| 초록 |
The crystallization and phase transformations of amorphous NiTi thin films were studied using in situ transmission electron microscopy (TEM). These films were sputter-deposited onto micromachined silicon-nitride membranes and subjected to heating and cooling conditions. The microstructural evolution was monitored and recorded during heating and cooling. Kinetic parameters such as the nucleation rate, the growth rate, and the area-fraction transformed were independently determined by noting the number of grains per frame and their change in size. Using the Johnson-Mehl-Avrami analysis, fitted kinetic parameters were determined and found to be consistent with TEM observations. With cooling, we observed directly the conversion of the high temperature phase (austenite) to its low temperature phases (R-phase and martensite). To explore the compositional sensitivity of crystallization, samples near-equiatomic and slightly Ti-rich were studied with these methods. TEM micrographs show that equiatomic films exhibit polymorphic crystallization. However, samples that are slightly off-stoichiometry did not exhibit this behavior. |
