Mechanical spectroscopy in Fe-Pd ferromagnetic shape memory alloys. Influence of defects on the irreversible phase transition

F. G. BONIFACICH; D. GARGICEVICH; F. TARDITTI; O. A. LAMBRI; V. SÁNCHEZ-ALARCOS; V. RECARTE; J. I. PÉREZ-LANDAZÁBAL

Bilbao

Conferencia; International Conference on Martensitic Transformations; 2014

The influence of defects on the irreversible FCT-BCT Martensitic Transformation (MT) of Fe-Pd ferromagnetic shape memory alloys has been studied from calorimetric, neutron diffraction and mechanical spectroscopy measurements. It is found that the partial substitution of Fe by Co or Mn affects both the reversible and irreversible MT temperatures and considerably decreases the amount of appearing BCT phase. The appearance of the undesirable BCT phase can be directly related to the tetragonality of the FCT structure and to the density of dislocations that can relief the appearing stresses. In this sense, it is shown that aging treatments at moderate temperatures stabilize the FCT phase, thus increasing the temperature range where the reversible MT can be produced. Mechanical spectroscopy confirms that the effect of aging on the transformation temperatures is associated to a relaxation processes consisting on a dislocation dragging mechanism controlled by the migration of vacancies without break-away.