Fracture of Silicon Carbide Fibre

Abstract

SILICON carbide fibre in the form of a 100 µm diameter polycrystalline coating on a 12 µm tungsten wire substrate is now commercially available. The short term strength of this material has been shown¹ to be essentially constant to 1,100° C, but creep rupture results (unpublished work of K. F. A. Walles) have shown that over a longer period there is a considerable loss of strength at 850°, and that at 1,100° C the strength after ten hours is only 10 per cent of that at room temperature. This behaviour is in marked contrast to bulk silicon carbide in either single crystal or polycrystalline form, where the strength has been shown to increase with temperature², and to reach values as high as 4,500 MN/m² (650 k.s.i.) at 1,750° for single crystals³. In view of this discrepancy, it seemed worthwhile to try to establish the cause of this loss of strength at temperatures in the region of 1,000° C.