Near-net-shaping techniques, such as additive manufacturing (AM), has attracted attention due to their effectiveness on the manufacture of complex structures with reduced material waste. Recent literature reports showed that is possible to achieve dense glass parts through Direct Ink Writing AM technology. However, optimizing the thermal post-processing to achieve fully dense glass and glass-ceramic parts by pressureless sintering is a quite complex task. The activation of the densification mechanisms is related with the same variables that induces crystals growth, e.g. reduction of the viscosity and local surface energy. Consequently, for most glass systems, devitrification is usually inevitable during the sintering process, and the maximum densification achievable of a glass compact may be determined by the preponderance of the sintering kinetics over the crystallization kinetics. Consequently, the control of the post-processing parameters related with debinding and sintering protocols (e.g. heating rate, temperature, duration and atmosphere) is essential to successfully densify glass-ceramic parts derived from AM technologies, such as Direct Ink Writing.
In this work, a high-end glass-ceramic system (SiO2-Li2O-K2O-P2O5-ZnO-Al2O3) with a narrow sintering window has been studied. The glass has been melted, poured on water, and milled for different periods of time to achieve an optimized particle size distribution. Inks containing a high solid load (47 vol.%) have been produced through a hydrogel route. The glass powder and the polymeric additive has been characterized by thermogravimetry and differential thermal analysis. The sintering behavior of the printed parts was analyzed by dilatometry and hot stage microscopy. The impact of the heating rate, sintering temperature and hold time on the residual porosity and mechanical properties of the glass ceramics is discussed.