This document discusses nickel alloys and their properties and applications. It begins by providing background on nickel and its unusual properties as an alloying element. It then discusses the various types of nickel alloys, including their compositions, properties, and common applications. Specific alloys covered include Monel, nickel-chromium alloys, superalloys used in gas turbines and other high temperature applications. The document concludes by discussing fabrication and welding considerations for nickel alloys.

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

3. 3
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

4. 4
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

5. 5
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

6. 6
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)

7. 7
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

8. 8
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.

9. 9
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

10. 10
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

12. 12
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.

13. 13
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)

18. 18
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)

20. 20
Fabrication
Fabrication & machining of many super alloys is
difficult
No hot or cold forming
Investment casting
Powder metallurgy
Electrochemical, electrodischarge or ultrasonic
machining

21. 21
Metallurgy of Fe, Ni & Co super alloys
Solid solution strengthened
Precipitation hardened
Oxide-dispersion strengthened

22. 22
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

24. 24
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

25. 25
Solid solution alloys
Inconels, Hastelloys, RA-333 used for furnace
parts
Nimonic® 75 for gas turbines

26. 26
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

28. 28
References
Nickel development institute (NiDI) provides
much free literature on nickel alloys and stainless
steel
Nidi.org
Haynesintl.com
ASM Handbook Vol 3