Spark plasma sintering ofα/β-SiAlON ceramic end mill rods:Electro-thermal simulation,microstructure,mechanical properties,and machining performance

Spark plasma sintering(SPS)is a highly efficient method for the preparation ofα/β-SiAlON ceramics.However,the rapid preparation of large-scaleα/β-SiAlON ceramic components with reliable mechanical properties is difficult via SPS due to their near-insulating properties.In this study,high-performanceα/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 theα/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,elongatedβ-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.

Microwave synthesis of duplexα/β-SiAlON ceramic cutting inserts:Modifying m,n,z values,synthesis temperature,and excess Y_(2)O_(3) synthesis additive

Duplexα/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 Y_(2)O_(3) 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 ofαphase while high z value over 1.0 resulted in the dissolution ofαphase intoβphase and intergranular phase.Increasing the amount of excess Y_(2)O_(3) could promote densification and elongatedβgrain growth;however,the excess Y_(2)O_(3) amount above 4 wt%resulted in substantial crystallization of M'SS phase,thus declining the mechanical properties and wear resistance.The microwave-synthesizedα/β-SiAlON cutting insert with modified parameters(m=1.7,n=1.0,z=0.7,and 3 wt%excess Y_(2)O_(3))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 commercialα/β-SiAlON cutting insert.