The document discusses intermetallic compounds, which are intermediate phases that form between two metals in an alloy system when the solute content exceeds the solid solubility limit. Intermetallics have a fixed stoichiometric composition and crystal structure different from the parent metals. They are very hard and brittle. Examples include Fe3C in steels and Mg2Ni in magnesium-nickel alloys. Intermetallics find use in applications requiring high strength and oxidation resistance at elevated temperatures, such as MoSi2 heating elements and TiAl turbine blades.

1. METALLIC MATERIALS - INTERMETALLICS
INTERMETALLICS
N PRAKASAN
ME METALLURGY
2

2. METALLIC MATERIALS - INTERMETALLICS
INTRODUCTION
 Intermediate
Phases:
 Most of the alloy system do not show complete solid
solubility. When the amount of solute element is more
than the limit of solid solubility, a second phase also
appears apart from the primary solid solution. The
second phase which forms is an intermediate phase.
 It
is a phase formed at intermediate composition
between the two primary components (pure metals).
 The
crystal structure of the intermediate phase is
different from the both primary components.
 Some
of these intermediate phases have a fixed
composition and are called Intermetallic compounds.
2

3. METALLIC MATERIALS - INTERMETALLICS
INTRODUCTION
 Intermediate
Phases:
 Intermetallics
are similar to alloys, but the bonding
between the different types of atoms is partly ionic,
leading to different properties than traditional alloys.
 In
general, the larger the electro negativity difference
between the host atom and the impurity, the greater
the tendency to form compounds and the less solubility
there is.
 So,
elements with similar electro negativities tend to
form alloy, whereas elements with large electro
negativity difference tend to have more ionic bonds.
3

4. METALLIC MATERIALS - INTERMETALLICS
INTRODUCTION
 Intermediate
Phases:
 An intermetallic compound contains two or more
metallic elements, producing a new phase with its own
composition, crystal structure, and properties.
 Intermetallic
compounds are almost always very hard
and brittle.
 Intermetallics
or intermetallic compounds are similar
to ceramic materials in terms of their mechanical
properties.
 Often
dispersion-strengthened alloys contain
intermetallic compound as the dispersed phase
an
4

5. METALLIC MATERIALS - INTERMETALLICS
Intermetallics:
 Classification:
 Stoichiometric
intermetallic compounds have a
fixed composition. They are represented in the phase
diagram by a vertical line.
 Examples:
•
•
•
•
•
•
Au2Pb in Au-Pb system,
AlSb in Al-Sb system,
MoSi2 in Mo-Si system,
Fe3C in Steels,
Mg2Pb in Mg-Pb system,
MgNi2, Mg2Ni in Mg-Ni system
5

6. METALLIC MATERIALS - INTERMETALLICS
Intermetallics:
 Classification:
 Nonstoichiometric
intermetallic compounds have a
range of compositions and are sometimes called
intermediate solid solutions.
 Examples:
• γ phase in Mo-Rh system,
• β’phase in brass,
• CuAl2 in Al-Cu system,
• Mg2Al3 in Al-Mg system,
• TiAl3 in Al-Ti system.
6

7. METALLIC MATERIALS - INTERMETALLICS
 Stoichiometric
intermetallic compounds:
Aluminum-antimony phase diagram includes a stoichiometric
intermetallic compound γ.
7

8. METALLIC MATERIALS - INTERMETALLICS
 Stoichiometric
intermetallic compounds:
19 wt% Mg-81 wt% Pb
Mg2Pb
Magnesium - Lead phase diagram includes a stoichiometric
intermetallic compound γ.
8

9. METALLIC MATERIALS - INTERMETALLICS
 Stoichiometric
intermetallic compounds:
Magnesium–Nickel binary phase diagram includes Mg2Ni, MgNi2
stoichiometric intermetallic compounds.
9

10. METALLIC MATERIALS - INTERMETALLICS
 Stoichiometric
intermetallic compounds:
Proeutectoid
cementite
pearlite
Hypereuctoid steel (1.2%C)
contains
metastable
proeutectoid and eutectoid
Fe3C, which has a fixed ratio
of three iron atoms to one
carbon atom (Interstitial
compound).
10

11. METALLIC MATERIALS - INTERMETALLICS
 Nonstoichiometric
intermetallic compounds:
The
molybdenum-rhodium
phase
diagram
nonstoichiometric intermetallic compound γ.
includes
a
11

12. METALLIC MATERIALS - INTERMETALLICS
 Nonstoichiometric
intermetallic compounds:
The Copper - Zinc Phase diagram, containing more than 30% Zn, a second
phase β’ forms because of the limited solubility of zinc in copper.
12

13. METALLIC MATERIALS - INTERMETALLICS
 Nonstoichiometric
Cartridge brass:
70% Cu + 30% Zn
intermetallic compounds:
Yellow brass:
65% Cu + 35% Zn
Muntz Metal
60% Cu + 40% Zn
β’ Brass alloy: More than 30% Zn addition provides
complex structure of α and β’ (CuZn) phases. The β
phase makes this alloy heat treatable.
13

14. METALLIC MATERIALS - INTERMETALLICS
 Nonstoichiometric
intermetallic compounds:
The Aluminium – Copper (Eutectic) Phase diagram, θ
(CuAl2) phase precipitates out during age hardening.
14

15. METALLIC MATERIALS - INTERMETALLICS
 Nonstoichiometric
intermetallic compounds:
Mg2Al3 Grain boundary
particles
The Aluminium – Magnesium Phase diagram, includes β
phase (Mg2Al3) compound.
15

16. METALLIC MATERIALS - INTERMETALLICS
 Nonstoichiometric
intermetallic compounds:
Petal-like TiAl3 particles in
α-Al solid solution
The Aluminium - Titanium (Peritectic)Phase diagram, Ti Al 3 act as a
nuclei for grains to grow. Multiple nucleation of averagely eight sites
16
may occur on each particle.

17. METALLIC MATERIALS - INTERMETALLICS
 Nonstoichiometric
intermetallic compounds:
Ni3(Al,Ti) (γ’ prime)
priciptate (FCC)
Carbids
(M23C6, M6C or MC)
γ Matrix
(FCC austenite)
Nickel base superalloys, addition of small amount of
Al, Ti, Nb forms precipitates with Cuboid shape.
The elements C, Cr, Ta, Hf, Ti, Nb,W forms Carbides.
The elements Co, Fe, Cr, Nb, Ta, Mo, W, V, Ti, B, Zr
and Al strengthen the Matrix.
17

18. METALLIC MATERIALS - INTERMETALLICS
 Properties
of some Intermetallic compounds
* B2 – Binary compound structure having 1:1 stoichiometry,
* L1 – Alloys.
18

19. METALLIC MATERIALS - INTERMETALLICS
 Properties
of intermetallic compounds:
Nickel-based superalloys
The unit cells of two intermetallic compounds: (a) TiAl has an
ordered tetragonal structure, and (b) Ni3Al has an ordered cubic
structure.
19

20. METALLIC MATERIALS - INTERMETALLICS
 Properties
of intermetallic compounds:
The strength and ductility of the intermetallic compound Ti3Al
compared with that of a conventional nickel superalloy. The Ti 3Al
maintains strength to higher temperatures longer than does the
nickel superalloy.
20

21. METALLIC MATERIALS - INTERMETALLICS
 Properties
and Applications:
 Molybdenum
disilicide (MoSi2)
 This
material is used for making heating elements for
high temperature furnaces.
 At
high temperatures (1000 to 1600°C), MoSi2 shows
outstanding oxidation resistance.
 At
low temperatures (500°C and below), MoSi2 is brittle
and shows catastrophic oxidation known as pesting.
21

22. METALLIC MATERIALS - INTERMETALLICS
 Properties
and Applications:
 Copper Aluminide (CuAl2)




Precipitation of the nonstoichiometric intermetallic copper
aluminide CuAl2 causes strengthening in a number of important
aluminium alloys.
Precipitation hardening – by forming θ (CuAl2) phase in α matrix,
gives high strength and toughness.
Properties:
• High strength (2119: σTS 505 - 520 MPa).
• Good creep strength at high temp.
• High toughness at cryogenic temp.
• Good machinability.
Applications:
• Fuel Tanks (2119)
• Pistons, rivets for aircraft constructions (2024-T4) : Al2CuMg
22

23. METALLIC MATERIALS - INTERMETALLICS
 Properties
and Applications:
 Al-Mg-Si Alloys (Mg2Si)

Mg and Si are added in balanced amount to form Mg2Si.

Mg + Si (0.8-1.2%) ; Mg + Si (> 1.4%)
Properties:
• Medium-strength structural alloys (most widely used 6063-T6,
σy 215 MPa, σTS 245 Mpa).


• Readily extruded
• Colour anodized.
Applications :
• Car bodies, Electric trains (6009)
• Structural Components (6061)
• Satellite dish (6005)
• Large water pipes (6063)
• Aircraft, Automotive (6013 – T6,T8)
23

24. METALLIC MATERIALS - INTERMETALLICS
 Properties
and Applications:
 Platinum silicide (PtSi2) :
 Intermetallics
based on silicon (e.g., platinum silicide)
play a useful role in microelectronics.
 Niobium family intermetallics:
 Certain intermetallics such as NbTi, Nb3Sn, NbZr,
Nb3Al,and Nb3Ge are used as superconductors.
β’ Brasses (α + CuZn):
24

25. METALLIC MATERIALS - INTERMETALLICS
 Properties
and Applications:
 TiAl and Ni3Al (Nickel base superalloys)




Properties:
TiAl and Ni3Al possess good combinations of high-temperature
mechanical properties and oxidation resistance up to
approximately 650 - 960°C.
Good Toughness and Corrosion resistance.
Applications:
• Aircrafts, space vehicles, rocket engines
• Industrial gas turbines (IN 738LC).
• Nuclear reactors, submarines.
• Steam power plants, petrochemical equipment.
• Combustion Engine Exhaust Valves
• Submarines
25

26. METALLIC MATERIALS - INTERMETALLICS
 Properties
and Applications: Ni-Base Superalloys
26

27. METALLIC MATERIALS - INTERMETALLICS
 References
:
 Donald
R. Askeland, Pradeep P. Fulay, Wendelin J. Wright,
The Science and Engineering of Materials, Sixth Edition.
 Robert Cahn, Peter Haasen, Physical metallurgy, Fourth
edition.
 William D.Callister, Fundamentals of Materials Science
and Engineering, Fifth edition.
 Brian
S.Mitchell, An introduction to Materials
engineering and science, John Wiley & Sons Inc.
 Vijendra singh, Physical Metallurgy
 Lecture 4, Copper and its alloys, Suranaree university of
technology.
 Lecture 6, Nickel and its alloys, Suranaree university of
technology.
 Loren A. Jacobson, Physical Metallurgy_class notes
27