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Subject: Composite Materials Science 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). Introduction.

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Subject composite materials science and engineering subject code 0210080060

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)


Introduction

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)


Introduction1

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

Manufacture MMCs at high temperature

Introduction


Introduction2

Introduction

  • Processing

    • Solid state

    • Liquid state

    • Deposition (vapor)

  • Interface reaction

  • Properties of MMCc

  • Some commercial MMCc


Metal matrix composites processing

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)


Metal matrix composites processing1

Metal Matrix Composites- processing

Solid state processing

Powder 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


Metal matrix composites processing2

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 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


Metal matrix composites processing3

Metal Matrix Composites- processing

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) reinforcementcasting:

    • liquid metal (matrix) infiltrates (渗透)a preform (reinforcement) under a pressure (P)

    • Limit of reinforcement <30%


Metal matrix composites processing4

Metal Matrix Composites- processing

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


Metal matrix composites processing5

Metal Matrix Composites- processing

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


Metal matrix composites processing6

Metal Matrix Composites- processing

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


Metal matrix composites interface

Impact energy (Kj/m2)

Axial

1000

500

0

transverse

0 5

Thickness of brittle layer (mm)

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


Metal matrix composites properties of mmcs

Physical properties

The coefficient of thermal expansion

Parts with close tolerance

Metal Matrix Composites- Properties of MMCs

Conductivity


Metal matrix composites properties of mmcs1

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 Young’s modulus of Al


Metal matrix composites properties of mmcs2

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


Metal matrix composites properties of mmcs3

Ductility and Toughness

Reasons

Fiber-matrix interface reaction

In-homogeneity of reinforcement distribution

Surface properties of reinforcement

internal stresses

Metal Matrix Composites- Properties of MMCs


Metal matrix composites properties of mmcs4

Metal Matrix Composites- Properties of MMCs

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


Metal matrix composites properties of mmcs5

Metal Matrix Composites- Properties of MMCs

  • Properties at elevated temperature (short time test)

Tensile strength Young’s modulus

at elevated temperature


Metal matrix composites properties of mmcs6

strain

Metal

MMC (long fiber)

MMC (short fiber)

time

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


Metal matrix composites properties of mmcs7

Stress amplitude △s(MPa)

300

200

100

0

103 104 105 106 107

Cycles to failure

Metal Matrix Composites- Properties of MMCs

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


Metal matrix composites some commercial mmcs

Metal Matrix Composites- some commercial MMCs

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

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


Metal matrix composites some commercial mmcs1

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,


Metal matrix composites some commercial mmcs2

(b)

(a)

Metal Matrix Composites- some commercial MMCs

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


Metal matrix composites some commercial mmcs3

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(模锻)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


Metal matrix composites mmcs for airspace application

Metal Matrix Composites- MMCs for airspace application


Subject composite materials science and engineering subject code 0210080060

  • Further reading

    Text Book:

    Composite Materials: Engineering and Science (pages 78-117).

    Other reference: Note 6


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