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Fundamental classification of Engineering materials-Short notes series for Mechanical Engineers

In this article, we will introduce the most fundamental topic in Material Science - Classification of Engineering Materials, which is the building block to take on advanced topics in the subject and is useful for candidates preparing for GATE and other engineering exams, like SSC JE, UPSC Engineering services etc.

All materials that are avaliable around us cannot be used for engineering purposes. The material being used should meet the service requirements in the engineering application, which means the material should be able to perform the function that it is expected to perform. 

How to select the materials?

As told above, all the engineering materials must meet the service requirements, so this calls for highly careful selection of materials. In addition to meeting the service requirements, the materials chosen must also be economical, easily available and environment friendly. Take a look at the list of factors on which the selection of materials will depend:

  • Stresses to which the workpiece/ component will be subjected to.
  • Corrosion resistance.
  • Temperature and wear and tear resistance.
  • Flexibility and rigidity.
  • How easy it is use the material for the intended manufacturing process.
  • Cost effectiveness for the product development.
  • Availability of the material.

Classfication of engineering materials.

Broadly, the engineering materials can be classified into:

  • Metals
  • Non metals
  • Materials made from combinations

Metals:

  • Metals can be used in applications where the permanent change of shape is needed, as metals are capable of changing their shape permanently.
  • They are good conductors of heat and electricity.
  • They are also good electrical conductors, as the number of valence electrons are high which help in the creation of the metallic bond.

Metals can be further divided into two types:

  1. Ferrous metals
  2. Non-ferrous metals

Ferrous metals:

  • Ferrous metals mainly consist of iron (Fe) and carbon (C) as their main constituents.
  • The behaviour and the property of the ferrous metals depend upon the percentage and the form of C present in them.
  • Popularly used ferrous metals are steel, cast iron (CI) and wrought iron.

Non ferrous metals:

  • These are metals, which do not contain the iron and carbon in them. 
  • Some examples of non ferrous metals are Aluminium (Al), Copper (Cu), Zinc (Zn), Nickel (Ni), Chromium (Cr) etc.
  • Among the non-ferrous metals, Aluminium and Copper are the electrical conductors.
  • Chromium is used as a corrosion resistant non ferrous metals.

Non metals:

  • In comparison to metals, which exist naturally, the non metals do not exist naturally, but are manufactured artificially.
  • The non metals are further classified in two categories:
  1. Ceramics
  2. Organic polymers

Ceramics:

  • Ceramics can either be metallic or non metallic oxides.
  • Rocks, fireclay and firebricks, cement etc are some of the commonly used ceramics.
  • The ceramics are physically separable and chemically homogeneous constituents of materials of different phases.

Organic polymers:

  • The organic polymers are mainly derived from hydrocarbons.
  • These materials consist of covalent bonds formed by carbon combined chemically with oxygen and hydrogen.
  • Polymerization helps create polymers from monomers.
  • These materials are light in weight and inert and possess high plasticity.
  • Some commonly used organic polymers are bakelite, polyethylene, nylon, teflon etc.

Materials due to combinations: 

These kind of materials are divided into two categories:

  1. Alloys
  2. Composites

Alloys: 

  • Two or more than two metals combine to form an alloy.
  • Alloys have properties which are different from their constituent materials. 
  • Depending on the type of constituent materials, the alloys can be ferrous or non ferrous.
  • Stainless steel (SS), high speed steel (HSS), brass, babbits etc. are some commonly used alloys.

Composites:

  • Composites can classified as organic or inorganic.
  • These materials consist of two or more than two constituents with dissimilar properties. 
  • The combinations used to make composites are: (1) Metals or ceramics, (2) Metals or polymers and (3) Ceramics or polymers.

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