Prior work in this system has indicated that, under favourable conditions, the formation of a martensitic transformation product on cooling may be preceded by a second-order cubic-rhombohedral transformation. In the present investigation, thin-film electron microscopy and diffraction have been employed to study the pre-transformation phenomena in the temperature range 20-300 °C. The results are interpreted in terms of localized thermal diffuse scattering, resulting from the transformation, in terms of lattice dynamics, is suggested. dark field micrographs of the rhombohedral phase suggest a moderate degree of co-operation between adjacent domains. Additional data is provided in the form of volumetric and x-ray intensity measurements. / Thesis / Master of Engineering (ME)

Prior work in this system has indicated that, under favourable conditions, the formation of a martensitic transformation product on cooling may be preceded by a second-order cubic-rhombohedral transformation. In the present investigation, thin film electron microscopy and diffraction have been employed to study the pre-transformation phenomena in the temperature range 20-300°C. The results are interpreted in terms of localized thermal diffuse scattering, resulting from incipient mechanical instability. A model for the cubic-rhombohedral transformation of the rhombohedral phase suggest a moderate degree of co-operation between adjacent domains. Additional data is provided in the form of volumetric and x-ray intensity measurements. / Thesis / Master of Engineering (ME)