Self-standing doughs of SiAlONs enable low-volume production through green machining

Official URL: https://dx.doi.org/10.1021/acsomega.6c05186

SiAlONs are silicon-, aluminum-, oxygen-, and nitrogen-based ceramic alloys used in high-performance applications for their thermal and mechanical properties. Their use requires custom geometries, and near-net shaping is typically carried out at the green state. This study reports the preparation of self-standing SiAlON doughs with a 0.9Y-0.5Sm-0.5Ca composition, produced by hand-mixing in under 2 min. These clay-like doughs overcome the limitations of powder-pressing and slurry-based methods. After hand-shaping or molding, they form green bodies suitable for CNC machining for low-volume production and custom-based design. A single additive, a poly(ethylene glycol)-grafted random copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, was used at 2 wt % to impart malleability to 72.7 wt % SiAlON suspensions. These doughs exhibited a flexural strength of ∼0.5 MPa, enabling machining without tool wear while maintaining integrity. Machining was performed at room temperature after drying. Mechanical and microstructural properties were compared with those of a wear part made by uniaxial pressing. After gas-pressure sintering, hardness and Vickers toughness values of dough-derived samples (13.48 ± 0.35 GPa, 6.22 ± 0.28 MPa·m1/2) were comparable to the uniaxially pressed samples (14.40 ± 0.39 GPa, 6.40 ± 0.40 MPa·m1/2). The doughs yield ceramics with 19% isotropic shrinkage and 3.24 g·cm–3 density (∼99.99% theoretical) postsintering, enabling efficient fabrication and prototyping of complex shapes.