Microstructure and mechanical behaviour of SrO doped Al2O3 ceramics

Abstract

Microstructure and mechanical behaviour of the SrO doped Al2O3 ceramics have been studied with a dopant concentration levels of, 0 ppm (AS0), 1000 ppm (AS1), 3000 ppm (AS3), and 5000 ppm (AS5), respectively. High density (~99.1%) and finer grain size (~3.4 µm) have been obtained for the Al2O3 ceramics at an optimum dopant concentration of 5000 ppm SrO (AS5) attributed to the important effects of in-situ formed strontium hexaluminates (SrAl12O19). Controlled grain growth behaviour in SrO doped Al2O3 (AS5) may be ascribed to the zener pinning stresses and solute drag effect actuated by the grain boundary phase SrAl12O19 with platelet morphology. Improved densification behaviour in SrO doped Al2O3 (AS5), presumably because of the lower interfacial energy of newly formed Al2O3/SrAl12O19 interfaces and key benefits of secondary phase (SrAl12O19) inhibited grain growth mechanism. The activation energy for densification in SrO doped Al2O3 (AS5) is found to be 550 ± 30 kJ/mol, which is higher compared to undoped Al2O3 and the estimated activation energies have been phenomenonlogically correlated to the lower energy of Al2O3/SrAl12O19 interfaces. Improved mechanical properties in terms of fracture toughness (~3.7 MPa. m1/2), strength (~890 MPa) and hardness (~13.8 GPa) in optimum SrO doped Al2O3 (AS5) ceramics are triggered by a combination of toughening mechanisms primarily including SrAl12O19 platelet grain bridging, crack deflection, grain pullout, and crack tip healing.