Phase diagram of Fe-Cr-Co permanent magnet system

Abstract

The miscibility gap of the α phase in Fe-Cr-Co permanent magnet alloys is constructed using mechanical hardness and Curie temperature measurements. It is found that the miscibility gap of the Fe-Cr binary system develops into Fe-Cr-Co ternary system, and that the addition of cobalt raises the decomposition temperature, and extends the difference in concentrations between the iron rich phase (α₁) and the chromium rich phase (α₂). For instance, the α phase of an Fe-31%Cr-23%Co alloy exhibits a miscibility gap below 670°C, and decomposes into the (α1) phase of 65%Fe-32%Co-3%Cr and the (α₂) phase of 69%Cr-21%Fe-10%Co at 600°C.