Effect of carbonaceous reinforcements on mechanical properties of ZrB2-SiC composites via nanoindentation study

Abstract

In the present work, silicon carbide (SiC) reinforced zirconium diboride (ZrB2) ceramic was studied. ZrB2 reinforced with 20 vol% SiC (ZS) and with additives multi-walled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs), and CNT + GNP were consolidated via spark plasma sintering. ZS with carbon additives (CNT + GNP) composite (ZSCG) showed the highest densification (98.2 %) than that of ZS sample (91 %) via Archimedes' method. Crystallite size calculated via XRD showed a value of (56 ± 1) for ZS and the lowest crystallite size value (47 ± 1) for ZSCG, attributed to the pinning effect of carbonaceous reinforcements (CNT + GNP) at the grain boundaries, which restrict the grain growth in the composite. Nanohardness for the composite samples ranges from ~24 to 33 GPa. ZSCG composite showed the highest nanohardness of 33 GPa attributed to the bridging of long and flexible CNTs adjacent to GNPs to form 3-D hybrid structures restricting their agglomeration, which resulted in a high interfacial area between the matrix and the hybrid reinforcement leading to better load transfer. The theoretically calculated Young's modulus from various models (rule of mixture, Voigt Reuss, and Halpin Tsai (HT)) was compared with the experimental Young's modulus. The calculated Young's modulus value via the HT model (370–411 GPa) is in close agreement with the experimental values (364–401 GPa) owing to consideration of porosity and the interfacial debonding factor. Also, the lowest debonding factor was determined for the ZSCG composite (0.47) in comparison with the ZSC composite (0.86) suggesting increased bonding strength which results in the enhancement of mechanical properties. So, it was finally concluded that the finer crystallite size, improved hardness, less debonding factor, and better load transfer mechanism can make ZSCG composite a viable candidate for high-temperature applications.