Published online by Cambridge University Press: 25 February 2011
The nature of the premartensitic state is still under debate. It is becoming evident that alloys which transform into a long period polymorph display the equivalent precursor strain modulations in the parent phases. The situation in alloys which transform in the center of the BZ is less clear, however. On the basis of electron microscopic [1,2,3] and X-ray diffraction data [4], it has been proposed for Fe-Pd alloy that the parent state consists of a coherent mixture of tetragonally distorted variants which may form a transitional phase. The interpretation is substantially based on the observation of 110 diffuse scattering and the softening of the elastic constant ½(C11 -C12) [1,2,5,6,7]. We have performed TEM studies of In-Tl alloys and investigated the low frequency mechanical response of In-Tl, In-Cd and Fe-Pd alloys. The phase diagrams of the three alloys [8,9,10], schematically presented in Fig. 1, show the common FCC-FCT martensitic transformation. Our studies indicate isotropic "elastic" softening and show that 111 streaking is present as well. This paper presents the mechanical results and their preliminary interpretation.