Investigation On The Reciprocity Of MgO-Al₂O₃ Based Investment And Ti Alloy

The investment for dental titanium casting should possess chemical stability, ventilate properties and dilatability, so MgO and Al₂O₃ with adhesive, NH₄H₂PO₄, have been taken as the investment in our research because of their excellent properties. In this study, physical properties of the investment have been measured, baking technics of the mould has been researched. The reactivity between Ti-6Al-4V alloy and investment, the fluidity of Ti-6Al-4V alloy in the mould are also be researched.The research indicated that ventilate property of the investment is suitable, average linear dilatability increased with baking temperature raising, holding time prolonging and powder-to-liquid weight ratio descending. The baking technics is established by baking experiment and DTA analysis. The interface microstructure consists of complete reaction layer, transition layer and matrix between investment and Ti-6Al-4V alloy. Max thickness of complete reaction layer is 42μm. Investigation on morphology of Ti-6Al-4V alloy showed a bulky widmanstatten with a network. The mold temperature was a very important factor, as it increasing, the complete reaction layer got thicker, acerate crystal structure growed up the ratio of mold flowing ascended and air hole enhanced.SEM showed that the Ti reacted with Mg, Al, P which belonged to the investment, through mechaochemical reaction, to form complete reaction layer with a loose structure, and the layer of element Mg was thicker than Al. It was difficult to diffuse into transition layer for element Mg, Al, P, thus plenty of element Ti was in the transition layer, and its density was very high. The phosphate and Ti alloy have strong reactivity, they form a thin reaction layer within the boundary between transition layer and matrix. This layer is harm to the casting and can not be eliminated...