magnetization direction is <111>, and {100}<001> cubic texture and chaotic orientation should be avoided Random texture. The alloy K1>0 with 45%~68% nickel has an easy magnetization direction of <100>, so in order to obtain high magnetic properties, the cubic texture should be obtained as much as possible. Specifically, large reduction amount cold rolling and lower temperature (900～1050℃) annealing can be used. The final annealing of permalloy should be in a pure hydrogen atmosphere with no oxygen and a dew point below -40℃ or a vacuum degree of 10-2～10-3Pa In the atmosphere.
Classification performance
Permalloy can be divided into 35%～40%Ni-Fe alloy, 45%～50%Ni-Fe alloy, 50%～65%Ni according to the composition -Fe alloys and 70%～81% Ni-Fe alloys in four categories. Each type can be made into materials with circular hysteresis loop, rectangular hysteresis loop or flat hysteresis loop.
35%～40%
In the range of 35%～40% nickel, the magnetocrystalline anisotropy K1 decreases with the increase of nickel content The square is smaller than Br/Bs, showing a circular hysteresis loop. This circular loop is combined with high resistivity (when the nickel content is 40%, ρ=60μΩ·cm; and at 48%, ρ=45μΩ·cm) and the fine-grain isotropic microstructure, it results in a relatively high resistivity. Low core loss. For example, a 40% Ni-Fe alloy strip with a thickness of 0.05 mm has a loss of 9 watts per kilogram at 0.1T and 20 kHz; the corresponding loss of a 48% Ni-Fe alloy strip is 14 watts per kilogram. This type of alloy is suitable for square wave transformers, DC converters, etc.
45%～50%
Alloys within this composition range have the highest saturation magnetization among permalloys, and K1>0, The easy magnetization direction is <100>. A rectangular hysteresis loop can be obtained by forming a cubic texture, which is used in magnetic amplifiers, chokes and transformers. It is also possible to form a secondary recrystallized {210} texture, or form a fine-grained isotropic microstructure with the aid of primary recrystallization to obtain a circular hysteresis loop. This alloy has high magnetic permeability and low coercivity, and can be used in current transformers, ground fault circuit breakers, micro motors and relays.
50%～65%
The alloy in this composition range has the highest Curie temperature, the saturation magnetization is also high, and it is in an orderly state K1 sub>≈0, so the effect of magnetic field heat treatment is particularly obvious, which can produce strong induced magnetic anisotropy. When the low temperature (about 130℃ below the Curie point) magnetic field heat treatment, the hysteresis loop is rectangular, the DC maximum permeability is high, but the dynamic characteristics are poor; when the high temperature (about 60℃ below the Curie point) magnetic field heat treatment, the loop The square ratio has decreased, the maximum DC permeability is not high, but the dynamic characteristics are good. The nickel-iron alloy (with 2% molybdenum) containing about 55% nickel is annealed at high temperature to form {210}<001> sub>i and μm. A 65% nickel-containing nickel-iron alloy with fine-grained isotropic microstructure is heat-treated in a longitudinal magnetic field to obtain a rectangular hysteresis loop material with good dynamic characteristics, which is suitable for magnetic amplifiers. This alloy is heat-treated in a transverse magnetic field to obtain a low Br flat loop, and the magnetic permeability changes little within a certain range of magnetic field strength. It is called a constant magnetic permeability alloy and is suitable for Do inductive components.
70%～81%
Permalloy with this composition range has the highest permeability. Although it is impossible for K1 and λ to be reduced to zero at the same time in binary nickel-iron alloys, adding an appropriate amount of alloying elements such as molybdenum, chromium, copper, etc. within this composition range, and then controlling the heat treatment The cooling rate can make K1 and λ approach zero at the same time, thereby obtaining high permeability and low coercivity. Generally, the μi of this alloy can reach 40-60mH/m. In 1947, the Americans such as RMBozorth and others used relatively pure raw materials, melted them in vacuum and finally annealed them in pure hydrogen at a high temperature of 1200～1300℃, and obtained μi and μ The extremely high Ni79Mo5 alloy is called superpermalloy. Its μi can reach more than 150mH/m, and μm can reach 1130mH/m. At the end of the 1960s, Japan added niobium and tantalum to 78% Ni-Fe alloys, and later added the fourth and fifth elements such as molybdenum, chromium, titanium, aluminum, and manganese. Permalloy with high hardness and high permeability, its hardness Hv>200, is called hard permalloy. This type of alloy is suitable for transformers, chokes, magnetic heads, magnetic shields, etc. In addition, by forming a cubic texture, the loop of this type of alloy can also be rectangular; at the same time, the order of the alloy is controlled to make K1 ≥ 0, and it shows good dynamic characteristics. It is very suitable for making magnetic modulators and so on. The powder core made by adding 2% of 80% to 82% Ni-Fe alloy powder has high resistance and good stability, and can be used at a frequency of 300 Hz.
Basic features
permalloy
It is an iron-nickel-based soft magnetic alloy with extremely high magnetic permeability in a weak magnetic field.
In order to increase resistivity and improve process performance, Mo, Cr, Cu and other elements are often added to Fe-Ni binary alloys. In addition to Fe-Ni alloys, there are also iron-silicon aluminum alloys and amorphous cobalt-based alloys belonging to permalloys.
Permalloy has excellent soft magnetic properties, the initial permeability μi is 37.5～125mH/m, and the maximum permeability μm It can reach 125～375mH/m, the coercivity Hc is 0.8A/m, and the resistivity ρ is 60～85μΩ·cm.
The alloy is smelted in a vacuum induction furnace and is made into cold-rolled strips, cold-drawn wires or hot-rolled (forged) plates and bars through hot and cold plastic deformation.
Used to make audio transformers, transformers, magnetic amplifiers, magnetic modulators, chokes, audio heads, etc.
Production process
The production process of permalloy is more complicated. For example, the plate rolling process, annealing temperature, time, cooling speed after annealing, etc. all have a great influence on the final magnetic properties of the material.
The grade of Permalloy in my country is 1JXX. Among them, J stands for "precision alloy", "1" stands for soft magnetic, and the number after it is the serial number, which usually indicates the nickel content in the alloy. For example, 1J50, 1J851, etc. Permalloy has high magnetic permeability, so it is often used in the core of medium and high frequency transformers or devices with strict requirements on sensitivity, such as high frequency (tens of kHz) switching power supply transformers, precision transformers, leakage switching transformers, Magnetic shielding, yoke, etc.
Nano effect
Ta/NiFe/Ta magnetoresistive films were prepared by magnetron sputtering, and CoFe-NOL and Al2O 3 Intercalation introduces NiFe film to study nano-oxidation.
The effect of layer (NOL) on the performance of NiFe film. The experimental results show that when CoFe-NOL is introduced into NiFe film, CoFe-NOL has an important influence on the performance of NiFe film, and the position of CoFe-NOL in the film Different effects are also different; when CoFe-NOL is at the Ta/NiFe interface, the texture of the NiFe film is destroyed, resulting in a decrease in the anisotropic magnetoresistance (AMR) value of the NiFe film and an increase in the coercivity. When NOL is at the NiFe/Ta interface, it will not damage the texture of the NiFe film, and its AMR value and coercivity will basically not change. The Al2O3 intercalation layer is introduced into the NiFe film, due to the "specular reflection of the Al2O3 intercalation layer "The effect, the appropriate thickness of Al2O3 intercalation layer can improve the microstructure of the film, increase the magnetic resistance value of the film, and improve the magnetic properties of the film. When the thickness of Al2O3 is 1.5 nm, the NiFe film has the best microstructure and performance.