Ceramic composites: A review of toughening mechanisms and demonstration of micropillar compression for interface propert
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Yevhen Zayachuk and David E. J. Armstrong Department of Materials, University of Oxford, Oxford OX1 3PH, U.K.
Takaaki Koyanagi and Yutai Katoh Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
Christian Deck Nuclear Technologies and Materials Division, General Atomics, 3550 General Atomics Court, San Diego, California 92121-1122, USA (Received 28 August 2017; accepted 8 December 2017)
Ceramic fiber–matrix composites (CFMCs) are exciting materials for engineering applications in extreme environments. By integrating ceramic fibers within a ceramic matrix, CFMCs allow an intrinsically brittle material to exhibit sufficient structural toughness for use in gas turbines and nuclear reactors. Chemical stability under high temperature and irradiation coupled with high specific strength make these materials unique and increasingly popular in extreme settings. This paper first offers a review of the importance and growing body of research on fiber–matrix interfaces as they relate to composite toughening mechanisms. Second, micropillar compression is explored experimentally as a high-fidelity method for extracting interface properties compared with traditional fiber push-out testing. Three significant interface properties that govern composite toughening were extracted. For a 50-nm-pyrolytic carbon interface, the following were observed: a fracture energy release rate of ;2.5 J/m2, an internal friction coefficient of 0.25 6 0.04, and a debond shear strength of 266 6 24 MPa. This research supports micromechanical evaluations as a unique bridge between theoretical physics models for microcrack propagation and empirically driven finite element models for bulk CFMCs.
I. INTRODUCTION
In the early 1970’s, emerging ceramic fiber–matrix composite (CFMC) technologies received significant attention due to their unique mechanical characteristics.1–5 The initial work was driven by the need for high performance materials in jet and rocket engines, where high temperature properties, high specific strength, and mechanical reliability and predictability are required. While CFMC research and development for aircraft applications continue today, advancement of these composites also led to new applications in the nuclear industry and for microwave absorption shielding.6–11 These materials show great promise for use in extreme environments, yet challenges remain that require further research and understanding of CFMC failure mechanisms.
Contributing Editor: Yanchun Zhou a) Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2017.473
The atomic bonding structure of ceramic materials can provide valuable high temperature (.800 °C) properties including strength, creep resistance, and a variety of unique electrical and optical properties. However, due to the same underlying physics, monolithic ceramics exhibit little to no dislocation movement at relatively low temperatures and are therefore inherently brittl
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