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Subject: Composite Materials Science and Engineering
Subject code: 0210080060
Prof C. H. XU
School of Materials Science and EngineeringHenan University of Science and Technology
Chapter 2: Matrix: metals and alloys
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Matrix
This chapter covers: Metal and Alloys
Ferrous and nonferrous Mechanical Properties
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Ferrous Alloys: Iron (Fe) is the prime element. Widely use in industry
Abundant quantity of iron-containing compounds on earth.
Metallic iron and steel alloys can be produced economically.
Ferrous alloys have wide range of mechanical and physical properties.
Disadvantages: corrosion properties are not good relatively high density a relatively low electrical conductivity
Classification: Steel and Cast irons
Matrix: Metal and AlloysFerrous
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Matrix: Metal and AlloysFerrous - Steels
Steels are iron-carbon alloys (C< 2.1%) that may contain other alloying elements;
Plain carbon steels contain carbon and residual concentrations of impurities, such as silicon (Si), manganese (Mn), sulfur (S), phosphorous (P).
Alloy steels have more alloying elements intentionally added.
α-Fe (BCC) Fe3C (iron carbide)-Fe (FCC)Martensite (α-Fe with high concentration C)
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Matrix: Metal and Alloys Ferrous - Cast Iron
Cast iron: ferrous alloys with carbon 2.14 – 4.5wt %
Low melting point 1150 -13000C, forming by casting.
Mechanical properties: brittle Four types of cast irons, according to their
microstructures Grey Cast Iron White Cast Iron Malleable Cast Iron Nodular Cast Iron
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Matrix: Metal and AlloysFerrous - Steels
Corrosion or Oxidation Resistance Au, Pt … not oxidize Al, Cr, Si: formation of dense oxide scale
Al2O3, Cr2O3, or SiO2 (good oxidation resistance)
Fe: formation of loose oxide scale (corrosion properties are not good).
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Stainless Steels (high alloy steels) they are highly resistant to corrosion,
especially at ambient temperature. Main alloy element is chromium (>11wt%Cr). Nickel (Ni) and molybdenum (Mo) improves
oxide scale connection. applications include gas turbines, high-
temperature steam boilers, heat-treating furnaces, aircraft, and nuclear reactors.
Matrix: Metal and Alloys ferrous - Stainless Steels
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Nonferrous alloys Copper and its alloys Aluminum and its alloys Magnesium and its alloys Titanium and its alloy Other alloys
Matrix: Metal and Alloys nonferrous
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Matrix: Metal and Alloys nonferrous
Aluminum Alloys Second most plentiful metal on earth high electrical and thermal conductivity, and resista
nce to corrosion. Aluminum and its alloys have low density (~2.7),
one-third the density of steel (high specific strength)[Specific strength = strength/density]
Main limitation is the low melting temperature (660o
C). Mechanical properties can be improved be cold-
worked or alloying. Aluminum alloys can be up to 30 times stronger than pure Aluminum
Applications; food/chemical handling, aircraft structures, bus wheels, fuel tanks
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Copper and Its Alloys Copper is soft and ductile, and is easy to machin
e. It is highly resistant to corrosion in various
environments. Greater density than steel Specific strengths less than aluminum Excellent ductility, corrosion resistance, electrical
and thermal conductivity The mechanical and corrosion-resistant propertie
s can be improved by alloying.
Matrix: Metal and Alloys nonferrous
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Brass: Copper-Zinc alloys < 40wt% Zn. The most common copper alloys are the brasses, which have substitutional zinc as the predominant alloying element. applications of brass alloys include costume
jewelry, cartridge, automotive radiators, musical instruments, electronic packing, and coins.
Bronzes are alloys of copper and several elements: tin (Sn), aluminum, silicon, and nickel.
Beryllium (Be) coppers are stronger, have good electrical and corrosion property.
Matrix: Metal and Alloys nonferrous
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Magnesium (Mg) Alloys Magnesium and its alloys have low density (1.74g/cm3,
lighter than Al) and are relatively soft. Specific strength comparable to Al Magnesium has an HCP structure, it and its alloys are
difficult to deform at room temperature. Magnesium has low melting temperature (651oC). Magnesium is susceptible to corrosion in marine
environments. Fine magnesium power ignites easily. Application: automotive wheels,
Matrix: Metal and Alloys nonferrous
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Titanium Pure metals have relatively low density (~4.5), a high
melting point (16680C). High strength-to-weight ratio Good mechanical properties to ~550°C Major limitation is the chemical reactivity with other ma
terials at high temperatures. But the corrosion resistance at normal temperatures is unusually high
Alloys are extremely strong, and highly ductile and easily forged.
Applications include airplane structures, space vehicles, and in the petroleum and chemical industries.
Matrix: Metal and Alloys nonferrous
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Beryllium (Be) Alloys Light metal (1.848 g/cm3), lighter than Al High modulus of elasticity (42 x 106psi), (stiffer
than steel) High specific strengths Very expensive Toxic to some individuals, BeO is a carcinogenic
material for some people. Oxidation at elevated temps.
Matrix: Metal and Alloys nonferrous
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Matrix: Metal and Alloys nonferrous
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Mechanical Properties of Metal & alloyTensile test
A standard tensile specimen
(ASTM E8 standard, USA)
Tension Test
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Mechanical Properties of Metal & alloy Tensile test Load or force F; (unit: newton N) Elongation l; l = li – l0 Where li is
instantaneous length, l0 is original length before load (unit: m)
Engineering stress σ;
where A0 is the original cross-section area before load (unit: MPa, 1MPa = 106 N/m2)
Engineering strain: ε(unitless)
0A
F
00
0
l
l
l
lli
Tensile load and
elongation
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Mechanical Properties of Metal & alloy Tensile Testing
Force – elongation curve
Engineering Stress - Strain curve (1) elastic deformation (2) yielding strength (3) plastic deformation (4) Tensile strength (5) necking (6) failure strain
stre
ss
2
1
4
3 5
6
Engineering stress-stain behavior
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Mechanical Properties of Metal & alloyTensile test -Elastic Behavior
Elastic deformation is recoverable.
In most materials, elastic deformation is linear.
σ=Eε (Hooke’s Law)
Where E is modulus of elasticity or Young modulus (unit: GPa; 1GPa = 109 N/m2)
In some materials, elastic deformation is non-linear
Slope = modulus of elasticity
Load
Unload
Strain ε
Stress σ
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Mechanical Properties of Metal & alloyTensile test - Poisson’s ratio
Axial Z: positive strain (elongation)
Axial X or Y: negative strains (contractions)
Poisson’s ratio :
Most metals exhibit values between 0.25 and 0.35
z
zz l
l
0
x
xx l
l
0
z
x
z
y
Strains at different direction
during a load at Z direction
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Mechanical Properties of Metal & alloy Tensile test – Yield stress
Plastic deformation: Irreversible Yielding: plastic deformation begins Yielding strength: σy = 0.002 strain offset or = Low
yield point.
σy
Stress-strain behavior for a metal: showing elastic plastic deformation and σy = σ0.002
Stress-strain behavior for some metals: showing yield point phenomenon
σy = σlow yield point
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Mechanical Properties of Metal & alloy Tensile test – tensile strength
Tensile strength σTS
maximum stress on engineering stress-strain curve
Strain < point ofσTS uniform plastic deformation
Strain > point ofσTS: necking deformation
Fracture strain
stre
ss
2
1
4
3 5
6
Engineering stress-stain behavior
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Mechanical Properties of Metal & alloy Tensile test - Ductility
Ductility is a measure of the degree of plastic deformation at fracture expressed as percent elongation
also expressed as percent area reduction
lf and Af are length and area at fracture
100*)(%0
0
l
ll f EL
100*)(%0
0
A
AA fAR
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Mechanical Properties of Metal & alloy Tensile test
Information: Elastic deformation Elastic modulus Plastic deformation Yield strength Elastic recovery during
plastic deformation Tensile strength Non-uniform plastic
deformation Fracture Ductility: Strain after
fracture
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Mechanical Properties of Metal & alloy Tensile Testing - Toughness
Toughness: the combination of strength and ductility.
Toughness measurement: total area under a stress-strain curve.
Physical means: the ability to absorb energy before fracture.
Stress-strain curves
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Mechanical Properties of Metal & alloy Tensile test
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Mechanical Properties of Metal & alloy Hardness
Hardness: material’s resistance to localized plastic deformation
Simple and inexpensive Nondestructive Both tensile strength and
hardness are indicators of a metal’s resistance to plastic deformation TS (MPa) = 3.45HB
TS (psi) = 500HB
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Further Reading
Reference Book:Introduction to Materials (材料概论 ) pages 35-
74
Other reference: lecture note 2
