Engineering MaterialsMetalsCeramics and othersPlasticsCompositesFerrousNonferrousSteelsStainless SteelsTool and Die SteelsCast IronsOxidesNitridesCarbidesGlassesGraphiteDiamondThermoplasticThermosetPolymer MatrixMetal MatrixCeramic MatrixAluminumCopperMagnesiumTitaniumPolyethylenePolypropyleneNylonABSPVCEpoxyPhenolicSilicone

Properties of Engineering Materials

Density Mechanical StrengthDuctilityHigh Temp. stabilityMetalsHighMediumHighGoodPlasticsLowLowVery High (thermoplastic) Low (thermoset)Not goodCeramicsMediumHighLowVery goodCompositesLowHighMediumNot good

IntroductionCompounds of metallic and non metallic elements.Ceramics comes from Greek word keramos means clay products.Earliest usage were pottery and bricks.Recently in automotive parts, tools and dies, electrical insulator and for high temperature uses.Some examples:Silica - silicon dioxide (SiO2), the main ingredient in most glass productsAlumina - aluminum oxide (Al2O3), used in various applications from abrasives to artificial bonesMore complex compounds such as hydrous aluminum silicate (Al2Si2O5(OH)4), the main ingredient in most clay products

Three Basic Categories of CeramicsTraditional ceramics clay products such as pottery and bricks, common abrasives, & cementNew ceramics more recently developed ceramics based on oxides, carbides, etc., and generally possessing mechanical or physical properties superior or unique compared to traditional ceramicsGlasses based primarily on silica and distinguished by their noncrystalline structure In addition, glass ceramics glasses transformed into a largely crystalline structure by heat treatment

Ceramic ProductsA variety of ceramic components. (a) High-strength alumina for high-temperature applications. (b) Gas-turbine rotors made of silicon nitride

Ceramic ProductsClay construction products - bricks, clay pipe, and building tile Refractory ceramics ceramics capable of high temperature applications such as furnace walls, crucibles, and molds Cement used in concrete - used for construction and roadsWhiteware products - pottery, stoneware, fine china, porcelain, and other tableware, based on mixtures of clay and other minerals

Glass bottles, glasses, lenses, window pane, and light bulbs Glass fibers - thermal insulating wool, reinforced plastics (fiberglass), and fiber optics communications lines Abrasives - aluminum oxide and silicon carbide Cutting tool materials - tungsten carbide, aluminum oxide, and cubic boron nitride Ceramic Products

Ceramic insulators applications include electrical transmission components, spark plugs, and microelectronic chip substrates Magnetic ceramics example: computer memoriesNuclear fuels based on uranium oxide (UO2)Bioceramics - artificial teeth and bonesCeramic Products

Simple ceramic crystal structure Containing various atoms of different size, most complex materials Bonded by covalent or/and ionic bonds which are much more stronger than metallic bonds Properties in terms of hardness, thermal and electrical resistance are superior than metals. Available in single crystals and polycrystalline Grain size major influence on the strength and properties of ceramics Finer the grain size the higher strength and toughness.

Silicate structure

Define a ceramic material.

Answer : Ceramic materials are inorganic, nonmetallic materials that consist of metallic and nonmetallic elements bonded together primarily by ionic and/or covalent bonds.

2) What are some of the properties common to most ceramic materials?

Answer : While the properties of ceramic materials vary greatly, most ceramic materials are hard and brittle with low toughness and ductility but good electrical and thermal insulating properties. Also, ceramic materials typically have high melting temperatures and high chemical stability.Tutorial

Imperfections in Crystal Structure of CeramicsCeramics contain the same imperfections in their crystal structure as metals vacancies, displaced atoms, interstitialcies, and microscopic cracks Internal flaws tend to concentrate stresses, especially tensile, bending, or impact Hence, ceramics fail by brittle fracture much more readily than metalsPerformance is much less predictable due to random imperfections and processing variations

Traditional CeramicsBased on mineral silicates, silica, and mineral oxides found in naturePrimary products are fired clay (pottery, tableware, brick, and tile), cement, and natural abrasives such as aluminaProducts and the processes to make them date back thousands of years Glass is also a silicate ceramic material and is sometimes included among traditional ceramics

Raw Materials for Traditional CeramicsMineral silicates, such as clays of various compositions, and silica, such as quartz, are among the most abundant substances in nature and constitute the principal raw materials for traditional ceramics.Other important raw materials for traditional ceramics are alumina, calcium, potassium, sodium.These solid crystalline compounds have been formed and mixed in the earths crust over billions of years by complex geological processes.

New CeramicsCeramic materials developed synthetically over the last several decadesThe term also refers to improvements in processing techniques that provide greater control over structures and properties of ceramic materials In general, new ceramics are based on compounds other than variations of aluminum silicate, which form most of the traditional ceramic materials New ceramics are usually simpler chemically than traditional ceramics; for example, oxides, carbides, nitrides, and borides

Oxide CeramicsMost important oxide new ceramic is alumina Although also included as a traditional ceramic, alumina is today produced synthetically from bauxite, using an electric furnace methodThrough control of particle size and impurities, refinements in processing methods, and blending with small amounts of other ceramic ingredients, strength and toughness of alumina are improved substantially compared to its natural counterpart. Alumina also has good hot hardness, low thermal conductivity, and good corrosion resistance.

1) Distinguish between traditional and engineering ceramic materials and give examples of each.

Traditional ceramic materials are typically made from three components clay, feldspar and silica whereas engineering ceramics consist of pure or nearly pure compounds such as aluminum oxide (Al2O3), silicon carbide (SiC), and silicon nitride (Si3N4).

Examples of traditional ceramics include bricks, tiles and electrical porcelain while applications of engineering ceramics include silicon carbide parts for high temperature gas turbine engine components, zirconium dioxide crucibles for melting superalloys, and high performance ball bearing and races made of titanium and carbon nitride.Tutorial

Products of Oxide CeramicsAbrasives (grinding wheel grit)Bioceramics (artificial bones and teeth)Electrical insulators and electronic componentsRefractory brickCutting tool inserts Spark plug barrelsEngineering components

Alumina ceramic components (photo courtesy of Insaco Inc.)

CarbidesSilicon carbide (SiC), tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), and chromium carbide (Cr3C2) Although SiC is a manmade ceramic, its production methods were developed a century ago, and it is generally included in traditional ceramics group WC, TiC, and TaC are valued for their hardness and wear resistance in cutting tools and other applications requiring these properties WC, TiC, and TaC must be combined with a metallic binder such as cobalt or nickel in order to fabricate a useful solid product

NitridesThe important nitride ceramics are silicon nitride (Si3N4), boron nitride (BN), and titanium nitride (TiN) Properties: hard, brittle, high melting temperatures, usually electrically insulating, TiN being an exception Applications: Silicon nitride: components for gas turbines, rocket engines, and melting cruciblesBoron nitride and titanium nitride: cutting tool material and coatings

GlassA state of matter as well as a type of ceramicAs a state of matter, the term refers to an amorphous (noncrystalline) structure of a solid materialThe glassy state occurs in a material when insufficient time is allowed during cooling from the molten state for the crystalline structure to form As a type of ceramic, glass is an inorganic, nonmetallic compound (or mixture of compounds) that cools to a rigid condition without crystallizing

Why So Much SiO2 in Glass?Because SiO2 is the best glass former Silica is the main component in glass products, usually comprising 50% to 75% of total chemistry It naturally transforms into a glassy state upon cooling from the liquid, whereas most ceramics crystallize upon solidification

Other Ingredients in GlassSodium oxide (Na2O), calcium oxide (CaO), aluminum oxide (Al2O3), magnesium oxide (MgO), potassium oxide (K2O), lead oxide (PbO), and boron oxide (B2O3) Functions: Act as flux (promoting fusion) during heatingIncrease fluidity in molten glass for processingImprove chemical resistance against attack by acids, basic substances, or waterAdd color to the glassAlter index of refraction for optical applications

Glass ProductsWindow glassContainers cups, jars, bottlesLight bulbsLaboratory glassware flasks, beakers, glass tubingGlass fibers insulation, fiber opticsOptical glasses - lenses

GlassCeramicsA ceramic material produced by conversion of glass into a polycrystalline structure through heat treatmentProportion of crystalline phase range = 90% to 98%, remainder being unconverted vitreous materialGrain size - usually between 0.1 1.0 m (4 and 40 -in), significantly smaller than the grain size of conventional ceramics This fine crystal structure makes glassceramics much stronger than the glasses from which they are derived Also, due to their crystal structure, glassceramics are opaque (usually grey or white) rather than clear

Elements Related to CeramicsCarbonTwo alternative forms of engineering and commercial importance: graphite and diamondSiliconBoronCarbon, silicon, and boron are not ceramic materials, but they sometimes Compete for applications with ceramics Have important applications of their own

GraphiteForm of carbon with a high content of crystalline C in the form of layersBonding between atoms in the layers is covalent and therefore strong, but the parallel layers are bonded to each other by weak van der Waals forcesThis structure makes graphite anisotropic; strength and other properties vary significantly with direction As a powder it is a lubricant, but in traditional solid form it is a refractoryWhen formed into graphite fibers, it is a high strength structural material

Structure of crystalline graphite

DiamondCarbon with a cubic crystalline structure with covalent bonding between atomsThis accounts for high hardnessIndustrial applications: cutting tools and grinding wheels for machining hard, brittle materials, or materials that are very abrasive; also used in dressing tools to sharpen grinding wheels that consist of other abrasives Industrial or synthetic diamonds date back to 1950s and are fabricated by heating graphite to around 3000C (5400F) under very high pressures

Synthetically produced diamond powders (photo courtesy GE Superabrasives, General Electric Company)

Physical Properties of CeramicsDensity in general, ceramics are lighter than metals and heavier than polymers Some ceramics are translucent, window glass (based on silica) being the clearest example.Melting temperatures - higher than for most metals Some ceramics decompose rather than meltElectrical conductivities - lower than for metals; but the range of values is greater, so some ceramics are insulators while others are conductors

Thermal Properties of CeramicsThermal Conductivities (refer to Figure 11.42 pg 618):lower than for metals; but the range of values is greater, most ceramics are thermal insulators while others are conductors.Due to their strong ionic-covalent bonding.Ceramics materials are used as refractories which resist the action of hot environment, both liquid and gaseous. Thermal expansion - somewhat less than for metals, but effects are more damaging because of brittleness

Mechanical Properties of Ceramic MaterialsTheoretically, the strength of ceramics should be higher than metals because their covalent and ionic bonding types are stronger than metallic bonding However, metallic bonding allows for slip, the basic mechanism by which metals deform plastically when subjected to high stressesBonding in ceramics is more rigid and does not permit slip under stress The inability to slip makes it much more difficult for ceramics to absorb stresses

Effect of grain size on ceramic propertiesFor porosity free-ceramics, the strength of a pure ceramic material is a function of its grain size.Finer grain size ceramics having smaller-size flaws at their grain boundaries.Finer grain size ceramics are stronger than large-grain-size ones.

Methods to Strengthen CeramicsDecrease grain size in polycrystalline ceramic products Make starting materials more uniformMinimize porosityIntroduce compressive surface stresses Use fiber reinforcementHeat treat

Quiz 8 1. Define ceramic materials.2. List three properties common to most ceramics.3. Define amorphous alloys (or metallic glasses).

Tutorial (Quiz8)1. Define ceramic materials.Answer : Ceramic materials are inorganic, non-metallic materials that consist of metallic and non-metallic elements bonded together primarily by ionic and/or covalent bonds.

2. List three properties common to most ceramics.Answer : Most ceramic materials are hard and brittle with low toughness and low ductilityGood electrical and thermal insulating properties. High melting temperatures and high chemical stability.

3. Define amorphous alloys (or metallic glasses).Answer : A class of metal alloys formed through rapid-solidification. It does not have long-range crystalline structure. Atoms are randomly and tightly arranged and no grain boundariesTutorial (Quiz8)

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Properties of Engineering Materials

Density Mechanical StrengthDuctilityHigh Temp. stabilityMetalsHighMediumHighGoodPlasticsLowLowVery High (thermoplastic) Low (thermoset)Not goodCeramicsMediumHighLowVery goodCompositesLowHighMediumNot good

CompositesA materials system composed of two or more physically distinct phases whose combination produces aggregate properties that are different from those of its constituents Properties depend on amount and distribution of each type of materialExamples:Cemented carbides (WC with Co binder)Plastic molding compounds containing fillers Rubber mixed with carbon blackWood (a natural composite as distinguished from a synthesized composite)

Why Composites are ImportantComposites can be very strong and stiff, yet very light in weight, so ratios of strengthtoweight and stiffnesstoweight are several times greater than steel or aluminum Fatigue properties are generally better than for common engineering metals Toughness is often greater too Composites can be designed that do not corrode like steel Possible to achieve combinations of properties not attainable with metals, ceramics, or polymers alone

ApplicationsExamplesSports equipment (golf club shafts, tennis rackets, bicycle frames) Aerospace materials Thermal insulation Concrete "Smart" materials (sensing and responding) Brake materialsFiberglass (glass fibers in a polymer) Space shuttle heat shields (interwoven ceramic fibers) Paints (ceramic particles in latex) Tank armor (ceramic particles in metal)

Application of advanced composite materials in Boeing 757-200 commercial aircraft.

Components in a Composite MaterialNearly all composite materials consist of two phases: Primary phase - forms the matrix within which the secondary phase is imbedded Secondary phase - imbedded phase sometimes referred to as a reinforcing agent, because it usually serves to strengthen the composite The reinforcing phase may be in the form of fibers, particles, or various other geometries

Our Classification Scheme for Composite MaterialsMetal Matrix Composites (MMCs) mixtures of ceramics and metals, such as cemented carbides and other cermets Ceramic Matrix Composites (CMCs) Al2O3 and SiC imbedded with fibers to improve properties, especially in high temperature applications The least common composite matrixPolymer Matrix Composites (PMCs) thermosetting resins are widely used in PMCs Examples: epoxy and polyester with fiber reinforcement, and phenolic with powders

Properties of Composite MaterialsIn selecting a composite material, an optimum combination of properties is usually sought, rather than one particular property Example: fuselage and wings of an aircraft must be lightweight and be strong, stiff, and tough Several fiberreinforced polymers possess this combination of properties Example: natural rubber alone is relatively weakAdding significant amounts of carbon black to NR increases its strength dramatically

Properties are Determined by Three Factors: The materials used as component phases in the compositeThe geometric shapes of the constituents and resulting structure of the composite systemThe manner in which the phases interact with one another

Figure 9.5 (a) Model of a fiberreinforced composite material showing direction in which elastic modulus is being estimated by the rule of mixtures (b) Stressstrain relationships for the composite material and its constituents. The fiber is stiff but brittle, while the matrix (commonly a polymer) is soft but ductile.

Figure 9.6 Variation in elastic modulus and tensile strength as a function of direction of measurement relative to longitudinal axis of carbon fiberreinforced epoxy composite

Define a composite material with respect to a materials system.

A composite material is a materials system composed of a mixture or combination of two or more micro- or macro constituents that differ in form and chemical composition and are essentially insoluble in each other.Tutorial

Polymer matrix composites (PMCs)Reinforced plastic also known as PMC and FRP, consist of fibers in a plastic matrix.Commonly used fibers are glass, graphite, aramids and boron.Strong and stiff, specific strength and specific stiffness.The matrix (plastic) is less strong and stiff, but is tougher than fibersThe percentage of fibers (by volume) in reinforced plastic usually ranges between 10% and 60%.More than 1 type of fibers used, it is called hybrid

Reinforcing FibersReinforcing fiber for PMC are generally glass, graphite, aramids or boron.

Glass fibers are widely used and less expensiveThis composite materials called GFRP Type of glass fibers are E type, S-type and E-CR type.

Graphite fibers more expensive but low density, high strength and high stiffness. Called CFRP.Different carbon and graphite;- carbon 80-90% , graphite;- 99% carbon

Reinforcing FibersAramids: toughest fibers; high specific strength, common aramids name Kevlar. Can undergo plastic deformation before fracture.

Boron: consist of boron deposited onto carbon fibers or tungsten fibers.These fibers high strength, and stiffness, both in tension and in compression and resistance to high temperatures.High density and expensiveOther fibers; nylon, silicon carbide, silicon nitride, aluminum oxide, steel tungsten and etc

Fiber size and lengthSize less than 0.01mm.Strong and stiff in tension, due to molecule in the fibers are oriented longitudinal direction, and their cross-section are so small that the probability is low in defects.Classified as long and short, or continuous and discontinuous. Short fibers aspect ratio 20 and 60, long fibers are 200 and 500.Reinforcement elements may also in the form of chopped, particles, or flakes, continuous roving, woven fabric and mats.

Typical Properties of Reinforcing FibersNote: These properties vary significantly depending on the material and method of preparation.

Type Tensile strength (MPa)Elastic modulus (GPa)Density( kg/m3)Relative costBoron 35003802600HighestCarbon High strength 30002751900Low High modulus 20004151900LowGlass E type 3500732480Lowest S type 4600852540LowestKevlar 29 2800621440High 49 28001171440High

Methods of Reinforcing PlasticsSchematic illustration of methods of reinforcing plastics (matrix) with (a) particles, and (b) short or long fibers or flakes. The four layers of continuous fibers in illustration (c) are assembled into a laminate structure.

Fiber ReinforcingCross-section of a tennis racket, showing graphite and aramid (Kevlar) reinforcing fibers. Cross-section of boron fiber-reinforced composite material.Fibers are the reinforcement and the main source of strength

Types and General Characteristics of Composite Materials

Material CharacteristicsFibersGlass High strength, low stiffness, high density; lowest cost; E (calcium aluminoborosilicate) and S (magnesia-aluminosilicate) types commonly used.GraphiteAvailable as high-modulus or high-strength; low cost; less dense than glass.Boron High strength and stiffness; highest density; highest cost; has tungsten filament at its center.Aramids (Kevlar)Highest strength-to-weight ratio of all fibers; high cost.Other fibersNylon, silicon carbide, silicon nitride, aluminum oxide, boron carbide, boron nitride, tantalum carbide, steel, tungsten, molybdenum.

Matrix materials Thermosets Epoxy and polyester, with the former most commonly used; others are phenolics, fluorocarbons, polyethersulfone, silicon, and polyimides.Thermoplastics Polyetheretherketone; tougher than thermosets but lower resistance to temperature.Metals Aluminum, aluminum-lithium, magnesium, and titanium; fibers are graphite, aluminum oxide, silicon carbide, and boron.Ceramics Silicon carbide, silicon nitride, aluminum oxide, and mullite; fibers are various ceramics.

Material Characteristics

Matrix MaterialHas 3 functions:To support the fibers in place and transfer the stresses to them, while they carry most of the loadTo protect the fibers against physical damage and the environmentTo reduce the propagation of cracks in the composite, by virtue of the greater ductility and toughness of the plastic matrix

Strength and Stiffness of Reinforced PlasticsSpecific tensile strength (tensile strength-to-density ratio) and specific tensile modulus (modulus of elasticity-to-density ratio) for various fibers used in reinforced plastics.

The effect of type of fiber on various properties of fiber-reinforced nylon. (Source: NASA)

Fracture Surfaces of Fiber-Reinforced Epoxy Composites(a) Fracture surface of glass-fiber reinforced epoxy composite. The fibers are 10 m (400 in.) in diameter and have random orientation. (b) Fracture surface of a graphite-fiber reinforced epoxy composite. The fibers, 9 m-11 m in diameter, are in bundles and are all aligned in the same direction.

Metal Matrix Composites (MMC) Higher elastic modulus, its resistance to elevated temperature, and its higher toughness and ductility.But higher density and difficulty in productionHigh specific stiffness, light weight, and high thermal conductivity.

A metal matrix reinforced by a second phase Reinforcing phases:Particles of ceramic (these MMCs are commonly called cermets)Fibers of various materials: other metals, ceramics, carbon, and boron Metal Matrix Composites (MMC)

Micrograph of silicon carbide whiskers used to reinforce MMC with 1 to 3 m diameter and 50 to 200 m long

CermetsMMC with ceramic contained in a metallic matrix The ceramic often dominates the mixture, sometimes up to 96% by volume Bonding can be enhanced by slight solubility between phases at elevated temperatures used in processing Cermets can be subdivided into Cemented carbides most commonOxidebased cermets less common

Cemented CarbidesOne or more carbide compounds bonded in a metallic matrix The term cermet is not used for all of these materials, even though it is technically correct Common cemented carbides are based on tungsten carbide (WC), titanium carbide (TiC), and chromium carbide (Cr3C2) Tantalum carbide (TaC) and others are less common Metallic binders: usually cobalt (Co) or nickel (Ni)

Figure 9.8 Photomicrograph (about 1500X) of cemented carbide with 85% WC and 15% Co (photo courtesy of Kennametal Inc.)

Figure 9.9 Typical plot of hardness and transverse rupture strength as a function of cobalt content

Applications of Cemented CarbidesTungsten carbide cermets (Co binder) - cutting tools are most common; other: wire drawing dies, rock drilling bits and other mining tools, dies for powder metallurgy, indenters for hardness testers Titanium carbide cermets (Ni binder) - high temperature applications such as gasturbine nozzle vanes, valve seats, thermocouple protection tubes, torch tips, cutting tools for steels Chromium carbides cermets (Ni binder) - gage blocks, valve liners, spray nozzles, bearing seal rings

Metal-Matrix Composite Materials and Applications

Fiber MatrixApplicationsGraphite Aluminum Magnesium Lead Copper Satellite, missile, and helicopter structuresSpace and satellite structuresStorage-battery platesElectrical contacts and bearingsBoron Aluminum Magnesium Titanium Compressor blades and structural supportsAntenna structuresJet-engine fan bladesAlumina Aluminum Lead Magnesium Superconductor restraints in fission power reactorsStorage-battery platesHelicopter transmission structuresSilicon carbide Aluminum, titanium Superalloy (cobalt-base) High-temperature structuresHigh-temperature engine componentsMolybdenum, tungsten Superalloy High-temperature engine components

Ceramic Matrix Composites (CMCs)A ceramic primary phase imbedded with a secondary phase, which usually consists of fibersAttractive properties of ceramics: high stiffness, hardness, hot hardness, and compressive strength; and relatively low density Weaknesses of ceramics: low toughness and bulk tensile strength, susceptibility to thermal cracking

Ceramic Matrix Composites (CMCs)CMCs represent an attempt to retain the desirable properties of ceramics while compensating for their weaknesses Composite with ceramic matrix are resistance to high temperature and corrosive environment.Can retain their strength up to 1700oC are silicon carbide, aluminum oxideApplication in jet and automotive engine, deep see mining equipment, pressure vessels, structural components, cutting tools, and dies for the extrusion and drawing of metals.

Tutorial1. Provide 2 functions of the matrix materials in composite.Answer : To support the fibers in place and transfer the stresses to them, while they carry most of the loadTo protect the fibers against physical damage and the environmentTo reduce the propagation of cracks in the composite, by virtue of the greater ductility and toughness of the plastic matrix

Tutorial2. Define Metal-Matrix Composites (MMCs) materials.Answer : MMC is composites materials of metal matrix and fibre materials. Metal matrix used are aluminium, aluminium-lithium, magnesium, copper, titanium (Any one example). Fibre materials such as graphite, aluminium oxide, silicon carbide, boron. (Any one correct answer)

Tutorial2. Describe the hysteresis loss in load-elongation curve of rubber and provide one (1) example of hysteresis importance for a typical elastomer in machinery or automotive application.Answer :

Rubbers experienced hysteresis loss in stretching or compression.They do not instantly follow the forces applied to them, or do not return completely to their original state(2 marks)Examples:Hysteresis gives rubbers the capacity to dissipate energy, damp vibration, and absorb shock loading, as is necessary in automobile tires and in vibration dampers placed under machinery.

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Final exam tips..15/11/2006

Question 1Atomic bondingBravais latticeCrystal structure (bcc/fcc/hcp) calculationsDislocations

Question 2Ductile fractureEngineering Stress-strainTrue stress-strainMaterials selection

Question 3Phase diagram reactionsPhase diagram calculationsIsothermal transformationHeat treatment

Question 4ASTM grain size calculationsGrain boundariesCold working

Question 5Plain carbon steelsAlloy steelsCast ironStainless steel (application)

Question 6CeramicsApplication of ceramicsMMCMetallic glasses

All the Best for Final Exam!Selamat Hari Raya& Happy Holiday

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