MICROSTRUCTURE AND MECHANICAL CHARACTERISTICS OF ALPHA-ALUMINA-BASED FIBERS

The high-temperature mechanical behaviour of alumina-based ceramic fib res has been investigated by the comparison of a dense pure alumina fi bre, a porous pure alumina fibre and a zirconia-reinforced dense fibre . Tensile and creep tests have been conducted up to 1300 degrees C in air in parallel with microstructural investigations on the as-received and tested fibres. Room-temperature behaviour of the fibres is close to that of bulk materials having the same microstructure, but the fibr e form allows higher failure stresses to be attained. High-temperature deformation of the three fibres is achieved by grain-boundary sliding (epsilon proportional to sigma(2)), and is accompanied by isotropic g rain growth. The specific microstructures of each fibre induce differe nces in the creep threshold levels as a function of temperature and st ress and also in creep rates and resistance to damage. Despite better resistance to creep and damage of the zirconia-reinforced fibre, alumi na-based fibres are limited to applications below 1100 degrees C. Grai n boundaries are the principal cause of mechanical degradation at high temperature with these fibres.