Phase equilibria in the Co-Mn-Ni system

Co-Mn-Ni alloys are promising shape memory alloys and functional materials. However, very limited information can be found regarding the phase transformations and magnetic properties in this ternary system. In this work, a series of 22 Co-Mn-Ni alloys with various compositions were selected and synthesized based on a computed phase diagram. Metallography, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), differential scanning calorimetry (DSC), hardness and Gleeble tests were used for microstructural characterization and phase transformation investigations. The results indicate that all samples show a face-centered-cubic (FCC) structure after quenching from 1000 °C. Phase transformations and Curie temperatures of the samples were obtained through a combined method of analyzing the heat effects and thermogravimetric behavior of the alloys in the presence of a magnetic field during differential scanning calorimetry. Thermal expansion tests indicate that the FCC to BCC transformation is a thermoelastic transformation whereas the shape memory effect was not observed in the Co-Mn-Ni alloys tested. [Display omitted] •A partial isothermal section of the Co-Mn-Ni system at 1000 °C was established.•The Curie temperature was determined using a combined magnetic TG and DSC method.•Austenitic and Martensitic transition temperatures were determined from DSC curves.•The FCC-BCC phase transformation is a thermoelastic transformation.•The shape memory effect was not observed in the Co-Mn-Ni alloys.