Processing, microstructure and mechanical properties of HfB2-ZrB2-SiC composites: Effect of B4C and carbon nanotube reinforcements

Abstract

The fully dense HfB2-ZrB2-SiC composites were processed using spark plasma sintering (SPS) at 1850 °C. The effect of reinforcements (B4C and CNT) on the densification as well as mechanical properties were investigated and compared (with monolithic) in the present study. The study showed that the addition of B4C and CNT were not only beneficial for the densification but also towards enhancing the mechanical properties (hardness, elastic modulus, and fracture toughness) of HfB2-ZrB2-SiC composites. The augmentation in the mechanical properties establish the synergy between solid solution formation (with the equimolar composition of HfB2/ZrB2) and the reinforcements (SiC, B4C, and CNT). The highest increase in the indentation fracture toughness with the reinforcements of B4C as well as CNT is >3 times (~13.8 MPam0.5 when it is 3–4 MPam0.5 for monolithic ZrB2/HfB2) on HfB2-ZrB2-SiC composites, which is attributed to the crack deflection and pull-out mechanisms. An increase in the analytically quantified interfacial compressive residual stresses in the composites during SPS processing with the synergistic addition of reinforcements (SiC, B4C, and CNT) and its effect on the indentation fracture toughness has also been addressed.