Effect of Oxygen Partial Pressure on the Creep of Polycrystalline Al2O3 Doped with Cr, Fe, or Ti

Abstract

Steady‐state creep was studied in hot‐forged polycrystalline Al2O3 (3 to 42 μm) of nearly theoretical density doped with≤1 cation % of Fe, Ti, or Cr. Tests were conducted at stresses between 10 and 550 kg/cm2 at 1375° to 1525°C under O2 partial pressures of 0.88 to 10−10 atm. Except in the 10‐μm Fe‐doped material tested at very small stresses, slightly nonviscous creep behavior was generally observed. The effects of Po2 on the creep rate indicated that increased concentration of a divalent (Fe2+) or quadrivalent (Ti4+) impurity in solid solution enhances the creep rate of polycrystalline Al2O3. The activation energies for the creep of Fe‐ and Ti‐doped Al2O3 samples (148 and 145 kcal/mol, respectively) were significantly higher than that for Cr‐doped material (114 kcal/mol). Taking into account the effects of Po2, temperature, and grain size, it was concluded that the steady‐state creep of transition‐metal‐doped Al2O3 is controlled by cation lattice diffusion.