HYDRATION RESISTANCE OF Y2O3 DOPED CaO AND ITS APPLICATION TO MELTING TITANIUM ALLOYS

Various amount Y2O3(18 mol%) doped CaO powder was synthesized by the solid state reaction method, the pellete and crucible were fabricated by the cold isostatic pressing and were sintered at 1750 degrees C for 4h. The microstructural characterization was revealed by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The XRD results showed that when Y2O3 doped 2 mol%, metastable CaY2O4 phase existed in CaO grain boundary, when Y2O3 doped 3 mol%-8 mol%, in addition to the above structure, Y2O3 phase also be found in CaO grain boundary. Hydration experiment results showed when Y2O3 doped 0 mol%4 mol%, CaO had excellent hydration resistance performance, Y2O3 doped 2 mol% had the best hydration resistance, its weight addition stored after 7 weeks (49 days) was only about 0.2 wt%. Melting experiment results showed that it was no reaction between crucible and alloy layer. Oxygen, calcium, titanium, nickle and yttrium element not diffusion between the CaO crucible and TiNi alloy, it was no oxygen content increase after melting.