Superhard B4C-ReB2 composite by SPS of microwave synthesized nanopowders

The challenge to develop new robust materials inspired the current research on a microwave synthesis and subsequent spark plasma sintering of a lightweight superhard B4C-27wt.%ReB2 ceramic composite. A strategy for fabricating high density parts was developed by sintering the microwave synthesized B4C-ReB2 composite without additives. The bulk material produced at 1900 °C temperature, 50 MPa pressure and dwell time of 10 min exhibited microhardness of 50 ± 3 GPa, estimated in the asymptotic-hardness region at 49 N load, exceeding the hardness of both constituents. Fractured surfaces of fully dense B4C-27wt.%ReB2 composite evidenced neither obvious pores nor undersintered areas. The high value of hardness ranks the composite among the superhard materials supposedly due to the strong interphase formation via increased number of boron atoms and increased number of sigma bonds in ReB2 unit cell.