TENSILE TESTING AT HIGH-TEMPERATURES OF EX-PCS SI-C-O AND EX-PCSZ SI-C-N SINGLE FILAMENTS

A microtensile tester consisting mainly of an induction-heated furnace, a 0-2 N load cell, a 0.1/1 mum sensitivity straining device and hot grips has been designed and used to test ceramic single ceramic filaments at 25-1600-degrees-C under vacuum (0.1 Pa) or in controlled atmospheres. Both failure strength and Young's modulus were measured with an isothermal gauge length of 30 mm. A system compliance correction was applied for each test temperature and material. The apparatus was used to characterize an ex-poly-carbosilane Si-C-O fibre (Nicalon NLM-202) and an ex-polycarbosilazane Si-C-N experimental single filament almost free of oxygen (gamma-ray curing). Both materials exhibit a significant strength loss at 1200-1600-degrees-C when tested under vacuum, assigned to a decomposition process with an evolution of gaseous species (SiO/CO or N2) and the formation of a mechanically weak decomposition surface layer. Conversely, the Si-C-N filament undergoes no strength loss when tested in an atmosphere of nitrogen (P = 100 kPa) at 1200-degrees-C, the decomposition being impeded by the external nitrogen pressure. In all cases, no significant decrease in Young's modulus was observed.