CYCLIC FATIGUE OF AL2O3 AND AL2O3-AL2TIO5 COMPOSITES IN DIRECT PUSH-PULL

A reaction sintering route is developed to produce, ''in situ'', compo sites of alumina-aluminium titanate using alumina and titania as start ing powders. Aluminium titanate, can be formed by a solid state reacti on between Al2O3 and TiO2 at temperatures above the eutectoid temperat ure of 1280 degrees C. These composites have different grain sizes of alumina matrix and a different quantity and distribution of aluminium titanate according to the heating cycle used. In the present work dire ct push-pull tests under cyclic loads have been carried out with both monolithic alumina and alumina-aluminium titanate composites. It has b een found that all the samples show a decrease in tensile strength wit h the number of applied cycles of loading when plotted in graphical fo rm but the slopes of these graphs for both Al2O3-Al2TiO5 composites ar e lower than for the alumina specimens. The role of aluminium titanate and the alumina matrix grain size in fatigue crack growth resistance has been studied during push-pull tests, where failure occurs by catas trophic propagation of small surface cracks after a very short regime of subcritical crack growth. These results have been compared with mea surements of slow stable fatigue crack growth rates in Al2O3-Al2TiO5 c omposites carried out elsewhere with pre-notched specimens of the comp act tension type. These latter tests provide information about the beh aviour of significantly long cracks, i.e. cracks that are several mill imetres long.