Control of Alpha Case on Investment Cast Ti 6Al‐4V Using An Industrial Shelling System

Abstract

Molten titanium has a strong reaction with most of the refractories used for mold building in investment casting. Calcia partially stabilized zirconia (PSZ) used as a facecoat material has a reduced reaction with molten titanium and is still offered at an affordable cost. However poor process control can greatly impair the formation of a thin alpha case, an essential condition to limit the amount of subsequent chemical milling. The effect of the prime stuccos, the viscosity of the prime slurry, and the shell mold preheating temperature on alpha case thickness have been evaluated for different casting wall thicknesses. Alpha case depth have been determined by metallographic techniques and microhardness measurements on different casting cross sections. Minimum achievable alpha case thickness has been determined with a calcia partially stabilized zirconia (PSZ) face coat.