Densification of hard β-boron based ceramics by spark plasma sintering at larger heating rate

Abstract

The densification process of β-boron via spark plasma sintering (SPS) with controlled heating rates (50–300°C/min) was investigated at different temperatures from 1000°C to 1800°C. Systematic characterization reveals that enhanced heating rates (300°C/min) effectively suppress the volatilization of B₂O₃ impurities, promoting in situ formation of boron-rich oxide (B₆O) through reactions between boron and B₂O₃. The amount of the retained B₆O phase in the boron matrix increased with heating rates, which effectively accelerate the densification behavior of boron  , achieving near-full density (2.33 g/cm³) with residual porosity < 0.3% in consolidated boron ceramics. Resultant ceramics demonstrate good combination of properties, including high Vickers hardness (31.0 ± 1.8 GPa at 9.8 N) and low thermal conductivity (13.8 W·m⁻¹·K⁻¹ at room temperature and 5.8 W·m⁻¹·K⁻¹ at 873 K), the latter was governed by intensified phonon–phonon scattering with less contributions from electrons (< 1‰).