磷对Ni3Al凝固组织的影响

磷(P)在Ni3Al中的溶解度很低，凝固过程中向剩余液体中偏聚，最终在晶界上析出富P相，凝固后期。P在剩余液体中的偏聚程度升高，降低形核率，抑制试样心部等轴晶的形成，促使试样外缘晶粒向心部延伸生长，增加柱状晶长度。P降低合金终凝温度，增如糊状区长度，阻碍液相补缩，增加形成疏松的倾向。P产生上述作用的根本原因是其降低固、液两相体积自由能差和原子跃迁穿过液／固界面的激活能。

Effect Of Phosphorus On Cast Microstructure Of Ni3Al

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 ofsolidification. The segregation of phosphorus in the residual liquids inhibits the nucleation of Ni_3Algrains and the formation of the equiaxed grains at the central part of the sample, and favors the growthof the columnar grains towards the central part of the sample. The reason for phosphorus to decreasethe nucleation rate of Ni_3Al is that it lowers the difference of free energy between solids and liquids, andincreases the activation energy for the atoms to transit through the liquid/solid interface. Phosphoruslowers the final solidification temperature of Ni_3Al, increases the length of mushy zone, inhibits thefeeding of casting, and hence increases the tendency of micropores formation.