Densification of B4C nanopowder with nanograin retention by spark-plasma sintering

Abstract

Densification of a commercially available B4C nanopowder by spark-plasma sintering (SPS) with nanograin retention was investigated, with emphasis on elucidating the potential of both single-step and two-step SPS cycles as well as the effect of pre-sintering annealing treatments of the nanopowders. It was found that single-step SPS does not allow a suitable processing window to obtain near-fully-dense B4C nanostructured ceramics from the as-received nanopowder, the cause being attributable to boria impurities producing coarsening. Pre-sintering annealing treatments of the nanopowder eliminate boria impurities thus facilitating the densification by single-step SPS, but at the expense of grain growth. Two-step SPS overcomes these drawbacks of the single-step approach (both without and with pre-sintering annealing treatments), enabling the desired densification of the as-received B4C nanopowder with nanograin retention (but nonetheless with a certain grain size heterogeneity). It was also found that the resulting ceramics are both superhard and toughened, highly desirable attributes in contact-mechanical and tribological applications.