M6

• Classifications of materialsbased on chemical make-up and atomic structure.


  • Metals
  • Ceramics
  • Polymers
• Most materials fall into one distinct group or another, with some intermediates
• Special classifications

  • Composites
  • Biomaterials
  • Semiconductors
• Metals


  Metallic elements, contains large numbers of non-localized (free) electrons, good conductors of electricity and heat, opaque, generally reflective (when polished), strong yet deformable

  
• Metals

  • Copper - Electrical conductor wire - Good electrical conductivity and formability
  • Alloy steel - Tools - High impact resistance
• Metal alloy classes

  • Ferrous alloys - iron is the principal constituent, include steels and cast irons.
  • Nonferrous alloys - alloys that are not iron based.

  
• Ferrous alloys

  • Produced in larger quantities than any other metal type
  • Iron containing compounds exist in abundant quantities within earth crust
  • Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques
  • Extremely versatile, may be tailored to have a wide range of mechanical and physical properties
  • Susceptible to corrosio

  
• Ferrous alloy classification

  • Steels
  • Cast irons
• Steels

  • Iron–carbon alloys that may contain appreciable concentrations of other alloying elements
  • mechanical properties are sensitive to the content of carbon (normally less than 1 wt%)
  • Some are classified according to carbon concentration (low, medium, and high).

  
• Plain carbon steels

  Contain only residual concentrations of impurities other than carbon and a little manganese
• Alloy steels

  More alloying elements are intentionally added in specific concentrations
• Low carbon steels

  • most produced steel , least expensive to produce
  • Generally contain less than about 0.25 wt% C,
  • unresponsive to heat treatments intended to form martensite
  • strengthening is accomplished by cold work
  • relatively soft and weak but have outstanding ductility and toughness
  • machinable and weldable
• Low carbon steel applications

  • Automobile body components
  • Structural shapes (I-beams, channel and angle iron)
  • Sheets used in pipelines, buildings, bridges and tin cans
• Plain low carbon steels


  Typically have Yield strength of 275 Mpa, tensile strength between 415 and 550 Mpa, and ductility of 25% EL
• High-strength, low-alloy (HSLA) steels

  Contain other alloying elements such as copper, vanadium, nickel, and molybdenum in combined concentrations as high as 10 wt%, possess higher strengths than the plain low-carbon steels, more resistant to corrosion

  
• Medium carbon steels

  Have carbon concentrations between about 0.25 and 0.60 wt%, applications include railway wheels and tracks, gears, crankshafts, and other machine parts and high-strength structural components calling for a combination of high strength, wear resistance, and toughness
• Plain medium-carbon steels

  Have low hardenabilities and can be successfully heat treated only in very thin sections and with very rapid quenching rates
• Heat treated medium-carbon steels

  Additions of chromium, nickel, and molybdenum improve the capacity of Plain medium–carbon steels to be heat treated giving rise to a variety of strength–ductility combinations, stronger than the low-carbon steels, but at a sacrifice of ductility and toughness
• High carbon steels

  Normally having carbon contents between 0.60 and 1.4 wt%, are the hardest, strongest, and yet least ductile of the carbon steels, almost always used in a hardened and tempered condition and, as such, are especially wear resistant and capable of holding a sharp cutting edge
• High carbon steel applications

  • Cutting tools and dies for forming and shaping materials, knives, razors, hacksaw blades, springs, high-strength wire
• Stainless steels

  Highly resistant to corrosion (rusting) in a variety of environments, their predominant alloying element is chromium; a concentration of at least 11 wt% Cr is required, corrosion resistance may also be enhanced by nickel and molybdenum additions

  
• Stainless steel classes

  • Martensitic
  • Ferritic
  • Austenitic
• Martensitic stainless steels

  Capable of being heat treated in such a way that martensite is the prime microconstituent, magnetic
• Ferritic stainless steels

  Magnetic, hardened and strengthened by cold work
• Austenitic stainless steels


  Most corrosion resistant because of the high chromium contents and also the nickel additions, produced in the largest quantities, hardened and strengthened by cold work

  
• Cast irons

  With carbon contents above 2.14 wt%, most contain between 3.0 and 4.5 wt% C and, in addition, other alloying elements, the most common cast iron types are gray, nodular, white, malleable, and compacted graphite

  
• Gray iron

  The carbon and silicon contents vary between 2.5 and 4.0 wt% and 1.0 and 3.0 wt% respectively, mechanically weak and brittle in tension, very effective in damping vibrational energy, high resistance to wear, among the least expensive of all metallic materials

  
• Gray iron applications

  • Base structures for machines and heavy equipment that are exposed to vibrations
• Ductile (or Nodular) iron


  Adding a small amount of magnesium and/or cerium to the gray iron before casting produces a distinctly different microstructure and set of mechanical properties, has mechanical characteristics approaching those of steel

  
• Ductile iron applications


  • Valves, pump bodies, crankshafts, gears, and other automotive and machine components
• White iron

  • A low-silicon cast iron (containing less than 1.0 wt% Si), extremely hard but also very brittle, to the point of being virtually unmachinable
  • White Iron is used as an intermediary in the production of yet another cast iron, malleable iron.
  • White Iron use is limited to applications that necessitate a very hard and wear-resistant surface, without a high degree of ductility—for example, as rollers in rolling mills
• Malleable iron

  Relatively high strength and appreciable ductility or malleability
• Malleable iron applications

  • Connecting rods, transmission gears, and differential cases for the automotive industry, flanges, pipe fittings, and valve parts for railroad, marine, and other heavy-duty services
• Compacted Graphite Iron (CGI)

  Carbon exists as graphite, which formation is promoted by the presence of silicon, silicon content ranges between 1.7 and 3.0 wt%, carbon concentration is normally between 3.1 and 4.0 wt%, higher thermal conductivity, better resistance to thermal shock, lower oxidation at elevated temperatures

  
• CGI applications


  • Diesel engine blocks, exhaust manifolds, gearbox housings, brake discs for high-speed trains, and flywheels
• Copper and its alloys

  The mechanical and corrosion-resistance properties of copper may be improved by alloying
• Aluminum and its alloys

  Characterized by a relatively low density, high electrical and thermal conductivities, and a resistance to corrosion in some common environments, including the ambient atmosphere
• Magnesium and its alloys

  Perhaps the most outstanding characteristic is its density, 1.7 g/cm3, which is the lowest of all the structural metals, used where light weight is an important consideration
• Titanium and its alloys

  Extremely strong, room temperature tensile strengths as high as 1400 MPa (200,000 psi) are attainable, yielding remarkable specific strengths
• Refractory metals

  Metals that have extremely high melting temperatures