1. 1
Nickel and other super alloys
EF420 Lecture 10

2. 2
Nickel
The name ‘nickel’ is from the German for ‘Old
Nick’s (the Devil’s) copper’ a derogatory term for
the hard useless metal yielded by what was
thought to be a copper-bearing ore
These days nickel is an important alloy element,
with much wider application than copper

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Unusual properties
Nickel-iron with low expansion coefficient (Invar)
Nickel-chromium resistance heating elements
Shape memory alloys (Ni-Ti)
Alloys with soft magnetic properties
Superalloys for gas turbine engines and other
high temperature uses

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Nickel
fcc metal, no solid phase changes.
Grey colour
43% of production used in stainless steels
20% in non-ferrous alloys
Alloy steels, foundry products
Other uses
 Chemicals, catalysts, ceramics, coinage, magnets

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Nickel alloys
About 60 alloys
Some with less than 50% nickel (or any other alloy
element)
Single phase alloys (fcc)
 Nickel has a high solubility of Cu, Cr, Mo, Fe, etc
Precipitation hardened alloys
 With Al, Ti or Nb in above 0.5%
Dispersion strengthened alloys
 Produced by powder metallurgy

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Alloy designations
The alloy names are based upon proprietary
names, usually from Inco, Haynes, Krupp-VDM,
 eg Alloy 625 was originally Inconel® 625
UNS number is a 5-digit numbers preceded by ‘N’
 eg Alloy 625 is UNS N06625
ISO 9722 numbers are often (but not always)
based upon the UNS numbers
 eg UNS N06625 is ISO NW6625
DIN designations are descriptive (NiCr22Mo9Nb)

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Properties
Corrosion resistance to neutral, acid, basic, oxidising or
reducing environments
 Piping, vessels for chemicals, seawater, etc
High temperature strength, corrosion and oxidation
resistance
 Up to 1200˚C
High cost
 Nickel alloy weld overlays commonly used
Nickel alloys are excellent filler metals for dissimilar welds

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Metallurgy of nickel alloys
Alloys are mostly single phase fcc
 Nickel has a wide range of solubility for other metals
 Alloys contain Cu, Cr, Mo, Fe,
Age hardenable alloys contain aluminium,
niobium and/or titanium
Dispersion-strengthened alloys contain 2% thoria
(ThO2) and are made by powder metallurgy.

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Commercially pure nickel
Nickel 200
 Up to 0.15% C as impurity; graphitises at over 320˚C
 Resists caustic soda & other alkalies
Nickel 201: 0.02% C maximum
Duranickel 301: Ni-4.4Al-0.6Ti
 Age hardening gamma prime

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Applications of pure nickel
Caustic soda handling equipment
Food processing
Laboratory crucibles
Chemical shipping drums
Electrical and electronics parts

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Nickel-copper (Monel metal)
Probably the best corrosion resistance to a wide range of
environments of any alloy
Monel® 400: 70Ni-30Cu fcc alloy: Rm 480 to 1170 MPa
 Cladding, vessels and piping for seawater, brackish water,
chlorinated solvents, many acids and alkalies
Monel 405: 0.04% S - free machining
Monel K-500: 2.7% Al, 0.6% Ti: Rm 1100 to 1240 MPa
 Age hardening - gamma prime phase
Steam turbine blades, etc

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Nickel-chromium alloys
Over 50% Ni with >15% Cr, Mo, Fe, C, W
Single phase fcc, solid solution strengthened
 Seamless transition to austenitic stainless steel
Wide range of temperatures (cryogenic to
1000˚C)
Acids, neutral and alkalies. Oxidising and
reducing chemicals.

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Examples of Ni-Cr alloys
Nichrome alloys
 80Ni-30Cr, 60Ni-16Cr-24Fe
 Electrical resistors & heating elements
Inconel® 600, 625, 671, 690
 Eg Inconel 625: 61Ni-21Cr-9Mo-3.6Nb
Hastelloy® C-4, C-276, G, G-3, N, S, W, X
 Eg Hastelloy® C-276: 59Ni-15.5Cr-16Mo-3.75W-5.5Fe

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Nickel-iron-chromium alloys
Cross between austenitic stainless steel and
nickel alloys
Incoloy® 800: 32.5Ni-21Cr-46Fe
RA333: 45Ni-25Cr-18Fe-3Mo-3Co-3W
 Excellent resistance to oxidation at high temperatures,
 Good resistance to corrosion in acids and salts, but not
halides

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Fabrication of Ni alloys
Casting is difficult, but castings are produced
Forming (hot & cold) is similar, but somewhat more
difficult than austenitic stainless steels
Weldability is excellent for many types (better than
austenitic stainless steel)
Heating operations are generally performed in controlled
atmospheres to avoid intercrystalline embrittlement
Avoid contamination with S, P, Pb, Zn, Sn
 Solidification or liquation cracking

16. Welding procedures
GTAW, GMAW, MMAW, SAW, PAW, OFW, RW, EBW,
Use matching or over-alloyed fillers
Keep arc energy low
 Segregation can result in loss of corrosion performance
Preheat not required
Keep clean to avoid cracking
Remove slag to avoid corrosion attack at high
temperatures

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Super alloys (high temperature)

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Super alloys
High temperature performance (strength)
Gas turbines, steam turbines, reciprocating
engines
Hot working and casting tools and dies
Aircraft & space vehicles
Heat treatment trays, fixtures, conveyors
Nuclear and chemical industries

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Alloy types
Selection depends on strength, creep & oxidation
performance at the elevated temperature
Iron based alloys
Nickel based alloys
Cobalt based alloys
Refractory metals (niobium, molybdenum, tantalum,
rhenium & tungsten)
Directionally solidified eutectics, single crystals,
intermetallic compounds
Non-metals (graphite, ceramics)

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Fabrication
Fabrication & machining of many super alloys is
difficult
No hot or cold forming
Investment casting
Powder metallurgy
Electrochemical, electrodischarge or ultrasonic
machining

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Metallurgy of Fe, Ni & Co super alloys
Solid solution strengthened
Precipitation hardened
Oxide-dispersion strengthened

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Cobalt-based alloys
Resistant to specific environments, eg engine
combustion gases at high temperature
High strength
 Ry up to 790 MPa & Rm up to 1170 MPa at room
temperature
 1000 hour rupture strength at 815˚C up to 230 MPa

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Typical cobalt-base alloys
650˚C to 1150˚C
 Haynes® 25, 188
Fasteners at 650˚C
 UMCo-50, S-816
Wear alloys
 Stellite® 6B
fcc with some tendency to transform to cph
Carbides and intermetallic compounds

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Nickel-based super alloys
Ni alloys have a better resistance to high
temperatures and have a higher strength than
stainless steels or cobalt alloys
 Ry up to 1200 MPa & Rm up to 1450 MPa at room temp
 1000 hour rupture strength at 850˚C up to 450 MPa

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Solid solution alloys
Inconels, Hastelloys, RA-333 used for furnace
parts
Nimonic® 75 for gas turbines

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Precipitation hardened alloys
Aluminium and titanium, gamma prime or gamma
double prime precipitates
Inconel X-750, Nimonic 80,
Aerospace applications
 Gas turbine blades

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Welding the PH Ni alloys
GTAW process only
 To avoid burn-out of strengthening alloys in fillers
Cracking can be experienced
 Anneal base material before welding
 Stress relieve and age weldments
 This also ensures welds have highest strength

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References
Nickel development institute (NiDI) provides
much free literature on nickel alloys and stainless
steel
Nidi.org
Haynesintl.com
ASM Handbook Vol 3