Significance of Environment in Thermal Fatigue Failure of SCS-6/Ti-24Al-11Nb Composite and Interfacial Shear Strength@@
Okazaki Masakazu; Nakatani Hiroshi; Asahi Shiroh
Abstract:Thermal fatigue tests of an unidirectional SiC fiber reinforced Ti 24Al 11Nb matrix composite, SCS 6/Ti 24Al 11Nb, have been carried out without external load in air and in vacuum, under various thermal cycle conditions. The fiber employed was a b- SiC fiber of 140mm diameter with a carbon rich graded silicon carbide coating on the surface: SCS 6. This paper covers the following characteristics of the material subjected to thermal fatigue, compared with those subjected to long term isothermal exposure: (I) change of the visible crack density with thermal cycling; (ii) change of the fiber/matrix interface morphology by means of EPMA and SEM; (iii) change of the interfacial shear strength by the push out tests, and (iv) effect of environment on the properties from (I) to (iii). Based on these systematic investigations, special attentions are paid to understand the mechanisms and mechanics of thermal fatigue failure, and how thermal fatigue damage should be assessed. Key Words:SCS-6/Ti-24Al-11Nb metal matrix composite, thermal fatigue, push-out test, interfacial shear strength, environment, depletion of carbon, coating, crack density