Formation of micropores in a DS Ni-Ti-C alloy

The aim of this experiment was to examine the formation of micropores during directional solidification of a Ni--5Ti--0.2C alloy in order to determine their precise origin and to verify some nearly developed theoretical formulae. A further aim is to elicit the factors responsible for the occurrence of the defects which seriously impair the mechanical properties of certain alloys. The technique of quenched directionally solidified rods was used in order to follow the development of solidification. The results show that solidification conditions influence microporosities formation through the fraction of eutectic and this suggests that it is possible to relate susceptibility to microporosity formation to the fraction of eutectic. The results also confirm that for solid solution alloys such as Ni--5Ti--0.2C, the fraction of eutectic increases when the ratio G/R (G: temp. gradient in mushy zone; R: solidification rate) decreases as described in the mathematical model developed.