OXIDE DISPERSED CERAMIC COMPOSITES - THEIR FRACTURE TOUGHNESS AND HARDNESS CHARACTERISTICS

Abstract

Ceramics are well known for their high relative hardness, high stiffness, chemical inertness and high temperature withstanding capacity. These abilities make such materials of great interest in demanding applications, such as in heat engines, turbines, automotive as well as aeronautical components. It is hoped that not only can the performance of these components be improved by low weight, high operating temperature properties of the ceramics, but also that their length of use can be increased. Incredibly low wear rates of ceramic materials is a great benefit to many applications. However, currently it is not possible to take full advantage of these properties due to the fact that ceramics generally have low fracture toughness. This is due to the nature of the bonds in the materials i.e. ionic and covalent, which prevents plastic deformation as dislocation movement is extremely limited. The present thesis aims at exploring and investigating fracture toughness and hardness characteristics of oxide dispersed A1203 based ceramic composites with a view to assess their suitability in the application of structural ceramics. The microstructural and grain morphological relationship with mechanical properties i.e. fracture toughness and hardness of the ceramic composites prepared has been investigated through this work. The presentation in the thesis is divided in the following seven chapters: The Chapter 1 provides an introductory overview of the rationale behind the selection of the problem and the objectives of the research work carried out. Chapter 2 present an overview of literature covering structure, toughening mechanisms, role of microstructural and morphological factors of A1203 and the relation of the mechanical properties with microstructural features. The related literature on Zr02 dispersed Al203 system and effect of rare earth elements doping in A1203 have also been discussed.