The enthalpy change of the hcp → fcc martensitic transformation in Fe–Mn–Co alloys: composition dependence and thermal cycling effects

Extending a recent calorimetric study of the Fe–Mn system the enthalpy change associated with the fcc→hcp martensitic transformation in the Fe–Mn–Co system has been determined in alloys with 13≤at.% Mn≤30 and up to 9 at.% Co. The heat effect has been measured by differential scanning calorimetry, whereas the fraction of material that transformed martensitically was determined by combining a dilatometric technique with the known molar volume versus composition relations. A detailed description of the various experimental and data processing procedures is reported. The enthalpy change is discussed as a function of composition and of the number of thermal cycles of transformation and retransformation. The picture of the energetics of the fcc→hcp martensitic transformation emerging from the present study should be useful in future attempts to model the thermodynamics and phase stability relations in the Fe–Mn–Co system.