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(Combination of two or more different materials)

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1 (Combination of two or more different materials)
TYPES OF MATERIALS MATERIALS Metals Polymers Ceramics Composites (Pure Metals, Metal Alloys) (Plastics, Rubber) ( Clay minerals, Cement, Glass) (Combination of two or more different materials) Why study Materials? Many applied scientist or engineer, whether mechanical, civil, chemical, electrical or mining, will at one time or another be exposed to a design problem involving materials. e.g: transmission gear, superstructure of a building, oil refinery component, integrated circuit chip, cone or roll crusher…

Extremely good conductors of electricity and heat,(the valence electrons are shared among all atoms and are free to travel everywhere…metallic bonding) No transparency of visible light Quite strong, yet deformable (high strength, high stiffness, good ductility) High fracture toughness, they withstand impact Extensive use in structural applications Some metals such as iron, cobalt and nickel are magnetic Some metals and intermetallic compounds become superconductors at low temperatures Pure Metals: Fe, Cu, Al… Metal Alloys: Contain more than one metallic element, eg: Stainless Steel (Fe, Cr, Ni…) Gold Jewelry (Au, Ni, Cu) Metals having high densities used in applications that require a high mass-to volume ratio. Metals having low density such as Aluminum are used in aerospace applications for fuel economy.

Include the familiar plastic and rubber materials Organic compounds that are chemically based on carbon, hydrogen and many other non-metallic elements Large repeating molecular structures (large chainlike structure) usually based on carbon backbone Low densities and lightweight May be extremely flexible Corrosion resistant Easy to process at low temperatures Low strength and high toughness Have softening and melting points Poor conductors of electricity and heat which makes them good insulators Inexpensive

Compounds between metallic and non-metallic (Inorganic non-metallic material) Oxides, Nitrides and Carbides Insulators (insulative to the passage of electricity and heat) High strength but brittle High melting temperature High stiffnes, hardness, wear and corrosion resistance Some ceramics are magnetic materials, piezoelectric materials ??? Have you ever known that some very special ceramics are superconductors at very low temperatures? Glasses are also inorganic non-metallic materials and doesnot have a crystalline structure, Such materials are said to be amorphous. e.g: soda-lime silicate glass in soda bottles, extremely high purity silica glass in optical fibers.

5 TYPES OF MATERIALS Composites Consist more than one material type
Are designed to display a combination of the best characteristics of each of the component materials e.g: Fiberglass: acquires strength from the glass and flexibility from the polymer Polymer/Ceramic, Metal/Ceramic Composites One of the materials is the matrix and the other one is the embedded material. Have superior property with respect to the individual material Not easy to produce, some special techniques are needed

6 TYPES OF MATERIALS Widely Used Engineering Materials
Metals and Metal Alloys Iron Iron is plentiful, exists in the earth crust (5% of the earth’s crust is iron and in some areas it concentrates in ores that contain as much as 70% iron) Relatively easy to refine using simple tools By heating, relatively easy to bend and shape using simple tools Can handle heat such that you can build engines Relatively speaking, iron is extremely strong The problems of iron are the corrosion and oxidation (or generally speaking, rust formation), however, controlling the corrosion with galvanizing, chrome plating or paint is applicable Common iron ores are: Hematite, Magnetite, Limonite, Siderite

7 TYPES OF MATERIALS Ferrous Alloys Iron is the prime constituent
Important for engineering construction materials since iron is the most abundant element in the earth’s crust Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying and fabrication techniques Have wide range of mechanical and physical properties Are susceptible to corrosion (disadvantage) Steels Cast Irons Low-Carbon Medium- Carbon High- Carbon White Iron Malleable Iron Gray Iron Ductile (Nodular) Iron

8 TYPES OF MATERIALS Cast Iron: is made by melting the pig iron and casting it into molds. Cast iron is too hard and brittle,but it is cheap and its fluidity when molten enables it to be cast easily, they can be used when great strength and ductility are not essential. Some special cast iron contain molybdenum and nickel which gives it more tensile strength. Most cast iron contains 2.5-4% of carbon and following elements as impurities: Si, S, Mn and P.

9 TYPES OF MATERIALS Gray Cast Iron: Carbon contens vary between wt% and Silicon contents vary between wt%. Sulphur, Manganese and Phosphorus contents are low. Cementite which is Fe3C decomposes into Fe and C. In gray cast iron the graphite exists in the form of flakes. Gray cast iron is brittle due to high carbon content and shape of the graphite and weak in tension. The gray or dark color is because of graphite. The resultant alloy microstructure is ferrite or pearlite matrix and graphite flakes. Gray cast iron has some advantages: Can be easily cast into complex shapes Can withstand to higher temperatures with respect to steel Machinable because of the lubricating effect of graphite Graphite network provides considerable degree of corrosion resistance Damps vibrations Compressive strength is high Cheap Application: Base structure of machines or heavy equipments due to its damping property.

10 TYPES OF MATERIALS Ductile (Nodular) Cast Iron: Special type of gray cast iron. Adding a small amount of Magnesium and/or Cerium before casting gray iron produces a different microstructure. Graphite still forms but in the form of nodules or sphere-like particles. The matrix phase is either ferrite or pearlite. The result is increased ductility and tensile strength. It is also as machinable as the gray cast iron. Typical applications are: materials include valves, pump bodies, crankshafts, gears, other automotive components.

11 TYPES OF MATERIALS White Cast Iron: For low silicon cast irons and rapid cooling rates, most of the carbons exists as cementite instead of graphite. Because of the absence of graphite, the structure is white and known as white cast iron. White cast iron is extremely hard, brittle and unmachinable. Limited application is rollers in rolling machine because it is wear resistant. Malleable Cast Iron: Heating white cast iron at temperatures between 800° and 900°C for a prolonged time period and in a neutral atmosphere causes the decomposition of the cementite, forming graphite, which exist in the form of clusters or rosettes surrounded by ferrite or pearlite matrix depending on the cooling rate is called malleable cast iron. The microstructure is similar to nodular cast iron with an appreciable ductility and strength. Representative applications are: Connecting rods, transmission gears, flanges, pipe fittins and valve parts for railroad, marine and other heavy duty services. 25μm

12 TYPES OF MATERIALS Low Carbon Steels Carbon content<0.25%wt
Two types of low carbon steels: Plain Carbon Steels: Steels produced in the greatest quantities fall within the low carbon classification. Carbon content is less than 0.25%wt. They also contain some other alloying elements such as Mn, Cu and Si. These are relatively soft and weak alloys but outstanding ductility and toughness. Strengthening could be accomplished by cold working. They are weldable and machinable and of all steels are least expensive to produce. Typical applications are automobile body components, structural beams, sheets that are used in pipelines, buildings and bridges. High Strength Low Alloy Steels: They contain other alloying elements such as Copper, Vanadium, Molybdenum and Nickel in combined concentration as high as 10%. They have higher strength than low carbon steel and in addition they posses ductility, formability and machinability. They are more resistant to corrosion. They have replaced in many applications where structural strength is critical such as bridges, towers and support columns.

13 TYPES OF MATERIALS Medium Carbon Steels
0.25%wt<Carbon content<0.60%wt These alloys can be heat treatable via austenitizing, quenching and then tempering to improve the mechanical properties. They are most often used as tempered conditions, having microstructure of tempered martensites. Additions of Chromium, Nickel and Molybdenum improve the capacity of these alloys to be heat treated. By heat treatment strength and ductility of the alloy can be altered. The heat treated alloys can be stronger than the low carbon alloy with the sacrifice of ductility and toughness. The applications of these alloys are railway wheels, tracks, gears and crankshafts. High Carbon Steels 0.60%wt<Carbon content<1.4%wt They are the strongest and hardest yet least ductile of the carbon steels. They are mostly used as hardened and tempered conditions. They usually contain Chromium, Vanadium, Tungsten and Molybdenum. These alloying elements combine with Carbon to form very hard and wear resistant carbide components (Cr23C6, V4C3 and WC). The tool and die steels are high carbon steels. The applications are cutting tools and dies for forming and shaping materials as well as knives, razors, blades, springs and high strength wire.

14 TYPES OF MATERIALS Stainless Steels Cr>11%wt
They are resistant to corrosion (rust) in variety of environments. The predominant alloying element is Chromium and others are Nickel and Molybdenum. They maintain their corrosion resistance and mechanical properties and at elevated temperatures. The applications of these alloys are gas turbines, high temperature steam boilers, heat treating furnaces, aircrafts, missiles and nuclear power generating units.

15 TYPES OF MATERIALS The effects of alloying elements in steels: Carbon:
Melting point of the steel decreases Steel becomes harder Tensile strength of steel increases Steel looses some of its ductility Steel becomes more wear resistant Steel looses some of its machinability Steel becomes more difficult to weld without cracking Steel becomes heat treatable Nickel: Refines the structure Increases the strength, ductility and toughness of carbon steel Chromium: is a hardening agent (steel with 1% Cr is used for dies, stamps and ball races

is present in small amounts in all steels. Steels with 1.5%Mn is used for couplings and cage chains. Steels with 50% Mn is exceptionally tough and resistant to abrasion and is used for jaws of the crushers or V ends of the railway crossings Molybdenum: Increases the creep resitance of steel (high temperature applications such as superheater tubes) Tungsten: is another hardening agent (often accompanying Cr) Silicon: Steels have high magnetic permeability and therefore used in transformer cores Cobalt: Steels are excellent for permanent magnets

17 Car makers test, utilize multi-materials designs, but steel remains dominant:
Steel is the material of choice for car bodies: 99% passenger cars have a steel body•60-70% of the car weight consisting of steel or steel-based parts The automotive industry makes excursions in light materials applications but there is only a slight actual increase in the use of Al, Mg and plastics

18 TRENDS IN CAR BODY MATERIALS: materials objectives for vehicle functionality
Lightweighting: mass “containment” and mass “reduction” Low gas mileage Less greenhouse gas emissions Passenger Safety: Low peak deceleration, long crush length, long time duration of crash pulse High energy dissipation with minimum intrusion Higher impact strength for A and B Pillars Noise and Vibration Vehicle Handling Stiffness and Torsional Rigidity Fatigue Dent resistance Perforation and cosmetic corrosion resistance Surface quality, visual appearance









27 Q&P: Quenching and Partitioning of Austenite AHSS: Advanced HSS
Q&T: Quenching and Tempering

28 BAKE HARDENING Dislocations are introduced by press forming a steel sheet, and strength is increased by the action of work hardening in which accumulated dislocations prevent the movement of other dislocations. When an automobile body is being manufactured, painting and baking are carried out after assembly. These processes involve heating the steel body panels to about 443K (170). At this temperature, the carbon atoms dissolved in the steel diffuse by jumping between lattice points, which occurs 103 to 105 times a second, segregating in the regions around dislocations where the stresses are compressive. This results in locking of the dislocations which is called strain aging. This mechanism makes the steel panels harder after baking than after press forming, and is referred to as bake hardening. The utilization of this bake hardening phenomenon has made it possible to utilize steel sheet that has good formability during press forming and that can withstand severe working, while being hard and less prone to denting when assembled in the automobile body.






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