COST 507 - Repositório Aberto da Universidade do Porto

Summary of final report
Directional solidification and phase equilibria in ΑΙ-Ni system
O. Hunziker and W. Kurz
CHI
Laser surface resolidification and Bridgman directional solidification experiments have been
performed in order to determine the microstructure selection map for Ni-rich Ni-ΑΙ alloys and
Ni-Al-Ti alloys.
It has been shown that taking into account disorder trapping is necessary in order to explain
why does γ'-Νί3Α1 only grow as primary phase from the liquid at low velocity (below 100 μιη/s).
The effect of disorder trapping in γ' has been evaluated by laser experiments on Ni3(Al,Ti), where
growth of γ' is thermodynamically favoured by the presence of Ti.
An interactive program calculating the microstructure map has been developed on the basis of
models for dendritic, eutectic and plane front growth. This program is an efficient tool in order to
optimise the phase diagram by fitting the calculated microstructure map to the experimental map.
The phase diagram determined by this optimisation method displays the following
characteristics, necessary to fit the solidification results:
- A very small temperature difference between the stable β-γ' and the metastable β-γ eutectics
(