A comparison of the chemical inertness of two Y₂O ₃-Al₂O₃-ZrO₂ and Y₂O ₃-Al₂O₃ face coat materials through sessile drop and investment casting methods

Investment casting is uniquely suited to the manufacture of Ti alloys for the production of near net-shape components, reducing material waste, and machining costs. Because of the high reactivity of titanium and its based alloy, the molds which are used in the investment casting process require high chemical inertness, which results in them being very costly and non-recyclable. In order to reduce the cost of these molds, traditionally using yttria as the face coat, two alternative molds are developed in this study with face coat materials of Y₂O₃-Al₂O₃ and Y ₂O₃-Al₂O₃-ZrO₂. The slurry properties and chemical inertness of the face coats were evaluated for viscosity, thermal expansion, friability, and phase development. The chemical inertness of these two molds were determined using both the sessile drop test and investment casting to identify the levels of interaction with a Ti-45Al-2Mn-2Nb-0.2B alloy. The results illustrated that the molds using Y ₂O₃-Al₂O₃ and Y₂O ₃-Al₂O₃-ZrO₂ as the face coats both showed excellent sintering properties and chemical inertness when compared to the yttria face coat. They can consequently be used as two alternative face coats for the investment casting of TiAl alloys.