Mechanical and structural characterisation of Nicalon SiC fibres up to 1300°C

Abstract

The resurgence of interest in metal matrix composites has been fuelled by the development of new fibres with high temperature characteristics. The new family of continuous fine ceramic fibres based on SiC or Al 2O 3 offers the possibility of producing high temperature composites with metal or ceramic matrices. The toughening of ceramics by these fibres is a particularly interesting prospect. Two types of continuous silicon carbide Nicalon monofilaments (NLP 101 and NLM 102) have been tested in air and argon up to 1300°C. Tensile and creep tests have shown that the tensile strength falls and the fibres creep above 1000°C. Different behaviour was found for the two types of fibres. The NLM 102 fibre was stronger and crept less at high temperature under small strains. However its creep lifetime was less than that of the NLP 101 fibres. These differences have been interpreted with the aid of a microstructural study. The fibres were found to contain silicon, carbon and oxygen (electron microphobe and Auger spectrometer) and SiC was also detected (X-ray diffraction and transmission electron microscopy). The modification of the amorphous and microcrystalline structures during creep have been investigated. A fine segregation of free carbon particles was detected (X-ray diffraction and ESR) and was seen to disappear during heat treatment in both types of environment studied.