Simulation and Control of Forming Defects in Gel Casting of Yttria-Stabilized Ceramic Molds for Titanium Alloy

Abstract:

To address nodular protrusions on titanium alloy-closed impellers caused by gas entrapment during gelcasting of integrated Y₂O₃ (yttria) ceramic molds, this work established a predictive and control framework that couples a Carreau non-Newtonian viscosity model with a transient two-phase volume-of-fluid filling solver. Rheological experiments were fitted to obtain the Carreau parameters for the yttria slurry (relative error < 5%), enabling time-space reconstruction of bubble generation-migration-entrapment throughout filling. Results show that the simulated entrapment locations exhibit strong spatial correspondence with computed-tomography voids in ceramic molds and nodular defects on Ti alloy castings at both the impeller and bottom regions. Parametric studies indicate that a moderate filling velocity of 0.05 m·s^–1 markedly reduces trapped-gas volume; a bottom-fill configuration essentially eliminates entrapment in the impeller region; on this basis, applying horizontal vibration (50 Hz, 1 mm) during and after filling removes the remaining bubbles. Ceramic molds fabricated with the optimized parameters were verified by scanning, confirming the disappearance of gas entrapment within the impeller. The study provides a reusable framework for defect prediction and active process control in gelcasting of complex Ti alloy components.