The Thermal Shock And Fatigue Behaviors Of Al₂O₃-TiC Composite Ceramic

This work in the thesis was undertaken to assess the thermal shock and thermal fatigue behavior of monolithic alumina and Al2O3-TiC composite ceramics. The damage introduced by single and 5 repeated thermal shocks (water-quench experiments) was characterized by degradation of flexural strength in three-point bending. An indentation-quench test was introduced to evaluate the thermal fatigue resistance. At first, by controlling the adding of Al2O3 and TiC starting powder size, Chapter 3 assesses the effect of Al2O3 and TiC starting powder size on the thermal shock resistance of composites, and Chapter 5 assesses the effect on the thermal fatigue resistance of composites. The second, Chapter 4 assesses the effect of the content of TiC on the thermal shock resistance of composites, and Chapter 6 assesses the effect on the thermal fatigue resistance of composites. From the studied of this thesis, main results and conclusions in the dissertation are as follows:1. The addition of TiC into alumina matrix remarkably improves the mechanical properties and thermal shock resistance of alumina ceramics. The thermal shock behaviors of monolith and composites are similar to the mode of Hassalman.2. Fined grains can further improve the mechanical properties, thermal shock and fatigue resistance of composites. But the densification of ceramic materials is vitally important to mechanical, thermal shock and fatigue properties. For Al2O3-30wt.%TiC composite ceramic, the thermal shock and fatigue resistance is: u m/submicrom> u m/ u m>submicrom /submicrom. The critical temperature difference( A Tc) of u m/submicrom composite is higher 100C than that of monolith.3. The influence of TiC content on the mechanical and thermal shock properties of Al2O3-TiC composite ceramic is unapparently. The main reason is that sintering ceramics are not full densification. The undesification of sintering ceramics decrease the contribution of TiC on the improvement of mechanical and thermal shockproperties. The A Tc of Al2O3-30wt.%TiC is the highest, 250癈, and the retained flexural strength( o rf) is the highest. It is due to its' high initialize strength. The thermal fatigue resistance of Al2O3-20wt.%TiC is the best, it is due to high KIC and pore of the material. The pore decrease the stress extension of tip of cracks and delay themal shock fatigue cracks extension.4. The △ a vs △T curves contain stable and unstable crack growth regimes of all studied materials. The thermal fatigue is due to a "true" cycling effect. The A a is a sensitive function to △T and N.5. The cracks propagation path of composites is zig-zag, but the cracks propagation path of monolith is smooth. During the thermal cycling cracks propagation, cracks deflection, bridge and pinning are the most predominant reasons that the improvement of thermal shock fatigue resistance of composites.