Development of highly hard and ductile composite with surface-modified cBN and TiN-TiB2 eutectic

RCVD可使cBN（芯）/SiO2（壳）中SiO2含量（cBN粉末上SiO2厚度）达到42wt%。研究了SiO2含量对放电等离子烧结cBN-SiO2复合材料致密化、相变和硬度的影响。采用放电等离子体烧结技术，在1873 K下烧结0.3 ks，使cBN/SiO2粉末致密化。cBN-SiO2复合材料中未观察到六方氮化硼（hBN）相，表明SiO2纳米层抑制了cBN向hBN的相变。cBN-SiO2的相对密度随SiO2含量的增加而增大。在CSiO2 = 38 wt%和负载0.98 n时，cBN-SiO2复合材料的最高硬度为17.5 GPa。采用火花等离子烧结（SPS）技术，在1773 ~ 1973 K温度下制备了cBN- tin - tib2复合材料。cBN(SiO2)TiN-TiB2复合材料中cBN的相变始于1973 K，比未涂覆cBN的相变温度高200 K。在1873 K下烧结的cBN（SiO2-TiN-TiB2）复合材料的相对密度为91.0&-96.2%，cBN含量为10-50 vol%。cBN(SiO2)-TiN-TiB2复合材料在10 vol% cBN时的维氏硬度为21.0 GPa。随着cBN含量从10%增加到50%，断裂韧性从4.1增加到7.3 MPa m1/2。cBN(SiO2)-TiN-TiB2复合材料在10 vol% cBN（SiO2）时表现出60 ~ 69 W m-1 K-1的高导热系数。

The SiO2 content (SiO2 thickness on cBN powder) in cBN(core)/SiO2(shell) was changed up to 42wt% by RCVD. The effects of SiO2 content on the densification, phase transformation and hardness of the cBN-SiO2 composites by spark plasma sintering were investigated. The cBN/SiO2 powder was densified by spark plasma sintering at 1873 K for 0.3 ks. The hexagonal boron nitride (hBN) phase was not observed in the cBN-SiO2 composites, indicating that the SiO2 nanolayer depressed the phase transformation from cBN to hBN. The relative density of cBN-SiO2 increased with increasing SiO2 content (CSiO2). The highest hardness of the cBN-SiO2 composite was 17.5 GPa at CSiO2 = 38 wt% and a load of 0.98 N.The cBN-TiN-TiB2 composites were fabricated by spark plasma sintering (SPS) at 1773-1973 K using cBN and SiO2-coated cBN (cBN(SiO2)) powders. The phase transformation of cBN in cBN(SiO2）TiN-TiB2 composites started at 1973 K which was 200 K higher than that of using un-coated cBN. The cBN(SiO2-TiN-TiB2 composites containing 10-50 vol% cBN sintered at 1873 K showed high relative density of 91.0&-96.2%. The Vickers hardness of the cBN(SiO2)-TiN-TiB2 composites was 21.0 GPa at 10 vol% cBN. With increasing cBN content from 10 to 50 vol% the fracture toughness increased from 4.1 to 7.3 MPa m1/2. The cBN(SiO2)-TiN-TiB2 composite at 10 vol% cBN(SiO2) exhibited high thermal conductivity of 60 to 69 W m-1 K-1.