A hybrid Cellular Automaton (CA) - Parabolic Thick Needle (PTN) model is developed for the simulation of an equiaxed dendritic grain. It implemented by solving conservation equations with Finite Element (FE) method at two scales. At scale microstructure, branches are approximated a network PTN. The solute field computed in liquid using FE mesh minimum size smaller than diffusion length ahead de...

During the direct chill (DC) casting process, primary cooling from mold and bottom block, secondary waterjets produce a concave solid shell. The depth of this liquid pocket mushy zone not only depends on solidification range alloy but also boundary conditions such as rates. Al-Li alloys solidify in long increasing susceptibility porosity nucleation semi-solid region. In study, effects rate form...

A unique gradient furnace for directional solidification experiments with bulk Al-alloy samples developed at German Aerospace Center is presented. It allows in situ process control solidifying by using x-radiography, and further insight into the gained combination x-ray computational tomography on solidified samples. Tracking of interfaces during via x-radiography (TIREX) enables investigation ...

We present new experimental results relating to the growth and evolution of sea ice. These show, in particular, that brine initially remains trapped in the interstices of the sea ice, only draining into the underlying ocean once the depth of the sea-ice layer exceeds a critical value. A general theory for convection within mushy layers is applied to develop a hypothesis for when brine drainage ...

The freezing of water to ice is a classic problem in applied mathematics, involving the solution of a diffusion equation with a moving boundary. However, when the water is salty, the transport of salt rejected by ice introduces some interesting twists to the tale. A number of analytic models for the freezing of water are briefly reviewed, ranging from the famous work by Neumann and Stefan in th...

Numerical and experimental studies were conducted to investigate the heat transfer, fluid flow, and keyhole dynamics during a pulsed keyhole laser welding. A comprehensive mathematical model has been developed. In the model, the continuum formulation was used to handle solid phase, liquid phase, and mushy zone during melting and solidification processes. The volume-of-fluid method was employed ...

A criterion for predicting the formation of freckles for Pb-Sn and Ni-base superalloys is evaluated using available experimental data. The criterion is based on a maximum value of the Rayleigh number, which indicates that the magnitude of buoyancy forces is largest with respect to the retarding frictional forces. The definition of the Rayleigh number involves a characteristic length scale. The ...