4. Solid Solutions
• A Solid solution may be defined as a solid that
consist of two or more elements atomically
dispersed in a single phase structure
Solute: It is the minor part of the solution.
Solvent: It is the major part of the solution.
5. Hume-Rothery’s rules
• It is also known as Factors governing Solid
Solubility
• In the formation of solid solution, the
solubility limit of a solute in the solvent is
governed by certain factors. These factors are
known as Hume-Rothery’s rules.
7. Size factor
• If the atomic sizes of
solute and solvent differ
by less than 15%,
conditions are favorable
for the formation of
solid solution. If the
atomic size difference
exceeds 15%, solid
solution formation is
extremely limited.
8. Crystal structure
• The material must have the same crystal
structure
• Otherwise, there is some point at which a
transition occurs from one phase to a second
phase with different structure.
9. Valence
• The atoms must have the
same valance.
• Otherwise the valence
electron difference
encourages the formation
of compounds
10. Chemical affinity
• Elements having lower chemical affinity have
greater solid solubility.
• Elements having higher chemical affinity have
tendency of formation of components and
hence restrict formation of solid solution.
11. TYPES OF SOLID SOLUTIONS
• SUBSTITUTIONAL SOLID SOLUTIONS
1. Random
2. Ordered
• INTERSTITIAL SOLID SOLUTIONS
12. SUBSTITUTIONAL SOLID SOLUTIONS
• When the solute atoms substitute for
parent solvent atoms in a crystal lattice.
They are called substitutional atoms and
mixture of two elements is called a
substitutional solid solution.
Example: Cu- Ni system
Cu- Solute atom
Ni- Solvent atom
22. PHASE
Definition:
• A phase may be defined as the physically
distinct, chemically homogenous and
mechanically separable portion of a
substance.
• A phase may be a portion of matter which
is homogenous
Examples: A pure substance such as water is a single
phase.
23. PHASES
WATER(2)
ILLUSTRATION OF PHASES:
Three forms of water: 1) Ice 2)water
3) water vapour are each a phase. 86
ICE (1)
WATER VAPOUR(3)
The pure substance water
can exist in solid, liquid
and vapour, each of these
states being a single
phase, as shown in fig
24. PHASE
• Now consider the effect of adding salt(Nacl) to
water. Salt will dissolve in water to give a
homogeneous solution.
• Thus the salt- water solution forms a single
phase as shown if fig
salt
Salt and water have unlimited
solubility(Homogeneous solution)- from a
single phase
25. PHASE
Salt and water have limited solubility
(Heterogenous solution)-from two distinct phases
S
O
N
A
Saturated brine
Excess salt
If more salt is added into water, then we have two
different phases as shown if fig.
26. PHASE
System composed of two or more phases
are termed as mixtures or heterogeneous
systems’.
Most metallic alloys, ceramic, polymers,
and composite are heterogeneous.
28. PHASES
• Solid may have one or many phases
1. Single phase solids
Ex: Single Crystal materials,
Pure metals ( Pure copper, Quartz,
Titanium)
2. Multiphase solids
Polycrystalline material and alloys
Ex: Rocks, Ceramics, Polymers, Wood, Iron
29. PHASE DIAGRAM
• Phase Diagrams
Phase diagrams are graphical
representation of what phases are present in
an alloy system at various Temperatures,
pressures, and compositions.
30. PHASE DIAGRAM
A phase diagram is a map showing
the structure or phase present as the
temperature and overall composition
of the material are varied.
Phase diagrams are also known as equilibrium
diagrams or constitutional diagrams.
31. Why should phase diagrams be
Studied?
60
The phase diagrams can answer the following
important questions:
What condition is the material in?
Is the composition uniform throughout?
If not, how much of each component is present?
32. Why should phase diagrams be
Studied?
Is something present that may give undesired
properties?
What will happen if temperature is increased or
decreased; pressure is changed or composition is
varied?
33. Terminology used in phase diagrams
1. Components
2. System
3. Alloy
4. Solid solution
5. Solute Solution
34. TERMINOLOGY USED IN PHASE
DIAGRAMS
34
6.Solvent
7. Phase
8. Equilibrium
9.Solubility limit
10.Degrees of freedom
1/5/20
13
SAB-AP/MECH
SONACT
35. TERMINOLOGY USED IN PHASE
DIAGRAMS
The various terms used in the study of phase
diagrams have been explained below:
1.COMPONENT: Component are pure metals
and or compounds of which an alloy is composed.
Eg: In a copper-zinc (brass), the components are
C U and Zn.
36. TERMINOLOGY USED IN PHASE
DIAGRAMS
2.SYSTEM: The system has two meanings in this
context
i.System: May refer to a specific body of
material under consideration.For Eg:A
ladle of molten steel is referred as a system.
37. TERMINOLOGY USED IN PHASE
DIAGRAMS
(ii)system: May also refer to the series of possible
alloys consisting of the same components. For
example, the Iron-Carbon system.
A system having one components is called a
Unary system, and the system having two, three and
four components are known as Binary, ternary and
quaternary systems, respectively.
38. TERMINOLOGY USED IN PHASE
DIAGRAMS
3. ALLOY:
An alloy is a mixture of two or more metals
or a metal (metals) and a non-metal (non-metals).
4.SOLID SOLUTION:
It is a solid that consist of two or
more elements atomically dispersed in a single- phase
structure.
39. TERMINOLOGY USED IN PHASE DIAGRAMS
5. SOLUTE SOLUTION:
It is the minor part of the solution or the
material which is dissolved.
6. SOLVENT:
The material which contributes the
major portion of the solution.
40. TERMINOLOGY USED IN PHASE
DIAGRAMS
7. PHASE:
A phase may be defined as a homogenous
portion of a system that has uniform physical and
chemical characteristics.
8. EQUILIBRIUM:
Equilibrium is said to exit when enough time
is allowed for all possible reactions to be completed.
41. TERMINOLOGY USED IN PHASE
DIAGRAMS
9. SOLUBILITY LIMIT:
It is the maximum concentration of solute that may be
added without forming a new phase
10. DEGREES OF FREEDOM:
It is the number of independent variables ( such as
temperature, pressure, and composition).That can be
changed independently without changing the phase or
phases of the system.
41
42. Gibb’s Phase Rule
• J.W. Gibbs, American physicist derived an
equation which established relationship in a system
between
the number of phases, number of degree of freedom
and the number of components.
F=C-P+2
Here,
F-Degree of freedom
C- No.of components of system
P-No. of Phases
2- Constant
43. Example
• Consider the application of Gibb’s phase rule
to the phase diagram of water system
44. Case 1 -Triple Point
Gibb’s phase rule,
F=C-P+2
In triple point condition :P=3,C=1
F=1-3+2,
Solution:Hence F=0(Zero degree of freedom)
45. Case 2 –liquid-solid freezing
Gibb’s phase rule,
F=C-P+2
In triple point condition :P=2,C=1
F=1-2+2,
Solution:Hence F=1(one degree of freedom)
46. Case 3 –water inside a single phase
Gibb’s phase rule,
F=C-P+2
In triple point condition :P=1,C=1
F=1-1+2,
Solution:Hence F=2(two degree of freedom)
47. Cooling Curves (Time Temperature
cooling curves)
• Cooling curves are obtained by plotting the
temperatures at equal intervals during the
cooling period of a melt to a solid
• The data obtained from these cooling curves
are useful in constructing the equilibrium
diagram.
49. ISOMORPHOUS SYSTEM
• Two elements are completely soluble in each other in
both the liquid and solid states. In these systems only a
single type of crystal structure exists for all
composition of the components and therefore they are
called isomorphous systems.
Common examples are
• Copper –Nickel system(Cu-Ni)
• Antimony-Bismuth system(Sb-Bi)
• Gold- Silver system(Au-Ag)
• Chromium-Molybdenum system(Cr-Mo)
• Tungsten-Molybdenum system(W-Mo)
• Copper- Gold system(Cu-Au)
52. Eutectic Reaction
• It is a reversible isothermal reaction of a
liquid which transforms to different solid
phases upon cooling.
• Liquid Cooling Solid 1 + Solid 2
heating
53.
54. Eutectoid Reaction
• It is a reversible isothermal reaction in which
one solid phase transforms in to intimately
mixed new solid phases upon cooling.
Solid 1 Cooling Solid 2 + Solid 3
heating
56. Peritectic Reaction
• In peritectic reaction , up on cooling , a solid
and liquid phase transform isothermally and
reversibly to a solid phase having a different
composition
Liquid + Solid 1 Cooling Solid 2
heating
57.
58. Peritectoid Reaction
• It is a reversible isothermal reaction in which
two solid phases transforms in to third solid
phase upon cooling.
Solid1 + Solid 2 Cooling Solid 3
heating
60. IRON-IRON CARBIDE EQUILIBRIUM
DIAGRAM
• To Understanding the microstructure and
properties of cast iron and carbon steels
• Used to understand the basic differences
among iron alloys and control of their
properties
• This phase diagram is constructed by plotting
the carbon composition (weight percent)
along the X-axis and temperature along the Y-
axis
61.
62. Important topics in Fe-Fe3C
• Solid phases in the phase diagram
• Invariant reactions in the phase diagram
• Eutectoid, hypoeutectoid and hypereutectoid
steels
• Eutectic, hypoeutectic and hypereutectic cast
irons
65. Eutectoid, hypoeutectoid and
hypereutectoid steels
• Steels contain 0.8% C are called eutectoid
steel
• Steels having less than 0.8%C are called
Hypoeutectoid steels
• Steels having more than 0.8%C are called
Hypereutectoid steels
66. Eutectic, hypoeutectic and
hypereutectic cast irons
• Cast irons contain 4.3%C are called eutectic
Cast irons
• Cast irons having less than 4.3%C are called
Hypoeutectic Cast irons
• Cast irons having more than 4.3%C are called
Hypereutectic Cast irons
