Phase equilibria of solid phases in the Co-W system were investigated using two-phase alloys and the diffusion couple technique. In addition, systematic studies of magnetic and martensitic transitions were conducted by Differential Scanning Calorimetry (DSC), Vibrating Sample Magnetomety (VSM) and dilatometric measurement. Phase separation into ferromagnetic αCo and paramagnetic αCo was confirmed on the Co-rich side. The Curie temperature and saturation magnetization decreased with increasing W content and vanished at around 25 at%W. Furthermore, thermodynamic assessment by the CALPHAD approach was performed. A set of thermodynamic values describing the Gibbs energy of the Co-W system was in good agreement with the experimental phase diagram. Calculation of metastable magnetically induced phase separation in the hcp phase along the Curie temperature was also performed.
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