Effect of Al2TiO5 Content and Sintering Temperature on the Microstructure and Residual Stress of Al2O3–Al2TiO5 Ceramic Composites

A series of Al2O3–Al2TiO5 ceramic composites with different Al2TiO5 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 Al2O3 matrix and Al2TiO5 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 Al2TiO5 content and sintering temperature. Moreover, as the Al2TiO5 grain size increased, microcracking occurred, resulting in decreased flexure strength. The sintering temperatures at 1450 and 1550 °C ensured the complete formation of Al2TiO5 during the reaction sintering and the subsequent cooling of Al2O3–Al2TiO5 composites. Some decomposition of AT occurred at the sintering temperature of 1550 °C. The mean phase residual stresses in Al2TiO5 particulates are tensile, and those in the Al2O3 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 Al2TiO5 content and sintering temperature of Al2O3–Al2TiO5 composites, since the different developed microstructures can produce stress-relief microcracks. The present work is beneficial for developing Al2O3–Al2TiO5 composites with controlled microstructure and residual stress, which are crucial for achieving the desired thermal and mechanical properties.

The use of fluorinated alumina as a support of the sulfated zirconia catalyst for isomerization of hexane

The study considers the effect of fluorine doping of the alumina matrix used for the synthesis of supported sulfated zirconia catalysts. Hydrofluoric acid served as a fluorinating agent. The addition of fluorine was shown to affect the textural characteristics of the Al2O3 matrix and hence the surface area of sulfated zirconia catalysts based on the doped systems. It was found that the introduction of fluorine into the catalysts increases their activity (the conversion of hexane) and the yield of high-octane isomer 2,2-dimethylbutane.

Experimental Results of SiC reinforced Al2O3 Matrix Ceramic Matrix Composites Validated with Finite Element Method

In this paper, SiCp /Al2O3 composites were fabricated through directed metal oxidation process. Experimental results of these composites validated or compared with Finite Element Method (FEM). Finite Element has become one in all the foremost necessary tools offered to an engineer. The finite part methodology is employed to resolve advanced analysis issues. In this paper, Finite Element Method based ANSYS software is used to FEM model to determine mechanical properties of SiC reinforced Al2O3 matrix composite by changing volume fractions of SiC. The comparison of experimental results with Finite element analysis provides detailed information about the results of these comparisons. The FA was competent of predict the information for several scenario quite fine

Design and Development of Hybrid Al2O3 Based Composites with Toughening and Self-Lubricating Second-Phase Inclusions

Polycrystalline ceramics, such as alumina (Al2O3), are brittle and they generally wear by fracture mechanism, which limits their potential in tribological applications. In the present work, computational design tools are used to develop hybrid Al2O3 composites reinforced with best combinations of toughening and self-lubricating second-phase particles for cutting tool inserts in dry machining applications. A mean-field homogenization approach and J-integral based fracture toughness models are employed to predict the effective structural properties (such as elastic modulus and fracture toughness) and related to the intrinsic attributes of second- phase inclusions in Al2O3 matrix. Silicon carbide (SiC), boron nitride (cBN and hBN), zirconia (ZrO2), graphite, titanium dioxide (TiO2), and titanium carbide (TiC) were found the most suitable candidates to be added in Al2O3 matrix as individual or hybrid combinations. A series of samples including standalone Al2O3, single inclusion composites (Al2O3/SiC, Al2O3/cBN) and hybrid composites (Al2O3/SiC/cBN, Al2O3/SiC/TiO2 and Al2O3/SiC/graphite) are sintered by Spark Plasma Sintering (SPS) for validation purpose. Properties of the sintered composites are measured and compared with the proposed computational material design. Composition and phase transformation of the sintered samples are studied using X-Ray diffraction (XRD) and Raman spectroscopy, while their morphology is studied using Field Emission Scanning Electron Microscope (FESEM). The presented nontraditional material design approach is found to significantly reduce experimental time and cost of materials in developing toughened and anti-friction ceramic composites.