Spark plasma sintering (SPS) is a highly efficient method for the preparation of α/β-SiAlON ceramics. However, the rapid preparation of large-scale α/β-SiAlON ceramic components with reliable mechanical properties is difficult via SPS due to their near-insulating properties. In this study, high-performance α/β-SiAlON ceramic end mill rods with large aspect ratios were successfully prepared via SPS. Two different types of sintering processes (namely vertical-round-rod (VRR) and horizontal-square-rod (HSR) processes) were developed, and their effects on the phase composition, microstructure, mechanical properties, and machining performance of the α/β-SiAlON ceramic end mill rods were studied. The electric and temperature field distributions during sintering were studied through an electro–thermal simulation. The simulated and experimental temperature distributions are in good agreement. In contrast to VRR samples, HSR samples with a small axial size show a uniform temperature distribution and satisfactory microstructures within a certain range of dimensions as well as the expected phase composition; furthermore, elongated β-SiAlON grains are preferentially oriented in the direction perpendicular to the sintering pressure direction. As a result, the HSR samples exhibit better mechanical properties and machining performance than the VRR samples.

Duplex α/β-SiAlON ceramic cutting inserts (30α:70β) were synthesized by microwave sintering. The effects of solid solution parameters (m, n, z), synthesis temperature, and amount of excess Y₂O₃ synthesis additive on phase assemblage, microstructure, mechanical properties, and cutting performance were systematically investigated. It was found that increasing m value could improve the formation of α phase while high z value over 1.0 resulted in the dissolution of α phase into β phase and intergranular phase. Increasing the amount of excess Y₂O₃ could promote densification and elongated β grain growth; however, the excess Y₂O₃ amount above 4 wt% resulted in substantial crystallization of M'_SS phase, thus declining the mechanical properties and wear resistance. The microwave-synthesized α/β-SiAlON cutting insert with modified parameters (m = 1.7, n = 1.0, z = 0.7, and 3 wt% excess Y₂O₃) was obtained with optimal comprehensive properties, whose tool life was found to increase by approximately 75% in high-speed milling of Inconel 718 superalloy compared to the commercial α/β-SiAlON cutting insert.