Interface Modification During Oxidation of a Glass-Ceramic Matrix / SiC Fibre Composite.

Abstract

Oxidation heat treatments between 375°C and 600°C for 100 hours in air, have been performed on the calcium aluminosilicate glass-ceramic matrix / Sic fibre reinforced composite CASMicalon (manufactured by Corning, USA). Using a commercial nano-indentation system to perform fibre push-down tests, the fibre-matrix interfacial debond fracture surface energy (Gi) and fictional shear stress (T) have been determined. Modification of interface properties, compared to the asfabricated material, was observed at heat treatment temperatures as low as 37SoC, where a significant drop in G, and an increase in r were recorded. With 45OoC, 525°C and 600°C heat treatments, an increase in G, but a dramatic increase in T were recorded. Under four-point flexure testing, the as fabricated and the 375°C heat treated materials displayed tough, composite behaviour with extensive fibre pull out, but at 245O"C, brittle failure with minimal fibre pull out, was observed. This transition from tough mechanical response to one of brittleness is due to the large increase in T reducing fibre pull out to a mmimum and therefore reducing the total required work of fracture. The large increases in r and Gi have been attributed to the oxidative removal of the lubricating, carbon interface and the compressive residual stresses across the interface.

Low‐Temperature Oxidation Embrittlement of SiC (Nicalon™)/CAS Ceramic Matrix Composites

“…3)). It was interesting to note from this prior study that, upon reloading, the debond load is essentially the same as the first loading cycle (i.e., ∼200 mN), which again indicates the lack of any interfacial chemical bond 30 …”

“…It is apparent that heat‐treatment temperature has a significant effect upon these interfacial properties. After heat‐treatment at 375°C the debonding energy is significantly lower than for the as‐received material, and essentially unchanged upon subsequent reloading, indicating that there is no real interfacial chemical bond present after this heat treatment 30 . However, the frictional sliding stress is comparable with the as‐received composite with a carbon interlayer.…”

“…Prior work has demonstrated the effects of oxidation (for 100 h) upon the interfacial micro-mechanical properties, namely the debonding energy (G i ) and frictional sliding stress (t). 30 Data obtained in that prior study is presented in Table II for reference. It is apparent that heat-treatment temperature has a significant effect upon these interfacial properties.…”

Die Rißzähigkeit und Brucharbeit von SiC-faser-verstärkten Glasmatrix-Verbundwerkstoffen: Bestimmung durch die Chevron-Kerb-Technik

“…Diese optimierte Grenzfla Ècheneigenschaften sind fu Èr das ,quasiduktileª Verhalten des Verbundwerkstoffes verantwortlich [6,11,12], und sie sind in der Regel durch eine du Ènne, kohlenstoffreiche Schicht zwischen Faser und Matrix gegeben. Fu Èr Anwendungen in oxidierender Atmospha Ère ko Ènnen diese Creichen-Schichten allerdings schon bei relativ niedrigen Temperaturen degradiert werden (ab etwa 400 8C) [13,14]. Auf Grund der C-Oxidation bilden sich im Temperaturbereich 500 ± 800 8C Hohlra Èume an den Faser/Matrix Grenzfla Èchen, die zu einer starken Abnahme der Bruchfestigkeit fu Èhren.…”

“…Bei noch ho Èheren Temperaturen (b 800 8C) kommt es auch zur Oxidation der Nicalon-Fasern. Damit verliert man das ¹quasi-duktileª Bruchverhalten des Verbundwerkstoffes, da die Faser-Matrix-Grenzfla Èchenfestigkeit durch Bildung von starren SiO 2 -Bru Ècken an den Grenzfla Èchen steigt und keine weiteren Pull-Out-Effekte (Faser-Herausziehen) stattfinden ko Ènnen [13,14]. Obwohl das thermomechanische Verhalten von Glas-und Glaskeramik-Matrix-Verbundwerkstoffen bei Temperaturen u Èber 400 8C in oxidierender Atmospha Ère wiederholt untersucht worden ist [13 ± 16] 3 , der Faservolumenanteil ist etwa 40%.…”