meca0462-2 metals i · [m.f. ashby and d.r.h. jones, engineering materials, vol. 2] grains size and...
TRANSCRIPT
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Metals I
Anne Mertens
"MECA0139-1: Techniques additives et 3D printing", ULg, 25/10/2016"MECA0462-2 : Materials Selection", 19/09/2017
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Outline• Introduction
– Metallic materials
– Materials Selection: case studies in metallic materials
• Metal structures
• Equilibrium constitution and phase diagrams
• Case studies in phase diagrams
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Introduction
Metallic materials
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Introduction - Metals (1)
Large variety of metallic materials!
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Introduction : Metals (2)
• Cohesion due to metallic bond
– Electrostatic attractive force between an electron cloud of delocalized electrons and positively charged metal ions
– Non directional
• Metallic materials:
– Generally good conductor of electricity and heat
– Relatively ductile ⇒ good formability
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Introduction
Materials Selection :
Case studies in metallic materials
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Materials selection for model steam engine (1)
Fully working model
– ≠ components
– ≠ requirements
– ≠ materials
[http://www.hobbydownloads.com/steamgeneral.html]
Ex: Boiler components must
withstand high T
[http://www.hobbydownloads.com/boilers.html]
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Materials selection for model steam engine (2)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Use of ferrous alloys
Wheels,
frame• low loads
(σy~220 MPa)
• easy to cut,
bend...
• cheap
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Materials selection for model steam engine (3)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Use of ferrous alloys
Drive shafts,
gear-wheel
teeths• higher
stresses
(σy~400 MPa)
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Materials selection for model steam engine (3)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Use of ferrous alloys
Mechanical
lubricator• High friction
and wear
• Quenched and
tempered high
carbon steels
(σy~1000MPa)
[http://ww3.tiki.ne.jp/~hwata/eW-lubricator.htm]
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Materials selection for model steam engine (4)
[M.F. Ashby and D.R.H. Jones,
Engineering Materials, vol. 2]
Use of ferrous alloys
Fire grates, in direct
contact with burning
coal• High T
• Oxidation
• Creep
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Materials selection for model steam engine (5)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Use of ferrous alloys
Fire grates• High T
• Oxidation
• Creep
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Materials selection for model steam engine (6)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Use of ferrous alloys
Cylinder
block• Low
stresses
• Easy to
cast
• Graphite
acts as
lubricant
[http://opensourcee
cology.org/wiki/File:
Design-7-A.png][http://core.materials.ac.uk/S
EARCH/detail.php?id=1415]
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Materials selection for model steam engine (7)
Use of other alloys
• Boiler and firetubes
– Load from pressurized
steam
– Corrosion
• Full size: mild steel
[http://www.hobbydownloads.com/boilers.html]
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Materials selection for model steam engine (8)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Copper alloys
• Boiler and firetubes
– High thermal conductivity
– Corrosion resistance in clean water
– High cost (prohibitive in full size)
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Materials selection for beverage can (1)
• Strong requirements
– No seam, no leak
– Use as little metal as possible
– Light
– High formability
– Recyclable
– Not toxic
– Corrosion resistance (even in coke that is highly acid)
– Cheap
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Materials selection for beverage can (2)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
• Aluminium alloys
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Materials selection for artificial hip joints (1)
• Requirements:
– Large loads
– High resistance to bending
– Resistance to high-cycle
fatigue
– Resistance to corrosion in
body fluids
– Bio-compatibility
– Light (density prosthesis =
density bone)
[https://www.news-
medical.net/Accolade-C-Femoral-
Component-from-Stryker]
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Materials selection for artificial hip joints (2)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
• Titanium alloys
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Partial summary (1)
• Materials selection ⇒ ≠ criteria
– Physical properties (density, conductivity...)
– Mechanical properties (yield stress, fatigue...)
– Corrosion resistance
– Bio-compatibility
– Processability, formability
– Cost
– ...
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Data for metals
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Data for metals
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Data for metals
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Data for metals
• Properties of metallic materials may be
– structure independent...
(= f(composition))
e.g.: Young's modulus...
– ... vs structure dependent
(=f(composition, (micro)structure → processing))
e.g.: yield strength, tensile strength...
• One must be really careful when dealing with
structure-dependent properties!
– influenced by cold deformation, heat treatments...
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Metal structures
How do we describe the structure of
a metal?
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Crystal vs glass
• Packing of atoms inside the materials
Long-range order Short-range order
[http://www.majordifferences.com/2013/02/difference-
between-crystalline-and.html#.Wb42e9E69PY]
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Common
crystalline
structures of
pure metals
[M.F. Ashby and D.R.H. Jones,
Engineering Materials, vol. 2]
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Polymorphism
• Some metals may change crystalline structure
depending on external conditions (p, T)
e.g.: Fe and Ti
• Polymorphism may be controlled by alloying
e.g.: addition of Ni in steel ⇒ FCC at Room T[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Solutions vs compounds (1)
• Metals are rarely used in pure state
– Addition elements ⇒ Alloys
– Alloying elements may be dissolved in the
crystalline lattice of the main element
– Up to the solubility limit
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Interstitial solution
e.g.: C in Fe
Substitutional solution
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Solutions vs compounds (2)
• Solutions may be random, but clustering or
ordering are also possible
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Random Clustered Ordered
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Solutions vs compounds (3)
• [alloying element] > solubility limit
Excess precipitates forming a new intermetallic
compound (with its own crystalline structure)
• Cu addition in Aluminium:
Formation of CuAl2
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
FCC structure of Al
[http://deuns.chez.com/sciences
/cristallo/cristallo2.html]
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Solutions vs compounds (4)
• [alloying element] > solubility limit
Excess precipitates forming a new intermetallic
compound
• Solubility limit of C in BCC Fe at R.T.: 10-5 mass %
• Excess C forms cementite (Fe3C)
[A. Mertens, ULg]
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Phases (1)
Phase = region of a material that has uniform
physical and chemical properties
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Phases (2)
• Liquid water = one phase
Ice = one phase
Liquid water + ice = two phases
• Cu fully dissolved in Al
= one solid solution
= one phase
• [Cu] > solubility limit in Al
= Al (solid solution) + CuAl2 (precipitates)
= two phases
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Grain and phase boundaries (1)
• A pure metal or a solid solution are single-phase
systems...
• ... but they are usually made of many crystals
(with the same crystalline structure and chemical
composition)
• Individual small crystal = grain
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Grains size and shape may
affect material properties!
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Grain and phase boundaries (2)
• Two-phases metallic materials are also made
from many grains of each of the phases
• Interphase boundaries: ≠ types
Nature of interphase
boundaries may affect
material properties!
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Grain and phase boundaries (3)
• Precipitates may take ≠ shape/morphology
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Partial summary (2)
• Some properties (e.g.: yield strength) are
influenced by the structure of the material.
– Crystalline (or amorphous) structure
– Phases (solid solution, intermetallic compounds...)
– Size and shape of grains
– Interphase boundaries
• Structure is determined by
– Chemical composition
– Processing method (deformation, heat treatments...)
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Outline• Introduction
• Metal structures
How can we understand/control the structure of a
metallic material?
– Influence of chemical composition?
• Equilibrium constitution and phase diagrams
• Case studies in phase diagrams
– Influence of processing method?
Today
Next week
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Outline• Introduction
• Metal structures
– Crystal vs glass
– Solutions and compounds
– Phases
– Grain and phase boundaries
• Equilibrium constitution and phase diagrams
• Case studies in phase diagrams
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Equilibrium constitution
and phase diagrams
How do we describe the influence of
the chemical composition and
external conditions (T,p) on the
structure of a metallic materials?
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Equilibrium (1)
Intuitively:
A system is in equilibrium when it exhibits no
further tendency to change with time
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Equilibrium (2)
Intuitively:
A system is in equilibrium when it exhibits no
further tendency to change with time
Thermodynamics:
A system is in equilibrium when its energy is
minimized
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Equilibrium (2)
Intuitively:
A system is in equilibrium when it exhibits no
further tendency to change with time
Thermodynamics:
A system is in equilibrium when its energy is
minimized
Equilibrium = G minimum with G: enthalpy
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Phase diagrams
• xB : fraction of element B1-xB : fraction of element A
• Atmospheric pressure
• Equilibrium = G minimum
• Equilibrium state of a binary system (A,B) at T3
– 2 phases are present (liquid, solid)
– Compositions of each phase
– Fractions of each phase
[L. Zhigilei, Phase diagrams and
Kinetics, University of Virginia]
100% B100% Ax1 x2
x1 x2
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Reading phase diagrams:
The Lever Rule• Binary system with 2 phases
(α, β)
• Relative fractions of each
phase
Wα = (Cβ-C0)/(Cβ-Cα)
Wβ = (C0-Cα)/(Cβ-Cα)
[L. Zhigilei, Phase diagrams and
Kinetics, University of Virginia]
CαCβC0
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Example: Al-Cu alloys (1)
Tmelting is minimum
⇒ Eutectic
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Example: Al-Cu alloys (2)
Intermetallic
precipitates
One single crystalline
structure (α Al): FCC
Eutectic
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Example: Al-Cu alloys (3)
Intermetallic
precipitates
One single crystalline
structure (α Al): FCC
Miscibility gap -
Solubility of Cu in Al
decreases with T
Eutectic
xCu
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Example: Pb-Sn alloys (1)
Eutectic
One phase: Liquid solution of Pb and Sn
Solid
solution of
Sn in PbTwo phases (i.e. solid solutions) co-exist
Common alloys for solder
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Example: Pb-Sn alloys (2)
• Consider an alloy with 50% Pb and 50% Sn
• Number of phases at R.T.: 2 (Sn) and (Pb)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Example: Pb-Sn alloys (3)
• Consider an alloy with 50% Pb and 50% Sn
• Composition of (Pb) at R.T.: 2 wt% Sn.
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Example: Pb-Sn alloys (4)
• Consider an alloy with 50% Pb and 50% Sn
• Fraction of (Pb) at R.T.: (50-0,3)/(98-0,3)=50,9 %
(50-0,3)
(98-0,3)[M.F. Ashby and D.R.H.
Jones, Engineering
Materials, vol. 2]
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Example: Pb-Sn alloys (5)
• Consider an alloy with 50% Pb and 50% Sn
• Shape and size of (Sn) and (Pb)?
– Not from phase diagrams
– Depend on processing method
⇒ Deformation, heat treatments (isothermal hold,
cooling rate...)
• How can we use phase diagrams for materials
selection?
⇒ Case studies in phase diagrams
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Outline• Introduction
• Metal structures
• Equilibrium constitution and phase diagrams
• Case studies in phase diagrams
– Materials for soft solders
– Pure silicon for microchips : zone refining
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Case studies in
phase diagrams
Selecting a material for soft solders
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Solder materials (1)
• Based on the Sn-Pb system
• For electronics: low melting T + easy flow
Eutectic
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Solder materials (2)
• Based on the Sn-Pb system
• For plumbing:
Pipes used to be made of Pb
Solders were built up in thick deposits around
joints
⇒ "Pasty" solder
Roman baths, Bath (GB) [A. Mertens]
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Solder materials (3)
• Based on the Sn-Pb system
• For plumbing:
"pasty" solder = solid + liquid mixture
Sn with 65 wt% Pb
Melting range: 183 - 244°C
At 210°C: L + (Pb) slurry
No risk of melting the Pb
pipes
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
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Solder materials (4)
[M.F. Ashby and D.R.H. Jones,
Engineering Materials, vol. 2]
• Boiler in model steam engines
High service T
⇒ Ag-based soft solder (Tmelting ~600°C)
⇒ High Pb-content soft solder
~ Tmelting pure Pb
i.e. 327°C
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Solder materials (5)
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Pb
Ag
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Case studies in
phase diagrams
Zone refining for the production of
pure silicon for microchips
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Zone refining (1)
• Starting from Si with a small content of impurity C0
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Impurity is "pushed" into the liquid
Local equilibrium at the liquid/solid interface
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Zone refining (2)
• Starting from Si with a small content of impurity C0
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Concentration of impurity in liquid ↑⇒ Concentration of impurity in the next solid layer ↑
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Zone refining (3)
• Starting from Si with a small content of impurity C0
[M.F. Ashby and D.R.H. Jones, Engineering Materials, vol. 2]
Impurity is removed from the left-hand side of the bar and
dumped at the righ-hand end.
Process may be repeated to increase the refined volume.
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Summary
• Materials selection ⇒ ≠ criteria
– Properties (physical, mechanical...)
– Cost
• Some properties are structure-sensitive
– Chemical composition
– Processing method (deformation, heat treatments...)
⇒ Understand/describe the structure of a material
– Equilibrium (phase diagram) - today
– Out-of-equilibrium - next week