Environmental ageing effects in a silicon carbide fibre‐reinforced glass‐ceramic matrix composite

Abstract

Summary A silicon carbide fibre‐reinforced glass‐ceramic composite, based upon a BaO–MgO–Al2O3–SiO2 (BMAS) matrix, has been used for a study of microstructural stability (specifically interface stability) after environmental exposure at elevated temperature. Characterization of the as‐received material demonstrated the presence of a thin ‘carbon‐rich’ interfacial layer between fibre and matrix, as typically observed in glass‐ceramic/silicon carbide fibre composite systems. Samples have been subjected to heat‐treatments in an oxidizing atmosphere at temperatures between 723 and 1473 K, for up to 500 h. Intermediate‐temperature ageing, between 873 and 1073 K, results in strong fibre/matrix bonding, with consequent degradation of strength and composite ‘ductility’. This is due to oxidative removal of the carbon interfacial layer and subsequent oxidation of the fibre surface, forming a silica bridge. Carbon is retained at higher ageing temperatures due to the formation of a protective surface oxide scale at exposed fibre ends. Attempts to pretreat the BMAS composite at high temperature (1273–1473 K), designed to inhibit intermediate‐temperature degradation via the formation of silica plugs at exposed fibre ends, has given mixed results due to the high residual porosity content in these materials, allowing paths of ‘easy’ oxygen ingress to be retained.

Notch sensitivity of fatigue life in a Sylramic TM/SiC composite at elevated temperature

“…This prediction is in reasonable agreement with the range obtained from the experiments (60-85 MPa), reaffirming the poor notch sensitivity associated with LCF fracture at the test temperature. Furthermore, the extreme sensitivity of the fracture time to the presence of matrix cracks is consistent with the oxidation embrittlement characteristics of other SiC-based CFCCs at intermediate temperatures [12,15,17,22,23,27,38].…”

“…The embrittlement most commonly occurs by oxygen ingress through matrix cracks, followed by reaction of the oxygen with the fibers and the fiber coatings [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The problem is particularly severe at intermediate temperatures (500-900 C) [6,15,[23][24][25][26][27][28][29][30][31][32][33][34]. It is expected to be exacerbated by cyclic loading, since under such conditions the reaction gases contained within the crack are expelled during unloading and the oxidizing atmosphere drawn into the composite through matrix cracks during reloading.…”

Thermal diffusivity measurement of SiC fibre reinforced BMAS glass ceramic composites exposed mechanical damage

“…As mentioned in earlier studies, 11,12,22 carbon rich interface is formed between fibre and matrix during the processing of glass ceramic matrix composites reinforced with continuous SiC fibre. Degradation of the carbon layer at the interface due to lower temperature heat treatment was confirmed by the observations of other researchers.…”

“…[2][3][4] Barium magnesium aluminium silicate (BMAS), that is also called as a barium osumilite in short and a glass ceramic matrix developed firstly by Brennan et al 5 and believed to be suitable for high temperature applications. A number of researches have focused on the mechanical behaviour [6][7][8][9][10][11][12] and thermal properties. 13 It is required from those materials to sustain under different conditions such as tensile, or compression loads and subjected to fatigue and creep conditions during the application.…”

Thermoschockbeständigkeit und das Verhalten von SiC-faserverstärkten Glas-Matrix-Verbundwerkstoffen bei einer thermischen Wechselbeanspruchung

“…Somit wird sich die m6gliche Degradierung der Faser-Matrix-Grenzfl/iche auf den Oberfl/ichenbereich beschr/inken wo die Fasern direkt der Luft ausgesetzt sind. Diese Form der mikrostrukturellen Sch/idigung wurde mehrmals in Alterungsversuchen an Verbundwerkstoffen der genannten Klassen beobachtet, und als ,,Pipeline" -Oxidation bezeichnet [37,41]. Somit ist bei den hier pr/isentierten Ergebnissen zu erwarten, daf die Grenzfl~ichendegradation im Oberfl/ichenbereich einsetzen wird und mit steigender Anzahl von thermischen Zyklen, d.h. mit einem 1/inger andauernden Einwirken h6herer Temperaturen, in das Werkstoffinnere fortschreiten wird.…”