these.book

TEM study of interfacial reactions and precipitation
mechanisms in Al O short fiber or high volume fraction SiC 2 3
particle reinforced Al-4Cu-1Mg-0.5Ag squeeze-cast
composites
THÈSE N° 2246 (2000)
PRESENTÉE AU DEPARTEMENT DES MATÉRIAUX
ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE
POUR L’OBTENTION DU GRADE DE DOCTEUR ÈS SCIENCES TECHNIQUES
PA R
Cyril CAYRON
Ingénieur Civil diplômé de l’Ecole des Mines de Nancy
originaire de Dijon (France)
Lausanne, EPFL
2000
Contents
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List of Acronyms vii
Summary viii
Version abrégée x

Chapter 1 Introduction ..................................................................................... 1
1.1 General Context ..................................................................................................1
1.2 Outline.................................................................................................................2
Chapter 2 Aluminum Matrix Composites: Processing and Properties ........ 5
2.1 Introduction to AMCs .........................................................................................6
2.1.1 Composites......................................................................................................... 6
2.1.2 Aluminum Matrix Composites (AMCs) ............................................................ 6
2.1.3 Fabrication of the AMCs....................................................................................8
2.2 Mechanical Properties of the AMCs...................................................................8
2.2.1 Elasticity............. 8
2.2.2 Yielding / Flow................................................................................................. 10
2.2.3 Fracture............................................................................................................. 11
2.2.4 Conclusions: Influence of the Microstructural Variables ................................ 13
2.3 The AlCuMgAg Based Composites13
2.3.1 Materials........................................................................................................... 13
2.3.2 Direct Squeeze-Casting Process....................................................................... 15
2.3.3 Tensile Properties............................................................................................. 16
2.4 Discussion .........................................................................................................20
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Contents
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Chapter 3 Transmission Electron Microscopy............................................. 21
3.1 Historical Introduction .....................................................................................22
3.2 Preparation of the TEM Samples ......................................................................22
3.3 Chemical Analyses by EDS ..............................................................................23
3.4 Electron Scattering: From Diffusion to Diffraction..........................................25
3.4.1 Diffusion........................................................................................................... 25
3.4.2 Kinematical Diffraction....................................................................................28
3.4.3 Bragg Law....... 30
3.4.4 Ewald Construction.......................................................................................... 30
3.4.5 Dynamical Diffraction......................................................................................31
3.5 Conventional Transmission Electron Microscopy............................................31
3.5.1 Imaging Mode .................................................................................................. 31
3.5.2 Diffraction Mode.............................................................................................. 33
3.5.3 Special TEM Techniques ................................................................................. 34
3.6 High Resolution Transmission Microscopy......................................................35
3.6.1 Propagation through the sample....................................................................... 35
3.6.2 Transfer by the optical system ......................................................................... 36
3.7 Quantitative Electron Crystallography..............................................................39
3.7.1 Phase Loss Problem in Diffraction................................................................... 39
3.7.2 HREM “Direct” Methods 39
3.7.3 HREM Simulations .......................................................................................... 41
3.8 TEM Facilities...................................................................................................41
Chapter 4 Microstructure of WFA/Al O /sf and WFA/SiC/p Composites 432 3
4.1 Grains and Microsegregation ............................................................................44
4.1.1 Grain Sizes and Morphologies ......................................................................... 44
4.1.2 Primary Intermetallics Compounds.................................................................. 45
4.1.3 Chemical Composition of the Matrices............................................................ 48
4.2 Interfacial Reactions .........................................................................................48
4.2.1 WFA/Al2O3/sf/s Composites........................................................................... 48
4.2.2 WFA/SiC/p Composites ................................................................................... 50
4.2.3 Al(Mg)/SiC/p Composites................................................................................ 53
4.2.4 Diffusion of Si, Mg and Cu.............................................................................. 57
4.3 Precipitation States............................................................................................57
4.3.1 Hardness Curves .............................................................................................. 58
4.3.2 Modification of the Precipitation State ............................................................ 59
4.4 Identification of the Precipitates .......................................................................61
4.4.1 θ' Plate-Shaped Precipitates ............................................................................. 61
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4.4.2 Rod-Shaped Precipitates .................................................................................. 64
4.4.3 Evolution of the Precipitation by Overaging at 300°C/24h ............................. 68
4.5 Conclusions and Prospects................................................................................71
4.5.1 Grains and Microsegregation ........................................................................... 71
4.5.2 Chemistry and Precipitation Modification of the Base Alloy ......................... 71
4.5.3 Effect of Binder on the WFA/Al2O3/sf AMC Tensile Properties ................... 72
4.5.4 Prospects for the Improvements of Tensile Properties..................................... 74
Chapter 5 Introduction to Order-Disorder Transitions............................... 77
5.1 Classification of the Phase Transitions .............................................................78
5.1.1 Chemistry ......................................................................................................... 78
5.1.2 Thermodynamics.............................................................................................. 78
5.2 Landau’s Phenomenological Approach ............................................................79
5.2.1 Second Order Transitions................................................................................. 80
5.2.2 First Order Transitions ..................................................................................... 80
5.3 Statistical Mechanics Approach........................................................................82
5.3.1 Canonical Ensembles ....................................................................................... 82
5.3.2 The Ising Model ............................................................................................... 82
5.3.3 Monte Carlo Simulations 83