Simulations of microporosity in IN718 equiaxed investment castings

A finite element model for simulating dendritic solidification of multicomp onent-alloy castings has been enhanced to include the calculation of pressu re and redistribution of gas-forming elements during solidification and coo ling. 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 pres sure with the local pressure, the model can predict regions of possible for mation of intergranular porosity. Calculations were performed on equiaxed N i-base superalloy (IN718) plate castings. The potential to form microporosi ty was analyzed with different variables including the mass transfer of hyd rogen and nitrogen from the casting to the casting/mold gap, the final grai n 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 r esults were also affected by the final grain size and grain-shape parameter . (C) 2001 Elsevier Science B.V. All rights reserved.