Evaluation of the Inertness of Investment Casting Molds Using Both Sessile Drop and Centrifugal Casting Methods

The investment casting process is an economic production method for engineering components in TiAl-based alloys and offers the benefits of a near net-shaped component with a good surface finish. An investigation was undertaken to develop three new face coat systems based on yttria, but with better sintering properties. These face coat systems were mainly based on an yttria-alumina-zirconia system (Y 2 O 3 -0.5 wt pct Al 2 O 3 -0.5 wt pct ZrO 2 ), an yttria-fluoride system (Y 2 O 3 -0.15 wt pct YF 3 ), and an yttria-boride system (Y 2 O 3 -0.15 wt pct B 2 O 3 ). After sintering, the chemical inertness of the face coat was first tested and analyzed using a sessile drop test through the metal wetting behavioral change for each face coat surface. Then, the interactions between the shell and metal were studied by centrifugal investment casting TiAl bars. Although the sintering aids in yttria can decrease the chemical inertness of the face coat, the thickness of the interaction layer in the casting was less than 10 μ m; therefore, these face coats still can be possible face coat materials for investment casting TiAl alloys.