Modification of CaO Refractory for Melting Titanium Alloys and Its Hydration Resistance

CaO is a promising refractory for melting TiNi shape memory alloys, the carbon contamination can be avoid by using CaO crucible instead of carbon crucible. However, its industrial application is limited by the easy hydration of CaO in the air. In this study, the hydration resistance of CaO is modified by the addition of ZrO(2), the powder of CaO adding 6.0 to 15.0mol% ZrO(2) and 2.0mol% TiO(2) is ball-milled, the mixture is shaped into the chip by the isostatic pressing method (IP), then the samples are sintered at 1750 degrees C. The X-ray diffraction analysis reveals that the sintered samples consist of CaO dissolved with ZrO(2) and CaZrO(3). The anti-hydration property is described by the weight addition of samples, which are stored at the room temperature and atmosphere. It is shown that the sample with 12% ZrO(2) of additive possesses the good hydration resistance, its weight addition stored after 56-days is less than 0.6wt%. Therefore, the powder of CaO with 12.0% ZrO(2) additive are used to prepare the crucible by IP, the green crucible is sintered at 1750 degrees C. This home-made crucible is used for melting TiNi alloy by means of the induction method at 1500 similar to 1800 degrees C temperature and the vacuum environment, it is found that, the internal and external surface of crucible were almost kept unchanged after melting, this refractory did not obviously react with titanium melts, this result may provide a support for searching a new refractory with the good hydration resistance for melting of titanium alloys.