Simulations of microporosity in IN718 equiaxed investment castings

A finite element model for simulating dendritic solidification of multicomponent-alloy castings has been enhanced to include the calculation of pressure and redistribution of gas-forming elements during solidification and cooling. The model solves the conservation equations of mass, momentum, energy and alloy components, and the gas-forming elements, hydrogen and nitrogen. By solving the transport of gas solutes and comparing their Sievert's pressure with the local pressure, the model can predict regions of possible formation of intergranular porosity. Calculations were performed on equiaxed Ni-base superalloy (IN718) plate castings. The potential to form microporosity was analyzed with different variables including the mass transfer of hydrogen and nitrogen from the casting to the casting/mold gap, the final grain size, a grain-shape parameter and the thickness of the plate casting. The most important factor was found to be the mass transfer coefficient. The results were also affected by the final grain size and grain-shape parameter.