Impact of mold surface material on the reaction titanium layer of castings

This study examines how Y2O3-based shell materials with different binders affect α-case formation in titanium castings. Four systems were tested: Y2O3 with zirconia, yttria, or silica sol binders, and a Y2O3 with ammonium metatungstate composite. Characterization revealed yttria sol binder performed best, forming the thinnest reaction layer (80 μm) due to its high stability. Zirconia and silica sol systems showed thicker layers (140 μm and 100 μm respectively), with ZrO2 formation and Si enrichment at the interface. The most severe reactions occurred with Y2O3 with ammonium metatungstate (230 μm), where tungsten enhanced oxygen diffusion. Key reaction products included TiO, TiO2, Ti5Si3,with thermodynamic analysis confirming Ti-Si compound preference. Binder stability (yttria > silica > zirconia) proved critical in controlling reaction thickness, while ammonium metatungstate decomposition worsened oxygen diffusion. These findings guide shell material selection for titanium casting applications.