A statistical approach towards processing optimization of ZrB₂–SiC–graphite nanocomposites. Part I: Relative density

The influence of sintering variables and nano-graphite addition on the densification behavior of ZrB₂–SiC based ceramics has been investigated. The ZrB₂ matrices, reinforced with 25 vol% submicron SiC particles and 0–10 wt% graphite nano-flakes, were fabricated by spark plasma sintering (SPS). The Taguchi design of experiment approach was employed to study the effects of SPS variables (temperature, dwell time, and pressure) and nano-graphite content. Statistical analysis of variance identified the SPS temperature and graphite content as the most influential parameters affecting the relative density of as-sintered ceramics, whereas the SPS pressure did not have an obvious impact on the densification process. The thermodynamical and microstructural analyses showed that the addition of graphite nano-flakes led to the removal of the thin oxide layers from the surfaces of the non-oxide starting materials. The elimination of such harmful oxides and the in-situ formation of nano-sized ZrC and B₄C phases resulted in the enhancement of sinterability of ZrB₂–SiC–graphite nanocomposites. A fully dense sample was achieved at optimal processing conditions; i.e. by sintering at 1900 °C for 7 min under 40 MPa and adding 5 wt% graphite nano-flakes.