Mechanism and Influence of Re-dissolution of Zirconium Diacetate-Yttria Shell for Titanium Investment Casting

The re-dissolution of zirconium diacetate-yttria shell (ZA-Y shell) and its impact were investigated. The re-dissolution rate under moisture condition was measured by a balance. Three-point flexural strength was measured using a universal testing machine, and the fracture index was calculated. The distribution of the surface precipitates was observed by optical microscope, and its morphology and composition were tested using scanning electron microscopy (SEM) combined with energy spectrum analysis (EDS). The composition of the ZA-Y shell was measured by X-ray fluorescence (XRF). The results show that the re-dissolution is limited. The maximum water penetration rate is 2.5% and the dissolution rate is 0.8% within 20 min. The strength decreases by 26% and fracture index reduces to 66%. The surface precipitates are attributed to dissolution of ammonium metatungstate (AMT) and there are two reasons: drastic pressure release or fast drying condition with slow heat dissipation.