Superplastic Flow in Fine‐Grained Alumina

Dense polycrystalline alumina having an average grain size of 1.6 μm was deformed to true strains of up to 60% in simple uniaxial compression at 1693 K without significant cavitation. A strain rate of ∼2 × 10 −4 s −1 was obtained at a uniaxial stress of ∼30 MPa. Such a reasonable flow stress at such high strain rates and a relatively low temperature raises a real possibility of isothermal superplastic forging of alumina ceramics. The mechanism of deformation was identified to be diffusion creep with grain boundaries as the dominant diffusion path. The specimens suffered considerable grain growth during deformation. Part of the grain growth resulted from time and temperature, but the majority was induced by deformation strain.