Densification of SiO2-cBN composites by using Ni nanoparticle and SiO2 nanolayer coated cBN powder

Cubic boron nitride (cBN) powder was coated with Ni nanoparticle and SiO2 nanolayer (abbreviated as cBN/Ni and cBN/SiO2, respectively) by rotary chemical vapor deposition (RCVD), and compacted with SiO2 powder by spark plasma sintering at 1473-1973 K for 0.6 ks. The effects of Ni and SiO2 coatings on the densification, phase transformation of cBN and hardness of SiO2-cBN composites were compared. The phase transformation of cBN to hBN was identified at 1973 K in SiO2-cBN/SiO2 composites, 300 K higher than that in SiO2-cBN/Ni composites, indicating that SiO2 retarded the transformation of cBN. The relative density of SiO2-cBN/SiO2 with 50 vol% cBN sintered at 1873 K was 99% with a hardness of 14.5 GPa. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.