CHAPTER 4 OUTLINE MAJOR CLASSES OF MATERIALS PART 1. Metals Ceramics Semi Conductors (Electronic Materials) Polymers Composites

Transcription

1 CHAPTER 4 MAJOR CLASSES OF MATERIALS PART 1 1 OUTLINE Metals Ceramics Semi Conductors (Electronic Materials) Polymers Composites 2 1

2 THE MATERIALS PENTAGRAM METALS SEMI CONDUCTORS CERAMICS NATURAL RESOURCES POLYMERS COMPOSITES 3 NATURAL RESOURCES ROCKS MINERALS FOSSIL FUELS 4 2

3 METALS - PROPERTIES Crystal structure: Atoms arranged in a regular repeating structure Relatively strong Dense Malleable and ductile: high plasticity Resistant to fracture: tough Excellent conductors of electricity and heat Opaque to visible light Shiny appearance 5 METAL ALLOYS Alloys are compounds consisting of more than one metal. Adding other metals can affect the density, strength, fracture toughness, plastic deformation, electrical conductivity and environmental degradation. Al-Fe = Iron will make it stronger. Cu-Sn = bronze, Cu-Zn = brass, Fe-C=steel, Fe-C-Cr = Stainless steel Pb-Sn = solder 6 3

4 METALS - APPLICATIONS Machine tools: hammers, screwdrivers, etc. Electrical wiring, Magnets, Catalysts Food processing and preservation: Microwave and conventional ovens and refrigerators and freezers. Structures: buildings, bridges, etc. Transportation: Cars, buses, trucks, trains, ships, and airplanes. Aerospace, Airplanes Shape memory materials Communications including satellites Computers and other electronic devices 7 METALS 8 4

5 METALS - PRODUCTION 9 METALS - PRODUCTION 10 5

6 METAL FABRICATION TECHNIQUES Forming Operations Forging Rolling Extrusion Drawing Casting Sand Die Investment Continuous Joining Powder metallurgy Welding 11 FORMING OPERATIONS Forging Deforming a single piece of a hot metal. Ex. Automotive crankshafts, piston connecting rods. 12 6

7 FORMING OPERATIONS Rolling: Passing a piece of metal between two rolls. Ex. Metal sheets, strips, foils. 13 FORMING OPERATIONS Extrusion: Forcing a bar of a metal through a die to reduce the cross-sectional area. Ex: Rods, tubing products. 14 7

8 FORMING OPERATIONS Drawing: Pulling of a metal piece through a die. Ex: Rods, wires, tubing products. 15 CASTING Molten metal is poured into a mold cavity. Casting techniques are used when: the finished shape is so large or complicated, an alloy is low in ductility, casting is the most economical compared to other fabrication techniques Ex: Automotive cylinder blocks, turbine blades 16 8

9 CASTING Metal Molds 17 JOINING Powder Metallurgy (Powder Processing) For metals having high melting temperatures or having low ductility, powdered metal is compacted and then heat treated to produce a denser piece. Ex: gears, knife blades etc. 18 9

10 JOINING Welding Two or more metal parts are joined to form a single piece when one-part fabrication is expensive and inconvenient. Welding railways 19 CLASSIFICATION OF METAL ALLOYS 20 10

11 FERROUS ALLOYS Iron is the main constituent in the alloy. They are important as building materials. Iron is the 4 th most abundant element (5%) of the earth s crust. Production of metallic iron and steel alloys is relatively economical. Ferrous alloys have a lot of important mechanical and physical properties. The main disadvantage: corrosion 21 FERROUS ALLOYS Steels: Iron carbon alloys. Global steel making in 2004 is now 1.01 billion (1.01x10 9 ) tones Mechanical properties are dependent on the content of carbon. Stainless steel 17 % Cr, 12 % Ni, 2.5 % Mo, 2 % Mn, 0.03 % C Stainless steel used in building can be used up to 1000 o C Density is about 7.9 g/cm

12 FERROUS ALLOYS Cast Irons Ferrous alloys with high carbon content, C% and other alloying elements 23 FERROUS ALLOYS Corrosion: Corrosion is the destructive attack of a metal by electrochemical reaction with its environment. Corrosion occurs between metal surface and the environment. Corrosion is often the life-limiting degradation process in engineering alloys Impact on Economy: $256 billion in US each yr

13 NON - FERROUS ALLOYS Copper Alloys Brass: Cu + Zn, Automotive radiators, coins, jewelry Bronze: Cu + Sn /Al/Si/Ni Good corrosion resistance Good tensile properties Piston rings, steam fittings, gears NASA All Copper Compliant Tube Regen Chamber Electroformed using new High Strength Materials 25 Carbon Steels Type of steel Low carbon (mild steel) Medium carbon High carbon (carbon tool steel) Percentage of carbon Properties Uses Easily cold worked Car bodies Wear resistant Rails and rail products: couplings, crank shafts, axles, gears, forgings Strong and wear resistant Cutting tools Railway lines Cast iron Easy to cast but brittle Pistons and cylinders 26 13

14 Stainless Steel Alloys Alloying element Properties given Uses to steel Cobalt High magnetic Magnets permeability Manganese Strong and hard Heavy duty railway crossings. Molybdenum Maintains high High speed drill tips strength at high temperature Nickel and chromium Resists corrosion Surgical instruments Titanium Tungsten Increased hardness and tensile strength High melting temperature, tough Vanadium Strong, hard Tools High speed tool steels, permanent magnets Cutting and drilling tools 27 NON - FERROUS ALLOYS Aluminum Alloys Principle alloying elements: Cu, Mg, Si, Mn, Zn Relatively low density: 2.7 g/cm 3 High electrical & thermal conductivity Resistant to corrosion Highly ductile Limitation: Low melting point of 660 o C. Fuel tanks, piping, light reflectors, window frames, aircraft parts 28 14

15 NON - FERROUS ALLOYS Magnesium Alloys Magnesium alloys are the lightest alloys used as structural metals. they have some advantages concerning to specific strength, specific elastic modulus and so on. applied to the structural materials for vehicles and electric equipments Major alloying elements: Al, Zn, Mn A very low density: 1.7 g / cm 3, therefore used as aircraft component They have replaced engineering plastics with higher densities Automobile seat frames, cellular phones, laptop computers Polymer coated magnesium alloy prototype (Housing of a cellular phone) 29 NON - FERROUS ALLOYS Titanium Alloys Major alloying elements: Al, Sn, V, Cu Extremely strong, highly ductile Corrosion resistant Limitation: Reactive at high temperatures. Space vehicles, airplane structures, petroleum & chemical industries 30 15

16 NON - FERROUS ALLOYS The Refractory Metals Tungsten (W), Tantalum (Ta), Molybdenum (Mo) Melting temperature range: o C Corrosion, heat resistant material making 31 FUTURE TRENDS Lightweight aluminum alloys: in automobiles to increase fuel efficiency. Heat resistant super-alloys: engines can operate at higher temperatures. Ceramic coatings: to protect metals from outside effects. Radiation-resistant alloys: allow nuclear power plants to operate longer Steel will continue to be the most commonly used metal Half of all aluminum, copper, and steels are being recycled