An alloy is a mixture of two or more elements that has metallic properties. A solid solution is formed when solute atoms are added to a host material (solvent) without changing the existing crystal structure. Hume-Rothery's rules state factors that influence solid solubility such as atomic radii difference of less than 15% and similar electronegativity. Phase diagrams graphically represent the phases present in a material system at different temperatures, pressures, and compositions.

1. ALLOY
• Alloy is a mixture of two or more elements
• In general, alloys have metallic properties
• An alloy can be formed by combination of
metal with another metal or metal with non-
metal.
• Alloy can have various phases at different
temperature and pressure.

2. SOLID SOLUTIONS
A solution can be defined as a homogeneous
mixture in which the atoms or molecules of one
substances are dispersed at random in to another
substance.
– Solute: A solute is the minor part of the solution or
the material which is dissolved.
– Solvent: Solvent constitutes the major portion of the
solution.
– A solid solution is formed when the solute atoms are
added to the host material (solvent), without
changing the existing crystal structure.

4. LATTICE
A regular geometrical arrangement of
points or objects over an area or in space.

7. HUME ROTHERY’S RULES
• The atomic radii of the solute and solvent
atoms must differ by no more than 15%
• The crystal structures of solute and solvent
must match.
• Maximum solubility occurs when the solvent
and solute have the same valence.
• The solute and solvent should have similar
electronegativity.

8. POSSIBILITIES OF SOLID SOLUTIONS
• Unsaturated Solid Solutions
• Saturated Solid Solutions
• Supersaturated Solid Solutions

9. TYPES OF SOLID SOLUTIONS
• Substitutional solid solutions
– Random
– Ordered
• Interstitial solid solutions

10. SUBSTITUTIONAL SOLID SOLUTIONS
• When the atoms of solute substitute for the
atoms of the solvent in its lattice, the solution
is known as Substitutional solid solution.
• The solute may incorporate in to the solvent
crystal lattice substitutionally by replacing a
solvent particle in the lattice.

11. RANDOM AND ORDERED SOLID
SOLUTION

12. INTERSTITIAL SOLID SOLUTIONS
Interstitial solid solutions are those in
which the solute atoms occupy the interstitial
positions (holes between the atoms in the
crystal lattice of the solute). Interstitial solid
solutions always have limited solubility of the
solute.

14. PHASE DIAGRAM
• Phase diagrams are graphical representations of
what phases are present in a materials system at
various temperatures, pressures and
compositions.
• Actually phase diagram is a map showing the
structures or phases present as the temperature
and overall composition of the material are
varied.
• It is also called as equilibrium diagrams or
constitutional diagrams.

15. WHY SHOULD PHASE DIAGRAM BE
STUDIED?
• What condition is the material in?
• Is the composition uniform through out? If
not, how much of each component is present?
• Is something present that may give undesired
properties?
• What will happen if temperature is increased
or decreased; pressure is changed; or
composition is varied?

16. INFORMATION FROM PHASE
DIAGRAM
• To show what phases re present at different
compositions and temperatures under
equilibrium conditions.
• To indicate the equilibrium solid solubility of
one element in another element.
• To indicate the temperature range over which
solidification of a material occurs.
• To indicate the temperature at which different
phases start to melt.