Effect of Oxygen Partial Pressure on the Creep of Polycrystalline Al 2 O 3 Doped with Cr, Fe, or Ti

Steady‐state creep was studied in hot‐forged polycrystalline Al 2 O 3 (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/cm 2 at 1375° to 1525°C under O 2 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 P o2 on the creep rate indicated that increased concentration of a divalent (Fe 2+ ) or quadrivalent (Ti 4+ ) impurity in solid solution enhances the creep rate of polycrystalline Al 2 O 3 . The activation energies for the creep of Fe‐ and Ti‐doped Al 2 O 3 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 P o2 , temperature, and grain size, it was concluded that the steady‐state creep of transition‐metal‐doped Al 2 O 3 is controlled by cation lattice diffusion.