It was noted that the small hysteresis in the martensitic transformations of shape-memory alloys permitted the very precise experimental determination of differences in enthalpy and entropy. Due to the diffusion-less nature of the martensitic transformation, the configurational entropy remained invariant, and the entropy difference resulted mainly from differences in the phonon spectra. These were accessible to experiment, especially the soft branches. From measured enthalpy differences in the long-range ordered alloys, those which corresponded to the disordered state could be deduced. These, together with the vibrational entropy differences, also provided valuable information on the equilibrium phases. Close-packed martensites with various stacking sequences were commonly observed and, from the critical transformation stresses, their relative stability could be assessed. Split dislocations in long-range ordered alloys with a stacking fault between them were similar to a thin martensite region, and it was therefore interesting to compare them.

On the Use of the Martensitic Transformation to Evaluate Dislocation Properties in Long-Range Ordered Alloys. A.Ahlers: Journal de Physique III, 1995, 5[C2], 35-9