Optimizing the fiber push‐out method to evaluate interfacial failure in SiC/BN/SiC ceramic matrix composites

Abstract

Accepted Article This article is protected by copyright. All rights reserved The investigation of several parameters during fibre push-out micromechanical tests on the interfacial shear strength (ISS) of the BN interphase in SiC f /SiC ceramic matrix composites (CMC) was undertaken to optimise experimental work. The SiC f /SiC composites-candidate materials for jet engine components-were manufactured with varying fibre types and interlayer thicknesses. Experimental parameters explored included analysing the effect of sample thickness on the success rate of micromechanical tests, the effect of fibre local environment whether at tow-level (intra-tow variability in ISS) or CMC architecture-level (inter-tow variability), the effect of nanoindenter flat-punch tip size & the effect of the interphase thickness itself. Over 1000 fibre push-outs were performed and analysed in this work-with data presented as cumulative distribution functions to compare and contrast samples. It was found that the ISS measured was strongly and statistically influenced by the underlying fibre roughness (interphase adherence), as well as its local fibre environment (e.g. number of nearest neighbours) only if the thickness of the interphase itself surpassed a threshold of 200 nm. Finally for thinner interphases, limited value was added to the CMC as the ISS measured were high and there was no effect from any local environment.

Relationship between both thickness and degree of crystallisation of BN interphases and the mechanical behaviour of SiC/SiC composites

“…contradicts, for example, the fibre push-out results obtained by De Meyere et al with their HNS/BN/SiC CMCs[14]. The number of tests performed is much smaller and therefore the statistical study is far from being as sound as that of De Meyer et al It should be noted, however, that with 9/ interphases our ISS values are globally higher than theirs, probably due to the initial fibre surface treatment.…”

“…The push-out tests were carried out with a nanoindenter (Micro Materials Ltd, NanoTest NTX) equipped with a flattened conical diamond tip of 5.5 µm diameter. This fulfils the optimal ratio of 1:2 for the tip:fibre diameter found by De Meyere et al to properly perform push-out tests independently on each fibre without cracking it [14]. The tests were performed under controlled force with a constant loading rate of 1 mN/s.…”

“…) to reach a total specimen thickness of about 100 µm. This low thickness allows achieving complete debonding and fibre sliding during the push-out test [24] as it avoids both excessive wear effects, exaggerated shear stresses at the interface and the risk of fibre misalignment [14]. The push-out tests were carried out with a nanoindenter (Micro Materials Ltd, NanoTest NTX) equipped with a flattened conical diamond tip of 5.5 µm diameter.…”

“…However, the thermal instability of the fibres, the sizing residues or unexpected effects during thermochemical treatments leading to the formation of undesired phases at the interfaces (free carbon and silica) often prevented a clear conclusion on the influence of the interphase itself on the mechanical properties of the CMC. In the case of latest generation fibres, De Meyere et al have also shown that the thickness of the BN interphase influences the interfacial properties measured from micro-mechanical push-out tests [14]. Fibre push-out tests provide a direct measure of the local fibre-matrix interfacial bond strength [15][16][17].…”

Shear behavior of SiCf/SiC interface under the thermo-chemo-mechanical influence and machine-learning-based interfacial microstructure design

“…Extensive experiments have been dedicated to the investigation of SiC f /SiC. De Meyere et al found that the interfacial shear strength of SiC f /SiC CMC is strongly and statistically influenced by the interfacial roughness [15]. Braun et al considered the coordination between Hi-Ni calon S fiber and SiC matrix and found that the residual thermal stress is closely related to the interfacial mismatch.…”