Investigation of inert refractory systems for investment cast tial alloys

The investment casting process offers great freedom of design with the economic advantage of near net shape production and has been widely used to process TiAl. An investigation was undertaken to develop a refractory slurry suitable for use as a face coat in investment casting of tita nium aluminide alloys, retaining chemical stability and smooth surface finish. Pure yttria (YY) and yttria zicornia (ZY) based slurry systems were investigated. After sintering, the chemical inertness of shells in contact with molten TiAl alloys were tested by simulating the casting process using a flash re-melting test, in which samples shells were contacted with titanium alunimide alloys at given temperatures for varying du rations and re-solidified. Investment castings were produced to further test face coat inertness. An yttia-zirconia slurry system was found to have a good chemical inertness similar to pure a yttria system,this was confirmed by measuring hardened layer thickness and changes of the wetting angle between the shell and alloy substrates as a function of interact time.