The Preparation Of MAX/cBN Composites By Spark Plasma Sintering

Ceramic-based PcBN tools have some defects such as high brittleness,poor toughness and low density in use.MAX phase has both excellent properties of metal and ceramics,and the hard phase produced by decomposition under certain conditions can meet the application requirements of superhard binder.The decomposition characteristics of MAX phase were explored by spark plasma sintering technology and based on this,the composite material of cBN combined with MAX was prepared.The comprehensive properties of the composite material were improved by adding rare earth oxides.The sintering temperature,holding time,sintering pressure,content of cBN,kinds of rare earth oxides,additions and mixing methods were investigated to prepare better MAX/cBN composite material.The results show that:?1?The decomposition degree of MAX phase increases from27.5%to 36.9%and from 37.4%to 54%when the holding time increases from 5 min to20 min under the conditions of temperature range of 1350-1450?,the holding time of5-20 min and pressure of 30-50 MPa.The decomposition degree of Ti₃SiC₂ increases from27.5%to 36.9%and Ti₃AlC₂ from 37.4%to 54%when holding time increases from 5 min to 20 min.When the phase coexists,Ti₃SiC₂ and Ti₃AlC₂ decompose completely at1350?,holding for 10 min and 30 MPa.?2?When the temperature is higher than 1500?,hBN begins to appear;when the sintering temperature is 1350-1550?,the holding time is 10 min,and the pressure is30-50 MPa,the hardness and density of Ti₃SiC₂/cBN composites obtained by spark plasma sintering with 70 wt.%MAX+30 wt.%cBN as the sintering temperature is1400?,the holding time is 10 min and the pressure is 30-50 MPa.The hardness and density of Ti₃AlC₂/cBN composites were 19.47 GPa and 96.58%,respectively.?3?The hardness and density of Ti₃SiC₂/cBN composites added with 5 wt.%La₂O₃were 17.88 GPa and 98.25%respectively at 1400?,holding for 10 min,30 MPa pressure and 70 wt.%MAX+30 wt.%cBN ratio,which were 49.25%and 7.27%higher than those without rare earth oxide.The hardness of Ti₃AlC₂/cBN composites with 5 wt.%CeO₂ was 21.46 GPa and 98.23%respectively,which were 10.22%and 1.71%higher than that without rare earth oxide.