Classification and properties of Permalloy

Permalloyscan be divided into four categories according to their composition: 35%-40% Ni-Fe Alloys, 45%-50% Ni-Fe alloys, 50%-65% Ni-Fe alloys and 70%-81% Ni-Fe alloys. Each type of alloy can be made into different hysteresis loop materials.

1. 35%～40% Ni-Fe alloy
   When the nickel content is between 35% and 40%, K₁ decreases with the increase of nickel content, and the square ratio Bᵣ/Bₛ also decreases, showing a circular hysteresis loop. The alloy has high resistivity and fine grain structure, and low core loss. For example, the loss of 0.05mm thick 40% Ni-Fe alloy strip at 0.1T and 20kHz is 9W/kg, while the corresponding loss of 48% Ni-Fe alloy strip is 14W/kg. It is suitable for square wave transformers, DC converters, etc.

2. 45%～50% Ni-Fe alloy
   The alloy has a high saturation magnetization, K₁ > 0, and an easy magnetization direction of <100>. A rectangular hysteresis loop is obtained when a cubic texture is formed, which is suitable for magnetic amplifiers, etc., while a circular hysteresis loop is obtained when a secondary recrystallized {210} texture or a fine-grained isotropic microstructure is formed. The alloy has high permeability and Low Coercivity, and is suitable for current transformers, etc.

3. 50%～65% Ni-Fe alloy
   The alloy has a high Curie temperature and high saturation magnetization, K₁ ≈ 0, and the magnetic field heat treatment effect is obvious. When heat treated at low temperature, the loop is rectangular, the DC permeability is high but the dynamic characteristics are poor; when heat treated at high temperature, the square ratio decreases, the DC peak permeability is low but the dynamic characteristics are good. 55% Ni alloy (with 2% Mo added) can improve μᵢ and μₘ after specific treatment; 65% Ni alloy can be used for magnetic amplifiers after longitudinal magnetic field heat treatment, and constant permeability alloy can be obtained by transverse treatment, which is suitable for inductor components.

4. 70%～81% Ni-Fe alloy
   The alloyof this composition has high magnetic permeability. By adding appropriate amounts of alloying elements and controlling the cooling rate, K₁ and λ can be made close to zero, thereby obtaining high magnetic permeability and low coercivity. In general, μᵢ reaches 40 to 60 mH/m. The Ni79Mo5 alloy (super Permalloy) obtained in 1947 has high μᵢ and μₘ, with μᵢ reaching more than 150 mH/m and μₘ reaching 1130 mH/m. In the late 1960s, hard Permalloy (Hv > 200) with high hardness and high magnetic permeability was obtained, which is suitable for transformers, etc. Rectangular loops can be obtained through specific treatment, and good dynamic characteristics can be obtained by controlling the degree of order, which is suitable for magnetic modulators, etc. The iron core pressed by 80% to 82%Ni-Fe alloy powder has high resistance and good stability and can be used at 300Hz.