Nucleation In Undercooled Melts Research Articles

Effect of electric field on nucleation in undercooled melt

A revised nucleation theory in undercooled melt with applied electric field is derived based on the Classical Nucleation Theory, and the undercooling decrease caused by Joule heat release is also considered. The effect of applied electric field on the nucleation process in undercooling melts is calculated and discussed. Taking pure Al as the validation example, results indicate that with increasing electric field, the nucleation rate keeps increasing with a decreased undercooling, and the enhancement of nucleation rate caused by the electric field is the reason for grain refinement during solidification with electric treatment, which can be observed from the experimental investigation.

Experimental analysis of heterogeneous nucleation in undercooled melts by infrared thermography

A new experimental technique for quantitative analysis of heterogeneous nucleation in undercooled melts is proposed in this paper. It is based on the observation by infrared thermography of the thermal behavior on cooling of a large population of small droplets deposited on a substrate. The method allows analyzing the influence of different parameters such as the size of the droplets, the cooling rate and the wettability of the substrate on the nucleation rate. The fundamentals of the method, the associated experimental set-up, and the mathematics required for data processing are described in the paper. The results of the nucleation analyses carried out using erythritol deposited on different substrates are also presented and discussed.

Crystal nucleation in undercooled melts of PdZr2

Crystal nucleation in undercooled melts of the stoichiometric PdZr2 compound is studied by measuring the nucleation undercooling of small droplets processed by containerless electrostatic and electromagnetic levitation. Owing to the avoidance of container walls usually acting as heterogeneous nuclei, large undercoolings are achieved. The statistics of crystal nucleation is investigated by measuring the nucleation undercooling of at least 100 melting and solidification cycles for both sets of experiments. The results are analyzed within a statistical approach based on the classical nucleation theory. Out of this two important parameters can be extracted. These are the activation energy, which needs to be overcome to form critical nuclei and, the pre-factor in the nucleation rate equation, which measures the number of potential nucleation sites per unit volume. The results are discussed with respect to the different experimental conditions, short-range order in the undercooled liquid state and its impact to the glass forming ability of this alloy.

Nucleation of crystals in deeply undercooled alloy melts

The CALPHAD approach coupled with modelling of solid-liquid interfacial energy has been used to calculate the driving force for nucleation in undercooled melts. Thermodynamic parameters needed in nucleation have been evaluated using simplified formulae or numerical methods from assessed phase diagrams. Various models for the interfacial energy and its temperature dependence have been used. Phase selection on solidification and devitrification of glasses as well as the range of amorphous phase formation have been predicted in the Al-Ce and Fe-B systems and compared with those experimentally determined. Furthermore, the formation of quasicrystals in the Al-Mn and the competition with other compounds has been investigated.