Prof. C. H. XU

1
Subject Composite MaterialsScience and
Engineering Subject code 0210080060

• Prof. C. H. XU
• School of Materials Science and Engineering
• Henan University of Science and Technology
• Chapter 6
• Metallic Matrix Composites (MMCs)

2
Introduction

• In comparison with bulk (monolithic) metals, MMCs
  have
• higher specific strength/modulus,
• better properties at high temperature,
• lower coefficients of thermal expansion
• better wear resistance
• In comparison with PMCs, MMCs have
• higher transverse strength (????) and stiffness,
• better high temperature capability (??)

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Introduction

• Most of metallic matrix composites (MMCs) in the
  development stage
• Manufacture MMCs at high temperature

4
Introduction

• Processing
• Solid state
• Liquid state
• Deposition (vapor)
• Interface reaction
• Properties of MMCc
• Some commercial MMCc

5
Metal Matrix Composites- processing

• Solid state processing
• Diffusion bonding
• (a) sandwich a fibre mat.
• (b) to form ply (??)
• (c) stacking plies
• (d) hot press (diffusion bonding)
• (e) clean and trim
• Foil matrix titanium, copper, nickel,
  aluminium Fibre mat polymer bonding fibers.
  E.g. aluminum reinforced with boron fibres
• Expensive and parts with simple shape
• Low temperature ?less interface reaction (compare
  with liquid processing)

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Metal Matrix Composites- processing

• Solid state processing
• Powder metallurgy (????)
• Matrix metal particles reinforcement
  discontinous fiber, whisker maximum of
  reinforcement to 50
• Processing
• Mixture of matrix and reinforcement
• Heat and pressure under inert gas
• Large surface area and high energy solid-gas
  interface
• Low temperature ?less interface reaction (compare
  with liquid processing)
• E.g. SiC whisker reinforced aluminum

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Metal Matrix Composites- processing

• Liquid processing (Casting technique)
• Barrier 1 fibre non-wetting and interface
  reaction between matrix and reinforcement at
  melting temperature. Interface reaction products
  may reduce the properties of composites
• Precoating the reinforcement with an appropriate
  materials to protect against any reaction and to
  enhance wetting e.g. pyrolitic graphite coating
  on SiC fibers
• Modify matrix e.g. add lithium (Li) to Al liquid
  to form Li2O5Al2O3 at the interface between
  alumina fibre and aluminum (Al) to enhance
  wetting
• Liquid processing can't be used for Ti alloys
  because of Ti high reactivity.
• Barrier 2 non-uniform mixture of metal and
  reinforcement

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Metal Matrix Composites- processing

• Liquid processing (Casting technique)
• Melt stirring (??)
• particle or short fiber reinforcement liquid
  metal matrix
• Stirring the mixture
• Improve non-uniform mixture of metal and
  reinforcement
• Rheocasting (????,?-????) (in order to modify
  melt stirring)
• particle or short fiber reinforcement liquid
  metal matrix
• Cool the melt mixture to a more viscous two phase
  solid-liquid state
• Stirring the mixture
• Limit of reinforcement lt20
• Preform (???) reinforcement casting
• liquid metal (matrix) infiltrates (??)a preform
  (reinforcement) under a pressure (P)
• Limit of reinforcement lt30

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Metal Matrix Composites- processing

• Preform 1 squeeze (??)casting
• Processing (a) insert preform into die cavity
  (b) meter in a precise quantity of alloy (c)
  close die and apply pressure (d) remove ram (e)
  extract component
• High cost of die
• E.g. Aluminum piston crowns (???)locally
  reinforced with a discontinuous alumina fibres

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Metal Matrix Composites- processing

• Preform 2 liquid melt infiltration under a gas
  pressure
• Processing (a) insert preform and close die (b)
  evacuate(??)air (c) apply gas pressure during
  solidification
• Small parts
• Low cost
• Common fibers include SiC, B, C, alumina

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Metal Matrix Composites- processing

• Deposition Spray(??)co-deposition
• Processing
• Atomizing a melt (e.g. Al) exists as discrete
  (????) droplets for short time
• Introducing the reinforcement particle (e.g. SiC)
  into the spray of fine metal droplets
• Metal and reinforcement are co-deposited on to a
  substrate
• High density, less interface reaction

Diagram of spray co-deposition production SiC
particulate reinforced metal
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Metal Matrix Composites- Interface

• Form Interface layer between matrix and
  reinforcement during service or fabrication at
  high temperature
• Coupling agent for wettability and interface
  bonding
• Li or Mg for Al-Al2O3
• Graphite or TiB2 for SiC Ti alloys
• Interfacial layers affect the mechanical
  properties of the composite

Effect of interfacial layer thickness on the
mechanical properties of a Ti-6Al-4V alloy with
35 SiC fibers coated with C
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Metal Matrix Composites- Properties of MMCs

• Physical properties
• The coefficient of thermal expansion
• Parts with close tolerance

Conductivity
materials Conductivity (Wm-1K-1)
Al 201
Al-15SiC 140
Epoxy 0.3
Epoxy-60Glass fiber 1.6
materials coefficient of thermal expansion
Mg 0.000018/K
Al 0.000017/K
Mg-Al2O3 0.000015/K
Al-SiC 0.000010/K
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Metal Matrix Composites- Properties of MMCs

• Mechanical Properties
• Elastic modulus
• Reinforcements increase elastic modulus of
  composite with matrix, Al, Mg.
• Modulus at longitudinal direction is higher than
  that transverse direction for composite with
  continuous fibers

Difference in the longitudinal and transverse
modulus for Al-Li alloy matrix with Al2O3 fibers
Effect of reinforcement on the Youngs modulus of
Al
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Metal Matrix Composites- Properties of MMCs

• Strength

Effects of angle between tensile axis and fiber
axis on the strength of continuous fiber
reinforced Ti alloy
Effect of volume of reinforcement on the tensile
strength of Al matrix
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Metal Matrix Composites- Properties of MMCs

• Ductility and Toughness

• Reasons
• Fiber-matrix interface reaction
• In-homogeneity of reinforcement distribution
• Surface properties of reinforcement
• internal stresses

matrix reinforcement Toughness K1C
Al - 20-45 MPa m1/2
Al SiC 5-25 MPa m1/2
matrix reinforcement Ductility ()
Al - 40
Al Alumina 4.0
Al-10Mg Alumina 1.3
Al alloy SiC 7.0
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Metal Matrix Composites- Properties of MMCs

• Specific strength and specific modulus of MMCs
  is superior to that of alloys

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Metal Matrix Composites- Properties of MMCs

• Properties at elevated temperature (short time
  test)

Tensile strength Youngs modulus at
elevated temperature
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Metal Matrix Composites- Properties of MMCs

• Properties at elevated temperature (long times
  test) Creep
• Permanent strain under a stress with time
• Metal 3 stages creep curve
• Continuous fiber MMC reinforcement hinders creep
• Discontinuous reinforcement MMC 3-stage creep
  curve and creep resistance

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Metal Matrix Composites- Properties of MMCs

• Fatigue(??)resistance
• Fatigue the failure of a component under cyclic
  stress
• MMCs fatigue resistance may increase or decrease
• More crack initiation sites for MMC Large
  ceramic particles, Unbonded clusters of particles
• Reduce of propagation rate of crack

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Metal Matrix Composites- some commercial MMCs

• Al reinforced with SiC particles
• SiC particles are cheaper than SiC long fibers
• Control volSiC in this MMC can match different
  materials (see top-figure)
• Techniques for this MMC
• heat treatment
• superplastic forming
• diffusion welding

Coefficient of thermal expansion of Al-SiC versus
vol SiC, showing matching with a range of metals
Aircraft panel produced by superplastic forming
of an Al-SiC composite
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Metal Matrix Composites- some commercial MMCs

• Cermets metal matrix (cobalt Co or nickel Ni)
  ceramic particles (tungsten carbide WC or
  titanium carbide, TiC)
• Mechanical Properties hard and enhanced
  toughness
• Ceramic particles provide the cutting surface
• Metal matrix withstands the cutting stress.
• Application cutting tools for hardened steels,
  glass,

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Metal Matrix Composites- some commercial MMCs

• Multifilamentary(???)superconductors Nb3Sn
• Nb3Sn brittle, difficult to form Nb3Sn
• Bronze route (niobium) NbSn (Cu-Sn) ? Nb3Sn
  layer
• The superconducting properties are a function of
  Nb3Sn layer thickness and the grain size
• Use as windings(??) for superconducting magnets

Multifilamentary superconducting composite with
41070 filaments of approximately 5mm diameter (a)
cross-section and (b) matrix etched away to show
the filaments
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Metal Matrix Composites- some commercial MMCs

• Production of Multifilamentary superconductors
  composite by bronze route
• (a) holes drilled in bronze block and niobium
  rods inserted
• (b) swaging(??)to reduce the cross-section of
  niobium
• (c) sectioning, rebuilding, canning in Cu can,
  and final reduction
• (d) heat treatment to form 2mm Nb3Sn between Nb
  and bronze

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Metal Matrix Composites- MMCs for airspace
application
Matrix Fiber application
Cu base C SiC W Combustion chamber Nozzle (rocket, space shuttle) Heat exchanger
Fe base W tubing
Ni base Al2O3 blades
Ti base SiC TiB2 TiC Housings, tubing Blades, Shafts, honeycomb
Al base SiC Al2O3 C Housings, mechanical connects, satellite, structures, wings, blades Fuselage Structure members
Mg base Al2O3 Structure members
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• Further reading
• Text Book
• Composite Materials Engineering and Science
  (pages 78-117).
• Other reference Note 6