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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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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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