Prodways, a French manufacturer of industrial 3D printers, has worked with HRL Laboratories in California to investigate how polymer-derived ceramics (PDCs) can be additively manufactured without introducing critical defects. Using the ProMaker L5000 digital light projection (DLP) system, HRL scientists fabricated carbosilane-based composites and monitored their transformation into silicon-oxycarbide (SiOC) ceramics. The research established size and geometry thresholds for reinforcement particles, identified processing bounds for defect-free printing, and measured mechanical properties that place additively manufactured composites in line with conventionally processed ceramics.
HRL researchers observed pyrolysis in real time with synchrotron X-ray computed tomography while heating printed specimens in argon up to ~1000 °C. Reinforcement particles larger than about 60 micrometers consistently produced radial microcracks in the shrinking matrix, while inclusions below ~5 micrometers did not generate damage. Particle morphology also proved decisive. Plate-like inclusions created stronger tensile stress fields than spherical ones, a conclusion reinforced by finite element analysis. The findings show that both size and shape determine whether reinforcements survive conversion from polymer to ceramic.
Experiments with siloxane-based preceramic resins defined additional processing limits. When reinforcement volume fractions exceeded ~20 percent, interparticle voids formed during pyrolysis, reducing mechanical integrity. At lower fractions, filler additions decreased shrinkage and improved mass retention, stabilizing the printed parts during conversion. Unfilled SiOC parts thicker than ~1 millimeter developed internal pores as volatile gases accumulated, while composites with 10 percent mullite tolerated nearly 3 millimeters before diffusion-limited porosity appeared. These results show that both reinforcement loading and wall thickness must be controlled to achieve dense parts.
Mechanical testing quantified how these conditions influenced performance. Unreinforced SiOC measured a fracture toughness near 1 MPa·m^1/2, characteristic of brittle glasses. Reinforced specimens reached values above 3 MPa·m^1/2 at 10–15 percent loading, before toughness declined again at higher fractions due to void formation. Three-point bending tests recorded strengths over 300 MPa in samples printed below their critical thickness. Density-specific strength ranged between 110 and 160 MPa per gram per cubic centimeter, comparable to technical alumina, while a Weibull modulus of 10 indicated strength variability consistent with conventionally processed ceramics.
Polymer-derived ceramics have long attracted interest for high-temperature applications such as propulsion and energy generation. Earlier processing routes relied on long silicon carbide fibers combined with polymer infiltration and pyrolysis cycles. Although these composites reached fracture toughness values approaching 30 MPa·m^1/2, the fiber-constrained matrices often cracked during conversion, necessitating multiple infiltration steps. Switching to discontinuous reinforcements such as particles and whiskers enabled finer geometric control and better compatibility with additive manufacturing, but also introduced challenges of porosity and cracking. Sub-micron particles were shown to suppress defects entirely, while larger inclusions consistently acted as crack initiators.
In HRL’s 2020 study of polymer-derived composites printed on the ProMaker L5000, adding 0.1 volume fraction of mullite particles doubled toughness without creating pores, but loadings above 0.2 introduced voids. Later work in 2024 confirmed that inclusions smaller than ~5 micrometers could be incorporated without damage, whereas particles above 60 micrometers always induced microcracks. These investigations collectively established a clear processing window for additively manufactured SiOC composites: reinforcement volume fractions below 20 percent, particle sizes below 5 micrometers, and wall thicknesses limited to a few millimeters.
Prodways has also expanded its technology base with ceramic-focused platforms such as the Ceram Pro 365, designed for research and development of new formulations and geometries. Alongside the ProMaker L5000 used in HRL’s experiments, these systems illustrate how industrial DLP printing equipment can serve both as production tools and as platforms for materials research.
By clarifying the conditions that lead to cracking and porosity, the collaboration between Prodways and HRL demonstrates how additive systems can advance ceramic science. High-resolution DLP printing enabled precise distribution of reinforcements, while synchrotron tomography and finite element analysis mapped the stresses and shrinkage mechanisms driving failure. The resulting composites matched conventional ceramics in strength and toughness when processed within identified bounds.
Additive manufacturing of polymer-derived ceramics remains constrained by thickness limits and filler thresholds, but the ability to produce dense, toughened SiOC parts directly from preceramic polymers represents a significant advance. The work provides a framework for designing ceramic composites that combine the geometric freedom of 3D printing with the thermal and mechanical resilience required in aerospace, energy, and defense components.
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Featured image shows 3D printed test piece produced from polymer-derived composites. Photo via Prodways.
