metallurgy

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candrew66
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139967
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metallurgy
Updated:
2012-03-08 02:31:05
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materials
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Aeronautical materials
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  1. definition of metallurgy
    a society's ability to develope and use materials is a measure of its technological sopistication and it's technological future
  2. definition of stress
    the force per unit area acting on a part or structure that attempts to change its dimensions
  3. definition of strain
    the measurable or visible result of stress/load applied to a structure. strain is measured by any dimensional change to a part or structure as a result of a load. expressed as a ratio new dimension/original dimension
  4. definition of plastic deformation
    a permanent change in the shape of a material due to the application of distorting forces
  5. different types of forces or stresses
    • tensile
    • compressive
    • shear
    • bending or torsion
  6. definition of tensile
    the capacity of a material to be stretched
  7. definition of compressive
    the capacity of a material to be crushed
  8. definition of shear
    the capacity of a material to pull apart in a planear surface
  9. definition of bending
    the capacity of a material to undergo compression, tension and shear forces simultaneously
  10. definition of torsion
    the capacity of being twisted
  11. 8 common mechanical properties
    • hardness
    • brittleness
    • toughness
    • strength
    • elasticity
    • ductility
    • malleability
    • creep
  12. definition of hardness
    the ability of resistance to surface deformation by penetration, scratching or abrasion
  13. definition of brittleness
    the ability to fracture without visible plastic deformation
  14. definition of toughness
    the ability to withstand sudden impact without failure
  15. definition of strength
    the ability to resist forces
  16. definition of elasticity
    the ability to return to original shape after deformation forces that are less than the plastic limit are removed
  17. definition of ductility
    the ability to under go plastic deformation without fracture as a result of tensile forces
  18. definition of malleability
    the ability to undergo plastic deformation without fracture as a result of compressive forces
  19. definition of creep
    the ability to plastically deform over a long period of time by forces less than the elastic limit when exposed to heat
  20. methods of testing for hardness
    • rockwell
    • brinell
    • vickers
  21. explain Moh's test
    is used to compare the hardness of a material where the ability of one material to scratch another material is a relative measure of a material's hardness
  22. how can you test for toughness
    • izod impact test
    • charpy impact test
  23. charpy or izod impact test are a measure for what
    • brittleness
    • toughness
  24. tensometer is a test for what
    • strength
    • elasticity
    • ductility
  25. basic methods of shaping metals
    • hot forming
    • cold formimg
    • casting
    • explosive forming
    • powder metallurgy
    • machining
  26. 4 hot forming techniques
    • forging
    • hot pressing
    • hot rolling
    • extruding
  27. explain forging
    is the plastic working of metal by means of compressive forces
  28. advantages of hot forging
    the creation of residual grain flow makes the piece stronger and tougher
  29. explain hot pressing
    a forging process using steady pressure of a large press instead of repeated hammer blows
  30. advantages of hot pressing
    the component can be made in 1 pressing and as a result is dimensionally more accurate. car bodies made this way
  31. explain hot rolling
    process of passing metal through pairs of rollers to reduce thickness
  32. advantages of hot rolling
    allows a quick reduction in thickness but at the expense of accuracy and surface finish
  33. explain extruding
    involves pushing a solid hot block of metal through a die to produce desired shape
  34. advantages of extruding
    possible to produce very complex shapes with little or no waste
  35. cold forming techniques
    • squeezing
    • bending
    • shearing
    • drawing
  36. advantages of cold forming
    • no heating needed
    • better surface finish
    • dimensional accuracy is greater
    • improved strength
    • directional properties can be given to component
  37. disadvantages of cold forming
    • higher forces are needed
    • heavier and morep powerful machinery is required
    • ductility of metal is less because it is cold
    • metal surface must be clean and scale free
    • strain or work hardening occurs and annealing (heating to soften) may be required before further shaping
    • directional properties given may be detrimental
    • undesirable residual stresses may be produced
  38. explain squeezing
    includes rolling, cold forging, extrusion, riverting
  39. explain bending
    includes angle bending, roll bending, roll forming, seaming, straightening
  40. explain shearing
    includes blanking piercing, notching, nibbling shaving trimming and cutoff
  41. explain drawing
    includes bar and tube drawing, wire drawing, spinning, embosing,explosive forming, stretch forming
  42. explain casting
    all casting involves the pouring of molten metal into a mould or die
  43. 5 major casting processes
    • sand casting
    • shell mould casting
    • die casting
    • centrifugal casting
    • investment casting
  44. explain sand casting
    uses sand as the mould material. sand adhering to the casting has to be removed of fettled
  45. pros and cons of sand casting
    • cheap process
    • further machining required
  46. explain shell mould casting
    variation on sand casting where the sand is mixed with a resin that is heated to cure it
  47. pros and cons of shell mould casting
    • shells are not reusable
    • finished product has a better finish than sand casting
  48. explain die casting
    molten metal is forced into a die under pressurse
  49. pros and cons of die casting
    fine sections and excellent detail can be achieved
  50. explain investment casting
    a wax pattern is made for each casting. the wax is coated in refactory material that sets hard, usually by baking. the heat from this melts the wax thus creating the mould for the casting. the metal is poured in and allowed to cool and solidify and then the mould is broken to extract the cast item
  51. explain powder metallurgy
    fine powder is pressed into shape in a die at high pressure. the compacted powder is heated at a temperature below the melting point of the major constituent, known as sintering
  52. basic steps of powder metallurgy
    • mixing and preparing the powder
    • pressing the powder into the desired shape
    • sintering the shape at an elevated temperature
  53. advantages of powder metallurgy
    • no waste
    • no machining needed
    • only semi skilled labour needed
    • unique properties can be obtained
    • unique alloys can be created
    • high production rates
    • high degree of unformity
    • complex shapes can be produced
  54. disadvantages of powder metallurgy
    • inferior strength properties
    • high cost of producing dies
    • high cost of materials - offset by lack of waste
    • design limitations
  55. explain explosive forming
    sheet metal is placed in a die with an explosive charge which when detonated forces the metal sheet into the shape of the die
  56. explain machining
    is the removal of unwanted pieces of metal in the form of chips
  57. disadvantages of machining
    • inefficient process
    • may produce undesirable side effects
    • wasteful of material
  58. name 3 other cutting methods
    • laser cutting
    • plasma
    • chemical etching
  59. what is a ferrous metal
    one where the major constituent is iron example cast iron, wrought iron, plain carbon steels
  60. what is a non ferrous metal
    one where the major constituent is not iron example aluminium, sliver copper bronze
  61. what is the percentage carbon in plain carbon steels
    • low carbon up to 0.25%
    • medium carbon 0.25% to 0.55%
    • high carbon 0.55% to 1.5%
    • cast iron 1.5% to 5%
  62. give a list and examples of steel and uses
    • mild steel - lightly stressed parts
    • structural steel - used for building and bridges
    • casting steel - medium strenght good machinability. casting
    • construction steel - axles crankshafts gears
    • tool steel- drills files knives
    • cast iron - piston rings
  63. what is critical temperature
    the temperature at which the internal structure of a metal takes on a particular crystalline form
  64. when steel is above the upper critical temperature it is called
    austenite
  65. steel when quenched from above upper critical temperature is called
    martensite
  66. qualities of martensite are
    very hard and brittle is not tough enough for engineering applications
  67. upper critical temperature is also known as
    the transformation temperature
  68. 2 main factors determining the outcome of the heat treatment process are
    • the temperature to which the steel is heated
    • the rate of cooling
  69. 3 types of heat treatment processes
    • annealing
    • hardening
    • tempering
  70. describe full annealing
    steel is heated to just above transfomation temperature and held there for a time. the cooling rate is controlled either in a furnace or for non critical parts by putting the steel in an inert material such as lime or ashes
  71. advantages of full annealing
    refines the grain structure and improves cold working propertiesas steel is more ductile and more malleable
  72. describe normalising
    steel is heated to just above the transformation temperature and held there for a time the cooling rate is not controlled in that it takes place in still air
  73. advantages of normalising
    used to refine grains in preparation for the hardening process
  74. describe the hardening process
    the hardness of the steel is controlled by the rate of cooling through the critical range, and this is determined by the quenching liquid used
  75. what is the result of hardening
    this very rapid cooling results in a very hard and brittle material called martensite
  76. describe tempering process
    the steel is heated to well below the lower critical temperature and then cooled. the cooling is not critical but is normally done in cool still air
  77. steel hard on the outside but tough on the inside is called
    surface hardening
  78. 6 methods to achieve surface hardening
    • carburising
    • cyanide hardening
    • nitriding
    • flame hardening
    • superficial hardening
    • induction hardening
  79. advantages of surface hardening
    would be used where we need the steel to be resistant to wear at the surface but tough enough to withstand sudden shock loads in normal operation
  80. briefly explain carburising
    steel packed in a sealed box with carburising compound rich in carbon, heated then cooled carbon is added to the surface needs to be harden and tempered
  81. briefly explain cyanide hardening
    steel heated in sodium cyanide bath, may be quenched further heat treatment may be applied if needed. iron nitrides formed at the surface and some carbon absorded
  82. explain nitriding
    heated in ammonia rich atmosphere. nitrogen absorbed forming hard wearing nitrides. low temperature so no quenching needed no carbon added
  83. explain flame hardening
    heated to just above UCT with oxy-acetylene flame then quenched, hardening superficial creates martensite on the surface no carbon added
  84. explain superficial hardening
    steel coated with cyanide paste then heated and quenched
  85. advantages of alloy steels
    enhances a materials properties by adding additional elements as well as carbon
  86. examples of heavy and light non ferrous alloys
    • light aluminium magnesium
    • heavy titanium copper nickel lead
  87. advantages of aluminium
    • resistant to corrosion
    • light
    • ductile
    • good strenght to weight ratio
    • good conductor of electricity and heat
  88. how does aluminium resist corrosion
    due to a presence of a stable oxide film at the surface
  89. disadvantages of aluminium
    • soft
    • weak
    • low melting point

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