Fabrication and casting simulation of composite ceramic cores with silica nanopowders

Silica-based composite ceramic cores doped with silica nanopowders were fabricated, and effects of nanopowder content on the properties of ceramic cores were investigated. With increasing content of nano-silica powders, the fraction of cristobalite crystallite showed monotonic increase in the sintered ceramic cores due to the high surface energy of nanopowders. The linear shrinkage, bulk density and chemical leachability initially decreased to a minimum value and then increased, and the flexural strength displayed an opposite tendency. When the fraction of silica nanopowders was 0.6 wt%, the ceramic cores exhibited superior properties, including linear shrinkage of 0.6%, apparent porosity of 27.5%, leachability of 0.28 g/min, creep deformation of 0.2 mm, and flexural strength of 30.5 MPa at room temperature and 28.9 MPa at 1540 °C. In casting simulation at 1540 °C, large quantities of cristobalite were crystallized, which might provide enhanced mechanical property in the casting, and the phase transition from α to β-cristobalite during cooling would introduce microcracks and lead to better leaching of ceramic cores after casting, which well meet the need of ceramic cores for hollow turbine blades.