| The in-situ integration synthesis technology is a new fabrication process, it can overcome some problems caused by the in-situ two-step process (for example the conversion ratio of the raw materials is less than100%and the matrix grains grow abnormally after secondary-sintering). In this paper, the ceramic cutting tool materials reinforced by whiskers/rod-like particles were fabricated by the in-situ integration synthesis technology; the cutting performances of the new fabricated ceramic cutting tool were also studied preliminarily.The proper environment of whiskers’growth was firstly investigated for the TBN (Ti, BN) system and TBCN (Ti, BN, B4C) system. The results show that the whiskers grow under pressure in the in-situ integration synthesis technology. Compared with the conventional carbon-thermal reduction process, the same of the two processes is that the whiskers’growth can be affected directly by the ratio of raw-materials and additives; however, the difference of them is that the pressure should be introduced at the right moment in the in-stiu integration synthesis technology. On one hand, the pressure is favorable for the whiskers’growth; on the other hand, it is the resistance to the whiskers’elongation.The following sintering process of the in-situ integration synthesis was optimized, and the microstructure, whiskers’ morphology, mechanical properties of the composites materials at different sintering temperatures and holding times were discussed. The result shows that the excellent performance of in-situ TiB2whiskers and particles reinforced ceramic cutting tool materials can be obtained at1700℃with holding time of40minutes. With this process, the in-situ TiB2rod-like particles and particles reinforced ceramic cutting tool materials named TBN5(the mole ratio of Ti and BN is2:1and the content of Ni is5wt%) was successfully fabricated, the flexural strength, fracture toughness and Vickers hardness of TBN5were1057MPa,8.82MPa·m1/2,19.87GPa respectively. The improvement of mechanical properties of TBN5is resulted from the reinforcing effect of particles and rod-like particles, as well as higher relative density.The microstructures of the composite materials were investigated by means of scanning electron microscope (SEM), according to which the toughening and strengthening mechanisms and the densification mechanism of the composites materials were studied. By observing the crack propagation path, it was found that when the crack encounters the TiB2whiskers and particles, there would be crack deflection, crack termination and bridging, pulling-out of the whiskers, along with the bridging of the TiB2particles and ductile particlesand the fracture of the weak grains. The TBN5system can reach a high relative density of99.8%by the new sintering process (SHS+hot-pressing sintering+liquid-phase sintering). The densification process involves two stages; the first is the liquid flow, particles’rearrangement at the violent reaction stage, and the second is the liquid further flow to fill in the interspace and following by the grains’ growth at the high holding temperature. The plastic flow mechanism was found in the TBCN system.In order to investigate the growth mechanism and the growth process of the whiskers, the means of interrupted experiment, SEM, XRD (X-ray diffraction) were introduced. The whiskers’growth process in in-situ integration synthesis technology is different from the traditional technology; its growth mechanism was in according with the crystal diffusion growth mechanism, which is different from the VLS, VS mechanism at the conventional carbon-thermal reduction process. The cutting performance of the new developed ceramic tool TBN5in turning the austenitic stainless steel1Crl8Ni9Ti was investigated experimentally with the comparation of the commercial tools LT55and SG4. Aiming at the materials removal amount, the best cutting parameters of the TBN5were obtained, as follows:the cutting speed was40m/min, the feed speed was0.125mm/r, and the cutting depth was0.3mm. With this cutting paramerers, TBN5shows better cutting performance than LT55and SG4, which was related to the higher fracture toughness and the higher thermal conductivity of TBN5. |
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