THE EFFECT OF SILICA-CONTAINING BINDERS ON THE TITANIUM FACE COAT REACTION/

The interactions of CP-Ti and Ti-6Al-4V with investment molds containi ng alumina/silica and yttria/silica face coat systems were studied. '' Containerless'' melting in argon was employed and small test samples w ere made by drop casting into the molds. The effects of the face coat material and mold preheat temperatures on the thickness of the alpha c ase in the drop castings were evaluated with microhardness and micropr obe measurements. It was found that the thickness of the alpha case wa s the same, whether a yttria/silica or alumina/silica face coat was us ed, indicating that the silica binder can reduce the apparent inertnes s of a more stable refractory, such as yttria. It was also found that the alloyed titanium castings had a thinner alpha case than those prod uced from CP-Ti, which suggests that the thickness of the alpha case d epends on the crystal structure of the alloy during cooling from high temperatures. Furthermore, the small drop castings made in small yttri a crucibles used as molds exhibited little or no alpha case.