Thermal properties of investment casting shells have a great influence on the solidification of metal and thus control the properties of the cast product. Computational simulation requires accurate thermal properties to better represent the real process. Due to the porosity and meta-stable materials used in the investment shells, it is difficult to determine the real time thermal properties as a function of components and thermal processing history. Previous studies measured the thermal properties using a variety of methods, but very few results can be directly used in simulations due to lack of accuracy.
This research developed a new methodology that combines the laser flash thermal diffusivity measurement technology and inverse method. This methodology was used to accurately characterize the thermal properties of the investment shells within the temperature range from 200 ºC to 1200 ºC. Tests were performed on the shells over a wide component range and different thermal processing histories (prefiring at 600 ºC, 850 ºC, 1000 ºC). It was also found that at under 1000ºC, a higher prefiring temperature reduces the reactivity of amorphous silica toward devitrification during the casting process, thus a lower thermal conductivity shell can be achieved.
Cenosphere particles were applied in the investment shells to engineer the investment shell thermal properties. Compared to introducing porosity by sacrificed phases, the use of cenospheres was found effective to lower the thermal diffusivity by up to 70% but retain a favorable thermal diffusivity/mechanical strength ratio.
Moreover, metal/mold interactions were analyzed for several prime coat materials, and some suggestions for zircon substitution were made. --Abstract, page iii
