Slayt 1

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TYPES OF MATERIALS
MATERIALS
Polymers
Ceramics
Metals
Composites
(Combination of two or more different materials)
(Pure Metals, Metal Alloys)
(Plastics, Rubber)
( Clay minerals, Cement, Glass)
Why study Materials? Many applied scientist or
engineer, whether mechanical, civil, chemical,
electrical or mining, will at one time or another
be exposed to a design problem involving
materials. e.g transmission gear,
superstructure of a building, oil refinery
component, integrated circuit chip, cone or roll
crusher
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TYPES OF MATERIALS

• Metals
• Extremely good conductors of electricity and
  heat,(the valence electrons are shared among all
  atoms and are free to travel everywheremetallic
  bonding)
• No transparency of visible light
• Quite strong, yet deformable (high strength, high
  stiffness, good ductility)
• High fracture toughness, they withstand impact
• Extensive use in structural applications
• Some metals such as iron, cobalt and nickel are
  magnetic
• Some metals and intermetallic compounds become
  superconductors at low temperatures

Pure Metals Fe, Cu, Al Metal Alloys Contain
more than one metallic element, eg Stainless
Steel (Fe, Cr, Ni) Gold Jewelry (Au, Ni, Cu)
Metals having high densities used in applications
that require a high mass-to volume ratio. Metals
having low density such as Aluminum are used in
aerospace applications for fuel economy.
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TYPES OF MATERIALS

• Polymers
• Include the familiar plastic and rubber materials
• Organic compounds that are chemically based on
  carbon, hydrogen and many other non-metallic
  elements
• Large repeating molecular structures (large
  chainlike structure) usually based on carbon
  backbone
• Low densities and lightweight
• May be extremely flexible
• Corrosion resistant
• Easy to process at low temperatures
• Low strength and high toughness
• Have softening and melting points
• Poor conductors of electricity and heat which
  makes them good insulators
• Inexpensive

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TYPES OF MATERIALS

• Ceramics
• Compounds between metallic and non-metallic
  (Inorganic non-metallic material)
• Oxides, Nitrides and Carbides
• Insulators (insulative to the passage of
  electricity and heat)
• High strength but brittle
• High melting temperature
• High stiffnes, hardness, wear and corrosion
  resistance
• Some ceramics are magnetic materials,
  piezoelectric materials
• ??? Have you ever known that some very special
  ceramics are superconductors at very low
  temperatures?

Glasses are also inorganic non-metallic materials
and doesnot have a crystalline structure, Such
materials are said to be amorphous. e.g
soda-lime silicate glass in soda bottles,
extremely high purity silica glass in optical
fibers.
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TYPES OF MATERIALS

• Composites
• Consist more than one material type
• Are designed to display a combination of the best
  characteristics of each of the component
  materials
• e.g Fiberglass acquires strength from the glass
  and flexibility from the polymer
• Polymer/Ceramic, Metal/Ceramic Composites
• One of the materials is the matrix and the other
  one is the embedded material.
• Have superior property with respect to the
  individual material
• Not easy to produce, some special techniques are
  needed

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TYPES OF MATERIALS

• Widely Used Engineering Materials
• Metals and Metal Alloys
• Iron
• Iron is plentiful, exists in the earth crust (5
  of the earths crust is iron and in some areas it
  concentrates in ores that contain as much as 70
  iron)
• Relatively easy to refine using simple tools
• By heating, relatively easy to bend and shape
  using simple tools
• Can handle heat such that you can build engines
• Relatively speaking, iron is extremely strong
• The problems of iron are the corrosion and
  oxidation (or generally speaking, rust
  formation), however, controlling the corrosion
  with galvanizing, chrome plating or paint is
  applicable
• Common iron ores are Hematite, Magnetite,
  Limonite, Siderite

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TYPES OF MATERIALS
Ferrous Alloys

• Iron is the prime constituent
• Important for engineering construction materials
  since iron is the most abundant element in the
  earths crust
• Metallic iron and steel alloys may be produced
  using relatively economical extraction, refining,
  alloying and fabrication techniques
• Have wide range of mechanical and physical
  properties
• Are susceptible to corrosion (disadvantage)

Cast Irons
Steels
High- Carbon
Low-Carbon
Medium- Carbon
White Iron
Malleable Iron
Gray Iron
Ductile (Nodular) Iron
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TYPES OF MATERIALS
Cast Iron is made by melting the pig iron and
casting it into molds. Cast iron is too hard and
brittle,but it is cheap and its fluidity when
molten enables it to be cast easily, they can be
used when great strength and ductility are not
essential. Some special cast iron contain
molybdenum and nickel which gives it more tensile
strength. Most cast iron contains 2.5-4 of
carbon and following elements as impurities Si,
S, Mn and P.
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TYPES OF MATERIALS
Gray Cast Iron Carbon contens vary between
2.5-4.0wt and Silicon contents vary between
1.0-3.0wt. Sulphur, Manganese and Phosphorus
contents are low. Cementite which is Fe3C
decomposes into Fe and C. In gray cast iron the
graphite exists in the form of flakes. Gray cast
iron is brittle due to high carbon content and
shape of the graphite and weak in tension.

• The gray or dark color is because of graphite.
  The resultant alloy microstructure is ferrite or
  pearlite matrix and graphite flakes.
• Gray cast iron has some advantages
• Can be easily cast into complex shapes
• Can withstand to higher temperatures with respect
  to steel
• Machinable because of the lubricating effect of
  graphite
• Graphite network provides considerable degree of
  corrosion resistance
• Damps vibrations
• Compressive strength is high
• Cheap

Application Base structure of machines or heavy
equipments due to its damping property.
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TYPES OF MATERIALS
Ductile (Nodular) Cast Iron Special type of gray
cast iron. Adding a small amount of Magnesium
and/or Cerium before casting gray iron produces a
different microstructure. Graphite still forms
but in the form of nodules or sphere-like
particles. The matrix phase is either ferrite or
pearlite. The result is increased ductility and
tensile strength. It is also as machinable as the
gray cast iron.
Typical applications are materials include
valves, pump bodies, crankshafts, gears, other
automotive components.
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TYPES OF MATERIALS
White Cast Iron For low silicon cast irons and
rapid cooling rates, most of the carbons exists
as cementite instead of graphite. Because of the
absence of graphite, the structure is white and
known as white cast iron. White cast iron is
extremely hard, brittle and unmachinable. Limited
application is rollers in rolling machine because
it is wear resistant.
Malleable Cast Iron Heating white cast iron at
temperatures between 800 and 900C for a
prolonged time period and in a neutral atmosphere
causes the decomposition of the cementite,
forming graphite, which exist in the form of
clusters or rosettes surrounded by ferrite or
pearlite matrix depending on the cooling rate is
called malleable cast iron.
The microstructure is similar to nodular cast
iron with an appreciable ductility and strength.
Representative applications are Connecting
rods, transmission gears, flanges, pipe fittins
and valve parts for railroad, marine and other
heavy duty services.
25µm
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TYPES OF MATERIALS
Low Carbon Steels Carbon contentlt0.25wt
Two types of low carbon steels Plain Carbon
Steels Steels produced in the greatest
quantities fall within the low carbon
classification. Carbon content is less than
0.25wt. They also contain some other alloying
elements such as Mn, Cu and Si. These are
relatively soft and weak alloys but outstanding
ductility and toughness. Strengthening could be
accomplished by cold working. They are weldable
and machinable and of all steels are least
expensive to produce. Typical applications are
automobile body components, structural beams,
sheets that are used in pipelines, buildings and
bridges. High Strength Low Alloy Steels They
contain other alloying elements such as Copper,
Vanadium, Molybdenum and Nickel in combined
concentration as high as 10. They have higher
strength than low carbon steel and in addition
they posses ductility, formability and
machinability. They are more resistant to
corrosion. They have replaced in many
applications where structural strength is
critical such as bridges, towers and support
columns.
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TYPES OF MATERIALS
Medium Carbon Steels 0.25wtltCarbon
contentlt0.60wt
These alloys can be heat treatable via
austenitizing, quenching and then tempering to
improve the mechanical properties. They are most
often used as tempered conditions, having
microstructure of tempered martensites. Additions
of Chromium, Nickel and Molybdenum improve the
capacity of these alloys to be heat treated. By
heat treatment strength and ductility of the
alloy can be altered. The heat treated alloys can
be stronger than the low carbon alloy with the
sacrifice of ductility and toughness. The
applications of these alloys are railway wheels,
tracks, gears and crankshafts.
High Carbon Steels 0.60wtltCarbon contentlt1.4wt
They are the strongest and hardest yet least
ductile of the carbon steels. They are mostly
used as hardened and tempered conditions. They
usually contain Chromium, Vanadium, Tungsten and
Molybdenum. These alloying elements combine with
Carbon to form very hard and wear resistant
carbide components (Cr23C6, V4C3 and WC). The
tool and die steels are high carbon steels. The
applications are cutting tools and dies for
forming and shaping materials as well as knives,
razors, blades, springs and high strength wire.
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TYPES OF MATERIALS
Stainless Steels Crgt11wt
They are resistant to corrosion (rust) in variety
of environments. The predominant alloying element
is Chromium and others are Nickel and Molybdenum.
They maintain their corrosion resistance and
mechanical properties and at elevated
temperatures. The applications of these alloys
are gas turbines, high temperature steam boilers,
heat treating furnaces, aircrafts, missiles and
nuclear power generating units.
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TYPES OF MATERIALS

• The effects of alloying elements in steels
• Carbon
• Melting point of the steel decreases
• Steel becomes harder
• Tensile strength of steel increases
• Steel looses some of its ductility
• Steel becomes more wear resistant
• Steel looses some of its machinability
• Steel becomes more difficult to weld without
  cracking
• Steel becomes heat treatable
• Nickel
• Refines the structure
• Increases the strength, ductility and toughness
  of carbon steel
• Chromium
• is a hardening agent (steel with 1 Cr is used
  for dies, stamps and ball races

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TYPES OF MATERIALS

• Manganese
• is present in small amounts in all steels. Steels
  with 1.5Mn is used for couplings and cage
  chains. Steels with 50 Mn is exceptionally tough
  and resistant to abrasion and is used for jaws of
  the crushers or V ends of the railway crossings
• Molybdenum
• Increases the creep resitance of steel (high
  temperature applications such as superheater
  tubes)
• Tungsten
• is another hardening agent (often accompanying
  Cr)
• Silicon
• Steels have high magnetic permeability and
  therefore used in transformer cores
• Cobalt
• Steels are excellent for permanent magnets

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• Car makers test, utilize multi-materials designs,
  but steel remains dominant
• Steel is the material of choice for car bodies
  99 passenger cars have a steel body60-70 of
  the car weight consisting of steel or steel-based
  parts
• The automotive industry makes excursions in light
  materials applications but there is onlya slight
  actual increase in the use of Al, Mg and plastics

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TRENDS IN CAR BODY MATERIALS materials
objectives for vehicle functionality

• Lightweighting mass containment and mass
  reduction
• Low gas mileage
• Less greenhouse gas emissions
• Passenger Safety
• Low peak deceleration, long crush length, long
  time duration of crash pulse
• High energy dissipation with minimum intrusion
• Higher impact strength for A and B Pillars
• Noise and Vibration
• Vehicle Handling
• Stiffness and Torsional Rigidity
• Fatigue
• Dent resistance
• Perforation and cosmetic corrosion resistance
• Surface quality, visual appearance

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