HIGH-TEMPERATURE CREEP AND KINETIC DECOMPOSITION OF NI2SIO4

To investigate high-temperature creep and kinetic decomposition of nickel orthosilicate (Ni2SiO4), aggregates containing approximately 3 vol% amorphous SiO2 have been deformed in uniaxial compression at a total pressure of one atmosphere. Twenty-three samples with grain sizes (d) from 9 to 30 mum were deformed at temperatures (T) from 1573 to 1813 K, differential stresses (sigma) from 3 to 20 MPa, and oxygen fugacities (f(0)2) from 10(-1) to 10(5) Pa. At temperatures up to 1773 K, the steady-state creep rate (epsilon) can be described by the flow law [GRAPHICS] 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.