Nickel and zirconia toughened alumina prepared by hydrothermal processing

Excerpt

Ceramics are attractive candidates for structural systems due to their strength at high temperatures. However, the major limitation to their application is their low fracture toughness. A major research objective for ceramic communities has, therefore, been to improve the fracture toughness of ceramics. The past two decades have seen the emergence of a number of studies concerned with toughening [1‐3]. There are two types of mechanisms to improve the resistance to crack propagation, that is, by increasing the inherent toughness (energy dissipation) of the material and reducing the local crack-tip driving force [4], such as residual stress effects, phase transition toughening, crack deflection, nano-composites toughing, and bridging by ductile particles, fibers, and whiskers [5]. The addition of a dispersed second-phase inclusion, which limits the propagation of cracks is one of the most commonly used approaches. With the addition of either zirconia particles [6] or silicon carbide whiskers [7], the fracture toughness and strength were increased [8, 9]. Alternatively, continuous metal and ceramic phases can improve fracture toughness and creep resistance, respectively. A tri-phase structure is of benefit for the suppression of grain growth [10]. In this paper, two toughening agents, nickel and zirconia particles, were added to an alumina matrix to enhance its toughness. Although the simultaneous use of nickel and zirconia particles is not new, few studies have been reported on tri-phase composite powders obtained by combining hydrothermal processing with co-precipitation. In the present communication, two-phase and tri-phase composites were investigated. …