Abstract
High temperature deformation and relaxation of two silicon nitride based materials (a reference commercial gas pressure sintered Si₃N₄ and a developed hot-pressed carbon-derived Si₃N₄/SiC nanocomposite) were investigated using quasi-static repeated loading-unloading experiments in range from 1000 to 1400 °C. This behaviour is described and evaluated in terms of a spring-dashpot model of separable elastic, visco-elastic and viscous deformation processes. The model enables to estimate the values of viscosity of the intergranular phase. The energy dissipation and then the internal friction are evaluated. The results show the significance of role played by intergranular phase that influences the deformation resistance more strongly than the microstructure. In spite of its much finer microstructure, the nanocomposite exhibits higher deformation resistance than the monolithic silicon nitride.

Key words
nanocomposites, grain boundaries, creep, Si₃N₄, SiC

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