The solidified structure An exAMp 
In the case of solidification of solid solutions, depending on the value of G and v, plane front, Experimen 
cellular, cellular dendritic or dendritic structure develops. The mezostructure can be columnar or 
equiaxed. The equiaxed structure is always dendritic, the columnar structure can be cellular, cellular gw il 
dendritic or dendritic. The characteristic geometric parameters of the cellular structure are the tip farmace - 
radius of the growing cell and the distance between the nearest cells. The dendritic structure is peri 
much more complicated. In the case of the dendritic structure secondary dendrite arms can be jemi: 
grown from the primary arms nearly perpendicular to those. Similarly, tertiary arms can be grown yas place 
from the secondary arms parallel with the primary arms. The characteristic geometric parameters of pled un’ 
the dendritic structure are the dendrite tip radius, the distance between the neighbouring primary, recorded ib 
secondary and tertiary dendrite arms (primary, secondary and tertiary dendrite arm spacing), the eure 
position of the firstly developed secondary dendrite arm and the diameter of the primary dendrite data The 
arm at the above mentioned position (dendrite trunk diameter). velocities 
During solidification the diffusion in the solid phase is restricted. As a result of the restricted solid calulated 
phase diffusion significant concentration differences develop across the dendrite arms. In addition, SPRITE. 
at the end of the solidification, eutectic can be formed in those alloys, which consist of only one 
phase (solid solution) after the equilibrium solidification. The phenomenon described above is 
called microsegregation. 
The second phase of the eutectic (the firstly solidified phase of eutectic is the solid solution) can be 
undercooled and then a metastable phase can develop in the structure (i.e. AlgFe instead of the 
AlsFe in the Al-Fe alloy). 
Solidification methods 
Numerous solidification methods were developed for the investigation of solidification processes. 
Basically these methods can be divided into two groups, such as the unidirectional (constrained) 
and non-unidirectional (non-constrained) solidification. At the unidirectional solidification heat is 
extracted mainly from one direction, while at the non-unidirectional solidification heat is extracted 
almost equally to the three directions of space in a controlled way (DTA, DSC, Newtonian cooling). 
During the unidirectional solidification the solidification parameters (G, v) may be constant (steady- 
state solidification) or may change (non-steady-state solidification). A special possibility of the 
unidirectional solidification is when the solidified material is transparent (i.e. SCN-Acetone 
system). Both the unidirectional and non-unidirectional solidification may be interrupted and 
thereby solidification processes can be investigated as a function of temperature or time. 
Investigation of solidified structures 
Numerous methods are available for the investigation of the solidified structures. The lattice of the 
phases can be determined by electron and X-ray diffraction, while the amount of the phases can be 
measured by image analysis or X-ray diffraction. The characteristic parameters of dendritic or % 
cellular structures can also be investigated by different methods of image analysis. The 
concentration distribution across the dendrite and the concentration of the second phases can be : 
measured by WDS or EDS. 
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Solution 
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