Densification and mechanical properties of cBN-TiN-TiB_2 composites prepared by spark plasma sintering of SiO_2-coated cBN powder

摘要

cBN-TiN-TiB_2 composites were fabricated by spark plasma sintering at 1773-1973 K using cubic boron nitride (cBN) and SiO_2coated cBN (cBN(SiO_2)) powders. The effect of SiO_2 coating, cBN content and sintering temperature on the phase composition, densification and mechanical properties of the composites was investigated. SiO_2 coating on cBN powder retarded the phase transformation of cBN in the composites up to 1873 K and facilitated viscous sintering that promoted the densification of the composites. Sintering at 1873 K, without the SiO_2 coating, caused the relative density and Vickers hardness of the composite to linearly decrease from 96.2% to 79.8% and from 25.3 to 4.4 GPa, respectively, whereas the cBN(SiO_2)-TiN-TiB_2 composites maintained high relative density (91.0-96.2%) and Vickers hardness (17.9-21.0GPa) up to 50vol% cBN. The cBN(SiO_2)-TiN-TiB_2 composites had high thermal conductivity (60Wm~(-1) K~(-1) at room temperature) comparable to the TiN-TiB_2 binary composite.