High-temperature compressive creep of spark-plasma sintered additive-free polycrystalline β-SiC

The high temperature mechanical behaviour of additive-free nano-size power of β-SiC sintered by spark-plasma sintering (SPS) technique has been studied. Samples had a mean grain size of 0.58 μm and 97.4% of relative density. They were deformed by means of constant load compression (creep) tests at temperatures between 1750 and 1850 °C and stresses between 200 and 500 MPa. The strain rates ranged from 1 × 10−7 s−1 to 1 × 10−6 s−1 depending on the test conditions. The activation energy Q and the stress exponent n parameters, which characterize the deformation mechanisms, were evaluated. The values obtained for the activation energy Q in the whole temperature range was 540 kJ mol−1, and the stress exponent n values were between 1.2 and 1.3 for T = 1750 °C and 2.6 for T = 1800 °C. The values of these parameters, together with the results of microscopy of the deformed samples, suggested that there are two mechanisms operating simultaneously: (i) grain boundary sliding (GBS) accommodated by diffusion of Si along the grain boundary and (ii) dislocation glide and climb (power law creep (PLC)). The contribution of the latter mechanism increases with temperature.