Powder synthesis and densification of ultrafine B4C-ZrB2 composite by pulsed electrical current sintering

Submicrometer sized B4C-30 vol% ZrB2 ceramic composites were made both by one-step in situ pulsed electric current sintering (PECS) of a B4C, ZrO2 and carbon black powder mixture or by PECS of B4C-ZrB2 powder mixtures synthesized by thermal treatment in vacuum at 1100–1400 °C for 2 h. The influence of the processing temperature on the phase evolution and chemical composition of the mixtures were investigated in detail by Rietveld XRD and SEM analysis. Conventional vacuum thermal treatments allowed to synthesize homogeneous and submicrometer sized B4C-ZrB2 powder mixtures at 1300 and 1400 °C for 2 h, whereas 37 and 11 wt% (m + t)-ZrO2 was present in the mixtures processed at 1100 and 1200 °C respectively. Subsequent PECS treatment at 2000 °C for 5 min allowed to obtain B4C-ZrB2 composites from these thermally treated B4C + ZrO2 + C powder mixtures. In the one-step in situ process, a PECS temperature of 1900 °C was necessary to complete the conversion of the in situ formed B2O3 to B4C to form B4C-ZrB2 composites. The composites prepared by both routes exhibited a Vickers hardness (HV10) of 30–32 GPa, a modest fracture toughness of 2.4–2.9 MPa m1/2 and a good flexural strength of 630–730 MPa.