Compositional effect on microstructure and mechanical properties of multication‐doped α‒β‐SiAlON ceramics

Abstract SiAlON ceramic cutting tools are well suited for high‐speed machining of heat‐resistant superalloys. The ever‐rising demands for higher productivity require the development of new SiAlON grades with better wear and fracture resistances. This investigation systematically studied the effects of Yb 2 O 3 /Y 2 O 3 ratio and La 2 O 3 content on the phase evolution, microstructure, elemental segregation, and mechanical properties of Y‒Yb‒La co‐doped SiAlON ceramics for the first time. Vickers hardness and fracture toughness were evaluated, while the precipitated phases and microstructural features were characterized using X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The critical role of La 2 O 3 in optimizing multication‐doped α‒β‐SiAlON was revealed. The addition of La 2 O 3 enhanced the elongation of columnar β‐SiAlON grains, suppressed the devitrification of intergranular phases and weakened the interfacial bonding particularly at low levels (0‒0.4 mol%), leading to higher fracture toughness due to more frequent bridging and grain pull‐out during crack propagation. The replacement of Y 2 O 3 by Yb 2 O 3 consistently increased hardness but reduced fracture toughness, attributed to the higher α‐SiAlON content and more isotropic grain morphology. Furthermore, an increase in the α‐SiAlON content was observed at higher synthesis temperatures for a given composition. This multication doping strategy offers a promising route to tailor the balance between hardness and toughness for advanced ceramic cutting tool applications with HV10 over 18 GPa and K 1C over 8 MPa/m 2 .