Understanding embrittlement in ceramic-loaded filaments: insights for additive manufacturing of 3-YSZ

Purpose The purpose of this study is to show how binder formulation is essential for successful material extrusion additive manufacturing of ceramics, especially with filament-MEX, where the brittle nature of filaments poses a significant challenge. This study focuses on the common yet complex phenomenon of filament embrittlement, which limits the long-term use of printable filaments as they become unmanageable, restricting marketability. Design/methodology/approach Through differential scanning calorimetry and mechanical testing of freshly extruded and aged filaments, the embrittlement mechanism is elucidated. Attention is directed toward the extrusion step, where the binder structure is established. The sensitivity of paraffin, a common binder constituent, to the rapid solidification (up to 89ºC min−1 measured with thermography), is studied through the melting enthalpy and Kissinger equation. Findings The results show that paraffin crystallization is impeded during cooling in the presence of ceramics, evidenced by an increase in the activation energy from 245 to 356.83 kJ mol−1, enhancing the crystallization barrier for this binder constituent. Recrystallization is confirmed through an increase in the melting enthalpy from 133.82 to 253.46 J g−1, which accompanied a decrease in filament manageability. Practical implications These findings manifest the necessity of filament monitorization together with the established printability criteria for the long-term validation of binder formulations. Originality/value This study highlights for the first time that the extrusion step and the presence of ceramic powders strongly impact the filament structure–property relationship, proving the dynamism of binders’ crystalline structure within filaments and emphasizing validation over time.