Synthesis and characterization of TiB2-TiC-Al2O3 based ternary composites

In this thesis study, TiB₂–TiC–Al₂O₃-based ceramic matrix binary and ternary composites were produced from TiO₂, B₂O₃, Al, and C powders through mechanochemical synthesis and mechanical activation followed by high-temperature annealing. The main objective of the study was to achieve the controlled synthesis of these ceramic phases and to systematically evaluate the effects of parameters such as milling time and annealing temperature on the final product. Experimental studies were conducted on four different initial powder systems: ternary TiO₂–B₂O₃–Al, TiO₂–B₂O₃–C, TiO₂–C–Al systems, and the quaternary TiO₂–B₂O₃–Al–C powder mixtures. In addition, the effects of different reaction stoichiometries in the quaternary TiO₂–B₂O₃–Al–C system were investigated. The study aimed to synthesize binary and ternary composite powders such as TiB₂–Al₂O₃, TiB₂–TiC, TiC–Al₂O₃, and TiB₂–TiC–Al₂O₃. During the mechanochemical synthesis process, the initial powder mixtures were subjected to high-energy ball milling for 8, 12, 18, 24, and 30 hours. In the mechanically activated annealing process, powders activated by 3 hours of high-energy milling were subsequently annealed at 900 °C, 1100 °C, 1200 °C, 1300 °C, and 1500 °C. In the mechanochemical synthesis process, the formation of TiB₂–Al₂O₃ composites in the TiO₂–B₂O₃–Al powder system was confirmed by XRD patterns and Rietveld analysis after 18 hours of milling. Furthermore, SEM and TEM analyses were carried out to examine the detailed morphology and phase characteristics of the powders. In the TiO₂–Al–C system, no reaction was observed even after 30 hours of milling, indicating that an appropriate heat treatment may be necessary to complete the reaction. In the quaternary TiO₂–B₂O₃–Al–C system, milling with different stoichiometries of x:1,2,3–y:1 revealed that TiB₂–TiC–Al₂O₃ ternary composite formation occurred after 24 hours of milling for x:2–y:1 and x:3–y:1 compositions, as confirmed by XRD analysis. However, no composite phase formation was detected after 30 hours of milling in the x:1–y:1 composition. Increasing the x/y ratio was found to promote the formation of TiB₂–TiC–Al₂O₃ ternary composites. In the mechanically activated heat treatment process, the TiO₂–B₂O₃–C system yielded TiB₂ and TiC phases at 1300 °C. In the TiO₂–B₂O₃–Al system, TiB₂ and Al₂O₃ phases were distinctly detected by XRD when the annealing temperature was raised to 1500 °C. Similarly, in the TiO₂–C–Al system, TiC and Al₂O₃ phases were identified at 1500 °C. For the quaternary TiO₂–B₂O₃–Al–C system with x:1,2–y:1 stoichiometries, Al₂O₃, TiC, and TiB₂ phases with high crystallinity and density were formed at 1300 °C. Detailed morphological investigations of the powders were further supported by SEM and TEM analyses. The results of this thesis demonstrate that multi-phase TiB₂–TiC–Al₂O₃-based ceramic powders with high hardness and thermal stability can be effectively synthesized from oxide-based and cost-effective raw materials using economic methods such as mechanochemical synthesis and mechanically activated annealing. The TiB₂–TiC–Al₂O₃ composites obtained have high potential for advanced engineering applications, particularly in cutting tools, coating materials, and components operating at high temperatures. This study makes a significant contribution to the literature by elucidating the reaction mechanisms of TiO₂–B₂O₃–Al–C-based ternary and quaternary systems and by presenting phase formation results that differ in temperature and duration compared to SHS and conventional sintering techniques.