Study On The Technology And Properties Of PcBN Tool Prepared By Nano/Submicron CBN Powder At High Temperature And High Pressure

Polycrystalline cubic boron nitride（PcBN）was prepared at high temperature and high pressure using nano/submicron cBN powders as raw materials.The effects of single and mixed particle sizes of cBN with different grain sizes on PcBN were studied.The effects of Al-Co-Ti N,Al-Ti-Al₂O₃ and Ti₃AlC₂ binder systems on the mechanical properties of PcBN were studied under the mixed particle size of cBN.The effects of adding nano-diamond and carbon nanotubes on the mechanical properties of PcBN were analyzed.The main results are as follows:（1）The particle size of cBN has a great influence on the performance of PcBN.When the grain size of cBN is 1-2μm,the relative density,bending strength,fracture toughness and wear ratio of PcBN have the maximum values of 97.6%,507 MPa,5.52 MPa·m^1/2 and6525,respectively.When the grain size of cBN is 2-4μm,the maximum microhardness is4054.8 HV.The more the particle size distribution of cBN,the better the performance of PcBN.The particle size distribution B1 with all four particle sizes has the best microstructure and mechanical properties.（2）PcBN was prepared by using cBN mixed powders with two grain sizes of 0-0.5μm and 0.5-1μm,and the relative density of PcBN increased with the increase of cBN content.When the cBN content is high,the cBN particles are closely connected with the binder and have better mechanical properties.Under the content of cBN in each group,the phase of Al-Co-Ti N binder system did not change.The formation of Al₃Ti diffraction peak was found in PcBN prepared by the low cBN content Al-Ti-Al₂O₃ binder system,and no Al₃Ti diffraction peak was found in the high cBN content.（3）When Ti₃AlC₂ is used as the binder,Ti₃AlC₂ decomposes directly to form Ti C and Al-Ti alloy under high temperature and high pressure and reacts with cBN.The main phases in the sintered body are cBN,Ti C,Al N,Ti B₂ and Ti C_0.7N_0.3.When the content of cBN is 75wt.%,the flexural strength,fracture toughness and wear ratio of PcBN reach the maximum values of 562 MPa and 6.18 MPa·m^1/2 and 7350,respectively.When the cBN content is 80wt.%,the relative density and microhardness of PcBN reach the maximum values of 98.5%,4386.7 HV.（4）By adding nano-diamond and carbon nanotubes during the sintering process of PcBN,it was found that neither of them participated in the reaction,but only distributed as a second phase at the grain boundary of cBN,which affected the properties of PcBN.When the addition amount of nano-diamond is 6 wt.%,the microhardness of PcBN reaches 4562.5HV,which is 9%higher than that without nano-diamond.When the addition amount of carbon nanotubes is 1.5 wt.%,the fracture toughness of PcBN is 6.82 MPa·m^1/2,which is11.4%higher than that without carbon nanotubes.When PcBN is subjected to external load,the PcBN after adding carbon nanotubes can be similar to the’reinforced concrete’structure,and the pull-out and bridging effects provide toughening for the material.