MATERIAL SCIENCE AND MATERIAL PROPERTIES


MATERIALS

Classification of materials 


Metals--All metals have crystalline structure.
Non metals--These are amorphous or measomorphic. 


OTHER CLASSIFICATION OF NONMETALS 
  • Ceramics 
  • polymers (plastics)
In engineering the important classification includes
Metals
Polymers 
Ceramics

 "Molecular and atomic forces are responsible for deciding property of material". Intermolecular distance determines the mechanical property. 

Molecular forces in decreasing order of magnitude 


1) COULOMB FORCE
2) IONIC FORCE
3) COVALENT FORCE
4) VANDERWAAL'S FORCE
 
Coulomb force is the strongest and vanderwaal is the weakest.

 METALS

Characteristics of metals:-

  • High density 
  • High binding energy 
  • Reusable 
  • Good thermal conduction 
  • High electrical conductivity 
  • Good strength 
Demerits:- 
  • heavy in weight (large density). 
  • effect of corrosion is large. 

POLYMERS


Characteristics of polymers:-

  • Contains carbon,hydrogen and oxygen 
  • Less binding energy 
  • Low strength 
  • Covalent force is present in bond 
  • Less weight due to low density 
  • Tough and ductile in nature Demerit:- 
  • It emits carbon monoxide on heating(co) 
  • Strength decreases at high temperature.

 CERAMIC MATERIAL

Characteristics of ceramic material:-

  • It is in powder form.
  • Bonding is by ionic or covalent force. 
  • Partial electrical conductivity. 
  • low thermal conductivity. 
  • Can't be reused. 


STEEL (BRIEF DISCRIPTION)
It is iron-carbon alloy in which the percentage of carbon is below 1.54% is called steel.
Carbon in the steel is in combined form of ferric carbide (Fe3C).
When the percentage of carbon in steel is in between 0.03%--1.5%, it is called plain carbon steel.
Mechanical properties mostly depends on the percentage of carbon, though small quantity of other elements are present.

Steel categorized on the basis of carbon percentage

MILD STEEL--------->0.03--0.4%
MEDIUM CARBON STEEL--->0.4--0.84%
HIGH CARBON STEEL--->0.84--1.5% 

Constituents of steel


SILICON------------->0.5%
MANGANESE------->1.5%
PHOSPHOROUS---->0.2%
SULPHUR----------->1.2%

Steel classification

1) Alloy steels
2) Stainless steel

  • Ferritic steel 
  • Austenitic steel 
  • Martensitic steels 

3) Spring steels

  • Chrom vanadium steel 
  • Silicon-manganese steel 
  • High carbon steel 

4) High speed steels

  • Tungsten based(18-4-1 HSS) 
  • Cobalt based HSS. 


METAL--BRIEF DESCRIPTION


These are the materials which give up electron and forms metallic bond, hence conducts electricity.
Iron,aluminium, copper are some the examples.

Classification of metals:-

Ferrous metals--Consists iron as the main constituent.
Non ferrous metal--Iron is not the major constituent.

1) Ferrous metal --These are generally in form of:

  • Cast iron 
  • Wrought iron 
  • Steels 

CAST IRON

Since pig iron is not of much importance, when it is remelted we obtain cast iron.
Remelting is done to dilute impurities and reduce carbon content.
carbon range in cast iron is---1.5%-4%.

Other constituent of cast iron are

PHOSPHOROUS---1% (Maximum).It adds fusibility and fluidity.
SILICON---4%(Maximum).It decomposes Fe3C to C with which grayness increases.
SULPHUR--3.1%(Maximum) helps in hardness and brittleness.
MANGANESE---0.75%(Maximum) used for hardening and white texture.

Classification of cast iron:-

  • Grey cast iron 
  • White cast iron 
  • Malleable cast iron 
  • Nodular cast iron 

GREY CAST IRON
Alloy of carbon, iron, silicon
carbon--------->3% to 3.6%
silicon---------->1.5% to 2.7%
manganese----->0.4% to 1%
phosphorous---->0.15% to 1%
manganese----->0.4% to 1%

rest is iron. 


  • It has grey colour because of graphite in free form.
  • Graphite acts as lubricating agent,hence it is highly machinable. 
  • Good compressive strength.
  • Poor ductility.
  • Low tensile strength.
USES
Machine tool bodies, agricultural equipment and their parts.


WHITE CAST IRON
Specification 

Carbon------->1.75% to 2.3%
Silicon-------->0.8% to 1.1%
Magnisium---->up to 0.4%
Phosphorous-->up to 0.2%
Sulphur-------->up to 0.1%

rest is iron..... 

CHARACTERISTICS
  • White in colour. 
  • High tensile strength. 
  • Not good machinability. 
  • Grinding is done to shape the white cast iron. 
  • Has high resistance to wear . 



MATERIAL PROPERTIES



The behavior of material under various load condition is important aspect for engineering.

The various classification of properties are

  • mechanical properties
  • magnetic properties
  • chemical properties
  • thermal properties
  • physical properties
  • electrical properties
Mechanical properties widely depends on the bond of molecule and structural arrangement. They widely respond to load applied. The important mechanical properties are

  • Elasticity
  • Plasticity
  • Toughness
  • Ductility
  • Malleability
  • Hardness
  • Brittleness
  • Creep
  • Strength

ELASTICITY


  • Under elasticity the material deforms under load and regains the original shape when load is removed.
  • Load is externally applied ,this give rise to stress and strain.
  • Hence elastic material fallow hook's law i.e. stress is directly proportional to strain.

PLASTICITY


  • Under this situation material deforms permanently on application of load.
  • This deformation cannot be recovered.
  • After attaining particular value material starts. yielding without any further increase in stress.

TOUGHNESS


  • It is the property of material by virtue of which it absorbs energy during plastic deformation.
  • Energy stored per unit volume is called modulus of toughness.

DUCTILITY

  • Ability of material to be drawn into wire is called ductility.
  • It is committed by pulling force.
  • It is measured in terms of
1)percentage of area reduced
2)percentage in elongation occurred.

MALLEABILITY

  • Ability of material to be drawn into thin sheet is called malleability.
  • Deformation is permanent in all directions
  • for malleability, ductility is important.

HARDNESS

  • Resistance to indentation ( even scratch)
  • It helps to protect those material who are under friction or rubbing.
  • Test for measuring hardness are:-
             1)Brinell's test
             2)Rockwell test
             3)Vicker's test

CREEP

  • Progressive or successive deformation of a material under load.
  • It is time functional.
  • Creep is more vulnerable at high temperature.
  • Measurement of creep is done in terms of plastic deformation.
  • Ionic and covalent structures are also affected by creep.
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