Published online by Cambridge University Press: 21 February 2011
Many ordered β-phase alloys of the B2 or D03 types exhibit unusual diffraction patterns and images when examined in the transmission electron microscope. These effects include “extra” diffraction spots, diffuse scattering, satellites, “tweed microstructures, spinodal decomposition and the formation of incommensurate phases. Examples of these phenomena will be presented and discussed. Although most of the β-alloys also undergo a martensitic transformation at some lower temperature it will be argued that the above effects are not “premartensitic” or precursory in nature. However many of them can be related to certain properties of the β-phase such as elastic anisotropy, a soft phonon mode and electronically driven instabilities.