Core technology of titanium alloy investment casting

Up to now, the titanium alloy casting shell materials used and currently used in the titanium casting industry mainly include: artificial graphite, refractory metals (W, Mo, Ta, Nb, etc.), special refractory oxides (alumina, silicon oxide based ceramic core), high-temperature resistant carbides (TiC, ZrC, NbC, SiC, boride, etc.); Rare earth oxides (ZrO2, Y2O3, CaO), and these materials are also the preferred materials in the research of core materials.

At present, titanium alloys mainly use inert oxide as the surface layer shell material. The order of various oxide materials according to their chemical stability to molten titanium alloys is from low to high: SiO2, MgO, Al2O3, CaO, ZrO2, Y2O3, ThO2. At present, most of them use stabilized fused yttrium oxide or zirconia as the surface layer powder, and can also use boron nitride and yttrium oxide mixed powder, calcium oxide powder as the surface coating. ZrO2, Y2O3 and ThO2 are the main materials used for the shell surface layer and adjacent surface layer of titanium alloy investment casting. A few manufacturers also choose CaO and Al2O3. The common investment casting adhesives such as water glass and ethyl silicate are often used for the back shell, and the surface layer adhesives mainly use colloidal oxides (such as colloidal zirconia, colloidal yttrium oxide, etc.) and organometallic compounds (such as zirconium acetate, zirconium nitrate, etc.). The Beijing Institute of Aeronautical Materials has developed Gu-1 and Gu-3 adhesives, and Harbin University of Technology has developed LJ-8 adhesives in 1997, It has been successfully applied to a variety of titanium alloy investment castings in China.

At present, the smelting equipment for titanium alloy investment casting and precision casting is mainly vacuum consumable electric arc shelling furnace. In 1962, the Beijing Institute of Aeronautical Materials first designed and manufactured the first vacuum consumable electrode electric arc shelling furnace in China, and then developed the vacuum induction combined water-cooled copper crucible shelling furnace. Guo Jingjie, from Harbin Institute of Technology, carried out systematic theoretical research and experimental verification on titanium alloy centrifugal casting in view of the problems of low superheat and poor fluidity of titanium alloy. At present, centrifugal casting has become the mainstream forming technology of investment casting for titanium alloy thin-walled complex components.