Thermodynamic calculation and enthalpy determination based on CEMS experimental data of martensitic transformation in Fe-Mn-Si shape memory alloys

J. MARTÍNEZ; S. M. COTES; J. DESIMONI

Physics Department, Fac.Cs.Exactas, Univ. Nac. de La Plata, La Plata, Argentine

Congreso; 11th Latin American Conference on Applications of Mössbauer Effect (LACAME'08); 2008

IBAME

The effect of chemical composition on the relative stability of the fcc and hcp phases of Fe-Mn and Fe-Mn-Si alloys and the effect on the martensitic transformation over the range of compositions where the fcc/hcp transformation takes place has been previously investigated using dilatometric measurements [1][2][3]. That information allowed assessing a phenomenological description, the Gibbs free energy of the fcc and hcp phases based on the Redlich-Kist model of [4]. Although this thermodynamic description has been widely used, its verification presents a major difficulty due to the lack of experimental data reported in the literature about the enthalpy of transformation. This difficulty comes from the fact that the amount of transformed material cannot be determined in polycrystalline alloys, which exhibit texture, using normal methods.Moessbauer spectroscopy presents advantages in the determination of the phase relative fractions when compared with neutron diffraction and dilatometry due to its low cost and accuracy.In this woek we have determined a systematically the enthalpy of transformation carried out together with an extension of the thermodynamics description cited above on FeMnSi alloys in the composition ranges from 0 to 12at%. [1] Cotes, S., Fernandez Guillermet, A y Sade, M. Journal of Alloys and Compounds,Vol. 280, (1998), pags. 168-177. [2] Cotes, S., Sade, M. y Fernandez Guillermet, A. Metallurgical and Materials Transactions A, Vol. 26A, (1995), pags. 1957-1969. [3] Cotes, S., Fernandez Guillermet, A y Sade, M. Journal of Alloys and Compounds,Vol. 278, (1998), pags. 231-238. [4] Redlich, O. y Kister, A. T. Industrial and Engineering Chemistry, Vol. 40, 2, (1948),pags. 345-348.