| Numerous potential applications have been found for shape memory materials and particularly NiTiNOL. It remained, however, to characterize the physical and mechanical properties of this material, with particular regard to the phase diagram, in order to intelligently utilize these properties. This dissertation conducts such a characterization.;The diffraction studies confirmed the TiNi austenitic structure to be B2 and the martensitic structure to be B19, however, a premartensitic structure was characterized that is similar to an athermal omega phase. Dilatometric and metallographic studies reevaluated the TiNi phase diagram in the vicinity of the equiatomic composition, including the martensitic transformation and reversion temperatures as functions of composition and prior thermomechanical treatment. Differential scanning calorimetry was used to determine the heat of transformation and the influences of mechanical strain on the martensitic transformation. Hardness and tensile testing were utilized to determine the mechanical properties of the system as functions of the alloy composition, prior thermomechanical treatment, and temperature of test.;Titanium-rich alloys were found to have mechanical properties that were independent of prior thermomechanical treatment. Three factors, however, strongly influenced the mechanical performance of nickel-rich alloys. These were: solid solution hardening, thermoelastic transformation, and second phase precipitation. The inter-relationships between these factors and the resultant mechanical properties are identified.;The physical properties of the TiNi system were studied using x-ray diffraction, neutron diffraction, metallography, dilatometry, and scanning calorimetry. The mechanical properties were determined using hardness and tensile measurements. Both the physical and mechanical properties were determined as functions of the bulk alloy composition, prior thermomechanical treatment, and temperature of test. |
