Effect of Casting Conditions on Layer Porosity and Entrained Bubbles in Gravity-filled TiAlNb Castings

Gravity-pouring of a TiAlNb alloy from an induction skull melting (ISM) furnace into a ceramic shell mould was carried out. The microstructure and gas defects were examined by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. Results show that the oxide films exist in the bubbles and porosity, and act as defects' heterogeneous nucleation sites. The bubbles consist of entrained and precipitable ones, while the porosity consist of layer and centerline ones. The diameter of casting bars, mould temperature and the partial pressure of argon influence the formation of gas defects.