Effect Of Phosphorus On Cast Microstructure Of Ni3Al
磷对Ni3Al凝固组织的影响

Phosphorus is hardly dissolved in the solidified Ni_3Al solids, and tends to be segre- gated in the residual liquids of Ni_3Al. The phosphorus--bearing phase is precipitated at the end of solidification. The segregation of phosphorus in the residual liquids inhibits the nucleation of Ni_3Al grains and the formation of the equiaxed grains at the central part of the sample, and favors the growth of the columnar grains towards the central part of the sample. The reason for phosphorus to decrease the nucleation rate of Ni_3Al is that it lowers the difference of free energy between solids and liquids, and increases the activation energy for the atoms to transit through the liquid/solid interface. Phosphorus lowers the final solidification temperature of Ni_3Al, increases the length of mushy zone, inhibits the feeding of casting, and hence increases the tendency of micropores formation.