Densification of SiO_2-cBN composites by using Ni nanoparticle and SiO_2 nanolayer coated cBN powder

摘要

Cubic boron nitride (cBN) powder was coated with Ni nanoparticle and SiO_2 nanolayer (abbreviated as cBN/Ni and cBN/SiO_2, respectively) by rotary chemical vapor deposition (RCVD), and compacted with SiO_2 powder by spark plasma sintering at 1473-1973 K for 0.6 ks. The effects of Ni and SiO_2 coatings on the densification, phase transformation of cBN and hardness of SiO_2-cBN composites were compared. The phase transformation of cBN to hBN was identified at 1973 K in SiO_2-cBN/SiO_2 composites, 300 K higher than that in SiO_2-cBN/Ni composites, indicating that SiO_2 retarded the transformation of cBN. The relative density of SiO_2-cBN/SiO_2 with 50 vol% cBN sintered at 1873 K was 99% with a hardness of 14.5 GPa.