SYNTHESIS AND CHARACTERIZATION OF SPARK PLASMA SINTERED Al2O3-ZrO2-CNT COMPOSITES

Abstract

Alumina (Al2O3) is widely used as structural ceramic because of its excellent properties, like, high melting point, good chemical stability, high elastic modulus and hardness, biocompatibility. It has potential application in various fields of cutting tools, light weight armours, refractories, orthopedic implants. The major drawback of alumina is its low fracture toughness, which restricts it from many applications. Fracture toughness of Al2O3 can be improved by reinforcing second phase particles, like, zirconia (ZrO2), carbon nanotubes (CNTs), into it. These second phase particles hinder crack propagation and improves the fracture toughness. The basic objective of present work was to study the effect of multi walled carbon nanotubes (MWCNTs) on structural and mechanical properties of zirconia toughened alumina composites. In this study, Al2O3-ZrO2-CNT composites, with varying concentrations (0, 0.10, 0.80 wt %) of multi walled carbon nanotubes (MWCNTs) were synthesized by Spark plasma sintering (SPS). The samples were sintered at 1250°C, 60MPa pressure and 5 minutes dwell time with a heating rate of 100°C/min. The density of sintered samples was measured by Archmedic‘s principle. The phase identification of powders and sintered composites were carried out by X-ray diffraction (XRD) analysis. The structural integrity of carbon nanotubes in sintered composites were characterized by Raman spectroscopy. The mechanical properties were studied by Vicker‘s hardness, and fracture toughness calculation. The increase in hardness was ~13.5% for 0.1wt% composite w.r.t. alumina at 1Kgf load. The fracture toughness improvement was of ~159% for 0.8wt% CNT composite at 0.5Kgf load. This improvement in hardness might be attributed to the uniform distribution of CNTs and effective load transfer from matrix. Crack deflection, crack bridging and CNT pull out at fracture surface were the major mechanics of fracture toughness enhancement.