The eutectoid transformation of Sm(Co,Cu)5

Diffusion couples formed in the range600 - 800\degC, between cobalt-copper alloys (0-25 at. % Cu) and Sm(Co,Cu)3containing the same amount of copper, have shown that copper progressively depresses the eutectoid transformation of SmCo5down to 600° C at 21 at. % copper. The data indicate the transformation temperature of SmCo5itself to be about 805° C. Subsidiary couples formed between cobalt-samarium (up to SmCo5) and copper-samarium alloys (up to SmCu6), taken with the above, show the SmCo5and SmCu5phases to be mutually soluble above the eutectoid transformation temperature. In addition, it is found that cobalt and Sm(Co,Cu)5come into direct equilibrium over a wide range of copper contents (10-70 at. %). The Sm2Co17phase field is consequently of very limited extent and can contain up to a maximum of 4 at. % copper at the solid solution limit at 800° C.