Potential of SiC as a heat exchanger material in combined cycle plant

The short and long term mechanical properties of a sintered silicon carbide intended as a heat exchanger material have been investigated. The short term strength shows an acceptable scatter characterised by a Weibull modulus of seven from room temperature up to 1400°C. In the time-dependent regime failure occurs by subcritical crack growth from surface located inherent defects at high stresses. Below a threshold stress oxidation blunting of these surface defects occurs and causes a transition from subritical crack growth to diffusion creep as life-limiting mechanism. Unlike other ceramics, the threshold stress for subcritical crack growth falls within the low probability range of fast fracture. Failure mechanism maps presenting the life-limiting mechanisms of the investigated sintered silicon carbide over a range of stresses and temperatures are presented.