Determination of heat transfer coefficient and ceramic mold material parameters for alloy IN738LC investment castings

Investment casting molds with different numbers of shells and pre-heating temperatures were investigated in this study. The primary layer consists of colloidal silica bound ZrSiO4 with additions of CoAl2O4 to achieve fine grains and to reach a good surface quality, whereas the following layers consist of mullite bound by colloidal silica. Interface temperatures (alloy/mold) that are necessary to determine heat transfer coefficients were obtained by linear extrapolation. Heat transfer coefficients in the range of 300–660 W/(m2 K) were obtained. The castings were examined with regard to grain size and secondary dendrite arm spacing. Physical properties of the investment casting mold were examined by differential scanning calorimetry (DSC) and Laserflash methods for temperatures up to 1300 °C. The specific heat capacity was determined to 1.13 J/(g K), thermal diffusivity was found to be in the range of (4–5) × 10−7 m2/s and the thermal conductivity to be 1 ± 0.1 W/(m K).