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

Abstract

Ternary B4C-SiC-ZrB2 ceramics with eutectic compositions were prepared in situ by reactive spark plasma sintering at 1600–1800 °C. The two-step sintering, including an in situ reaction 2ZrSi2 + 5B4C+ 3 C= 4B4C+ 4SiC+ 2ZrB2 at 1600 °C and sintering at 1800 °C, is superior to combined one-step sintering at 1800 °C. The as-sintered 40B4C-40SiC-20ZrB2 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 m1/2 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 × 104 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.