High-temperature creep and kinetic decomposition of Ni₂SiO₄

To investigate high-temperature creep and kinetic decomposition of nickel orthosilicate (Ni₂SiO₄), aggregates containing ∼3 vol% amorphous SiO₂ have been deformed in uniaxial compression at a total pressure of one atomsphere. Twenty-three samples with grain sizes (d) from 9 to 30 μm were deformed at temperatures (T) from 1573 to 1813 K, differential stresses (σ) from 3 to 20 MPa, and oxygen fugacities (fo₂) from 10^-1 to 10⁵ Pa. At temperatures up to 1773 K, the steady-state creep rate (ɛ) can be described by the flow law Under these conditions, the dominant deformation mechanism is Coble creep, rate-limited by grain boundary diffusion of silicon. At temperatures between 1803 and 1813 K, the samples of Ni₂SiO₄ plus amorphous SiO₂ exhibit enhanced creep rates and increased ductility. This behavior is associated with fast diffusion through a thin intergranular film produced by kinetic decomposition of Ni₂SiO₄ under the imposed stress gradient.