| Cubic boron nitride(cBN)has attracted much attention because of its excellent physical and chemical properties,especially the high inertness to iron-based elements,with a broad application prospect in the fields of precision machining,electronic and optical device.In this paper,cBN composites were prepared by high-temperature and high-pressure technology(HTHP).The correlation between raw materials of cBN,phase composition of binder,sintering process and properties was researched.Effects of dispersed particles,whiskers and Y2O3 on the mechanical properties of cBN composites were evaluated;cBN composites for cutting nickel alloys were experimentally researched,comparing with cBN tools of well-known commercial brands.The main results are as follows:1.The selection of raw materials is crucial to obtain cBN composites with excellent properties.Effects of cBN powders and particle size gradation on the properties of sample were systematically studied.The results indicated that cBN powders of A had higher purify,more uniform particle size distribution and higher thermal stability,contributing to the great overall performance of synthesized cBN composites,which was suitable for research requirements of cBN composites;cBN composites of particle size distribution with large bulk density had better microstructure and mechanical properties.2.The mechanical properties of TiN/Al/Co/cBN composites first increased and then decreased as the holding time increased.When the holding time was 110 s,specimen obtained a dense intercrystalline structure and the maximum bending strength of 600 MPa,hardness of 51.0 GPa and abrasion ratio of 2.0.The fine-grained diamond had a significant effect on the properties of composites,the flexural strength of sample incorporating 1 ?m diamond was 791 MPa,increased by 37.6%than that without diamond,and the hardness of the sample increased from 47.5 GPa to 60.1 GPa.TiB2 nanoparticles had a significant influence on the fracture toughness of cBN composites through the crack deflection,sample with 6 wt.%TiB2 nanoparticles achieved the maximum fracture toughness of 7.4 MPa·m1/2,which was 32.1%higher than that without TiB2.3.Sialon generated in Si3N4/Al2O3/Al/cBN composites had self-toughnening effect through thermodynamic calculations and experimental researchs.The introduction of Y2O3 improved the sintering ability of composites and promoted the generation of Sialon.The fracture toughness of cBN composites incorporating 5 wt.%Y2O3 reached a maximum value of 7.2 MPa·m1/2.Si3N4 whiskers and nanoparticles had momentous synergistic toughening and reinforcing effects on cBN composites through crack deflection,whisper bridging and pull-out.Specimen with 5 vol.%Si3N4 whisper and 15 vol.%Si3N4 nanoparticles reached a maximum flexural strength(683 MPa),which was 36.4%higher than the monolithic composites.Meanwhile,fracture toughness of cBN composites adding 10 vol.%Si3N4 whisper and 5 vol.%Si3N4 nanoparticles achieved the maximum value of 7.7 MPa·m1/2,which was 16.4%higher than that without addition.4.The hardness of Si/Ti/cBN composite reached 64.0 GPa when the molar ratio of Si:Ti was 1:1,at this time the composites obtained the tightest covalent bond between cBN.Ti3SiC2 decomposition was controlled by temperature,contributing to improve the properties of Ti3SiC2/cBN composites.Ti3SiC2/cBN composites possessed high fracture toughness 7.6 MPa·m1/2 due to the decomposition and plastic deformation of Ti3SiC2.5.The verification research results of cBN composites for cutting nickel alloys showed that the cutting life of cBN composites was related to the mechanical properties,of which abrasive ratio and fracture toughness had a greater effect on the tool life.The tool life of cBN composites was better than cBN tools of well-known commercial brands,met the requirements as commercial cutting tools. |
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