In situ synthesis of TiB2 rod crystal reinforced PcBN mechanical properties: First-principles calculations and experimental study

Abstract

In this work, a combination of first-principles calculations and experiments is used to not only reveal the growth mechanism of hexagonal rod-shaped crystals TiB2 and its theoretical influencing factors, but also to experimentally regulate the growth of TiB2 rod-shaped crystals to obtain polycrystalline cubic boron nitride (PcBN) composites with excellent comprehensive mechanical properties. The calculation results reveal that under Ti-rich or B-rich conditions, both the surface energies of (0001) and (101̄0) are lower than the surface energy of (112̄0). The growth of TiB2 is interpreted at the atomic level as being composed of (0001) and (101̄0) surfaces, and it preferentially grows as rod crystals along the (0001) crystal plane. The calculations further indicate that the hexagonal morphology of TiB2 is determined by the atomic concentration within the melt. It exhibits a higher propensity for nucleation under Ti-rich conditions than under B-rich conditions. And it is predicted that a lower relative concentration of Ti atoms promotes the growth of TiB2 into hexagonal rod crystals. In addition, PcBN composites with TiB2 reinforced phase are synthesized in situ by modulating the Ti-Al molar ratio. The experimental results demonstrate that as the concentration of Ti atoms decreases, the nucleation of TiB2 decreases, while the growth of TiB2 rod crystals increases, which aligns with the predicted calculations. Moreover, the presence of rod crystals greatly enhances the densities and flexural strength of PcBN composites. When the Ti-Al molar ratio is adjusted to 1:2, a substantial quantity of high-quality TiB2 rod crystals are cultivated, leading to PcBN composites exhibiting outstanding mechanical properties.