Cracking defect and porosity evolution during thermal debinding in ceramic injection moldings

Abstract

Formation of cracking defect during thermal debinding of a wax-based zirconia–binder system has been investigated at varying binder formulations (volumetric ratio of low-melting vs high-melting binder constitutes ranging from 1.7 to 2.8), heating rates (5–30°C h −1) and the use of wicking powders in ceramic injection moldings. Increase of the low-melting binder ingredients to a critical ratio of 2.8 resulted in an apparent cracking at a relatively low pyrolysis temperature of 250°C as the heating rate was increased to 30°C h −1. The cracking was avoided by use of wicking powders during thermolysis. The most frequent pore diameter of samples debound without the packing powders rapidly increased by nearly 3-fold over a temperature range from 200 to 250°C; contrarily, a gradual increase in the pore size was resulted when moldings were debound under the identical condition but with the packing powders. This finding is correlated with the incidence of cracking and its possible causes are discussed.