Ceramic-Matrix Composites

Microstructure, Properties and Applications

I M Low

• Publisher: Woodhead Publishing
• Year: 2006
• Print ISBN: 9781855739420
• eBook ISBN: 9781845691066
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

The advent of engineering-designed polymer matrix composites in the late 1940s has provided an impetus for the emergence of sophisticated ceramic matrix composites. The development of CMCs is a promising means of achieving lightweight, structural materials combining high temperature strength with improved fracture toughness, damage tolerance and thermal shock resistance. Considerable research effort is being expended in the optimisation of ceramic matrix composite systems, with particular emphasis being placed on the establishment of reliable and cost-effective fabrication procedures.Ceramic matrix composites consists of a collection of chapters reviewing and describing the latest advances, challenges and future trends in the microstructure and property relationship of five areas of CMCs. Part one focuses on fibre, whisker and particulate-reinforced ceramic matrix composites, part two explores graded and layered ceramics, while the five chapters in part three cover nanostructured CMCs in some detail. Refractory and speciality ceramic composites are looked at in part four, with chapters on magnesia-spinel composite refractory materials, thermal shock of CMCs and superplastic CMCs. Finally, part four is dedicated to non-oxide ceramic composites.Ceramic matrix composites is a comprehensive evaluation of all aspects of the interdependence of processing, microstructure, properties and performance of each of the five categories of CMC, with chapters from experienced and established researchers. It will be essential for researchers and engineers in the field of ceramics and more widely, in the field of inorganic materials. - Looks at the latest advances, challenges and future trends - Compiled by experienced and established researchers in the field - Essential for researchers and engineers

Part I

Fibre-whisker- and particulate-reinforced ceramic composites

Outline

Chapter 1: Fibrous monolithic ceramics

Chapter 2: Whisker-reinforced silicon nitride ceramics

Chapter 3: Fibre-reinforced glass/glass-ceramic matrix composites

Chapter 4: Particulate composites

1

Fibrous monolithic ceramics

Y-H KOH, Seoul National University, Korea

Publisher Summary

Fibrous Monolithic Ceramics (FMs) consist of a hexagonal arrangement of submillimeter cells of strong polycrystalline ceramic and a network of crack-deflecting weak cell boundaries. These composites are sintered or hot-pressed monolithic ceramics with a distinct fibrous texture. This unique architecture opened new avenues for ceramic composites, in which they fail in a nonbrittle manner because of crack interactions with weak cell boundaries, such as crack deflection or crack delamination. This approach provides a simple and versatile method for manufacturing nonbrittle ceramic composites from a variety of different material combinations that include oxide ceramics (Al₂O₃/Al₂O₃–ZrO₂) and non-oxide ceramics (SiC/graphite, SiC/BN and Si₃N₄/BN.) In the last 10 years, significant advances in fibrous monolithic ceramics have been achieved. A variety of materials in the form of either oxide or nonoxide ceramic for cell and cell boundary have been investigated. As a result of these efforts, FMs are now commercially available from the ACR company, which is the Advanced Ceramics Research, Inc., Tucson, Arizona. These FMs are fabricated by a coextrusion process. In addition, the green fiber composite can then be wound, woven or braided into the shape of a desired component.

1.1 Introduction

Fibrous monolithic ceramics (FMs) consist of a hexagonal arrangement of submillimeter ‘cells’ of strong polycrystalline ceramic and a network of crack-deflecting weak ‘cell boundaries’ [1, 2]. These composites are sintered or hot-pressed monolithic ceramics with a distinct fibrous texture. This unique architecture opened new avenues for ceramic composites, in which they fail in a nonbrittle manner because of crack interactions with weak cell boundaries, such as crack deflection or crack delamination. This approach provides a simple and versatile method for manufacturing nonbrittle ceramic composites from a variety of different material combinations that include oxide ceramics (Al₂O₃/Al₂O₃–ZrO₂ [3]) and non-oxide ceramics (SiC/graphite [4, 5], SiC/BN [6] and Si₃N₄/BN [1, 7–16]).

This chapter presents an overview of these composites with a variety of material combinations, as well as their architectures. The major objectives of this chapter are the following: (a) to briefly discuss the history and main concepts of FMs in section 1.2; (b) to address the experimental ways to prepare these composites, including coextrusion, microfabrication by coextrusion, and hybrid extrusion and dip-coating, in section 1.3; (c) to demonstrate the various types of FMs in the form of oxide-based or *;*;*;nonoxide-based composites, as well as their various architectures in section 1.4; (d) to discuss the mechanical properties of Si₃N₄/BN FMs at room and high temperatures, as well as their fracture mechanisms, in section 1.5; and finally (e) to give a personal perspective on the future of these wonderful composites in section 1.6.

1.2 History

Ceramics have been well known to offer potential benefits over metal parts in high-temperature environments, such as higher strength, lower density, and greater resistance to oxidation. In spite of these merits, their low fracture resistance with poor reliability has long been a major concern. A number of potential toughening mechanisms have been proposed [17, 18]. One of the most successful techniques is the fiber-reinforced ceramic composites [19, 20]. In a tough ceramic composite, the matrix crack is deflected at the interface and ceases to propagate, allowing the composite to possess high toughness along with nonbrittle failure by extensive crack interactions, such as bridging of the primary crack, crack deflection along the fiber/matrix interface and frictional sliding with fiber pullout of the matrix [20]. However, fiber-reinforced ceramic composites have not been fully utilized yet because of their manufacturability and cost. Also, densification techniques such as (hot pressing and hot isostatic pressing) often lead to fiber damage, deteriorating its mechanical properties.

Another toughening concept was introduced by Cook and Gordon in 1964 [21 They suggested crack propagation in brittle materials could be controlled by incorporating a fabric of microstructural features that change the crack path, resulting in high toughness by crack blunting at the weak interface and crack delamination. Rather than rely on bridging mechanisms to improve toughness, the advancing crack was blunted at the weak interface and forced to reinitiate in order to continue propagation. Based on this concept, in 1988 Coblenz described a method for producing a pressureless sinterable ceramic composite consisting of a strong load-bearing phase surrounded by a continuous weak crack-deflecting phase [2].

Another variation on the concept of Cook and Gordon was introduced by Clegg et al. in 1990 [22]. This approach involves alternating layers of the strong load-bearing phase and the weak crack-deflecting phase, allowi...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• Contributors contact details
• Introduction
• Part I: Fibre-whisker- and particulate-reinforced ceramic composites
• Part II: Graded and layered composites
• Part III: Nanostructured ceramic composites
• Part IV: Refractory and speciality ceramic composites
• Part V: Non-oxide ceramic composites
• Index