Analyzing coarsening versus densification phenomenon present in partial sintering of Al2O3/TiO2 composites

Alumina–titania (Al2O3/TiO2) composites are well-known for their physical and microstructural properties, which allow several engineering applications. However, these properties change when different sintering temperatures are used, due to the existence of two antagonistic phenomena (grain coarsening versus densification) that occurs during sintering process. The aim of this study was to evaluate the microstructural and physical properties of the alumina–titania composites and to understand these two antagonistic phenomena when different partial sintering temperatures are used. The composites were prepared from alumina and titania powders by uniaxial pressing and sintered at different temperatures (1100–1400 °C). The structural analysis showed that in addition to expected phases (α-Al2O3 and rutile), the alumina–titania composite sintered at 1100 °C presents anatase phase, while those obtained at 1300 and 1400 °C present tialite phase. The morphology analysis revealed a random distribution of grains with irregularly shaped pores. According to the Archimedes-based immersion test, all composites have a relative bulk density ranging 60.43–73.59%, showing that none of them reached the final sintering stage. Statistical analysis revealed that the average grain size of the matrix ranges from 3.62 to 5.24 μm. Moreover, the statistical analysis also showed that the grain coarsening predominates over densification for the composites sintered from 1100 to 1150 °C. The densification predominates over grain coarsening for the composites sintered from 1150 to 1200 °C, and from 1250 to 1400 °C. The two phenomena coexist only for the composites sintered from 1200 to 1250 °C.