Visco-elastic analysis of internal friction on engineering ceramics

Internal friction of alumina and silicon nitride was measured using a torsion pendulum, and was analyzed with the four-element visco-elastic model. The grain size dependence of internal friction of alumina was also discussed. Alumina showed no peaks in temperature dependence of internal friction, and it increased exponentially with ascending temperature. The calculated activation energy was relatively close to the value for creep deformation, but the calculated strain rate was much larger than the experimental data. Silicon nitride showed a peak in temperature dependence of internal friction, and this temperature dependence was well expressed with the four-element model. However, the calculated activation energy was smaller than the experimental value. The calculated relaxation time was quite short, and it does not explain the transient creep behavior of silicon nitride. Grain size exponents for internal friction of alumina between 0.55 and 0.87 were obtained. This grain size exponent shall become 1, from the discussion of the diffusion creep model.