With increasing carbon concentrations in Alnico alloys the effective number of conduction electrons increases, which increases the thermal stability of γ phase. A single-phase structure cannot be obtained with over 0.05% C.
The precipitation of strongly magnetic phase from the supercooled solid solution occurs at 620–880°. The presence of γ phase in the original structure, the amount of which increases with the carbon content of the alloy, inhibits the formation of high-coercivity structure, and impairs the magnetic properties.
With increasing amounts of carbon the temperature of the αγ→γ polymorphous transformation shifts to higher temperatures — from 480° with 0.005% C to 520° with 0.2% C.
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Kuznetsov, V.M. Carbon in hard magnetic alloys. Met Sci Heat Treat 19, 133–136 (1977). https://doi.org/10.1007/BF00703159
- Solid Solution
- Thermal Stability
- Magnetic Property
- Carbon Content