Fabrication And Cutting Performance Of New Si₃N₄-based Micro-nano Composite Ceramic Cutting Tool

Ceramic tools material have a great advantage in improving machining efficiency and difficult machine materials because of their excellent mechanical properties, such as great hardness, high strength and high wear resistance to thermal shock. Therefore, they have a very broad application prospects in the cutting area. In this dissertation, in order to solve the problem of ceramic tool materials with low fracture toughness and flexural strength, a type of Si3N4-based micro-nano-composite ceramic tool material (ST3) was fabricated via hot pressing technique by adding Si3N4and SiC nanoparticles and with Al2O3and Y2O3as additives. And it’s mechanical properties, microstructure and crack propagation morphology were investigated. Micro-nano-composite ceramic material ST3has its flexural strength, fracture toughness and Vickers hardness with1000Mpa,8.5MPa·m1/2and19.5GPa respectively. Macro and micro design, component ratio and toughening mechanism of ST3were investigated. Fabrication process as well as the effects of the volume fraction of nano-TiC particles in ST3on mico-structures and mechanical properties of ceramic tool materials were studied, and the process parameters of holding time and sintering temperature were optimized.Cutting performance and wear mechanism in dry machining of40CrNiMoA and T10A with Si3N4-based micro-nano-composite ceramic tool were discussed, in comparison with a commercial Si3N4-based ceramic tool (FD-01). The morphology and rake face or flank wear of ceramic tools were investigated by SEM and USB microscope.The results show that:Hot-Pressed Si3N4specimens of tool material were composed of overlapping of rod-like β-Si3N4grains with various aspect ratios. The fracture surface was rough and grain pull-out was clearly visible. After add nanoscale particles in the micron powder as a toughening mechanism, the strength with very little reduction as well as the hardness improve greatly. The most frequently observed toughening mechanisms in the specimens are crack bridging and crack deflection. As for the high-speed dry cutting of hardened40CrNiMoA, the cutting performance of ST3is significantly better than that of FD-01. The main wear form of ST3is adhesive and abrasive wear, and accompanied by the minor micro-chipping. The continuous cutting quenching T10A under lower speeds, the wear patterns of ST3is previously flank crater wear, flank wear and boundary wear mainly accompanied by a significant micro-cracks. With the increase in cutting speed (vc>150m/min), main failure mode of ST3is chipping, chopped damaged, and FD-01is completely state of the tool tip chipping. The failure modes of both tools are mechanical fatigue and thermal fatigue.