Solid-state interfacial reactions and compound morphology of cBN grain and surface Ti coating

in order to research thoroughly the mechanism of the solid-state interfacial reactions and the induced compound morphology of cubic boron nitride (cBN) abrasive grains and the surface Ti-coating layer, annealing experiments of Ti-coated cBN grains were conducted at different temperatures of 550-950 degrees C for dwell times of 60min under high-vacuum conditions. The corresponding interfacial characteristics were investigated by differential thermal analysis, X-ray diffraction and scanning electron microscopy. The results show that the relevant interfacial reactions and compound morphology between cBN and Ti are significantly influenced by the heat-treatment temperature. No reaction occurs below 550 degrees C, and TiN is the sole reaction product during heating from 650-750 degrees C. Three kinds of compounds, TiN, TiB2 and TiB, can exist in the interfacial region at 950 degrees C. Here, the favorable interfacial structures, cBN/TiB2/TiB/ (TiB + TiN)/TiN/Ti, are developed for the excellent mechanical and chemical transition effects between cBN grains and Ti coating. The thermodynamic analysis finally predicts that there is a reasonable probability for the formation of such a special interfacial transition layer. (c) 2006 Elsevier Ltd. All rights reserved.