Ni Alloys1

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S

Nickel and other superalloys

TSUF 06 Materiales Aeronauticos

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Nickel

S The name nickel is from the German forOld Nicks (the

Devils) copper a derogatory term for the hard useless metalyielded by what was thought to be a copper-bearing ore

S These days nickel is an important alloy element, with much

wider application than copper

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Unusual properties

S Nickel-iron with low expansion coefficient (Invar)

S Nickel-chromium resistance heating elements

S Shape memory alloys (Ni-Ti)

S Alloys with soft magnetic properties

S Superalloys for gas turbine engines and other high

temperature uses

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Nickel

S fcc metal, no solid phase changes.

S Grey colour

S 43% of production used in stainless steels

S 20% in non-ferrous alloys

S Alloy steels, foundry products

S Other uses

S Chemicals, catalysts, ceramics, coinage, magnets

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Nickel alloys

S About 60 alloys

S Some with less than 50% nickel (or any other alloy element)

S Single phase alloys (fcc)S Nickel has a high solubility of Cu, Cr, Mo, Fe, etc

S Precipitation hardened alloysS With Al, Ti or Nb in above 0.5%

S Dispersion strengthened alloysS Produced by powder metallurgy

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Alloy designations

S The alloy names are based upon proprietary names, usually fromInco, Haynes, Krupp-VDM,

S eg Alloy 625 was originally Inconel 625

S UNS number is a 5-digit numbers preceded by N

S eg Alloy 625 is UNS N06625

S ISO 9722 numbers are often (but not always) based upon the UNSnumbers

S eg UNS N06625 is ISO NW6625

S DIN designations are descriptive (NiCr22Mo9Nb)

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Properties

S Corrosion resistance to neutral, acid, basic, oxidising orreducing environments

S Piping, vessels for chemicals, seawater, etc

S High temperature strength, corrosion and oxidation resistanceS Up to 1200C

S High cost

S Nickel alloy weld overlays commonly used

S Nickel alloys are excellent filler metals for dissimilar welds

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Metallurgy of nickel alloys

S Alloys are mostly single phase fcc

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Nickel has a wide range of solubility for other metalsS Alloys contain Cu, Cr, Mo, Fe,

S Age hardenable alloys contain aluminium, niobium and/or

titanium

S Dispersion-strengthened alloys contain 2% thoria (ThO2) and

are made by powder metallurgy.

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Commercially pure nickel

S Nickel 200

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Up to 0.15% C as impurity; graphitises at over 320CS Resists caustic soda & other alkalies

S Nickel 201: 0.02% C maximum

S Duranickel 301: Ni-4.4Al-0.6Ti

S Age hardening gamma prime

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Applications of pure nickel

S Caustic soda handling equipment

Food processing

S Laboratory crucibles

S Chemical shipping drums

S Electrical and electronics parts

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Nickel-copper (Monel metal)

S Probably the best corrosion resistance to a wide range of environmentsof any alloy

S Monel 400: 70Ni-30Cu fcc alloy: Rm 480 to 1170 MPaS Cladding, vessels and piping for seawater, brackish water, chlorinated solvents,

many acids and alkalies

S Monel 405: 0.04% S - free machining

S Monel K-500: 2.7% Al, 0.6% Ti: Rm 1100 to 1240 MPa

S Age hardening - gamma prime phase

S Steam turbine blades, etc

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Nickel-chromium alloys

S Over 50% Ni with >15% Cr, Mo, Fe, C, W

S Single phase fcc, solid solution strengthened

S Seamless transition to austenitic stainless steel

S Wide range of temperatures (cryogenic to 1000C)

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Acids, neutral and alkalies. Oxidising and reducing chemicals.

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Examples of Ni-Cr alloys

S Nichrome alloys

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80Ni-30Cr, 60Ni-16Cr-24FeS Electrical resistors & heating elements

S Inconel 600, 625, 671, 690

S Eg Inconel 625: 61Ni-21Cr-9Mo-3.6Nb

S Hastelloy C-4, C-276, G, G-3, N, S, W, XS Eg Hastelloy C-276: 59Ni-15.5Cr-16Mo-3.75W-5.5Fe

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Nickel-iron-chromium alloys

S Cross between austenitic stainless steel and nickel alloys

S Incoloy 800: 32.5Ni-21Cr-46Fe

S RA333: 45Ni-25Cr-18Fe-3Mo-3Co-3W

S Excellent resistance to oxidation at high temperatures,

S Good resistance to corrosion in acids and salts, but not halides

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Fabrication of Ni alloys

S Casting is difficult, but castings are produced

S Forming (hot & cold) is similar, but somewhat more difficult thanaustenitic stainless steels

S Weldability is excellent for many types (better than austenitic stainlesssteel)

S Heating operations are generally performed in controlled atmospheresto avoid intercrystalline embrittlement

S Avoid contamination with S, P, Pb, Zn, SnS Solidification or liquation cracking

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Welding procedures

S GTAW, GMAW, MMAW, SAW, PAW, OFW, RW, EBW,

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Use matching or over-alloyed fillersS Keep arc energy low

S Segregation can result in loss of corrosion performance

S Preheat not required

SKeep clean to avoid cracking

S Remove slag to avoid corrosion attack at high temperatures


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S

Super alloys (hightemperature)

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Super alloys

S High temperature performance (strength)

S Gas turbines, steam turbines, reciprocating engines

S Hot working and casting tools and dies

S Aircraft & space vehicles

SHeat treatment trays, fixtures, conveyors

S Nuclear and chemical industries

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Alloy types

S Selection depends on strength, creep & oxidation performance at theelevated temperature

S Iron based alloys

S Nickel based alloys

S Cobalt based alloys

S Refractory metals (niobium, molybdenum, tantalum, rhenium &tungsten)

S Directionally solidified eutectics, single crystals, intermetalliccompounds

S Non-metals (graphite, ceramics)

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Fabrication

S Fabrication & machining of many super alloys is difficult

S No hot or cold forming

S Investment casting

S Powder metallurgy

S Electrochemical, electrodischarge or ultrasonic machining

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Metallurgy of Fe, Ni & Co super alloys

S Solid solution strengthened

S Precipitation hardened

S Oxide-dispersion strengthened

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Cobalt-based alloys

S Resistant to specific environments, eg engine combustion

gases at high temperature

S High strength

S Ry up to 790 MPa & Rm up to 1170 MPa at room temperature

S 1000 hour rupture strength at 815C up to 230 MPa

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Typical cobalt-base alloys

S 650C to 1150C

S Haynes 25, 188

S Fasteners at 650C

S UMCo-50, S-816

S Wear alloys

S Stellite 6B

S fcc with some tendency to transform to cph

S Carbides and intermetallic compounds

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Nickel-based super alloys

S Ni alloys have a better resistance to high temperatures and

have a higher strength than stainless steels or cobalt alloys

S Ry up to 1200 MPa & Rm up to 1450 MPa at room temp

S 1000 hour rupture strength at 850C up to 450 MPa

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Solid solution alloys

S Inconels, Hastelloys, RA-333 used for furnace parts

S Nimonic 75 for gas turbines

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Precipitation hardened alloys

S Aluminium and titanium, gamma prime or gamma double

prime precipitates

S Inconel X-750, Nimonic 80,

S Aerospace applications

S Gas turbine blades

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Welding the PH Ni alloys

S GTAW process only

S To avoid burn-out of strengthening alloys in fillers

S Cracking can be experienced

S Anneal base material before welding

S Stress relieve and age weldments

S This also ensures welds have highest strength

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References

S Nickel development institute (NiDI) provides much free

literature on nickel alloys and stainless steel

S Nidi.org

S Haynesintl.com

S ASM Handbook Vol 3

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Ni Alloys1