Effect of Al(2)TiO(5) Content and Sintering Temperature on the Microstructure and Residual Stress of Al(2)O(3)–Al(2)TiO(5) Ceramic Composites

A series of Al(2)O(3)–Al(2)TiO(5) ceramic composites with different Al(2)TiO(5) contents (10 and 40 vol.%) fabricated at different sintering temperatures (1450 and 1550 °C) was studied in the present work. The microstructure, crystallite structure, and through-thickness residual stress of these composites were investigated by scanning electron microscopy, X-ray diffraction, time-of-flight neutron diffraction, and Rietveld analysis. Lattice parameter variations and individual peak shifts were analyzed to calculate the mean phase stresses in the Al(2)O(3) matrix and Al(2)TiO(5) particulates as well as the peak-specific residual stresses for different hkl reflections of each phase. The results showed that the microstructure of the composites was affected by the Al(2)TiO(5) content and sintering temperature. Moreover, as the Al(2)TiO(5) grain size increased, microcracking occurred, resulting in decreased flexure strength. The sintering temperatures at 1450 and 1550 °C ensured the complete formation of Al(2)TiO(5) during the reaction sintering and the subsequent cooling of Al(2)O(3)–Al(2)TiO(5) composites. Some decomposition of AT occurred at the sintering temperature of 1550 °C. The mean phase residual stresses in Al(2)TiO(5) particulates are tensile, and those in the Al(2)O(3) matrix are compressive, with virtually flat through-thickness residual stress profiles in bulk samples. Owing to the thermal expansion anisotropy in the individual phase, the sign and magnitude of peak-specific residual stress values highly depend on individual hkl reflection. Both mean phase and peak-specific residual stresses were found to be dependent on the Al(2)TiO(5) content and sintering temperature of Al(2)O(3)–Al(2)TiO(5) composites, since the different developed microstructures can produce stress-relief microcracks. The present work is beneficial for developing Al(2)O(3)–Al(2)TiO(5) composites with controlled microstructure and residual stress, which are crucial for achieving the desired thermal and mechanical properties.