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

Abstract

Abstract Submicrometer sized B 4 C-30 vol% ZrB 2 ceramic composites were made both by one-step in situ pulsed electric current sintering (PECS) of a B 4 C, ZrO 2 and carbon black powder mixture or by PECS of B 4 C-ZrB 2 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 B 4 C-ZrB 2 powder mixtures at 1300 and 1400 °C for 2 h, whereas 37 and 11 wt% (m + t)-ZrO 2 was present in the mixtures processed at 1100 and 1200 °C respectively. Subsequent PECS treatment at 2000 °C for 5 min allowed to obtain B 4 C-ZrB 2 composites from these thermally treated B 4 C + ZrO 2 + 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 B 2 O 3 to B 4 C to form B 4 C-ZrB 2 composites. The composites prepared by both routes exhibited a Vickers hardness (HV 10 ) of 30–32 GPa, a modest fracture toughness of 2.4–2.9 MPa m 1/2 and a good flexural strength of 630–730 MPa.