CALORIMETRIC INVESTIGATION OF THE MARTENSITIC TRANSFORMATION IN NEAR STOICHIOMETRIC AND STOICHIOMETRIC Fe3Pt AND SHAPE MEMORY EFFECT

Heats and temperatures of the r 3 d martensitic transformation in the FegPt alloy have been measured after quenohing and annealing at 820 K. The results obtained are discussed in terms of heterogeneous atomic ordering A14L12 and eutectoid decomposition x-= d + Ee3Pt, which occur during annealing and preceed the martensitic transformation. 1ntroductlon.Alloys of the Fe-Pt system close to the Fe3Yt composition undergo a YSo( martensitic transformation, being of particular interest, since properties of the martensite are governed by the other phase transformations, rival to the martensitic one. So the martensitic transformation of rapidly quenched alloys is not thermoelastic and is accompanied by a significant thermal hysteresis, When the martensitic transformation is preceeded by the atomic ordering AI*L12 it becomes a thermoelastic one and has a small thermal hysteresis, The alloys are capable of recovering their shape. The effect of atomic ordering on the martensitic transformation in the iron-base alloys with 23-2746 Yt has been discussed often /I-7/. Various criteria were proposed to determine the thermoelasticity of transformation. According to /I/ the major oriterion is given by some level of the Ms point, depending on the degree of the long-range ordering, which should necessarily be below the Curie point. This level determines a small thermal hysteresis of transformation, certain tetragonality of the and o( -phases,enhancing crystallographic rearrangement, and sma& volume change during the z= d transformation. One of the important properties of the thermoelastio transformation is its small driving force as oompared to that of the non-thermoelastic one / 8 / . It oan be expressed in terms of the heat effect and the transformation temperature /9-II/. The latent heat of the 7-t in helium and cast into a cylindrical mould. This Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982455