Classification of Engineering Materials

Generally, engineering materials are classified in four types viz. Metals and alloys, Ceramics and glasses, polymers, and composites. Let's have a look at them.
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Classification of Engineering Materials

1. Metals and Alloys : Inorganic materials composed of one or more metallic elements.
  • They usually have crystalline structure and are good thermal and electrical conductors.
  • They maintain their good strength at high and low temperatures.
  • Many metals have high elastic strength and high elastic module.
  • They are least resistant to corrosion.
  • They have sufficient ductility.
  • One more important characteristic, they can be strengthened by alloying and heat treatment.
2. Ceramics and Glasses : Inorganic materials consisting of both metallic and non-metallic materials bonded together chemically.
  • They can be crystalline (ceramics), non-crystalline (glasses) or mixture of both (glasses and ceramics).
  • They have high hardness, high moduli and high temperature strength.
  • Since they are brittle, they cannot be used as good as metals.
  • Generally, they have high melting point and high chemical stability.
  • Ceramics are generally poor conductors of electricity.
  • Ceramics have high strength on compression.
3. Polymers : Organic materials which consist of long molecular chains or networks containing carbon.
  • They generally have low densities and low rigidity.
  • Their mechanical properties may vary considerably.
  • Most polymers are non-crystalline but some consist of mixture of both crystalline and non-crystalline regions.
  • Most of them are corrosion resistant, but they cannot be used at high temperatures.
  • Most of them are poor conductors of electricity due to the nature of atomic bonding.
  • They generally have good strength to weight ratio.
4. Composites : Materials where two or more of the above materials are brought together on macroscopic level.
  • They are designed to combine the best properties of each of its components.
  • Usually they consist of a matrix and a reinforcement.
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