Transcript types of materials - Hacettepe University Department of Mechanical

TYPES OF MATERIALS
MATERIALS
Metals
Polymers
Ceramics
(Pure Metals,
(Plastics,
( Clay minerals,
Metal Alloys)
Rubber)
Cement,
Composites
(Combination of two
or more different
materials)
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…
TYPES OF MATERIALS
Metals
•Extremely good conductors of electricity and heat,(the valence electrons are shared
among all atoms and are free to travel everywhere…metallic 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.
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
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.
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
TYPES OF MATERIALS
Widely Used Engineering Materials
Metals and Metal Alloys
Iron
•Iron is plentiful, exists in the earth crust (5% of the earth’s 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
TYPES OF MATERIALS
Ferrous Alloys
•Iron is the prime constituent
•Important for engineering construction materials since iron is the most abundant
element in the earth’s 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
LowCarbon
MediumCarbon
HighCarbon
Gray Iron
Ductile
(Nodular)
Iron
White Iron
Malleable
Iron
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.
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:
1) Can be easily cast into complex shapes
2) Can withstand to higher temperatures with
respect to steel
3) Machinable because of the lubricating effect of
graphite
Application: Base structure of
machines or heavy equipments
due to its damping property.
4) Graphite network provides considerable degree
of corrosion resistance
5) Damps vibrations
6) Compressive strength is high
7) Cheap
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.
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
900°C 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
TYPES OF MATERIALS
Low Carbon Steels
Carbon content<0.25%wt
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 0.25%wt. 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.
TYPES OF MATERIALS
Medium Carbon Steels
0.25%wt<Carbon content<0.60%wt
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
0.60%wt<Carbon content<1.4%wt
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.
TYPES OF MATERIALS
Stainless Steels
Cr>11%wt
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.
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
TYPES OF MATERIALS
Manganese:
•is present in small amounts in all steels. Steels with 1.5%Mn 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
• 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 body•60-70% of the car weight consisting of
steel or steel-based parts
• The automotive industry makes excursions in light materials
applications but there is only a slight actual increase in the
use of Al, Mg and plastics
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
Q&P: Quenching and Partitioning of Austenite
Q&T: Quenching and Tempering
AHSS: Advanced HSS
BAKE HARDENING
• Dislocations are introduced by press forming a steel sheet, and strength is
increased by the action of work hardening in which accumulated dislocations
prevent the movement of other dislocations. When an automobile body is
being manufactured, painting and baking are carried out after assembly.
These processes involve heating the steel body panels to about 443K (170).
At this temperature, the carbon atoms dissolved in the steel diffuse by
jumping between lattice points, which occurs 103 to 105 times a second,
segregating in the regions around dislocations where the stresses are
compressive. This results in locking of the dislocations which is called strain
aging. This mechanism makes the steel panels harder after baking than after
press forming, and is referred to as bake hardening. The utilization of this
bake hardening phenomenon has made it possible to utilize steel sheet that
has good formability during press forming and that can withstand severe
working, while being hard and less prone to denting when assembled in the
automobile body.