Reactive spark plasma sintering of an electrically conductive B₄C-SiC-ZrB₂ composite with enhanced mechanical properties

Ternary B4C-SiC-ZrB2 ceramics with eutectic compositions were prepared in situ by reactive spark plasma sintering at 1600-1800 C-degrees. The two-step sintering, including an in situ reaction 2ZrSi(2) + 5B(4)C+ 3 C= 4B(4)C+ 4SiC+ 2ZrB(2) at 1600 C-degrees and sintering at 1800 C-degrees, is superior to combined one-step sintering at 1800 C-degrees. The as-sintered 40B(4)C-40SiC-20ZrB(2) composites (sample 16R18) had grain sizes of microns with a density over 97%. The Vickers hardness, bending strength and fracture toughness of the ternary ceramic reached 28.6 GPa, 631 MPa and 5.50 MPa m(1/2) respectively. Crack deflection and branching were ascribed to improved fracture toughness. The elongated plate-like ZrB2 grains not only had toughening effects but also helped to lower the percolation threshold of the electrical conductivity. The 16R18 sample possessed an electrical conductivity of 5.38 x 10(4) S/ m, owing to the tiny conductive ZrB2 grains with aspect ratios of 3-4, which is beneficial for the electro-discharge machining of the B4C-SiC based composites.