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

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Prof. C. H. XU

School of Materials Science and EngineeringHenan University of Science and Technology

Chapter 6:Metallic Matrix Composites (MMCs)

Subject: Composite MaterialsScience and Engineering

Subject code: 0210080060

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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 ( 横向强度 ) and

stiffness, better high temperature capability ( 性能）

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Introduction

Most of metallic matrix composites (MMCs) in the development stage

Manufacture MMCs at high temperature

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Introduction

Processing Solid state Liquid state Deposition (vapor)

Interface reaction Properties of MMCc Some commercial MMCc

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Metal Matrix Composites- processing

Solid state processing Diffusion bonding

(a) sandwich a fibre mat. (b) to form ply （板层） (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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Solid state processingPowder metallurgy （粉末冶金） 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- processingLiquid 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 Li2O·5Al2O3 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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Liquid processing (Casting technique) Melt stirring （搅动） :

particle or short fiber reinforcement + liquid metal matrix Stirring the mixture Improve non-uniform mixture of metal and reinforcement

Rheocasting （流变铸造，固 - 液态搅动 ) (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 <20%

Preform ( 预成形 ) reinforcement casting: liquid metal (matrix) infiltrates （渗透） a preform (reinforcement)

under a pressure （ P ） Limit of reinforcement <30%

)(

)(

metalmoltenatcurvatureofradii

energysurfaceatmospheremeltP

j

MG

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Preform 1: squeeze （模压） 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 ( 活塞顶） locally reinforced

with a discontinuous alumina fibres

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Preform 2: liquid melt infiltration under a gas pressure; Processing (a) insert preform and close die; (b) evacuate （排

出） air; (c) apply gas pressure during solidification Small parts Low cost Common fibers include SiC, B, C, alumina

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Deposition: Spray （喷溅） co-deposition

Processing Atomizing a melt (e.g.

Al) exists as discrete ( 不连续的 ) 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-6%Al-4%V alloy with 35% SiC fibers coated with C

Axial

transverse

Thickness of brittle layer (m)

Impa

ct e

nerg

y (K

j/m2)

0 5

1000

500

0

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Metal Matrix Composites- Properties of MMCs

materials coefficient of thermal expansion

Mg 0.000018/K

Al 0.000017/K

Mg-Al2O3 0.000015/K

Al-SiC 0.000010/K

Physical propertiesThe coefficient of thermal

expansion Parts with close

tolerance

materials Conductivity

(Wm-1K-1)

Al 201

Al-15%SiC 140

Epoxy 0.3

Epoxy-60%Glass fiber

1.6

Conductivity

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Mechanical PropertiesElastic 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

Effect of reinforcement on the Young’s modulus of Al

Difference in the longitudinal and transverse modulus for Al-Li alloy matrix with Al2O3 fibers

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Metal Matrix Composites- Properties of MMCs Strength

0

400

800

1200

1600

10 20 30 40 50 60 70

Vol ume of rei nf orcement (%)

Stre

ngth

(MP

a)

Al -B(conti nour Fi ber)

Al -Al 2O3(conti nour Fi ber)

Al -Si C(parti cl e)

Effect of volume of reinforcement on the tensile strength of Al matrix

Effects of angle between tensile axis and fiber axis on the strength of continuous fiber reinforced Ti alloy

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Metal Matrix Composites- Properties of MMCsDuctility 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-10%Mg Alumina 1.3

Al alloy SiC 7.0

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

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Properties at elevated temperature (short time test)


Tensile strength Young’s modulus

at elevated temperature

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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


Metal

MMC (long fiber)

MMC (short fiber)

time

stra

in

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Fatigue （疲劳） 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


103 104 105 106 107

Cycles to failure

Str

ess

ampl

itude

△(M

Pa)

300

200

100

0

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Al reinforced with SiC particles

SiC particles are cheaper than SiC long fibers

Control vol%SiC in this MMC can match different materials (see top-figure)

Techniques for this MMC: heat treatment superplastic forming diffusion welding

Metal Matrix Composites- some commercial MMCs

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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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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Multifilamentary （多纤维） superconductors Nb3Sn Nb3Sn brittle, difficult to form Nb3Sn Bronze route: （ niobium) Nb+Sn (Cu-Sn) → Nb3Sn layer The superconducting properties are a function of Nb3Sn layer

thickness and the grain size Use as windings （线圈） 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

(a) (b)

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Production of Multifilamentary superconductors composite by bronze route

(a) holes drilled in bronze block and niobium rods inserted

(b) swaging （模锻） to reduce the cross-section of niobium

(c) sectioning, rebuilding, canning in Cu can, and final reduction

(d) heat treatment to form 2m Nb3Sn between Nb and bronze


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Metal Matrix Composites- MMCs for airspace application

Matrix Fiber application

Cu base CSiCW

Combustion chamberNozzle (rocket, space shuttle)Heat exchanger

Fe base W tubing

Ni base Al2O3 blades

Ti base SiCTiB2

TiC

Housings, tubingBlades, Shafts, honeycomb

Al base SiC

Al2O3

C

Housings, mechanical connects, satellite, structures, wings, bladesFuselageStructure 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

Documents

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