A newly developed calcia/titanium modified magnesia-based investment mold for titanium casting

Calcia (CaO) investment has the high stability with melted pure titanium (Ti) but the poor manipulation usually leads to low success rate of complete castings. Magnesia (MgO)-based investment can produce the high success rate of pure Ti casting though. However, the MgO-based investment should be accompanied with Ti powder to meet the accuracy of Ti castings. In this study, a pure titanium casting using Ti powder modified MgO-based investment and 0.1-0.5 wt.% CaO additive was investigated. Experimental results showed that pure Ti cast with a modified MgO-based dental investment with Ti/CaO resulted in a higher success rate of the complete casting and a decrease in the interfacial surface reaction at high casting temperatures as compared to unmodified MgO-based investments with Ti powder. This newly developed Ti modified MgO-based investment and 0.1-0.5 wt.% CaO additives had an acceptable marginal accuracy with a marginal gap of less than 50 μm; the 0.4 wt.% CaO additive gave the best accuracy. Based on a micro-chemical analysis, the addition of 0.1-0.5 wt.% CaO to the Ti modified MgO-based investment significantly reduced the reaction layers and casting defects in pure Ti casting, which had proven to enhance Ti-porcelain bonding; the investment modified with 0.5 wt.% CaO had the thinnest reaction layer.