Lecture 6
Nickel and its alloys
Subjects of interest
• Objectives/Introduction
• Production of nickel and nickel alloys
• Commercially pure nickel
• Nickel-copper alloys (Monels)
• Nickel-chromium alloys
• Nickel-base superalloys
• Single crystal castings of nickel-base
superalloys
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Objectives
• This chapter provides fundamental knowledge of
different methods of productions of nickel alloys and the
use of various types of nickel alloys.
• The influences of alloy composition and microstructure
on chemical and mechanical properties of nickel alloys will
be discussed in relation to its applications.
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Introduction
Properties
• Silvery shiny appearance
• High toughness and ductility
• Good high and low
temperature strength
• High oxidation resistance
• Good corrosion resistance
• Ferro-magnetic
Limitations
• Relatively high cost
• Not mixed with cheap
alloying elements.
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FCC
28
Ni
Nickel
58.71
Crystal structure
Atomic number
Atomic weight
Density (g.cm-3)
Melting point (oC)
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FCC
28
58.71
8.89
1455
May-Aug 2007
Applications
• Applications required necessary corrosion or heat- resisting
properties and for special engineering applications.
• Chemical plant, heat exchanger, reaction furnace, rotary kiln,
turbine blades.
• Used as alloying elements in stainless steels, and in other
elements such as copper, cobalt, chromium, etc.
Reaction furnace
Heat exchangers
www.msm.cam.ac.uk
Turbine blades
www.immnet.com
Aerospace flow bodies
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Rotary kiln
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Production of nickel
First discovery of nickel mineral by the German was
mistakenly misunderstood to be rich-copper mineral.
There are three major types of nickel deposits (sources):
1) Nickel-copper sulphide
2) Nickel silicates
3) Nickel laterites and serpentines
home.arcor.de
www.mii.org
Nickeline or niccolite
research.eas.ualberta.ca/ egg/nilaterite.jpg
Nickel laterite deposits
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Serpentine deposits
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Extraction of nickel
Iron ore
recovery plant
Pure nickel and
other nickel alloy
products
Nickel-sulphide ore
(Fe, Cu)
Crushing
Iron sulphide
(pyrrhotite
concentrate)
Nickel refinery
Copper
smelter
Grinding
Different grade
of nickel oxides
Magnetic separation
Remaining ore
(Ni, Cu)
Roasting
Froth flotation treatment
Copper sulphide
Nickel concentrate
Nickel sulphide
Copper concentrate
Froth flotation
Roasting
Cooling
(Reverberatory furnace) Smelting
Bessemer matte
(Ni and Cu sulphides)
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Recrystallisation
Crushing & grinding
Crystals of Ni and Cu
sulphides.
Ni-Cu metallic alloy
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Classification of nickel alloys
There are different types of nickel and nickel alloys;
1) Commercially pure nickel
2) Nickel-copper alloys (Monels)
3) Nickel-chromium alloys
4) Nickel-base superalloys
5) Nickel-iron superalloys
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Commercially pure nickel
• High purity nickel contains 99.99% Ni.
• Commercially pure nickel contains
99.5% Ni (+Co).
• Microstructure consists of solid solution
phase in annealed condition.
100 x
Properties
• Good mechanical properties
and retains its strength at
elevated temperature.
• Excellent resistance to most
corrosive environment.
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Cold drawn Nickel 200 annealed
at 829oC
Applications
• Food processing equipment
• Electrical & electronic parts
• Caustic handling equipment.
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Nickel-copper alloys (Monels)
• Ni and Cu form complete solid solution.
• Most important Ni-Cu alloy contains
67%Ni and 33%Cu, called Monels.
Properties
• High strength and toughness over
a range of temperature.
• Good weldability
• Excellent corrosion resistance
Ni-Cu phase diagram
Applications
• Values, pumps, marine fixtures
and fasteners.
• Chemical processing equipment.
• Oil-well drill collars and
instruments.
250 x
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Microstructure of
cold drawn Monel
R405 and
annealed at 829oC,
showing solid
solution phase of
Ni-Cu with
sulphide stringers
(black)
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Nickel-chromium alloys
• Cr forms solid solution with Ni up to~30%
at RT. High corrosion resistance is due to
high Cr addition.
• Inconel 600 (15.5%Cr, 8%Fe) is a
standard engineering alloy. Other Ni-Cr
alloys are Inconel 601 and 625 with
improved properties.
Properties
Ni-Cr phase diagram
• High corrosion resistance at
high temperature.
• High strength and workability.
Applications
• Heat exchanger tubing
• Chemical and food
processing equipment.
• Furnace muffle.
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1500 x
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Inconel 600, solution
heat-treated at
1200oC/1h+870oC/4h,
showing solid solution
phase with chromium
carbide precipitates at
GBs and some titanium
carbides and nitrides
within the grains
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Nickel-base superalloys
• High temperature heat-resistance alloys, which can retain
high strengths at elevated temperatures.
• There are three types of Ni-base superalloys; nickel base, nickeliron base and cobalt base. The alloys contain high Cr with Ti, Al to
from precipitates and additions of Mo, Co, Nb, Zr, B, Fe.
• Microstructures are complex.
Properties
• Heat resistant and high strength at high
temperature (760-980oC).
• Good corrosion resistance.
• Good oxidation resistance.
Applications
• Aircrafts, space vehicles, rocket engines
• Industrial gas turbines, high temp applications.
• Nuclear reactors, submarines.
• Steam power plants, petrochemical equipment.
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www.stratcor.com
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Microstructure of nickel base superalloys
Carbides
at GB
10,000 x
Complex microstructure of astroloy
forging after heat treatments
The major phases present in the nickel-base superalloys:
1) γ (gamma) phase – the continuous matrix of FCC austenite.
2) γ’ (gamma prime) phase – the major precipitate phase
(more cubic shape).
3) Carbides –various types, mainly M23C6 and MC. M = metal.
Note: GB carbides affect high-temp strength, ductility, creep.
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Nickel- iron superalloys
• Fe is added to replace some of Ni as it has lower cost. lowering
the properties as compared with nickel base superalloy. therefore it is used at lower temperatures.
• Ni-Fe superalloys contains 25-45%Ni and 15-60%Fe.
• Higher Ni content increases operating temp (upto 815oC), due to
improved stability but more costly.
• Ex: Inconel 707, 718, 901.
• Microstructure consists of
austenistic FCC matrix and can
be strengthened by solid solution
strengthening (Mo, Cr), and
precipitation hardening (Ti, Nb, Al)
by forming intermetallic phases.
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15,000 x
Optical micrograph of
SEM micrograph of Inconel 718
Inconel 901 after
after exposure at 705oC/6,048
precipitation hardening h, 37 ksi
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Single-crystal castings of
nickel-base superalloys
• A major increase in strength and temperature capability of
superalloy casting has been much improve with the introduction of
columnar-grained and single crystal casting.
Competitive
grain
Diagram of setup
for single crystal
casting
Simulation of
evolution of grain
structure in a single
crystal casting.
Turbines blades are
cast using a spiral
starter
www.nap.edu
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www.msm.cam.ac.uk
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Applications of single-crystal castings of
nickel-base superalloys
• Used in production of aerofoils, gas turbine engines,
which allow the operating temperature range ~ 50oC higher
than normal materials.
Property
comparison
between
polycrystal,
columnar
crystal and
single crystal
(a) Polycrystal
(b) Columnar
crystal
(c) Single
crystal
Single crystal casting
of superalloy
www.grc.nasa.gov
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References
• , กกก, 2536, ก
ก
!"
", ISBN
974-582-155-1.
• Smith, W.F., Structure and properties of engineering
alloys, second edition, 1993, McGraw-Hill, ISB 0-07-59172-5.
• www.cda.org.uk.
• Heußner, U., Nickel alloys, 1998, Marcel Dekker, Inc., ISBN
0-8247-0440-1.
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