This document provides an overview of phase diagrams and their components. It discusses that a phase diagram shows the phases that are present at equilibrium under different temperature and composition conditions. It outlines the key components of phase diagrams, including phase boundaries, triple points, solidus and liquidus lines. It also describes the different types of phase diagrams - unary, binary, and ternary - as well as common binary phase diagrams like eutectic, peritectic, and solid solution types. The document emphasizes that phase diagrams are important for understanding phase transformations and determining properties of materials at different temperatures and compositions.

1. PHASE DIAGRAMS
Prof. H. K. Khaira
Professor
Deptt. of MSME
M.A.N.I.T., Bhopal

2. Phase
• Phase is a homogenous, physically distinct and
mechanically separable part of the material
with a given chemical composition and
structure.

3. Properties of a Materials
Properties of a materials depend on
1. Number of phases present
2. Types of phases present
3. Amount of phases present and
4. Distribution of the phases present
The Properties can be changed by altering these
quantities.
In order to make these changes, it is essential to
know the conditions under which these quantities
exist and the conditions under which a change in
phase will occur.

4. Phase diagrams

5. Phase Diagram
• A phase diagram is a type of chart used to show
conditions at which thermodynamically distinct
phases can occur at equilibrium at different
temperature, pressure and composition.
• The best method to record the data related to
phase changes in many alloy systems is in the
form of phase diagrams, also known as
equilibrium diagrams or constitutional
diagrams.

6. Phase diagrams
• In order to specify completely the state of a
system in equilibrium, it is necessary to specify
three independent variables.
• These variables, which are externally
controllable, are temperature, pressure and
composition.
• Phase diagram is the graphical presentation of
the phases present in a system under different
conditions of pressure, temperature and
composition.

7. Components of a Phase Diagram
• Common components of a phase diagram are lines of equilibrium or phase
boundaries, which refer to lines that mark conditions under which
multiple phases can coexist at equilibrium. Phase transitions occur along
lines of equilibrium.
• Triple points are points on phase diagrams where lines of equilibrium
intersect. Triple points mark conditions at which three different phases
can coexist. For example, the water phase diagram has a triple point
corresponding to the single temperature and pressure at which solid,
liquid, and gaseous water can coexist in a stable equilibrium.
• The solidus is the temperature below which the substance is stable in the
solid state.
• The liquidus is the temperature above which the substance is stable in a
liquid state. There may be a gap between the solidus and liquidus; within
the gap, the substance consists as a mixture of solid and liquid (like a
"slurry").[1]

8. A typical phase diagram for Water
• The simplest phase
diagrams are pressuretemperature diagrams of a
single simple
substance, such as water.
• The axes correspond to the
pressure and temperature.
• The phase diagram
shows, in pressuretemperature space, the
lines of equilibrium or
phase boundaries between
the three phases of
solid, liquid, and gas.

10. Phase diagrams in Metallurgical
Systems
• In metallurgical systems, the pressure is usually taken as
atmospheric pressure. Thus the phase diagram shows the
phases present at different compositions and
temperatures.
• With pressure assumed to be constant at atmospheric
pressure, the equilibrium diagram indicates the structural
changes due to variation of temperature and composition.
• Phase diagrams show the phases present under
equilibrium conditions, that is, under conditions in which
there will be no change with time.
• Equilibrium conditions may be approached by extremely
slow heating and cooling, so that if a phase change is to
occur, sufficient time is allowed.

11. Types of Phase Diagrams
• The phase diagrams may be divided into the
following three catagories
– 1. Unary Phase Diagram
– 2. Binary Phase Diagram
– 3. Ternary Phase Diagram

12. Unary Phase Diagrams

13. Unary Phase Diagrams
• Unary Phase Diagrams
are phase diagrams for
single component
systems.
• Phase diagram for
water, discussed earlier, is
an example of Unary
Phase Diagram.
• Another example is the
diagram showing
allotropy of iron or any
other element.

14. Binary phase diagrams

15. Binary phase diagrams
• The phase diagrams which
contains two components are
known as binary phase diagrams.
• In that case concentration
becomes an important variable.
• Phase diagrams are usually
plotted with composition on X
axis and the temperature on Y
axis.
• The iron–iron carbide (Fe–Fe3C)
phase diagram is shown here. The
percentage of carbon present and
the temperature define the
phases of the iron carbon alloy.

16. Types of Binary Phase Diagrams
• Binary phase digrams can be of three types
1. Complete solid solution type
2. Eutectic type
3. Peritectic type

17. Complete solid solution type

18. Complete solid solution type
• The phase diagram in which
both the constituents are
soluble in each other in
solid state at all
proportions, is known as
complete solid solution type
phase diagram.
• The phase diagram in Figure
displays an alloy of two
metals which forms solid
solution at all
concentrations of the two
species

19. Complete solid solution type
Nickel-Copper Phase Diagram

20. Complete solid solution type
Germanium-Silicon Phase Diagram

21. Eutectic Type

22. Eutectic Phase Diagram
• A phase diagram having a
eutectic reaction is
known as eutectic phase
diagram.
• In eutectic reaction, a liquid
phase (L) decomposes into a
mixture of two solid phases (α
and β) at a constant
temperature on cooling.
• Eutectic reaction is :
L = α (s) + β (s)
• It is a reversible reaction.

23. Fe-C Diagram
• A phase diagram of great technological
importance is that of the iron-carbon system
for less than 6.67% carbon.
• The x-axis of such a diagram represents the
concentration variable of the mixture.

24. Eutectic Diagram
•
•
•
•
Figure shows the eutectic phase diagrams.
The components are A and B, and the possible phases are pure crystals of A, pure
crystals of B, and liquid with compositions ranging between pure A and pure B.
Compositions are plotted across the bottom of the diagram.
Temperature is plotted on the vertical axis.

25. Eutectic Diagram
•
•
The curves separating the fields of A + Liquid from Liquid and B + Liquid from
Liquid are termed liquidus curves.
The horizontal line separating the fields of A + Liquid and B + Liquid from A + B all
solid, is termed the solidus.

26. Eutectic Diagram
•
•
At the eutectic point in this two component system, all three phases, that is
Liquid, crystals of A and crystals of B, all exist in equilibrium.
Note that the eutectic is the only point on the diagram where this is true.

27. Eutectic Diagram
•
•
The eutectic point is an invariant point. If we change the composition of the liquid
or the temperature, the number of phases will be reduced to 2.
If the system contains only pure A, then the system is a one component system
and phase A melts at only one temperature, the melting temperature of pure
A, TmA. If the system contains only pure B, then it is a one component system and B
melts only at the melting temperature of pure B, TmB.

28. Eutectic Diagram
•
•
•
For all compositions between pure A and pure B, the melting temperature is
reduced, and melting begins at the eutectic temperature TE.
The eutectic composition melts at only one temperature, TE.
For all compositions between A and B, other than eutectic composition, the
melting occurs over a range of temperatures between the solidus and the liquidus.
This is true for all compositions except one, that of the eutectic.

29. Eutectic Phase Diagram
Tin-Lead Phase Diagram

30. Eutectic Phase Diagram
Gold-Germanium Phase Diagram

31. Eutectic Phase Diagram
Copper-Silver Phase Diagram

32. Peritectic Phase Diagram
• It is a phase diagram
containing peritectic reaction.
• Peritectic reaction is :
L + α (s) = β (s)
• In peritectic reaction, a liquid
(L) and a solid (α) transform in
to another solid (β) on cooling.
• It is a reversible reaction.
• Figure shows phase diagram
for Fe–C system (dotted lines
represent iron-graphite
equilibrium).

33. Application of Phase Diagrams
• Phase diagram gives us
–
–
–
–
–
–
–
–
Overall Composition
Solidus line
Liquidus line
Limits of Solid Solubility
Chemical Composition of Phases at any temperature
Amount of Phases at any temperature
Invariant Reactions
Development of Microstructure

34. Overall Composition
• Concentration: Relative amounts of each
constituent
• It is the horizontal axis in all binary phase
diagrams
• The scale can be in weight %, atomic % or
mole %
• Normally concentration is denoted by weight
% on X axis.

35. Solidus and Liquidus Points
• Solidus point
– Temperature up to which alloy is completely solid
– Temperature at which melting begins
• Liquidus point
– Temperature up to which alloy is completely liquid
– Temperature at which solidification begins

36. Chemical Composition of Phases
• It is the chemical composition of each phase
in the system
• In a system having more than one phase, each
phase will have a unique chemical
composition which will be different from each
other, and will also be different from the
overall composition
• Not to be confused with overall composition

37. Invariant Reactions in Phase Diagrams
•
•
•
•
•
Eutectic: L = α (s) + β (s); e.g., Pb-Sn
Peritectic: α (s) + L = β (s); e.g., Pb-In
Monotectic: L1 = α (s) + L2; e.g., Cu-Pb
Syntectic: L1 + L2 = α (s); e.g., Na-Zn
Metatectic: β (s) + α (s) = L1 e.g., U-Mn

38. THANKS