engineering materials (part ii)

7/29/2019 Engineering Materials (PART II)

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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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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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2

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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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.

R f t H d M t l


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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.

R f t H d M t l


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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

engineering materials (part ii)

Documents