Study On Ti(C,N)-BN Composite Cermet Cutting Tools And Cutting Performance

Ti(C,N)-based cermets have higher flexural strength and fracture toughness compared with most ceramic materials, but it is still brittle materials. Boron nitride nanotubes(BNNTs) have been used as the strengthening additives for ceramic composites due to its high strength and toughness. So far, cubic boron nitride(c-BN) is known as the the second hardest material after with higher thermostability than diamond, and it has chemical inertness with the family of iron metal, so c-BN is more suitable for machining the materials with high hardness and toughness. Ti(C,N)-based cermet tool materials were developed by hot-pressing sintering technology using BNNTs and c-BN as strengthening agency and Mo-Ni as binder phase. The effect of BNNTs content, c-BN content and sintering process on the mechanical properties and microstructure of Ti(C,N)/BNNTs and Ti(C,N)/BN composites were studied. The toughening and strengthening mechanisms of Ti(C,N)/BNNTs composites were analyzed. The cutting^performance of TMNC1.0and TMN cermet tools was investigated by turning the austenitic stainless steel1Cr18Ni9Ti.The effect of sintering process, initial powder size and binder content on mechanical properties and microstructure of Ti(C,N)-based cermets were investigated. It was shown that the best mechanical properties were obtained when the sintering temperature was1500℃under the sintering process of two stages of holding time. A lower sintering temperature led to insufficient liquid-phase sintering process, which can reduce the density of the composite. A higher temperature and longer holding time resulted in abnormal grain growth, which was not good for improving the mechanical properties of the composite. With the refinement of the initial powder size of Ti(C,N), the fracture toughness reduced slightly, while the flexural strength and Vickers hardness increased. The cermets with the binder phase content designed based on the eutectic composition of Mo-Ni binary alloy phase diagram could achieve better mechanical properties.Using the pre-optimized sintering process, initial powder size and binder content, the Ti(C,N)/BNNTs composites were fabricated by hot-pressing using BNNTs as strengthening additives. The content of BNNTs, the sintering temperature as well as the holding time of Ti(C,N)/BNNTs composites were optimized, and their effect on mechanical properties and microstructure were studied. The best mechanical properties were obtained for TMNB0.5composite at1500℃under32MPa in vacuum with a holding time of30minutes. Its flexural strength, Vickers hardness and fracture toughness were1785MPa,18.49GPa and5.69MPa.m1/2respectively. The toughening and strengthening mechanisms of TMNB0.5included crack deflection, crack bifurcation, grain bridging, transformation of fracture mode and residual stress toughening.The effect of h-BN and c-BN particles on mechanical properties of Ti(C,N)-based cermets were also studied for comparision. The mechanical properties of the Ti(C,N)/h-BN composite were decreased sharply with an increased content of h-BN particles. The study showed that h-BN particles are not suitable for ceramic tool materials. The content of c-BN, the sintering temperature as well as holiding time of Ti(C,N)/c-BN composites were optimized, and their effect on mechanical properties and microstructure were studied. The best mechanical properties were obtained for TMNC1.0composite at1550℃under32MPa in vacuum with a holding time of30minutes. The flexural strength, Vickers hardness and fracture toughness were1490MPa,18.39GPa and5.15MPa.m1/2respectively.The cutting performance of TMNC1.0was investigated by turning the austenitic stainless steel1Cr18Ni9Ti with a comparison to TMN and commercial tool LT55. The best cutting parameters of TMNC1.0obtained through orthogonal experiments under wet cutting condition were as follows:the cutting speed was160m/min, the cutting depth was0.2mm, and the feed speed was0.15mm/r. With these cutting parameters, the cutting performance of LT55, TMN and TMNC1.0in dry cutting and wet cutting was studied, and the wear mechanisms of the tools were analyzed. In the condition of dry cutting, TMNC1.0showed better cutting performance than TMN and LT55. The main tool wear mechanisms of TMNC1.0and TMN were adhesive wear, diffusive wear, oxidation wear and abrasive wear. The main tool wear mechanisms of LT55were adhesive wear, diffusive wear and oxidation wear. In the condition of wet cutting, the cutting performance of TMN was the best, the second was TMNC1.0, and the cutting performance of LT55was the worst. The main tool wear mechanisms of TMNC1.0and TMN were adhesive wear, diffusive wear and a slight of abrasive wear. The main tool wear mechanisms of LT55were adhesive wear and diffusive wear.