engineering materials (part ii)
TRANSCRIPT
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ME 215 Engineering Materials I
Dr.Ouzhan YILMAZ
Associate Professor
Mechanical Engineering
University of Gaziantep
Chapter 1 Engineering Materials (PART II)
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1
Non-Ferrious Metals
The arbitrary classifications of the non-ferrous metals are:
1. Light metals:Aluminum, Magnesium, Titanium, Beryllium.
2. Heavy metals: Copper, Zinc, Lead, Tin, and so on.
3. Precious metals: Gold, Silver, Platinum.
4. Refractory metals: Tungsten, Nickel, Molybdenum, Chromium, and so on.
Aluminum is the highest ranking material in use next to steel. Copper and its
alloys (brass and bronze) rank second, and Zinc ranks third in consumption.
Light weight of certain nonferrous materials are of special importance in aircraftand space industry. Zinc, tin and lead with low melting points are used in special
appllications. Tungsten, molybdenum and chromium are used in products that
must resist high temp. Nickel and cobalt are also suitable as heat resistant
alloys. Precious metals (with high cost) are not only used in jewelry, but also in
many applications requiring high electrical conductivity and corrosion resistance.
By definition, all metallic materials that do not have iron (Fe) as their major
ingredient are called non-ferrous metals.
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Light Metals
The border of light and heavy metals is around 5000 kg/m3. Metals with densities
below 5000 kg/m3 are called light metals.
The lightest metal is Lithium with the density of 530 kg/m3 and the heaviest
metal is Osmium with density of 22500 kg/m3. Steel has a density of 7800 kg/m3.
Aluminum (Al):
Aluminum is probably the most important nonferrous metal. It is outstanding for
physical properties such as light weight, high thermal and electrical conductivity andcorrosion resistance. It is suitable for all machining, casting and forming operations.
Titanium (Ti):
It is used in corrosive environments or in applications oflight weight, high strength
and nonmagnetic properties. It has good high temperature strength compared withother light metals.
Titanium is available in many forms and alloys such as pure titanium (98.9-99.5%),
titanium-0.2% palladium alloy or high strength Ti-Al-V-Cr (alpha-beta type) alloys.
Ti-6Al-4V (6% Al, 4% V, remainder Ti) and Ti-3Al-13V-11Cr (3% Al, 13% V, 11% Cr,
remainder Ti) are the most commonly used ones in specific industries.
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Light Metals
Beryllium (Be):
Beryllium is a recently emergent material which has several unique properties of
low density (one third lighter than aluminum), high modulus/density ratio (six times
greater than ultrahigh-strength steels), high melting point, dimensional stability,
excellent thermal conductivity and transparency to X-rays.
However, it has serious deficiencies ofhigh cost, poor ductility and toxicity. It is not
especially receptive to alloying.
All conventional machining operations are possible including some nontraditional
processes like EDM and ECM. However, it must be machined in specially equipped
facilities due to its toxic effect. In addition, surface of beryllium is damaged after
machining, and hence secondary finishing operations must be carefully conducted.
It is typically used in military aircraft brake systems, in missile guidance systems,
satellite structures and X-ray windows.
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4
Light Metals
Magnesium (Mg):
It is the lightest engineering material available. The combination oflow density
and good mechanical strength of magnesium alloys has made it one of the most
specified materials in aircraft, space, portable power tools, luggage and similar
applications as competing with the aluminum alloys.
Alloys of magnesium are the easiest of all engineering metals to machine. They
are amenable to die casting, and they are easily welded. Also, magnesium partscan be joined by riveting and adhesive bonding. Other notable characteristics are
high electrical and thermal conductivity, and very high damping capacity.
On the down side, magnesium is highly susceptible to galvanic corrosion since it
is anodic. Under certain conditions, flammability can be a problem as it is anactive metal.
Magnesium alloys are best suited for applications where lightness is of primary
importance. When lightness must be combined with strength, the aluminum
alloys are better material alternatives.
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Heavy Metals
Copper (Cu):
Copper is probably the first engineering metal to be used. Unlike other metals, it
can occur in nature in the metallic form as well as an ore. It has very good heat
and electrical conductivity and resists to corrosion when alloyed with other metals.
However, due to lower density, aluminum has higher conductivity per unit weight.
Copper alloys consist of the following general categories:
1. Coppers (minimum 99.3% Cu)2. High coppers (99.3-96% Cu)
3. Brasses (Cu-Zn alloys with 5-40% Zn)
4. Bronzes (mainly Cu-Sn alloy and also alloys of Cu-P, Cu-Al and Cu-Si)
5. Copper Nickels (Cu-Ni alloys, also known as cupro-nickels)
6. Nickel Silvers (Cu-Ni-Zn alloys which actually do not certain silver)
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Heavy Metals
Zinc (Zn):
Zinc is an inexpensive material with moderate strength. Chemically, it is similar to
magnesium. Mechanically, however, zinc is more ductile but not as strong.
Although its metal and alloy forms are important, zinc is most commonly used to
extend the life of other materials such as steel (galvanizing), rubber and plastic
(as an aging inhibitor), and wood (in paint coatings).
The zinc-base alloys have an imprortant place as a die-casting metal as it has a
low melting point of 419.5 C which does not affect steel dies adversely, and hence
it can be made into alloys with good strength properties and dimensional stability.
Tin (Sn):
It is commonly used as a coating for other metals such as tin cans, copper cookingutensils. Other applications include die-casting alloys, pewter chemicals, bronze,
bearing alloys and solder.
As with many metals, pure tin is too weak to be used alone for most mechanical
applications. Tin is often alloyed with elements such as copper, antimony, lead,
aluminum and zinc to improve mechanical or physical properties.
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Heavy Metals
Lead (Pb):
Lead is a versatile material due to special properties of high atomic weight and
density, softness, ductility, low strength, low melting point, corrosion resistance and
ability to lubricate. Toxicity is one of the chief disadvantages.
There are two principal grades: chemical lead and common lead. Typical uses
include chemical apparatus, batteries and cable sheathing. For corrosion
resistance and X-ray and Gamma-ray shielding, pure lead gives best performance.
Lead is alloyed with tin and antimony to form a series of useful alloys employed for
their low melting points. Solder is the alloy of lead and tin containing small amount
of antimony and silver. The solders are mainly used in soldering electronic circuits
due to their lower melting points.
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Refractory Metals
Tungsten, molybdenum, tantalum and columbium (with melting points above
1900C) are characterized by high-temp. strength and corrosion resistance.
In addition to these, chromium and nickel have major importance as high-temp.materials. Although nickel has a lower melting point (1455C), it is also categorized
in this group due to its specific corrosion resistance or high-temp. strength.
Columbium (Niobium Nb) & Tantalum (Ta):
They are distinguished by excellent ductility even at low temp. Both metals occur
together in ores and they must be separated for nuclear use since tantalum has
a higher neutron absorption than columbium.
They can be fabricated by most conventional processes, usually worked at room
temp. They are usually considered together since most of their working operationsare identical. They are used as anode and grid elements in medium to high-power
tubes, in capacitors and foil rectifiers.
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Refractory Metals
Tungsten (Wolfram W) & Molybdenum (Mo):
Tungsten is the only refractory metal with good electrical and thermal conductivity,
excellent erosion resistance, low coefficient of expansion and high strength at hightemp. Although having low ductility and malleability, it can be fabricated into many
forms with proper procedures. Thomas Edison's trials with tungsten during invention
of incandescent lamp was the most important application. Other uses are electrodes
for inert-gas welding, electron tube filaments, anodes for X-ray and electron tubes.
Molybdenum is a special metal having some resistance to hydrofluoric acid. It is very
similar to tungsten, but more ductile, easier to fabricate and cheaper. Electron tube
anodes, grids for high-power electron tubes, dies withstanding thermal cycling, and
supports for tungsten filaments in light bulbs are its typical applications.
Both metals have brittleness at room temp. and oxidation at relatively low temp.
Chromium (Cr): Most refractory metals oxidize and lose their strength at high temp.
whereas chromium (less subjected to oxidation) loses strength above 1090 C. It is
used in chrome-plating and steel alloys to improve hardness, strength at high temp.
and corrosion resistance. Its brittleness may limit its application areas.
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Refractory MetalsNickel (Ni):
Nickel alloys have desirable properties like ultra-high strength, high proportional limit
and high modulus of elasticity. Commercial pure nickel has good electrical, magneticand magnetostrictive properties. Nickel alloys are still strong, tough and ductile at
cryogenic (very low) temperatures.
Most nickel alloys can be hot and cold worked, machined and welded successfully.
They can be joined by shielded metal-arc, gas tungsten-arc, gas metal-arc, plasma-
arc, electron beam, oxy-acetylene, resistance welding, brazing and soft soldering.
Hafnium (Hf): Melting point of 2130 C. Exist in all zirconium ores. Not commercially
available. Limited use in rectifiers and electronic applications in aerospace.
Rhenium (Re): High strength, good ductility and high melting point (3165 C), butstrong oxidation tendency. Used in filaments in high-power vacuum tubes and high-
temperature thermocouples.
Vanadium (V): Melting point of 1900 C. Added to steels in small amounts.
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Precious Metals Precious metals can be divided into three (3) subgroups: (1) gold and gold alloys,
(2) silver and silver alloys, (3) platinum group metals (consists of six metals
extracted from nickel ores: platinum, palladium, rhodium, iridium, ruthenium
and osmium).
These metals are nearly completely corrosion resistant. Platinum metals withstand
up to 1760 C without any evidence of erosion and corrosion.
Gold (Au): Extremely soft, ductile material that undergoes very little work hardening.
It is often alloyed with other metals (such as copper) for greater strength. It has
occasional uses as a reflecting surface, attachments to transistors and jewelry.
Silver (Ag): The least costly metal of this group. Very corrosion resistant. Plated
onto low-voltage electrical contacts to prevent oxidation of surfaces when arcing
occurs. Used in photographic emulsions due to photosensitivity of silver salts.
Platinum (Pt):A silver-white metal. Extremely malleable, ductile and corrosion
resistant. When heated to redness, it softens and easily worked. Since it is inert,
nearly non-oxidizable and stable even at high temp. Used for high-temp. handling
of high purity of chemicals and laboratory materials. Also used in thermocouples,
spinning and wire-drawing dies, components of high power vacuum tubes, glass-
working environment and electrical contacts as well as in medical purposes.
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Precious Metals
Ruthenium: Very hard and brittle metal. Its tetraoxide is quite volatile and poisonous.
It is added to platinum to increase resistivity and hardness.
Osmium: The heaviest known metal, having a density of about three times that of
steel. It oxidizes readily when heated in air to form a very volatile and poisonous
tetraoxide. It has been used predominantly as a catalyst.
Palladium (Pd):A silver-white metal. Very ductile, slightly harder than platinum.
Principally used in telephone relay contacts and as a coating on printed circuits.
Rhodium (Rh): The hardest metal with the highest electrical and thermal conductivity
in platinum group. Its high polish and reflectivity make it ideal as a plated coating for
special mirrors and reflectors. Rhodium and its alloys are used in furnace windings
and in crucibles at certain temperatures that are too high for platinum.
Iridium (Ir): The most corrosion-resistant metallic element. Together with Cobalt-60,
radioisotope Iridium-192 satisfies most of the industrial radiography requirements.
It has high-temp. strength comparable to that of tungsten up to 1650 C. It is used for
spark plug electrodes in aircraft and other engines where high reliability is needed.
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Palladium (Pd):
Rhodium (Rh):
Iridium (Ir): Ruthenium Osmium
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Other Nonferrous Metals
Bismuth (Bi): The common constituent of all low melting alloys (95-150 C) and
ultra-low melting groups. Increases in volume on solidification, which makes its
alloys excellent for casting as they pick up every detail when expand into the mould.
Antimony (Sb):Also expands upon solidification. Used as a hardener in bearing
alloys and semiconductors, and as alloying element in thermoelectric materials.
Cadmium (Cd): Easy to deposit, excellent ductility and good resistance to salt water
and alkalies. Used for plating of steel hardware and fasteners, as an alloy in bearing
materials and in special batteries. Not permitted in food industry due to toxicity.
Indium (In): Similar in colour to platinum. One of the softest metals. Can be deformed
almost indefinetely by compression. Used in semiconductor devices, bearing metals
and fusible alloys.
Cobalt (Co): Hard metal melting at 1493 C. Used in superalloys, hot-working steels,heat-resisting castings and sintered carbide cutting tools. Invar alloy (54% Co, 36%Ni)
is used in strain gauges. Co-Cr alloys are used in dental and surgical applications.
Zirconium (Zr): Outstanding corrosion resistance to most acids and chlorides.
Increase in its mechanical strength when alloyed with hafnium. Consumed in fuel
rods for nuclear reactors.
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Bismuth (Bi): Antimony (Sb Cadmium (Cd):
Indium (In): Cobalt (Co): Zirconium (Zr):
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Polymers (Plastics)
The word plastic is from the Greek
wordplastikos, meaning capable of
being molded and shaped. Plastics can be formed, machined,
cast, and joined into various shapes
with relative ease.
Because of their many unique and
diverse properties, polymersincreasingly replaced metallic
components in industrial applications.
Relatively low cost and ease of manufacture
Corrosion resistance and resistance to chemicals
Low electrical and thermal conductivity Low density
High-strength to weight ratio
Noise reduction
Wide choice of colors and transperincies
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Polymers (Plastics)
A plastic is a synthetic material (not
found in nature) of high molecular
weight, composed oforganicchemical units (C & H). Plastics can
be moulded or formed into useful
shapes by various processes usually
involving heat and/or pressure.
Plastic polymers are always composed
of atoms of carbon in combination with
other elements. At present, only eight
elements are utilized to createthousands of different plastics. These
eight elements are carbon, hydrogen,
nitrogen, oxygen, fluorine, silicon,
sulfurand chlorine.
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Polymers (Plastics)
Plastics are made from basic
chemical raw materials called
monomers.
A polymer made from two different
monomers is called a
copolymer, and one with three
different monomers isterpolymer.
When a polymer family includes
copolymers, the term
homopolymer
is used toidentify single monomer type.
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Thermoplastics and Thermosets
Thermoplastics (linear plastics) can be re-shaped upon being heated. Therefore,they can be reground orremolded. Since they can be reused, there is little waste.
Thermoplastics can be obtained in any shape and any desired colouras well as in
any desired degree of transparency including crystal clear and opaque. This is a
definite advantage to eliminate painting or other finishing operations required to
achieve the desired sales appearance.
On the other hand, thermosets (crosslinked plastics) complete the polymerization
under heat and effect of other agents. Thus, remoulding is not permitted.
Thermosets have improved resistance to heat (so that they cannot be remolded),
chemical attack, stress cracking and creep in comparison with the same plastic in
thermoplastic form. In addition, thermosets have better dimensional stability and
electrical properties as compared with thermoplastics. However, they are more
difficult to process and more brittle than thermoplastics.
Plastics are classified into two main groups: thermoplastics and thermosets
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Thermoplastics and Thermosets
Thermoplastics
Acrylonitrile Butadiene Styrene (ABS)
AcrylicPhenylene Oxide
Polyster *
Acetal
Polyphenylene Sulfide
Polysulfone
Polyethylene
Polypropylene
Polystyrene
Polycarbonate
Fluoroplastics
Vinyls
Polyimide *
Cellulosics
Nylon (Polyamides)
Polyurethane *
Thermosets
Alkyd
AllylicEpoxy
Aminos (Urea, Melamine)
Polyster *
Phenollic
Polyimide *Silicone
Polyurethane *
* These plastics are available in formsof thermoplastics and thermosets.
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General prop. and appl. of Thermoplastics
The general characteristics and typical applications of major thermoplastics, related
to the manufacturing and service life of the products:
Acetals: have good strength, good stiffness and good resistance to abrasion,
moisture, heat and chemicals.Typical applications: Bearings, cams, gears, bushings,
and rollers, impellers, wear surface pipes, valves, shower heads and housings.
Acrylics: possess modarate strength and good optical properties. They are
transparent (but can be made opaque), are generally resistant to chemicals, andhave good electrical resistance. Typical applications are: lenses, lighted signs,
displays, window glazing, automotive lenses, lighting fixtures and furniture.
ABS: is rigid and dimensionally stable. It has good impact, abrasion, and chemical
resistance; good strength and toughness; good low-temperature properties and high
electrical resistance. Typical applications: pipes, fittings, helmets, tool handles,
automotive components, telephones, luggage etc.
Nylons: have good mechnaical properties and abrasion resistance. They are self-
lubricating and resistant to most chemicals. Typical applications: gears, bearings,
rollers, fasteners, zippers, electrical parts, combs, surgical equipments.
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General prop. and appl. of Thermoplastics
Polyesters: have good mechanical, electrical, and chemicals properties; good
abrasion resistance; and low friction. Typical applications: gears, cams, rollers,
pumps, and electro-mechanical components.
Polyvinyl chloride (PVC): has a wide range of properties, is inexpensive and water
resistant, and can be made rigid or flexible. It is not suitable for applications requiring
strength and heat resistance. Rigid PVC is tough and hard; it is used for signs and in
the construction industry (in pipes, windows, doors etc.). Flexible PVC is used wire
and cable coatings, in low pressure flexible tubing and hose, and in footwear,imitation leather, gaskets etc.
Polystyrenes: generally have average properties and are somewhat brittle, but in
expensive. Typical applications: disposable containers, packaging, trays for meats,
automotive and radio/TV components, toys and furniture parts.
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General prop. and appl. ofThermosets
Alkyds: have good electrical insulating properties, impact resistance, dimensional
stability, and low water absorption. Typical applications: electric and electronic
components.
Epoxies: have excellent mechanical and electrical properties, good dimensional
stability, strong adhesive properties and good resistance to heat and chemicals.
Typical applications: electrical components requiring mechanical strength and high
insulation, tools and dies, and adhesives.
Polyimides: have good mechanical, physical and electrical properties at elevated
temperatures; they also have good creep resistance, low friction and low wear
characteristics. Typical applications: pump components (bearings, seals, valve seats,
piston rings), aerospace parts, sports equipment ans safety vests.
Silicones: have properties that depend on composition. They have excellent electrical
properties over a wide range of humidity and temperatures and resist chemicals and
heat. Typical applications: electrical components requiring strength at elevated
temperatures, oven gaskets, heat seals, and waterproof materials.
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Additives
Nearly all plastics contain additives to facilitate processing or reduce costs.
Colourants: Improve sales appearance of plastics. Great variety of pigments.
Available as metal-base (cadmium, lead and selenium) and liquid.
Fillers: Being inert (inactive). Used to reduce cost and increase bulk. Common
types are wood-flour, chopped fabrics, talc, asbestos, mica, milled glass.
Catalysts: Keep curing cycle in control by regulating the polymerization. Used
to improve the shelf-life of plastics. Available as metallic or organic compounds.
Plasticizers:Added in minimum amount to improve flowability and flexibility.
Phthalates of high boiling points and polysters of low molecular weight are used.
Stabilizers:Added to prevent breakdown or deterioration when exposed to heat,
sunlight, oxygen or ozone. They are metal compounds, phenols and amines.
Fire Retardents: Limiting the spread of fire (not improving the heat resistance)
of flammable polymers (notable exception is PVC).
Lubricants:Added in minimum amounts to improve mouldability and facilitate
removal of parts from moulds. Wax, stearates and some soaps are used.
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Fiber-Reinforced Plastics
The fastest growing engineering materials. Though their cost is higher, they offer
properties and performance benefits considerably beyond unreinforced resins.
They are extremely versatile composites with relatively high strength-to-weight ratiosand excellent corrosion resistance. In addition, they can be formed economically into
any shape and size (from tiny electronic components to large cruising boat hulls).
They are composed of three (3) major components: (1) matrix, (2) fiber, and (3)
bonding agent. Most plastic resins serve as the matrix having embedded fibers.
Adherence of matrix and fibers is achieved by a bonding agent of binder (also calledcoupling agent). In addition to these three, various fillers are used to meet specific
needs.
1. Glass-Reinforced Thermoplastics: Practically all thermoplastics such as nylons,
polypropylenes and polystyrenes (and their copolymers) are available in this form.
Their mechanical properties (tensile modulus and strength, dimensional stability,impact strength, fatigue endurance, etc.) are improved by a factor of two or more.
2. Carbon-Reinforced Thermoplastics:Available in a number of thermoplastics
including nylon, polysulfone, polyster, polyphenylene sulfide and fluorocarbon.
These materials cost about two or more times than glass-reinforced thermoplastics,
but offer highly improved tensile strength and stiffness.
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Fiber-Reinforced Plastics
3. Reinforced Thermosets: Compared with metals, these plastics have improved
mechacial properties, better dimensional stability and weight saving.
a. Resins: Polyster and epoxy resins, phenolics, melamines, and silicones.Improved properties for use in various specific applications.
b. Reinforcements: In addition to epoxies, phenolics, melamines and silicones;
glass, asbestos, carbon graphite and boron are other reinforcements.
4. Laminated and Sandwich Plastics: They consist ofplies of reinforced materials
that are formed with bonded thermosets and cured underheat and pressure. They
can be in the form of laminated, sandwich, honeycomb, corrugated or waffle.
a. Resins: Phenolics, melamines, epoxies, polyesters and silicones.
b. Reinforcements: Papers, cotton, paper-type asbestos, woven and nylon fabrics.
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Glass-Reinforced
Thermoplastics
Carbon-Reinforced
Thermoplastics
Reinforced Thermosets
Reinforced ThermosetsLaminated and Sandwich Plastics
El
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Elastomers
Elastomers (rubbers) can be stretched at room temperature to at least twice of
their original length and will return to original length upon release of the stress.
Termoplastic Elastomers (Elastoplastics): They have similar properties with
thermoset rubbers plus the advantages of thermoplastic materials (polyurethanes,
copolysters, styrene copolymers, olefins).
Thermoset elastomers have the following classes:1.R class: with unsaturated carbon chain (natural rubber, polyisoprene, styrene
butadiene, isobutene isoprene, neoprene, nitrile butadiene)
2.M class: with saturated chain of polymethylene type (polyacrylic, ethylene
propylene, chlorosulfonated and chlorinated polyethylene, fluorocarbon)
3.O class including silicone rubbers (fluorosilicone)
4.U class having carbon, oxygen and nitrogen in the polymer chain (polyurethane)
C i
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Ceramics
Ceramics are made ofmetal oxides, metal carbides and silicates. Hard and brittle, and
cannot endure high tensile loads orsudden impact. On the other hand, they have high
compressive strengths and resistance to high temperature.
Engineering ceramics
are preferred to meet
special requirements
such as extreme rigidity,
creep resistance, high-
temperature corrosion
resistance and special
physical properties.
Class Examples Typical Uses
Single Oxides Alumina (Al2O3) Electrical insulators
Chromium Oxide (Cr2O3) Wear coatings
Zirconia (ZrO2) Thermal insulations
Titania (TiO2) Pigment
Silica (SiO2) Abrasive
Metal Oxides Kaolinite Clay products
Carbides Vanadium carbide (VC) Wear-resistant materials
Tantalum carbide (TaC) Wear-resistant materials
Tungsten carbide (WC) Cutting tools
Titanium carbide (TiC) Wear-resistant materials
Silicon carbide (SiC) Abrasives
Chromium carbide (Cr3C2) Wear coatingsBoron carbide (B4C) Abrasives
Sulfides Molybdenum disulfide (MoS2) Lubricant
Tungsten disulfide (WS2) Lubricant
Nitrides Boron nitride (BN) Insulator
Metalloid Elements Germanium (Ge) Electronic devices
Silicon (Si) Electronic devices
Intermetallics Nickel aluminide (NiAl2) Wear coatings
They are mainly used in
turbine blades, grinding
wheels and carbide bits
of cutting tools as well
as in electrical industry
due to high electrical
resistance.
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Refractory Hard Metals
These metals, also called cemented carbides (cermets), are a composite of a
metal and a ceramic. They combine some of the high refractoriness of ceramics
with toughness and thermal-shock resistance of metals.
To produce parts from cermet materials, powders are pressed into moulds at
medium and high presses, and then sintered in controlled atmosphere furnaces
at about 1650 C. Oxide-based cermets are primarily chromium-alumina based
or chromium-molybdenum-alumina-titania based.
Carbide-based cermets are based on tungsten or titanium and tantalum
carbides.
Four different systems are used for structural (not for metal cutting) applications:
1. Tungsten carbide with 3% to 10% matrix of cobalt is often specified for combined
wear and impact resistance.
2. Combination of tungsten and tantalum carbides in a matrix of nickel, cobalt orchromium provides a formulation especially suited for a combination of corrosion
and wear resistance.
3. Tungsten titanium carbides (WTiC2) in cobalt is used primarily for metal forming
dies and similar applications.
4. Titanium carbide has a molybdenum or nickel matrix, formulated for high-temp. use.
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Refractory Hard Metals
Cermets
cutting tool insert
Oxide-based cermets Carbide-based cermets
Gl
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Glass
Glass is a noncrystalline or amorphous solid, i.e. its atoms never arrange
themselves in a crystalline order. However, atomic spacing in glass is tight.
Glass has no distinct melting or freezing point; thus its behavior is similar to that
of amorphous alloys and polymers.
All glasses are contaning at least 50% silica (glass former).
Additions: aluminum oxides, sodium, calcium, barium, boron, magnesium,titanium, lead and potassium.
There are 750 types of commercially available glasses:
-Window glass to glass for containers
- cookware
- lighting and view screens for television sets and mobile phones
- anti-chemical, corrosion, and optical characteristics.
- Special glasses for fiber optics
Gl
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Glass
Nonsilicate-system glasses, account for a minor percentage of all glass produced
including phosphate glasses (resist hydrofluoric acid), rare-earth borate glasses
(for high refractive index), heat absorbing glasses (made with FeO) and systemsbased on oxides of aluminum, vanadium, germanium and other metals.
Most glass is based on silicate system that is made from three major constituents:
(1) silica (SiO2), (2) lime (CaCO3) and (3) sodium carbonate (NaCO3).
Additions of oxides of boric, aluminum, zinc and lead as well as other materials are
used to tailor some properties of glass (such as strength and viscosity) to meet
specific requirements.
Silicate-system glasses are soda-lime glass, borosilicate glass, aluminosilicateglasses, lead glass, and fused-silica glass.
Gl
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Glass
Types of Glasses:
-Soda-lime glass- Lead alkali glass
- Borosilicate glass
- Aluminosilicate glass
- 96%-silica glass
- Fused Silica glass
Properties:
-Low thermal conductivity
- high electrical resistivity and dielectric strength
- thermal expansion coefficients are lower than those for metals and plastics
- Resistant to chemical attacts
Carbon
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Carbon
Carbon, a nonmetallic element, exists in three generic forms: diamond, graphite
and black (amorphous) carbon. They are useful engineering materials.
Diamond is used for engineering purposes primarily as it is the hardest naturally
occurring material (although synthetic boron nitride or "borazon has similar
mechanical properties and will scratch diamond). Pure diamonds are colourless,
but diamonds containing mineral impurities may be red, blue, green, yellow or
black. Black diamonds are industrial diamonds that are not valuable for jewels
and used in cutting tools, grinding wheels and other high-hardness applications.
Graphite is soft, shiny material formed of layers of carbon atoms. Their compounds
usually contain black carbon added to improve mechanical properties. Graphite is
readily machinable, resists heat and thermal shock, a good heat conductor and
chemically inert to almost all corrosives (except strong oxidizing agents).
Black carbon is specified for low-friction applications. The coefficient of friction
between carbon and another material depends on the grade of carbon and other
specific factors.
Composite Materials
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Composite Materials
It is often difficult to obtain the most desirable combination of properties for a single
application from a single metal, plastic or ceramic material. Therefore, different type
of materials having specific properties are brought together to produce composite
materials with superior properties.
Composites usually consist of a matrix material with the reinforcing elements
to give enhanced mechanical properties to the final product. Matrix gives composite
its bulk form and structural constituents (fibres, particles, laminas, flakes and fillers)
determine the character of the composites internal structure.
Composite Materials
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Composite Materials
Composite Materials
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Composite Materials
Metal Matrix Composite Materials
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Metal-Matrix Composite Materials
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Cross-section of a
composite sailboard, an
example of advanced
materials