Combined effect of low ZrO2 content and carbon nanostructures on mechanical and wear properties of hot-pressed Al2O3/ZrO2 hybrid nanocomposites

Abstract

Al2O3/ZrO2 systems with higher ZrO2 amounts (≥20 wt%) are known to offer improved properties such as fracture toughness, but are restricted in their hardness, wear and strength performances. The incorporation of a third phase carbon nanostructure (such as CNTs and GN) to Al2O3/ZrO2 reinforced with low ZrO2 content (≤5wt%) has emerged as a novel process to overcome this property trade-off by exploring the remarkable mechanical properties of these hybrid nanocomposite systems. Therefore, in the current work, colloidal mixing followed by hot-pressing process (@ 1600°C) were used to consolidate monolith Al2O3, Al2O3/ZrO2, Al2O3/ZrO2/CNTs and Al2O3/ZrO2/GN nanocomposite structures using low ZrO2 content (4wt%) and optimum amounts of CNTs (2wt%) and GN (0.5wt%) as the hybrid reinforcement phases. Microhardness, fracture toughness and flexural strength properties were improved from 19GPa, ∼3MPa.m1/2 and ~260MPa up to 24GPa, ∼7MPa.m1/2 and ~374MPa respectively, with hybrid additions of ZrO2/CNTs and ZrO2/GN to the monolith Al2O3. The primary source of the property enhancement in the hybrid nanocomposites was due to reduction in the matrix and ZrO2 grain sizes (decreased up to ∼78%), good interaction between reinforcement phases and combined mechanisms such as crack bridging and deflection, matrix grain wrapping and grain gluing by CNTs and GN. The wear rate of the parent Al2O3 was also improved from 9.71 × 10−5 mm3/N.m up to 0.81 × 10−5 mm3/N.m (showing ∼92% decrease) with ZrO2/CNTs and ZrO2/GN hybrid inclusions, which was attributed to the overall enhanced mechanical properties and wear resistant mechanisms during the dry sliding.