PREPARATION OF CERAMIC COMPOSITES. AND THEIR FRACTURE TOUGHNESSES

Abstract

Ceramic and ceramic composites are promising materials having rather high strength characteristics but quite low crack resistance property at the same time. This is one of the major factors hindering the wide scale application of this material in various fields of human activities. The crack resistance is critical not only for ceramic product operating under extreme mechanical and thermal load but also for structural component whose brittle fracture is intolerable even under arbitrary loads. For many years, the performance has been evaluated on the basis of full-scale test; however, their fracture toughness characteristics have not been always the object of scientific interests. Wide scale fracture toughness investigations were stated only recently with an aim at the assessment of the actually and reliability of the data obtained by commonly accepted test methods. In the present dissertation vork, the samples of the ceramic composites in the form of rare-earth oxide (Y203) added A1203 were prepared by standard ceramic processing route following solid state sintering at high temperature. The samples were characterized for their hardness measurement using Vickers indentation method under different loads for indentation. Fracture toughness characteristics of the samples showing crack initiation and propagation evaluated by mechanical properties of the samples essentially depends on their microstructure. The microstructural investigations were carried out and the microstructure features were attempted to correlate with the properties. In order to address the present problem, the samples were prepared in three different compositions of the rare earth oxide and the compacted samples were sintered at 1500°C in all the cases for three different soaking time periods i.e. 3hrs, 6hrs and 9hrs.