The allotropic, martensitic phase transformation hcpfcc in cobalt was investigated by differential scanning calorimetry (DSC) upon isochronal annealing at heating rates in the range from 10 K min -1 to 40 K min -1 . The microstructural evolution was traced by light optical microscopy (LM) and X-ray diffractometry (XRD). The kinetics of the phase transformation from hcp to fcc Co upon isochronal annealing was described on the basis of a modular phase transformation model. Appropriate model descriptions for athermal nucleation and thermally activated, anisotropic interface controlled growth tailored to the martensitic phase transformation of Co were implemented into the modular model. Fitting of this model of phase transformation kinetics to simultaneously all isochronal DSC runs yielded values for the energy of the interface separating the hcp and fcc Co phase and the activation energy for growth.
The kinetics of the precipitation of Co from a supersaturated solid solution of Cu-0.95 at. pct Co was investigated by isochronal annealing applying differential scanning calorimetry (DSC) with heating rates in the range 5 to 20 K min -1 . The corresponding microstructural evolution was investigated by high-resolution transmission electron microscopy (HRTEM) in combination with electron energy loss spectroscopy (EELS). Upon isochronal annealing, spherical Co precipitates of fcc crystal structure form. Kinetic analysis by fitting of a modular phase transformation model to, simultaneously, all DSC curves of variable heating rate measured for Cu-0.95 at. pct Co showed that the precipitation-process mechanism can be described within the framework of this general phase transformation model by continuous nucleation and diffusioncontrolled growth. By introducing additional microstructural information (here, the precipitateparticle density), for the first time, values for the separate activation energies of nucleation and growth could be deduced from the transformation kinetics.
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