Understanding Nicalon® fibre

Coustumer, Philippe Le; Monthioux, Marc; Oberlin, A.

doi:10.1016/0955-2219(93)90040-x

Cited by 113 publications

(42 citation statements)

References 20 publications

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“…Other studies have proved that the Nicalon ® bre is not thermodynamically stable (Mah et al 1984, Clark et al 1985, Johnson et al 1988, Le Coustumer et al 1993). …”

mentioning

confidence: 96%

SiC Nicalon fibre-glass matrix composites: interphases and their mechanism of formation

Strat¹,

Lancin²,

Fourches-Coulon³

et al. 1998

Philosophical Magazine A

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The ® bre± matrix reaction that occurs during the processing of a Nicalon SiC ® bre± Pyrex glass matrix composite is analysed. Interphases are characterized by means of various complementary techniques: electron di raction, HRTEM, EDX, EELS, SIMS and XPS. Neither the results of the present study nor those previously obtained for Nicalon SiC ® bre± LAS (Li 2 O± Al 2 O 3 ± SiO 2) glass or LAS + MAS (MgO± Al 2 O 3 ± SiO 2 ) glass± ceramic matrix composites support the available model of reaction. An alternative reaction mechanism is suggested whereby the dissolved and non-bridging oxygen atoms of the matrix di use and oxidize SiC and SiO x C y in the ® bre. The reaction yields carbon and silicon oxycarbide in the ® bre and SiO 2 which dissolves into the matrix. When the oxygen in excess in the matrix is consumed, the reaction stops and the phases undergo a reorganization in the reaction layer which generates two interphases, one carbon rich and the other silicon oxycarbide rich. These interphases are observed at the ® bre periphery in all glass or glass± ceramic matrix composites. § 1. Introduction Glass or glass± ceramic matrix composites are developed for thermostructural applications such as in aircraft parts submitted to severe thermomechanical stresses. Glass± ceramic is reinforced by means of long ® bres that are essentially stronger and less brittle than the matrix. This reinforcement yields composites with high strength and a`pseudoplastic' strain su cient to alleviate the catastrophic rupture mode of a brittle material. Amongst commercial ® bres, the SiC Nicalon 202 ® bre has been successfully used in the last years. The mechanical properties of Nicalon± glass matrix composites depend on the nature of the interphases that develop during material processing (Brennan 1988, Lancin 1991. A good characterization of the reaction between the ® bre and the matrix together with the understanding of this reaction are essential in order to elaborate composites with required speci® cations.Studies of the interphases produced in the course of the ® bre± matrix reaction have been conducted in a number of composites based on various matrices (Brennan 1988, Chen et al. 1989, Bonney and Cooper 1990. The most currently used are Li 2 O-Al 2 O 3 -SiO 2 (LAS) or CaO± Al 2 O 3 -SiO 2 (CAS) containing some additives such as niobium, arsenic or yttrium. In order to explain the formation of interphases, one usually refers to the model proposed by Cooper and Chyung (1987) which

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“…Other studies have proved that the Nicalon ® bre is not thermodynamically stable (Mah et al 1984, Clark et al 1985, Johnson et al 1988, Le Coustumer et al 1993). …”

mentioning

confidence: 96%

SiC Nicalon fibre-glass matrix composites: interphases and their mechanism of formation

Strat¹,

Lancin²,

Fourches-Coulon³

et al. 1998

Philosophical Magazine A

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“…The differences between the mechanical characteristics and thermal stability of stoichiometric SiC and the SiCbased ceramic from PCS are due to the existence of the intergranular phase and free carbon (Simon & Bunsell, 1984;Porte & Sartre, 1989;Le Coustumer et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

Microstructural evolution of the latest generation of small‐diameter SiC‐based fibres tested at high temperatures

Hochet

Berger

Bunsell

1997

Journal of Microscopy

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SummaryThe new generation of silicon-carbide-based fibres made from organosilicon precursors, cross-linked by electron irradiation, have been compared with the earlier fibres which have undergone cross-linking in air. The latest fibres, known as Tyranno Lox-E and Hi-Nicalon, possess a lower oxygen content (Ϸ5 wt% and Ϸ0 : 5 wt%) whereas the NLM202 fibres contain 12 wt% and the Tyranno Lox-M 13 wt% of oxygen. The Tyranno fibres have been produced with a precursor similar to that used to produce the Nicalon fibres, but modified by the addition of titanium. All fibres possess a structure composed of b-SiC grains, free carbon aggregates, with no crystallized titanium compounds in the Tyranno fibres and an oxygen-rich intergranular phase, except in the Hi-Nicalon fibre. The Hi-Nicalon fibre has the largest grain size and its free carbon content is higher than in the NLM202 fibres. For all the fibres, the b-SiC grains grow when the temperature increases, whilst the strengths and Young's moduli decrease. The NLM202 shows the least change in grain size and tensile properties. The Hi-Nicalon is stiffer and stronger than the others at high temperature. TEM results show that grain growth is isotropic, even during creep tests. The growth depends on the nature and amount of the intergranular phase. Mechanical changes as a function of temperature can be explained by external oxidation during tensile tests in air and internal oxidation facilitated by the nanoporosity, which is greater in the Tyranno than in the Nicalon fibres. The presence of the oxygen-rich phase in the three fibres containing the most oxygen decreases the creep resistance. Titanium does not improve the mechanical properties and the creep resistance beyond 1523 K and does not have any positive influence in limiting the SiC grain growth. Tyranno fibres are less well stabilized than the Nicalon fibres. The Hi-Nicalon fibres have been shown to possess consistently better mechanical properties at all temperatures, including creep resistance, than the other fibres studied. All the fibres are sensitive to external oxidation at high temperature.

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“…I), yielding scattered data [6][7][8][9][10][11][12][13][14]. This lack of coherence among reported data may be ascribed to the accuracy of the different techniques used, to compositional variations between the outer and inner regions of the fibres, and to compositional fluctuations during processing.…”

Section: Introductionmentioning

confidence: 99%