Fibre-reinforced Glass-ceramic Matrix Research Articles

Effect of heat treatment in air on the thermal properties of SiC fibre-reinforced composite. Part 1: a barium osumilite (BMAS) matrix glass ceramic composite

The thermal properties have been studied on a glass ceramic composite comprised of a barium osumilite (BMAS) matrix reinforced with SiC (Tyranno) fibres which has been subjected to a heat treatment in air in the range of 700–1,200 °C. Microstructural studies were carried out especially on of the interface between fibre and matrix. The presence of a carbon thin layer in the interface is a typical observation in SiC fibre-reinforced glass ceramic matrix composite systems. The microstructural evaluation and thermal properties showed a degradation of interfacial layer occurred at low heat treatment temperatures, (700–800 °C) this was attributed to the fact that, at those heat treatment temperatures the carbon rich layer formed during processing was oxidised away leaving voids between fibre and matrix, which were linked by isolated silicon-rich bridges. After heat treatment at higher temperatures of 1,000–1,200 °C, the thermal properties were retained or even enhanced by leaving a thick interfacial layer.

Effect of cyclic loading on interfacial shear stress in SiC–CAS glass ceramic matrix composite

Mechanical fatigue has been observed to occur in the Nicalon–CAS continuous fibre reinforced glass ceramic matrix composite under cyclic loading at room temperature, and both microcrack proliferation and propagation are induced. In situ fibre push down tests within a scanning electron microscope have then been used to assess changes in interfacial properties as a result of this mechanical cyclic loading. Both the interfacial shear stress and the interfacial fracture energy decrease when specimens are subjected to mechanical cyclic loading. It is deduced that a decrease in interfacial shear stress is the most likely mechanism driving stable and progressive microcrack propagation.

Tension-compression fatigue behaviour of fibre-reinforced ceramic matrix composite with circular hole

The tension-compression fatigue behaviour of a silicon carbide fibre-reinforced glass ceramic matrix composite, SiC/1723, with a circular hole was investigated at room temperature. Two laminate lay-ups were studied: cross-ply, [0/90] 2s, and unidirectional, [0] 8. At first, the fatigue limit based on one million cycles was established for the tension-tension fatigue condition. Then, the fatigue response under fully reversed (tension-compression) cycling loading with a maximum stress equal to the tension-tension fatigue limit was investigated. This tension-compression loading resulted in an increased amount of damage and ultimately led to the specimen failure well before one million cycles. In the cross-ply laminate, the damage mechanisms in the 90° plies involved transverse cracks only during tension-tension cycling, and transverse and longitudinal cracks during tension-compression cycling. In the unidirectional laminate, the longitudinal cracks which initiated at the hole periphery grew longer in tension-compression fatigue than in tension-tension fatigue. On the other hand, no damage and consequently no effect on fatigue life was observed during the compression-compression fatigue condition only.

Tension-Compression Fatigue Behavior of a Silicon Carbide Calcium-Aluminosilicate Ceramic Matrix Composite

The fatigue behavior of a silicon carbide fiber reinforced glass ceramic matrix composite, SiC/CAS subjected to tension-compression cycling was investigated. Two laminate layups were studied: cross-ply, [0/90]25 and unidirectional, [0]16. At first, the fatigue limit based on one million cycles was established for a tension-tension fatigue condition. Then, compression cycling was superimposed on this measured fatigue limit. The addition of this compression loading resulted in the development of longitudinal cracks parallel to the loading direction. This increased the amount of damage and ulti mately led to total specimen failure prematurely. The larger the magnitude of the compres sion cycle, the earlier the development of longitudinal crack occurred and, consequently, the earlier failure occurred. This behavior was due to the inherently poor interfacial bond between matrix and fiber of the tested ceramic matrix composite.

Tension-Compression Fatigue Behavior of a Silicon Carbide Calcium-Aluminosilicate Ceramic Matrix Composite

The fatigue behavior of a silicon carbide fiber reinforced glass ceramic matrix composite, SiC/CAS subjected to tension-compression cycling was investigated. Two laminate lay-ups were studied—cross—ply, [0/90]2 s and unidirectional, [0]16. At first, the fatigue limit based on one million cycles was established for a tension-tension fatigue condition. Then, compression cycling was superimposed on this measured fatigue limit. The addition of this compression loading resulted in the development of longitudinal cracks parallel to the loading direction. This resulted in an increased amount of damage and ultimately led to total specimen failure. The larger the magnitude of the compression cycle, the earlier the development of longitudinal cracks occurred and, consequently, the earlier failure occurred. This behavior was due to the inherently poor interfacial bond be tween matrix and fiber of the tested ceramic matrix composites.

Glass-ceramic matrix composites with high oxidation embrittlement resistance

A new concept is introduced to minimize the oxidation embrittlement problem exhibited by Nicalon fibre-reinforced glass-ceramic matrix composites. A small amount of glass is added to the matrix and deforms at temperatures of interest to prevent microcrack formation. The graphitic interphase is thus shielded from an oxidative environment. The composites fabricated with the glass-doped matrices show excellent room- and elevated-temperature strengths and withstand high stresses at elevated temperatures in air for greater than 100 h without any deterioration in properties. The modulus of the glass-ceramic phase, the stiffness percentage of dopant glass and the process temperature were found to affect composite properties significantly.

Fracture and fatigue of a Nicalon/CAS continuous fibre-reinforced glass-ceramic matrix composite

The fracture and fatigue behaviour of Nicalon/CAS continuous fibre-reinforced glass-ceramic matrix composite was studied at temperatures of up to 1000°C in both air and vacuum. Using chevron-notched test-pieces in bending, high nominal toughness values are measured at ambient temperature and at 1000°C in vacuum. In contrast, toughness values obtained in air decrease progressively with test temperature increase from 600 to 1000°C, and at 1000°C they are reduced by a factor of three from their values at ambient temperature. Marked changes in micromechanisms of crack growth under cyclic loading are also observed in air as the test temperature is increased: multiple cracking occurs at ambient temperature, while dominant Mode I cracks can be produced at 1000°C. A further study has been carried out in air on plane-sided test-pieces at a temperature at 1000°C, under both monotonic and cyclic loading. At ambient temperature, effects of cyclic loading have been deduced, while crack growth at 1000°C in air appears to be dominated by static loading with little effect of cyclic loading. These subcritical crack growth and toughness observations are consistent with changes that occur in the fibre/matrix interfaces at elevated temperatures in air reported in the literature.

Interface analysis of Si-C-O fibre/magnesium aluminosilicate matrix composites

Interface characteristics of Si-C-O (NicalonR) fibre-reinforced glass ceramic matrix composites were studied using scanning Auger microscopy (SAM). Composites with and without the cation additions of Ba, Nb, Zr, Li and Li-Zr-Nb to the magnesium aluminosilicate (MAS) matrix were fracturedin situ under ultrahigh vacuum. SAM depth profiles and flexural strength results showed the compositional effects of the additives in the fibre-matrix interface region.