Solid Freeform Fabrication of Silicon Nitride Ceramics

Abstract

Silicon nitride ceramics have been prepared using the fused deposition (FD) process in a Stratasys 1650 modeler. Two types of silicon nitride have been prepared: GS44 and AS800. AS800 is processed and used at higher temperatures than GS44. The strength of machined surfaces of either type of silicon nitride prepared using FD is comparable to conventionally processed material. Using standard build conditions strengths for as-built and as-sintered surfaces are approximately 50% lower. The additive nature of solid freeform processes also allows multi-material combinations to be deposited which result in enhanced performance. For example, combinations of silicon nitride based materials with different thermal expansion coefficients have been prepared which demonstrate strength increases > 20%. In addition, components containing complicated internal cavities may also be fabricated.

Nanofiber‐reinforced polymers prepared by fused deposition modeling

“…The concepts used to create functional ceramic parts with FDM could be used to remove the polymer matrix surrounding nanofibers such as VGCFs and SWNTs to create a part consisting of only nanofibers or a nanofiber template to be infiltrated with another material 1. Novel piezoelectric ceramic/polymer composite materials, functional ceramic materials, and porous ceramic biomaterials have been produced in this manner 20–23. A part of the research to produce these ceramic‐filled feedstock materials has been focused on achieving dispersion and controlling viscosity to achieve uniform dispersion of the ceramic particles in the polymer binder 20–25.…”

“…Novel piezoelectric ceramic/polymer composite materials, functional ceramic materials, and porous ceramic biomaterials have been produced in this manner 20–23. A part of the research to produce these ceramic‐filled feedstock materials has been focused on achieving dispersion and controlling viscosity to achieve uniform dispersion of the ceramic particles in the polymer binder 20–25. These investigations are useful and relevant to the current research because issues of viscosity and dispersion were crucial to their success.…”

Microstructural Characterization and Mechanical Properties of Si3N4 Formed by Fused Deposition of Ceramics

“…It is no surprise that build defects can easily lead to reduced σ f , as can be seen from Table II. In addition, in previous studies using higher temperature Si 3 N 4 material (AS800), samples tested under a condition where the “as‐built” surface (no machining) was placed in tension suffered a significant strength loss: σ f from 746 MPa for machined surfaces to 394 MPa, but without a decline in the Weibull modulus “m.” 35 …”

“…Volume defect‐containing samples had a Weibull modulus of 3.9, and the specimens that showed surface failures had a higher Weibull modulus of 11.7. Other work has reported that for the high‐temperature‐grade Si 3 N 4 (AS800), an optimized FDC process that removed the Fe contamination yielded a material with a significantly higher Weibull modulus (>20) 35 …”

“…Other work has reported that for the high-temperature-grade Si 3 N 4 (AS800), an optimized FDC process that removed the Fe contamination yielded a material with a significantly higher Weibull modulus (420). 35 An important consideration of layer-by-layer manufacturing of parts for structural applications is the quality of the surface finish (and hence as-built surface strength), as some of the applications will require asbuilt surfaces to be under stress. The strength of GS44 Si 3 N 4 bars made by FDC was measured in the as-built surface condition (no machining) and was determined to be significantly lower than that of diamond-ground surfaces.…”