Microstructure and mechanical properties of an HfB2+30 vol.% SiC composite consolidated by spark plasma sintering

An ultra-high-temperature HfB2-SiC Composite was successfully consolidated by spark plasma sintering. The powder mixture of HfB2 + 30vol.% beta-SiC was brought to full density without any deliberate addition of sintering aids, and applying the following conditions: 2100 degrees C peak temperature, 100 degrees C min(-1) heating rate, 2 min dwell time, and 30MPa applied pressure. The microstructure consisted of regular diboride grains (2 mu m mean size) and SiC particulates evenly distributed intergranularly. The only secondary phase was monoclinic HfO2. The incorporated SiC particulates played a key role in enhancing the sinterability of HfB2. Flexural strength at 25 degrees C and 1500 degrees C in ambient air was 590 +/- 50 and 600 +/- 15 Wa, respectively. Fracture toughness at room temperature (RT) (3.9 +/- 0.3 Wa root m) did not decrease at 1500 degrees C (4.0 +/- 0.1 MPa root m). Grain boundaries depleted of secondary phases were fundamental for the retention of strength and fracture toughness at high temperature. The thermal shock resistance, evaluated through the water-quenching method, was 500 degrees C. (c) 2006 Elsevier B.V. All rights reserved.