Metals and alloys

1. Constitution of alloys And Solid solutions
Prepared By
Dr.S.S.Saravanakumar, M.E., Ph.D,
Associate professor,
Department of Mechanical engineering,
Kamaraj college of engineering and technology,
Virudhunagar.

2. Alloy
An Alloy is a substance that has metallic properties and is composed of
two or more chemical elements , of which at least one is a metal
If the system is made up of two elements, it is called binary alloy
system; three elements, ternary alloy system; etc.
solid state there are three possible phases:
• Pure metal
• Compound or intermediate alloy phase and
• Solid solution

3. Pure metal
All metals show a definite melting or freezing point.
If a cooling curve is plotted for a pure metal, it will show a horizontal line
at the melting or freezing point as shown in above figure.

4. Compounds
In many binary alloy systems, when the chemical affinity of elements is
great, their mutual solubility becomes limited and compounds (also
called intermediate phases) are formed (rather than solid solutions)
When compound is formed, the elements loose their individual identity
and characteristic properties to a large extent. Water (H2O) is
composed of elements that are normally gases at room temperature,
yet the compound is liquid at room temperature. The compound will
have its own characteristic physical, mechanical and chemical
properties.

5. Solution
A solution is a homogeneous mixture composed of two or more
substances. In such a mixture, a solute is a substance dissolved in
another substance, known as a solvent. The solvent is a chemical
substance and can be in a solid, liquid or gaseous state. Thus solution
can exist in a gaseous, liquid or solid state.

6. Solid Solutions
The amount of solute that may be dissolved by the solvent is generally
a function of temperature (with pressure constant) and usually
increases with increasing temperature.

7. Substitutional solid solutions
some of the solvent(Cu) atoms are substituted by atoms of the solute
(alloying element)(Ni) atoms. Several factors are now known largely
through the work of Hume-Rothery that control the range of solubility
in the alloy system.

8. Hume-Rothery Rule for Substitutional solid
solutions
S.NO Factors Completed /Extended Solid
solubility
NIL/Limited Solid solubility
1 Crystal structure Same Different
2 Size Same/Variations ±10% >20%
3 Chemical Affinity less More
4 Valance Same/Different is less More differen

9. Interstitial Solid Solutions
These are formed when atoms of small atomic radii fit into the spaces or
interstices of the lattice structure of the larger solvent atoms as shown in
figure
Since the spaces of the lattice structure are restricted in size, only atoms
with radii less than one angstrom are likely to form interstitial solid solutions.
These are hydrogen, boron, carbon, nitrogen and oxygen.