Thermal Cycling, Thermal Aging and Thermal Shock Behavior of Nicalon-Fiber Reinforced Glass Matrix Composites

摘要

Experimental results on damage evolution in commercially available Nicalon fiber reinforced glass matrix composites during thermal aging and thermal cycling, as well as under thermal shock conditions are presented. The thermal shock tests involved quenching the samples from high temperatures (500-710℃) in a water bath at room temperature. Thermal aging was investigated by long-term (up to 1000 h) air exposures at elevated temperatures (T= 500-700℃). 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 were employed to characterize the samples and to assess damage development. Based on the experimental results, plots depicting the overall materials response under the different loading conditions were constructed. In samples thermally shocked from intermediate temperatures (i.e. 650℃ ), microstructural damage is ascribed to matrix microcracking, which is induced by the thermal stresses generated during quenching. Thermal cycling in air from 700℃ resulted in a different form of damage, characterized by both interfacial degradation and porosity formation in the matrix. An aging process during the holding period at the high temperature, rather than any significant effect from transient thermal stresses, is expected to occur in these samples.