The premartensitic instability in near-equiatomic TiNi

Abstract

The premonitory events leading to the thermal martensite transformation in near-equiatomic TiNi were studied by transmission electron microscopy, single crystal X-ray diffraction, warm and cold stage light microscopy, and electrical resistivity. Well above theMs temperature (as defined by surface relief) {111} planes of diffuse intensity begin to form in reciprocal space and slowly intensify with further cooling. Within 20° to 30°C ofMs the {111} planes diminish in intensity and new discrete maxima in reciprocal space are formed. These intensify rapidly with further cooling down to theMs temperature where a discontinuous change in crystal structure occurs as indicated by surface relief. The premartensitic phenomena are discussed in terms of lattice vibrations reflecting an incipient mechanical instability of theB2 lattice. Some observations on the martensite transformation itself are also presented.