Powder synthesis and densification of ultrafine B_4C-ZrB_2 composite by pulsed electrical current sintering

摘要

Submicrometer sized B_4C-30 vol% ZrB_2 ceramic composites were made both by one-step in situ pulsed electric current sintering (PECS) of a B_4C, ZrO_2 and carbon black powder mixture or by PECS of B_4C-ZrB_2 powder mixtures synthesized by thermal treatment in vacuum at 1100-1400℃ 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_4C-ZrB_2 powder mixtures at 1300 and 1400℃ for 2h, whereas 37 and 11 wt% (m + t)-ZrO_2 was present in the mixtures processed at 1100 and 1200℃ respectively. Subsequent PECS treatment at 2000℃ for 5 min allowed to obtain B_4C-ZrB_2 composites from these thermally treated B_4C + ZrO_2 + C powder mixtures. In the one-step in situ process, a PECS temperature of 1900℃ was necessary to complete the conversion of the in situ formed B_2O_3 to B4C to form B_4C-ZrB_2 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 m~(1/2) and a good flexural strength of 630-730 MPa.