Seminarium AMAS

Thermal cycling, thermal aging and thermal shock behavior of SiC-fiber reinforced glass matrix composites

dr A.R. Boccaccini

środa, 14 stycznia 2004

14:00, room 104


Continuous fiber-reinforced glass and glass-ceramic matrix composites are candidate materials for various structural and other specialized applications involving moderate (up to 1000°C) temperatures. To be considered realistically for these applications, however, the materials must exhibit mechanical and dimensional stability under different thermal loadings, including thermal aging, thermal cycling and thermal shock conditions. Particularly the behavior of such composites when subjected to abrupt severe temperature gradients has not yet been studied extensively. In this presentation, we will summarize experimental results obtained to date on damage evolution under thermal aging, thermal cycling and thermal shock conditions in oxidizing atmospheres as part of an on-going research effort to gain insight into the thermomechanical behavior of commercially available SiC-Nicalon® fiber reinforced glass matrix composites. The thermal shock tests involved quenching the samples from high temperatures (500-710°C) in a water bath at room temperature. Thermal aging was investigated by long-term (up to 1000 h) air exposures of as-received samples at elevated temperatures (T= 450-700 °C). For the thermal cycling tests the samples were alternated between a furnace at high temperature and room temperature for up to 1000 cycles. Both destructive and non-destructive techniques, including fiber push-out tests, were employed to characterize the samples and to detect differences in behavior for the various thermal loading conditions. For thermally shocked samples, it is found that the non-destructive resonant frequency technique employed is more sensitive than the destructive three-point flexural test for detecting matrix crack development in the early stages of damage. In particular internal friction is found to be a very sensitive parameter by which to assess microcracking. A model was developed to correlate the degree of microstructural damage in the form of matrix microcracking with the internal friction value.

A crack healing process in the glass matrix may result in an extension of the life of the components. The possibility of healing the induced microcracks by an optimized post-thermal shock heat-treatment (annealing) schedule exploiting the viscous flow of the glass matrix will be discussed.