MME445: Lecture 13 Common engineering...
Transcript of MME445: Lecture 13 Common engineering...
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MME445: Lecture 13
Common engineering materials: 8. Nickel and its alloys
A. K. M. B. Rashid Professor, Department of MME
BUET, Dhaka
Learning Objectives
Knowledge &
Understanding Knowledge about properties and uses of different nickel alloys
Skills & Abilities Ability to know the character and potential use of nickel alloys
Values & Attitudes Aware of the importance and limitation of using nickel alloys
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Outline of the lecture …
Properties of nickel
Physical metallurgy
Commercially pure nickel
Nickel base alloys
Single crystal castings of nickel-base superalloys
Introduction
Nickel and nickel-base alloys are
vitally important to modern industry
because of their ability to withstand
a wide variety of severe operating
conditions involving corrosive
environments, high temperatures,
high stresses, and combination of
these factors.
Nickel and its alloys, like stainless
steels, offer a wide range of corrosion
resistance.
However, nickel can accommodate
larger amount of alloying elements –
mainly Cr, Mo, and W – in solid solution
that iron.
Therefore, nickel based alloys in
general can be used in more severe
environments than stainless steels.
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Typical properties
Silvery shiny appearance
High toughness and ductility
Good high and low temperature strength
High oxidation resistance
Good corrosion resistance
Ferro-magnetic
Crystal structure FCC
Atomic number 28
Atomic weight (g/mol) 58.71
Density (g/cc) 8.89
Melting point (C) 1455
Boiling point (C) 2913
Disadvantages
Relatively high cost
Not mixed with cheap alloying elements
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About 60% of nickel production is used as alloying elements in stainless and
nickel-alloy steels, and in other elements such as copper, cobalt, chromium, etc.
Most of the remainders is used for high-nickel alloys and for electroplating
Typical applications
Nickel and nickel alloys are used for
a wide variety of applications, the
majority of which involve corrosion
resistance and/or heat resistance
chemical plant, heat exchanger, reaction
furnace, rotary kiln, turbine blades.
A number of other applications for Ni alloys
involve the unique physical properties of
special-purpose nickel-base or high-nickel
alloys. These include:
• low-expansion alloys
• electrical resistance alloys
• soft magnetic alloys
• shape memory alloys
• Aircraft gas turbines: disks, combustion
chambers, bolts, casings, shafts, exhaust
systems, cases, blades, vanes, burner cans,
afterburners, thrust reversers
• Steam turbine power plants: bolts, blades,
stack gas reheaters.
• Reciprocating engines: turbochargers,
exhaust valves, hot plugs, valve seat inserts
• Metal processing: hot-work tools and dies
• Medical applications: dentistry uses,
prosthetic devices
• Space vehicles: aerodynamically heated
skins, rocket engine parts
• Heat-treating equipment: trays, fixtures,
conveyor belts, baskets, fans, furnace mufflers
• Nuclear power systems: control rod drive
mechanisms, valve stems, springs, ducting
• Chemical and petrochemical industries:
bolts, fans, valves, reaction vessels, piping,
pumps
• Pollution control equipment: scrubbers,
flue gas desulfurization equipment (liners,
fans, stack gas reheaters, ducting)
• Metals processing mills: ovens, after-
burners, exhaust fans
• Coal gasification and liquefaction systems:
heat exchangers, reheaters, piping
• Pulp and paper mills: tubing, doctor blades,
bleaching circuit equipment, scrubbers
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Physical Metallurgy
Nickel is a versatile element; alloys with most metals.
Complete solid solubility exists between nickel and copper.
Wide solubility ranges between iron, chromium, and nickel
possibility of many alloy combinations
The FCC structure of the nickel matrix (g) can be strengthened by
① solid-solution hardening
② carbide precipitation, or
③ precipitation hardening.
Co, Fe, Cr, Mo, W, V, Ti, and Al are all solid solution hardeners in nickel.
These elements differ with nickel in atomic diameter from 1 to 13 %.
Above 0.6Tm, which is the range of high-temperature creep, strengthening is
diffusion dependent and large, slow diffusing elements such as Mo and W
are the most effective hardeners.
Solid solution hardening
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Nickel is not a carbide former; other elements present in nickel form carbides.
This is either a bane or a blessing to the designer of alloys. An understanding of
carbide class and its morphology is critical for alloy design.
Carbide strengthening
The alloy chemistry, its prior processing history, and the heat treatment given to the
material influence carbide precipitation and ultimately performance of the alloy.
• MC – large blocky carbide, randomly distributed,
not desired
• M6C – blocky; formed in grain boundaries (can
be used to control grain size), or precipitated in a
Widmanstaitten pattern throughout the grain
(impair ductility and rupture life)
• M7C3 – form intergranularly; beneficial if
precipitated as discrete particles, or cause
embrittlement if they agglomerate and form
continuous grain-boundary films.
• M23C6 – form as grain-boundary precipitates;
influential in enhancing rupture properties
Most common carbides forms: MC, M6C, M7C3, and M23C6.
Precipitation hardening
The precipitation of g’, Ni3(AI,Ti) in a high-
nickel matrix provides significant
strengthening to the material.
This unique intermetallic phase has a FCC
structure similar to that of the matrix and a
lattice constant having 1% or less
mismatch in the lattice constant with the g
matrix. This close matching allows low
surface energy and long time stability.
Precipitation of the g’ from the
supersaturated matrix yields an increase
in strength with increasing precipitation
temperature, up to the overaging or
coarsening temperature.
The amount of g’ formed is a function of the
hardener content of the alloy. Al, Ti, Nb, and
Ta are strong g’ formers.
Effective strengthening by g’ decreases above
about 0.6Tm as the particles coarsen.
The g’ phase can transform to other (Ni3X)
precipitates if the alloy is supersaturated in Ti,
Nb, or Ta (indicated as X) and modify
mechanical properties.
The phases precipitated are functions of alloy
chemistry and the heat treatment given the
material prior to service or the
temperature/time exposure of in-service
application.
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① Commercially pure nickel
② Nickel-copper alloys (Monels)
③ Nickel-chromium alloys
④ Nickel-iron and Nickel-chromium-iron alloys
⑤ Nickel-base superalloys
Classification of Nickel Alloys
Commercially pure nickel
High purity nickel contains at least 99 % Ni
Commercially pure nickels also have Co and such impurities
like Mn, Fe, Si, and Cu to enhance specific properties.
These alloys are non-heat treatable and may be hardened by
cold work.
Some alloys containing Al and Ti are heat treatable and may
be strengthened by precipitation hardening
Microstructure consists of solid solution g phase in annealed
condition Cold drawn Nickel 200
annealed at 829 C
Typical properties
Good mechanical properties and retains its
strength at elevated temperature
Excellent resistance to most corrosive
environment
Applications
Food processing equipment
Electrical and electronic parts
Caustic handling equipment
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Alloy Major Mechanical Principal Typical Designation Composition Properties Characteristics Applications Pure nickel 99.99 Ni (min) TS = 46 ksi E = 30% A nickel 99.40 Ni+Co TS = 70 ksi Used where strength in combination Chemical and soap E = 40% of corrosion and oxidation resistance industry HBN = 100 are required D nickel 95.00 Ni+Co TS = 75 ksi Improve resistance to atmospheric Spark plug electrode, 4.75 Mn E = 40% attack at high temperature; ignition tube HBN = 140 strength greater than A nickel Duranickel 93.90 Ni+Co TS = 100 ksi High strength in combination with spring for laundry clip, 4.5 Al, 0.45 Ti E = 40% excellent corrosion resistance; jewelry parts, optical 0.55 Si HBN = 160 age hardenable frames; instrument parts Parmanickel 98.65 Ni+Co TS = 105 ksi Strength and corrosion resistance Used in place of duranickel 0.45 Ti, E = 45% similar to duranickel; good electrical where good conductivity 0.35 Mg HBN = 160 and thermal conductivity; and magnetic properties age hardenable are required
Nickel - copper alloys (Monels)
Ni and Cu form complete solid solution
Ni-Cu alloy (a.k.a. Monels) contains 29-33 %
Cu as the major alloying element
Ni-Cu alloys containing Al and Ti ( K Monel)
is heat treatable and may be strengthened by
precipitation hardening
Microstructure of cold drawn Monel R405 and
annealed at 829 C, showing solid solution
phase of Ni-Cu with sulphide stringers (black)
Typical properties
Mechanical properties higher than brasses
and bronzes but lower than alloy steels
Good toughness and fatigue strength over a
range of temperature
Good formability and weldability, but poor
machinability
Excellent corrosion resistance to acid, alkalis,
brines, waters, food products, and atmosphere
Reduced price
Applications
Values, pumps, marine fixtures and fasteners
Chemical processing equipment
Oil-well drill collars and instruments
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K Monel
Addition of ~3% Al make it age hardenable
Non-magnetic, corrosion resistant material
with extra strength and hardness
Uses: marine pump shaft, springs, aircraft
instruments, ball bearings, safety tools
H and S Monel
Contains 3% and 4% Si, respectively; casting alloy
High strength, pressure tightness, corrosion resistance
H Monel, containing less silicon has better machinability
Uses: valve seats, pump liners, impellers
Constantan
Contains 45% Ni and 55% Cu
Highest electrical resistivity
Uses: thermocouple
Alloy Principal composition Condition TS, ksi 0.2PS, ksi %E in 2” BHN
Monel 66.15 Ni+Co, 31.3 Cu, 1.3 Fe Annealed 75 35 40 125
K-500 Monel 65.25 Ni+Co, 29.6 Cu, 2.75 Al Annealed 100 45 40 155
H Monel 63.0 Ni+Co, 30.5 Cu, 3.2 Si As-cast 115 70 10 265
Constantan 44-46 Ni, Bal. Cu Annealed
Cold-worked
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100
Electrical resistivity
= 49 mOhm-cm
Ni-Cu alloys
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Nickel - chromium alloys
Cr forms solid solution with Ni up to ~30% at RT,
resulting high corrosion resistance
Alloys containing 80Ni-20Cr compositions (Chromel
A, Nichrome V) and 60Ni-16Cr-24Fe compositions
(Chromel C, Nichrome) are used as electric
heating elements
The alloy forms nickel-rich single phase solid solution
having annealing twins.
Properties
High electrical resistance
High corrosion resistance at high temperature
High strength and workability
Applications
Heat exchanger tubing
Heaters for electric furnace, cookers,
kettles, immersion-heaters, hair-dryers,
toasters, etc.
Resistivity is ~108 mohm-cm
Change in electrical resistivity is
not constant with temperature
Value depends on heat treatment;
annealing improves resistivity
Nickel-iron and Nickel-chromium-iron alloys
Optical micrograph of Inconel 901
after precipitation hardening
SEM micrograph of Inconel 718
after exposure at 705 C/6,048 h
Fe added to replace some of Ni
lower cost
lower properties (as compared with nickel base superalloy)
used at lower temperatures
Ni-Fe alloys contains 25-45%Ni and 15-60%Fe
Higher Ni content increases operating temp (up to 815 C)
due to improved stability but more costly
microstructure consists of austenitic FCC matrix
can be strengthened by solid solution strengthening
(Mo, Cr), and precipitation hardening (Ti, Nb, Al) by
forming intermetallic phases
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Non-heat-treatable Ni-Cr-Fe alloys
The major alloying elements of these alloys (15-22% Cr and up to 46% Fe) form single phase solid solution with nickel
May be hardened by cold working
Alloys are identified according to trade names: Inconel, Incoloy, and Hastelloy
Good mechanical strength and high resistant to creep combined with excellent corrosion resistance to chloride-ion solution, sulphur compounds and other organic and inorganic compounds
Good machinability, weldability and workability
Used for furnace and heat treating equipment (nitriding container, carburizing boxes, retorts).
Heat-treatable Ni-Cr-Fe alloys
These alloys contains 15-22% Cr and up to 33% Fe as the major alloying elements
May be strengthened by precipitation hardening due to the presence of additional alloying elements: Al, Be, Ti, Si
Trade names of some alloys: Nimonic, Inconel X-750, Udimet, Waspaloy, Rene, Astroloy
Very high mechanical strength and high resistant to creep at temperatures up to 815 C combined with good corrosion and oxidation resistance
Used for making gas turbine components, parts of nuclear steam generators, hot working tools, exhaust valves for IC engines
Alloy Principal composition Condition TS, MPa 0.2PS, MPa %E
Inconel Ni 72% min, Cr 14-17%, Fe 6-10% Annealed 655 310 45
Incoloy 800 Ni 30-35%, Cr 19-23%, Fe 39.5% min,
Al 0.15-0.60%, Ti 0.15-0.6% Annealed 600 275 45
Incoloy 800HT Ni 30-35%, Cr 19-23%, Fe 39.5% min,
Al 0.15-0.60%, Ti 0.15-0.6% Annealed 560 250 45
Hastelloy X Ni 45-50%, Cr 20.5-23%, Fe 6-10%,
Mo 8-10%, W 0.2-1.0%, Co 0.5-2.5% Annealed 765 380 44
Non-heat-treatable Ni-Cr-Fe alloys
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Alloy Principal composition Condition TS, MPa 0.2PS, MPa %E
Nimonic 80A Ni 69% min, Cr 18-21%, Fe 3% max,
Al 1.0-1.8%, Ti 1.8-2.7% Precip. hard. 1250 780 30
Nimonic 115
Ni 54% min, Cr 14-16%, Fe 1% max,
Al 4.5-5.5%, Ti 3.5-4.5%,
Mo 3-5%, Co 13-15.5%
Precip. hard. 1300 850 25
Inconel X-750
Ni 70% min, Cr 14-17%, Fe 5-9%,
Al 0.4-1.0%, Ti 2.25-2.75%,
Mo 8-10%, Nb 0.7-1.2%
Precip. hard. 1250 850 30
Waspaloy
Cr 18-21%, Fe 2% max, Al 1.0-1.5%,
Ti 2.6-3.25%, Mo 3.5-5%, Co 12-15.5%,
Ni balance
Precip. hard. 1250 850 30
Rene 41
Cr 18-20%, Fe 5% max, Al 1.4-1.6%,
Ti 3.0-3.3%, Mo 9-10.5%, Co 10-12%,
Ni balance
Precip. hard. 1420 1062 14
Heat-treatable Ni-Cr-Fe alloys
Nickel based superalloys
High temperature heat-resistance
alloys, which can retain high
strengths at elevated temperatures
Three types of Ni superalloys
① nickel base
② nickel-iron base, and
③ cobalt base containing nickel
Alloys contain high Cr with
Ti and Al to from precipitates, and
additions of Mo, Co, Nb, Zr, B, Fe.
Complex microstructures
Properties
Heat resistant and high strength
at high temperature (760-980 C)
Good corrosion resistance
Good oxidation resistance
Applications
Aircrafts, space vehicles, rocket engines
Industrial gas turbines, high temperature
applications
Nuclear reactors, submarines
Steam power plants, petrochemical
equipment
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These superalloys are “super” because of the g’ precipitation strengthening effect
g’ is an intermetallic compound (Ni3Al) with ordered fcc structure
Amazing property of superalloys: they become stronger at higher temperature
Ni atoms
Ni atoms
Al atoms
fcc Ni g
matrix
ordered fcc g’ ppt.
(cuboid in shape)
Turbine blades in a jet engine experience:
• Mechanical forces – (1) creep, (2) fatigue, (3) thermomechanical fatigue
• High temperature environment – (1) oxidation, (2) hot corrosion
Turbine blades
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Turbine blade heat treatment
As-cast dendritic microstructure
precipitation hardening
(solution treatment + ageing)
precipitation hardened
g’ in g matrix
g’ g
The major phases present in the nickel-base superalloys:
• g (gamma) phase – the continuous matrix of FCC austenite
• g’ (gamma prime) phase – the major precipitate phase (more cubic shape)
• carbides – various types, mainly M23C6 and MC (M = metal)
Note: GB carbides affect high-temp strength, ductility, creep
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Single-crystal castings of nickel-base superalloys
A major increase in strength and
temperature capability of superalloy
casting can be obtained with the
introduction of columnar-grained and
single crystal casting
equiaxed
crystal
directionally
solidified
columnar crystals
single
crystal
property comparison between polycrystal,
columnar crystal and single crystal
Next Class
MME445: Lecture 14
Introduction to CES EduPack 2016