Abstract
A thermodynamic study of thermoelastic martensites has been made with particular reference to some experimental results previously obtained for iron-platinum alloys. The effect of parent phase ordering in depressing the T 0 temperature has been satisfactorily explained using a quasichemical approach and a consequent difference in bonding enthalpies. The transformation latent heat was determined by calorimetry for the parent-martensite transformation in both ordered and disordered Fe-Pt alloys. For transformation in the ordered alloy the latent heat ΔQ is much smaller (83 cal/mole) than that for the corresponding disordered alloy (570 cal/mole). These measurements implement the quasichemical interpretation. Other results of general applicability were also obtained. The stored non-chemical free energy difference Δε nc has been analytically expressed in terms of the characteristic temperatures T 0 and T ′0, and the transformation latent heat ΔQ. It is indicated that the separation of T 0′ from T 0 is directly proportional to the value of Δε nc . The quantity (T 0-T 0′) T 0 is seen to provide a reasonable estimate of the ratio Δε nc ΔQ . Following a statistical expression for the free energy, a simple development enables the calculation of the Debye temperature of the martensite, and a comparison of the parent phase and martensite Debye temperatures is made.
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