Effects of refiners on grain structures of superalloy in 718 at high pouring temperature

In order to improve the filling ability of large complex thin wall castings, the pouring temperature should be increased, but this will result in grain size coarsening. Therefore, effects of refiners on grain structures of superalloy Inconel 718 have been investigated. It is shown that, adding mixed refiner consisting of two ternary intermetallic compounds at pouring temperature of 1520°C, the average equiaxed grain size could be refined from 10.56 to 2.71mm and the proportion of equiaxed grains at cross-section could be improved from 10 to 84%. At the same pouring temperature, the amount of porosity in specimens could be greatly decreased by adding refiners into the melt. Moreover, experimental results indicate that trace addition of refiners to the melt neither introduces inclusions nor changes the phase constituents of the alloy. Grain refinement mechanisms are also discussed.