MICROTWIN SEQUENCES IN THERMOELASTIC NIXAL100-X MARTENSITE STUDIED BYCONVENTIONAL AND HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY

Microtwin sequences in thermoelastic NixAl100-x martensite plates of d ifferent size and composition (62.5 less-than-or-equal-to x less-than- or-equal-to 66.0) were investigated by conventional and high-resolutio n electron microscopy. The average twin width increases with increasin g twin length and with increasing Ni content. No systematic behaviour of the volume fraction of microtwin variants could be detected, partia lly due to the numerous stacking irregularities. Such irregularities a re attributed to changing boundary conditions during the transformatio n, leading to multiple needle-shaped microtwins.