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effect of Alloying Elements
• Dislocation movement
• Polymorphic transformation temperature
• Molybdenum, chromium, tungsten, silicon, vanadium and titanium – A3 A4
• Strengthening of ferrite
• Formation and stability of carbides
• Nickel, aluminium and silicon – do not form carbides
• Titanium, niobium, chromium, molybdenum, tungsten, vanadium and manganese – from carbides
• Displacement of eutectoid point
• Nickel, manganese lowers eutectoid temperature
• Retardation of transformation rates
• Nickel, manganese - lowers austenitic temperature – austenite stabilizer
Dr. Jenson Joseph. E, Prof & Head, Dept of Automobile, SCMS
School of Engg & Tech

effect of Alloying Elements
• Lowering of critical cooling rates
• Improvement in corrosion resistance
• Aluminium- forms aluminium oxide – prevent corrosion
• Chromium – 13%
• Influence on grain growth
• Chromium – grain growth
• Nickel, vanadium – grain refiners

• Properties of composite materials depends on characteristics of reinforcements
• Concentration
• Shape
• Size
• Distribution
• Orientation
Composite Materials

• Particle Reinforced composites
• Large particle reinforced composites
• Dispersion strengthened composites
• Fibre reinforced composites
• Continuous fibre reinforced composites
• Discontinuous fibre reinforced composites
Classification based on Reinforcement Geometry

• Particle size - 1-50µm
• Concentration – 15-40% by volume
• Particulate phase is harder and stiffer than matrix
• Particle phase restrain the movement of matrix phase
• Matrix phase transfer the load to the particles
• Mechanical properties increases with increasing particle content
• Even distribution
• Examples
• WC in MMC
• Carbon black in rubber
Large particle reinforced composites

• Particle size <0.1µm
• Volume fraction – 5-15%
• Particles- metallic, non-metallic
• Examples – carbides, oxides and borides
• Matrix is the load bearing phase
• Dispersions prevent the motion of dislocations
• High strength at elevated temperatures and extended time
Dispersion strengthened composites

• Fibre – length =100Xdiameter
• Small diameter fibre is stronger than larger diameter fibre
• Types
• Whiskers ((large length-diameter ratio)
• Fibres (Dia – 5-10µm)
• Wires
• Properties of composites affected by – type, Volume fraction and orientation of fibre
• Critical length Lc = 1mm(20 to 150 times of fibre dia)
• Classifications
• Continuous – L >15Lc
• Discontinuous – l=Lc to 15Lc
Fibre reinforced composites

• Binds and holds the reinforcing medium
• Acts as medium through which the external loads are transferred
• Matrix separates the fibres from each other
• Matrix protects the fibres form surface damage
• Matrix withstand heat, cold, electrical resistance, chemical attack
Roles of Matrix Phase

• Classifications
• Thermosetting plastics
• Thermo plastics
• Properties
• Low density
• High specific strength
• High specific stiffness
• Easy fabrication
• Low cost
Polymer matrix composites

• Glass Fibre Reinforced Polymer Composites (GFRP)
• Diameter – 3-20 µm
• High strength but not suitable for structural applications (Not stiff & Rigid)
• Automotive bodies, marine bodies, storage containers, industrial floorings, plastic pipes
• Carbon Fibre Reinforced Composites ( CFRP)
• Carbon fibre properties - High strength at elevated temperatures
• Not affected by moisture
• 4-10 µm
• Aerospace structural components, rocket motor cases
• Composite properties – High strength, stiffness, wear and impact resistance
• Aramid Fibre Reinforced Polymer Composites
• Polyamide – high strength
• Kevlar and Normex
• Applications – Bullet proof vests, , automotive brakes, clutch linings, tyres
Polymer matrix composites

• Withstand high temperature than polymers
• Metal is reinforced to increase specific strength, abrasion resistance, creep resistance etc.,
• Metal matrix – aluminium, magnesium, titanium and their alloys
• Reinforcements – particulates, fibres and whiskers
• Concentration – 10-60%
• Reinforcements – SiC, Boron Carbide, Aluminium oxide
• Applications – Automobile and aerospace
Metal matrix composites

• High melting point and good resistance to oxidation
• Brittle, low tensile strength and impact strength
• Reinforcements – Zro2, SiC
• Applications – Aircraft turbine engines, cutting tool inserts
Ceramic Matrix Composites

• Air craft and aerospace
• Automotive applications
• Marine applications
• Sporting goods
• Biomaterials
Applications of Composite materials

• The term ceramic – originates from the greek word kermikos(means burnt stuff)
• The properties are achieved by “firing” process.
• It is formed as a combination of metallic and non metallic elements.
• Properties:- high hardness, high brittleness, high MP, chemical inertness, electrical insulation.
• Reason for properties:-presence of strong ionic and covalent bonds
• Ceramic material has more than one type of bonds in them.
• Metallic ions (cations) are +ve ly charged, non metallic (anoins) are –ve ly charged.
• Ratio rc ra is known as radius ratio.
• Co-ordination number is the number of nearest ions for a specific ion.
Ceramics

• AX type
• Equal number of cations (A)and anions (X)
• Different crystal structures
• NaCl, MgO,FeO
• AmXp type
• M not equal to p
• CaF2,Zro2
• AmBnXp
• More than one type of cations
• BaTio3,SrZno3 Fe Al2o3
Crystal structure

• Glasses
• Clay products
• Refractories
• Abrasives
• Cements
• Advanced ceramics
Applications

• Liquid cools without crystallization
• Supercooled liquid
• Brittle, transparent, chemically inert
• Basic ingredients – silica sand. Other elements – CaCO3, Na2CO3,CaO,Na2O
• Construction and engineering applications
• Glass fibres – insulation, reinforcing elements
• Automobile glasses – sandwich of tough plastic between glasses
Glass

• Non-crystalline glass subjected to high temperature treatment →crystalline material
• Fine grained polycrystalline material
• Cooling rate should be lesser than critical cooling rate
• Characteristics
• High mechanical strength
• Low coefficient of thermal expansion
• High temperature resistance
• Good bio compatibility
• Ease of fabrication
• Application – table ware, electrical insulators
Glass ceramics

• Clay ceramics
• Raw material – clay
• Bricks, tiles
• Whiteware – become white at high temperature firing
• Refractory ceramics
• Furnace lining
• Classification – fireclay(silica and alumina), silica, basic(magnesia) and special refractories(alumina, silica,magnesia,beryllia, zirconia)
• Abrasives
• Grind /cut away soft materials
• Silicon carbide, tungsten carbide, aluminium oxide and silica sand
• Cements
• Advanced ceramics – PZT
Ceramics –Applications

• High strength and creep strength at elevated temperatures
• Classification
• Nickel based (Haste alloy, nichrome, kanthol,udimet and Inconel)
• Cobalt based (Stellite, hayness and vitallium)
• Iron based (Incoloy)
• Solid solution strengthening, precipitation hardening and dispersion hardening
• Applications
• Aerospace
• Industrial gas turbine blades
• Engine valves
Super alloys

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