Preparation and Mechanical Properties of the CIP and HIP Fabricated Alumina Ceramics
The starting alumina powders were prepared by chemical synthesis at pH 6.5 and pH 8.5. Powders made at pH 8.5 exhibited finer particle size, high surface area and crystalline structure. These powders were fabricated by (1) cold isostatic press (CIP) and (2) hot isostatic press (HIP) at 1550°C and 1650°C sintering temperatures. The microstructure of both compacts showed abnormal grain growth but to a greater extent in those prepared by CIP. This was attributed to the presence of Ca in the starting alumina powders. The HIP fabricated alumina compacts at pH 8.5 and sintered at 1650°C, gave high flexural strength and fracture toughness due to the formation of fine-needlelike grains in between the fine-grains of alumina. The CIP fabricated alumina compacts at pH 8.5 and sintered at 1650°C showed relatively low values of flexural strength due to the growth of large alumina grains.
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