Phase diagram of Fe-Cr-Co permanent magnet system

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.