Enhanced densification and mechanical properties of β-boron by in-situ formed boron-rich oxide

摘要

We report nearly full densification of polycrystalline rhombohedral beta(β)-boron without the addition of sintering aids via spark plasma sintering(SPS).The analytical aberration corrected transmission electron microscope observations have revealed in-situ growth of nanocrystalline boron-rich oxide precipitates that contain approximately 4 at.%of oxygen and beget the densification of β-boron.Further electron energy loss spectroscopy and diffraction analysis confirmed that the newly formed boron-rich oxide(nominally B_(96)O_(4))structure with B-O σ-bonding belongs to space group R■m.Depth sensitive nanoindentation showed boron-rich oxide phase has a hardness of about 41±2 GPa,which is 10%higher than that of β-boron matrix.The estimated hardness and fracture toughness of β-boron were approximately 31 GPa and 2.2 MPa m^(1/2),respectively,using Vickers microindentation,which falls in the range of those commercially used boron carbides.These results suggest that the enhanced densification and mechanical properties arise from the newly formed boron-rich oxide inβ-boron during SPS experiments.