LIU Wenguang, CHEN Gong, QU Shengwen, WANG Xingguo, XU Zuquan, FENG Hao

(Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China)

Extended Abstract:[Background and purpose] The combination of precursor-derived ceramic technology and 3D printing technology eliminates the need to control particle size and avoids the influence of binders and sintering aids with relatively low pyrolysis temperatures. Among the various 3D printing technologies, direct ink writing (DIW) is known for its low cost and high material versatility, making it particularly suitable for printing complex formulations, intricate structures, and large components, and hence attracting significant interest from researchers. However, current DIW processes for precursor ceramics often encounter issues, such as unstable ink rheology, printing collapse, delamination defects and difficulties in achieving large-sized structures. To address these challenges, various auxiliary techniques have been introduced, such as near-infrared (NIR) upconversion particle-assisted photopolymerization and high-temperature platform heating. However, the outcomes are still unsatisfactory. In this study, a relatively cost-effective precursor ceramic material was used as the carrier, while a near-infrared laser was introduced as a secondary heat source to complement the high-temperature platform, thus addressing the issue of insufficient heat absorption in the upper layers. The process parameters of the DIW process were optimized.[Methods] The printing slurry was prepared by sequentially adding and stirring the following raw materials with a magnetic stirrer: hydrogen-containing polymethylsiloxane (PHMS, hydrogen content 1.6), tetramethyl tetravinyl cyclotetrasiloxane (D₄Vi), polydimethylsiloxane (PDMS), methylvinylsiloxane-coordinated platinum catalyst, aluminum oxide (Al₂O₃) powder, boron carbide (B₄C) powder and sodium carboxymethyl cellulose (CMC-Na). The samples were printed using a custom-built thermally assisted DIW printing device. The temperature of the heated platform could be adjusted in the range of 0–300 ℃, while the rated power of the near-infrared laser was 1 W. During printing, the slurry was extruded through a screw, irradiated with a near-infrared laser and finally accumulated and shaped under program control. The main printing parameters included laser power, platform temperature, printing speed and printing height.[Results] The curing effect of the slurry was dependent significantly on the laser power. At too low laser powers, the printed samples collapsed and became uneven. Conversely, when the laser power was too high, bubbles and deformations occurred in the printed samples, with severe surface carbonization or ablation occurring. At an appropriate laser power (duty cycle of 29%), the samples exhibited relatively high forming quality. When the platform temperature was set below 100 ℃, the curing of the slurry was insufficient, leading to poor layer accumulation. When the temperature exceeded 100 ℃, slurry extrusion became difficult, negatively impacting the formation. At 100 ℃, the slurry was adequately cured, the line width was minimized, continuity was optimal and the cross-section was well formed, resulting in the highest forming quality. At printing speed of 5.00 mm·s⁻¹, the exposure time of the slurry under the laser was reduced, resulting in insufficient energy absorption and curing inability in time, so that the printed items tended to bend and collapse. At speed of 3.34 mm·s⁻¹, the exposure time was extended, causing the slurry to be cured too quickly, resulting in nozzle clogging, slow material output, material breakage and unstable extrusion. At speed of 4.17 mm·s⁻¹, the samples exhibited high forming quality with complete shapes, while no collapse and no nozzle clogging occurred. When the printing height was below 0.5 mm, the nozzle scraped the previously printed layer during printing of the subsequent layer, reducing the surface quality and potentially causing nozzle clogging. When the printing height exceeded 0.6 mm, material breakage occurred and the shape accuracy decreased. At printing height of 0.55 mm, the printing process was smooth, with no lateral overflow of the slurry. The line width was moderate, the continuity was good and the printing results were optimal. Additionally, the green bodies with the addition of boron carbide had slightly higher compressive strength, as compared without those without boron carbide. However, after sintering, the compressive strengths of the boron-carbide-containing samples were lower than those of the samples without the additive.[Conclusions] A near-infrared laser was introduced as a secondary heat source, while the key printing parameters were systematically studied using a controlled variable method. The assistance of the near-infrared laser and high-temperature platform effectively enhanced the forming capability of the ceramic slurry, eliminating the need for an oven curing process and significantly increasing curing efficiency. This method effectively reduced the requirements for slurry viscosity and fluidity during the 3D printing process. The controlled variable method was used to evaluate the parameters for direct ink-writing ceramic 3D printing. The optimal printing process parameters included duty cycle of 29%, platform temperature of 100 ℃, printing speed of 4.17 mm·s⁻¹ and printing height of 0.55 mm.

Key words: near-infrared laser; precursor-derived ceramic; 3D printing; direct ink writing