Silicon nitride, with its low dielectric constant and capacity for high thermal loads, is a candidate material for many high temperature applications. In the work reported here, the effect of two different sintering aids and/or the addition of carbon fibers on ink printability and densification was studied. Rheology, varying printing parameters, SEM microstructural studies and mechanical properties were used to quantify differences as a result of composition changes.

 

40 vol% to 47.5 vol% colloidal suspensions were additively manufactured via direct ink write (DIW), varying the amount of carbon fiber from 0 vol% to 10 vol%. When present, the carbon fiber are aligned along the print path, uniaxially. Rheology measurements showed that with the addition of carbon fiber, viscosity decreased even with the overall increase in the solids vol% of the colloidal suspension. The samples manufactured with 5 w% alumina and 5w% yttria resulted in a higher relative density versus their 5 w% ytterbia counterparts. This resulted in a corresponding decrease in flexural strength on par with the decreased density. XRD was used to verify the transition of alpha phase silicon nitride into beta phase silicon nitride. SEM and optical microscope are used to study the fracture surface, verifying fiber pullout, and the alignment of the carbon fiber along the print path.