Lecture 20
Ceramic Matrix Composites (CMCs)
Dr. J. Ramkumar
Professor
Dept of Mechanical & Design Program
IIT Kanpur, India.
Contents






Introduction to Ceramic matrix Composites (CMCs)
Types of CMCs
Properties of CMCs
Interfaces
Fabrication methods of CMCs
◦ Polymer Infiltration and Pyrolysis
◦ Chemical Vapor Infiltration
◦ Liquid Silicon Infiltration
◦ Direct Oxidation Process
◦ Slurry Infiltration
◦ Selective Laser Sintering
Applications of CMCs
Classification of composites based on
matrices
Composite
materials
Matrices
Polymer Matrix
Composites (PMC)
Metal Matrix
Composites (MMC)
Ceramic Matrix
Composites (CMC)
Metals
Ceramics
Introduction
Ceramic Matrix Composites (CMCs)
Matrices
Reinforcements
CMCs
Introduction
CMCs
Introduction
Ceramic matrix composites (CMCs) are a subgroup of composite
material as well as a subgroup of technical ceramic.
• By definition, ceramic matrix composites are materials in which
one or more distinct ceramic phases are intentionally added to
another, in order to enhance some property that is not
possessed by the monolithic ceramic materials.
• In ceramic matrix composites, a given ceramic matrix is
reinforced with either discontinuous reinforcement, such as
particles, whiskers or chopped fibers or with continuous fibers.
• The basic reinforcements which are included in the ceramic
matrices are carbon, glasses, glass-ceramics, oxides and nonoxides
Introduction
Cross section through an Ox/Ox CMC reinforced by a 2D
woven fabric
Raether, F. (2013). Ceramic matrix composites- an alternative for challenging construction
tasks. Ceramic applications, 1(1), 45-49.
Introduction



The fracture toughness of ceramics is improved by introduction of
secondary phases into matrix materials when the secondary phases
are chosen to act as barriers to crack propagation.
Whiskers introduced into a ceramic matrix, for example, can retard
the crack propagation because the stresses in a whisker spanning
the crack plane will tend to pull the crack shut. This phenomenon,
known as "crack bridging", leads to higher fracture toughness due
to the additional stress required for further propagation of the
crack.
Moreover, continuous fiber composites exhibit quasi-ductile
fracture behavior resulting from extensive fiber bridging.
Introduction
Ceramic matrix composites may be classified into two categories.
• One is a group of toughened ceramics reinforced with
particulates and whiskers, and these materials exhibit brittle
behavior in spite of considerable improvements in fracture
toughness and strength. The maximum in fracture toughness is
around 10 MPam1/2 or more.
• The second consists of continuous-fiber composites exhibiting
quasi-ductile fracture behavior accompanied by extensive fiber
pull out. The fracture toughness of this class of materials can be
higher than 20 MPam1/2 when produced with weak interfaces
between the fibers and matrix.
Types of CMCs
Types of CMCs
Type of composites:
(a) short-fiber,
(b) long fiber,
(c) layered,
(d) particle,
(e) FGM (functionally
gradient material),
(f) polycrystalline with
different fracture
properties of grain
boundary,
(g) polycrystalline with
small interfaces, and
(h) polycrystalline with
thick interfaces
Properties of CMCs
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
High strength-to-weight ratio
Wear resistance
Corrosion resistance
Greater Fatigue life
Low Electrical conductivity
Anisotropic
Lower Cost
Easy Processing
The matrix is relatively hard and brittle
The reinforcement must have high tensile strength to arrest
crack growth
11. The reinforcement must be free to pull out as a crack
extends, so the reinforcement-matrix bond must be relatively
weak
Properties of CMCs
Swain, Jitamitra, et al. "A Brief Review on Ceramic Matrix Composites, It's Attributes And It's Utility In Future Generation Gas Turbine."
International Journal 1: 290-292.
Properties of CMCs
Thermal, electrical conductivities and expansion of different matrix
composites
Properties of CMCs
Swain, Jitamitra, et al. "A Brief Review on Ceramic Matrix Composites, It's Attributes And It's
Utility In Future Generation Gas Turbine." International Journal 1: 290-292.
Interfaces
Interfaces
Direct bonding between primary and secondary phases
Hull, D. "Composite Materials—An Overview." Glass… Current Issues. Springer
Netherlands, 1985. 593-594.
Interfaces
Addition of a third ingredient to bond the primary phases and
form an interphase
Hull, D. "Composite Materials—An Overview." Glass… Current Issues. Springer
Netherlands, 1985. 593-594.
Interfaces
Additional interphase layers (for example a film of silicon carbide of the
thickness 0.5-5 μm) provide protection of the fibers from either
environmental attacks (e.g. oxidation) or aggressive action of the infiltrated
material (e.g. liquid silicon).
Interfaces : importance of…


Such large differences are shared through the interface.
Stresses acting on the matrix are transmitted to the fiber across
the interface.
The interfacial bond can influence
• Composite strength
• Modes of failure
• Young’s modulus
• Inter laminar shear strength
• Compressive strength
• Environmental resistance
• Structural stability at elevate temperatures
• Fracture and fatigue behavior
Cracks at interface
Sadowski, T., and L. Marsavina. "Multiscale modelling of two-phase Ceramic Matrix
Composites." Computational Materials Science 50.4 (2011): 1336-1346.
Cracks at interface
Sadowski, T., and L. Marsavina. "Multiscale modelling of two-phase Ceramic Matrix
Composites." Computational Materials Science 50.4 (2011): 1336-1346.
Cracks at interface
Sadowski, T., and L. Marsavina. "Multiscale modelling of two-phase Ceramic Matrix
Composites." Computational Materials Science 50.4 (2011): 1336-1346.
Cracks at interface
Sadowski, T., and L. Marsavina. "Multiscale modelling of two-phase Ceramic Matrix
Composites." Computational Materials Science 50.4 (2011): 1336-1346.
Wettability
• Is defined the extent where a liquid will spread over a solid surface
• Good wettability means that the liquid (matrix) will flow over the
reinforcement, covering every ‘bump’ and ‘dip’ of the rough surface
of reinforcement and displacing all air.
• Wetting will only occur if the viscosity of the matrix is not too
high.
• Interfacial bonding exists due to the adhesion between the
reinforcement and the matrix (wetting is good)
Wettability
Raj, Rishi, Shalabh C. Maroo, and Evelyn N. Wang. "Wettability of graphene." Nano letters 13.4 (2013):
1509-1515.
Wettability
Poor wettability
Global market for CMCs, 2008-2015
https://www.bccresearch.com/pressroom/avm/global-market-ceramic-matrix-composites-worth-$1.3billion-2015
The next generation of CMCs
Wadley Research Group, Univ. of Virginia
Applications of CMCs
Automotive Ind.-Braking systems
Automotive Ind.-Brake
Brake Tech Ceramic Matrix Composite (CMC) Rotor on a
BST Carbon Fiber wheel, paired with Brembo Monobloc
Calipers, custom anodized spacers & bottoms and Ohlins
Superbike Forks.
The Porsche Carrera GT's carbonceramic (SiC) composite disc brake
http://www.oppracing.com/category/808-braketech-brake-rotors/
Automotive Ind.-Clutches
Aerospace Ind.-Nozzle
An F-16 Fighting Falcon F100 engine
exhaust nozzle with five A500
ceramic matrix composite divergent
seals, identified by the yellow arrows.
(Air Force photo)
Oxide
CMC
exhaust
ground
test
demonstrator consists of a 1.60-m diameter
nozzle and 1.14-m diameter × 2.34-m conical
center body with titanium end cap inspection
portal
CMCs are excellent candidates for replacing the nickel-based super alloys
currently used in exhaust nozzle parts, primarily due to their capacity to
withstand the high temperatures and severe operational environment for
much longer periods of time with minimal changes in structural behavior.
Aerospace Ind.-Nozzle
Aero engine Composites :The CMC invasion
SiC Nuclear application
1. Jet Engine
2.Turbine Blade
3. Hot Fluid
Channel
Advantages of CMC’s
1.
2.
3.
4.
5.
6.
7.
Excellent wear and corrosion resistance in a wide range of
environments and temperature
Higher strength to weight ratio
Higher strength retention at elevated temperature
Higher chemical stability
Non-catastrophic failure
High hardness
Lightweight
Disadvantages of CMC’s
1.
Processing routes for CMCs involve high temperatures – can only
be employed with high temperature reinforcements.
2.
CMCs are designed to improve toughness of monolithic ceramics,
the main disadvantage of which is brittleness.
3.
High processing temperature results in
manufacturing and hence expensive processing.
4.
Difference in the coefficients of thermal expansion between the
matrix and the reinforcement lead to thermal stresses on cooling
from the processing temperatures.
complexity
in

Assignment