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 less than or equal to at.% Mn less than or equal to 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. (C) 2003 Elsevier B.V. All rights reserved.