Tesis doctoral de Pere Bruna Escuer
The aim of this thesis is to study the kinetics of primary crystallization in metallic glasses by means of phase-field simulations. A primary crystallization is a solid-solid phase transformation where the crystallized phase (transformed phase or secondary phase) has a chemical composition different than the precursor phase (untransformed phase or primary phase). Experimental data from calorimetric studies of primary crystallization are usually studied in the framework of the kjma model (kolmogorov, johnson & mehl, avrami). This model yields the temporal evolution of the transformed fraction on the basis of three main assumptions: a random distribution of particle nuclei of the secondary phase. The growth of these nuclei is isotropic. The growth is only halted by direct collisions (hard impingement). in the crystallization of metallic glasses, a slowing down of the kinetics respect the behavior calculated with the kjma kinetics has been observed. This delay is explained in the literature by the fact that in this kind of transformations, that are diffusion controlled, the interaction between the crystals is not direct but through the concentration profiles (soft impingement) and moreover, the evolution of these profiles causes changes in the concentration of the amorphous matrix, stabilizing it and thus, the nucleation of new nuclei become non random. Several authors had proposed modifications to the kjma model to try to overcome these limitations, based either on geometrical considerations or in mean field approaches. However, none of these models is able to explain the observed kinetics in primary crystallizations. The aim of this work has been the realistic simulation of the kinetics of primary crystallization to find a explanation to the differences between the experimental data and the available theoretical models. In order to describe in a realistic way the process of a primary crystallization, the nucleation and growth process of the secondary phase has to b
Datos académicos de la tesis doctoral «Microstructural characterization and modelling in primary crystallization«
- Título de la tesis: Microstructural characterization and modelling in primary crystallization
- Autor: Pere Bruna Escuer
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 15/11/2007
Dirección y tribunal
- Director de la tesis
- Daniel Crespo Artiaga
- Tribunal
- Presidente del tribunal: María teresa Mora aznar
- clara Conde amiano (vocal)
- lindsay Greer (vocal)
- laureano Ramirez de la piscina millan (vocal)