Engineering Materials

Classification of Engineering Materials

Basic Classification of Engineering Materials

Basically Engineering Materials Can be classified into two categories-

1. Metals
2. Non-Metals

Metals

Metals are polycrystalline bodies which are having number of differentially oriented fine crystals. Normally major metals are in solid states at normal temperature. However, some metals such as mercury are also in liquid state at normal temperature. All metals are having high thermal & electrical conductivity. All metals are having positive temperature coefficient of resistance. Means resistance of metals increase with increase of temperature. Examples of metals – Silver, Copper, Gold, Aluminum, Iron, Zinc, Lead, Tin etc. Metals can be further divided into two groups-

1. Ferrous Metals – All ferrous metals are having iron as common element. All ferrous materials are having very high permeability which makes these materials suitable for construction of core of electrical machines. Examples: Cast Iron, Wrought Iron, Steel, Silicon Steel, High Speed Steel, Spring Steel etc.
2. Non-Ferrous Metals- All non-ferrous metals are having very low permeability. Example: Silver, Copper, Gold, Aluminum etc.

Non-Metals

Non-Metal materials are non-crystalline in nature. These exists in amorphic or mesomorphic forms. These are in both solid & gases forms at normal temperature. Normally all non-metals are bad conductor of heat & electricity. Examples: Plastics, Rubber, Leathers, Asbestos etc. As these non-metals are having very high resistivity which makes them suitable for insulation purpose in electrical machines.

Difference between Metals and Non Metals

Sl. No.	Property	Metals	Non-Metals
1.	Structure	All metals are having crystalline structure	All Non-metals are having amorphic & mesomorphic structure
2.	State	Generally metals are slid normal temperature	State varies material to material. Some are gas state and some are in solid state at normal temperature.
3.	Valance electrons & conductivity	Valance electrons are free to move with in metals which makes them good conductor of heat & electricity	Valence electrons are tightly bound with nucleus which are not free to move. This makes them bad conductor of heat & electricity
4.	Density	High density	Low density
5.	Strength	High strength	Low strength
6.	Hardness	Generally hard	Hardness is generally varies
7.	Malleability	Malleable	Non malleable
8.	Ductility	Ductile	Non ductile
9.	Brittleness	Generally non brittle in nature	Brittleness varies material to material
10.	Lustre	Metals possess metallic lustre	Generally do not possess metallic lustre (Except graphite & iodine)

Other classification of engineering materials:

Engineering materials can also be classified as below-

1. Metals & Alloys
2. Ceramic Materials
3. Organic Materials

Metals & Alloys:

Metals are polycrystalline bodies which are have number of differentially oriented fine crystals. Normally major metals are in solid states at normal temperature. However, some metals such as mercury are also in liquid state at normal temperature. Pure metals are having very low mechanical strength, which sometimes does not match with the mechanical strength required for certain applications. To overcome this draw back alloys are used. Alloys are the composition of two or more metals or metal & non-metals together. Alloys are having good mechanical strength, low temperature coefficient of resistance. Example: Steels, Brass, Bronze, Gunmetal, Invar. Super Alloys etc.

Ceramic Materials:

Ceramic materials are non-metallic solids. These are made of inorganic compounds such as Oxides, Nitrides, Silicides and Carbides. Ceramic materials possess exceptional Structural, Electrical, Magnetic, Chemical & Thermal properties. These ceramic materials are now extensively used in different engineering fields. Examples: Silica, glass, cement, concrete, garnet, Mgo, Cds, Zno, SiC etc.

Organic Materials:

All organic material are having carbon as a common element. In organic materials carbon is chemically combined with oxygen, hydrogen & other non-metallic substances. Generally organic materials are having complex chemical bonding. Example: Plastics, PVC, Synthetic Rubbers etc.