Solid-solid phase transformation kinetics [article]

Rico Bauer, Universität Stuttgart, Universität Stuttgart
Chapter 2 of this thesis presents the investigation of the microstructural evolution of Co precipitates formed upon isochronal annealing of an initially supersaturated Au 10.12 at. % Co solid solution. It was proven, that initially plate like bcc Co precipitates have formed, which deviates from the expected stable fcc Co crystal structure. Upon prolonged annealing, i. e. with ongoing precipitation reaction, the bcc Co was transformed into fcc Co accompanied with a morphological change of the Co
more » ... al change of the Co precipitate shape from plates to equiaxed particles. Quantitative (high resolution) transmission electron microscopy (HR)TEM analysis and a thermodynamic examination were done. In chapter 3 the microstructural evolution and the kinetics of the precipitation of Co from an initially supersaturated Au – 10.12 at.% Co upon isothermal and isochronal annealing were described. The precipitation reaction was followed by DSC, XRD, (HR)TEM and microhardness measurements in order to understand the microstructural evolution. The isothermal and isochronal precipitation kinetics were analyzed using analytical expressions for the description of the phase transformation applying the modular phase transformation model in combination with an appropriate impingement correction. In chapter 4 the kinetics of the precipitation of coherent, spherical fcc Co from an initially supersaturated Cu – 0.95 at. % Co solid solution upon isochronal annealing is described. The precipitation reaction was followed by DSC and (HR)TEM. Kinetic parameters were obtained from an analytical modular model approach of phase transformation kinetics. A special case of the application of this approach is presented. In chapter 5 the microstructural evolution of the allotropic hcp to fcc phase transformation in bulk Co upon isochronally conducted thermal cycling experiments as well as the corresponding kinetics were investigated. Therefore, differential scanning calorimetry (DSC), X ray diffractometry (XRD) and light optical microscopy (LM) were applied. The phase transf [...]
doi:10.18419/opus-6752 fatcat:q3ka464ouvb7vo33vjbezdjtwm