Effect of TiO ₂ addition on microstructure and mechanical properties of alumina‐based cores prepared by sol‐gel method

Abstract Alumina‐based ceramic cores have widespread applications especially in the investment casting of turbine blades due to chemical inertness with most of the superalloys, capability of machining in the green state, and their mechanical stability at high temperatures. The present work studied the effects of TiO ₂ addition to the alumina‐based cores. These cores were prepared via the sol‐gel method process by mixing alumina powders with NH ₄ Cl and silica sol. The effects of adding different amounts of titania from 5 to 30 wt% and different sintering procedures on mechanical, physical, thermal, chemical, and microstructural features of the bodies were investigated. According to the results of rheology measurements of the slurries and flexural strength of the green bodies, the suitable amount of solid loading was 45 vol. %. The results showed that there is an optimum content for TiO ₂ addition. The specimen contained 15 wt. % titania and sintered at 1400°C for 2 hours had the thermal expansion coefficient as low as 4.8 × 10 ⁻⁶ /°C (25‐900°C), suitable mechanical properties as a result of tialite formation, and apparent porosity of 28 vol. %, respectively. The result of creep deformation test showed that this specimen had near zero deformation at 1650°C.