Nickel-based Superalloys

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Nickel-based Superalloys
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• During last two decades a large attention has
  been paid to develop new high-temperature
  structural materials that could overcome
  properties, reliability and performance in
  service applications of existing ones.
• Due to long-range ordered crystal structure and
  specific properties, the intermetallic alloys
  were assumed to fill an existing gap between
  structural ceramics and classical metallic
  alloys.

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Nickel, titanium and iron based intermetallic
alloys represent a group of advanced materials
with low density, high melting temperature,
ordered structure and resistance to
high-temperature oxidation developed for
high-temperature applications.
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Multiphase nickel based intermetallic alloys

• Since some properties (mainly brittleness at room
  temperature and low creep resistance at high
  temperatures) of single phase intermetallic
  compounds Ni3Al and NiAl are not sufficient for
  many structural applications, recent research was
  focused on multiphase alloys and intermetallic
  matrix composites.
• Several new original multi-component alloys with
  a complex type of microstructure were developed
  and prepared by casting technology.

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• Ternary system Ni-Al-Cr was doped by Fe,
  Ti, Ta, Mo, Zr and B additions in order to
  improve room temperature ductility and achieve
  superior creep strength at intermediate
  temperatures.
• With ? (Ni based solid solution) primary
  solidification phaseWith ß (NiAl) primary
  solidification phaseNear eutectic Ni-Al-Cr-Fe
  alloy.

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Main research activities within new nickel based
intermetallic alloys

• Fundamentals of solidification - growth at
  planar, cellular and dendritic solid-liquid
  interfaces

• Microstructure
• characterization of
• Ni-Al-Cr
• based alloys

• Heat treatments of Ni-Al-Cr based alloys
• Room and high-temperature mechanical properties
  of Ni-Al-Cr based alloys  

•  

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•                         (a)                       
                         (b)(a) Dendritic
  structure of multiphase Ni21.9Al8.1Cr4.2Ta0.9M
  o0.3Zr (at.) intermetallic alloy, (b) SEM
  micrograph showing coexisting regions in after
  directional solidification at V 2.78 10-5
  ms-1, D dendrite, I interdendritic region, P
  Cr-based particles.

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Properties

• Resistance to high temperature oxidation,
  nitridation and carburization
• Fatigue resistance superior to that of nickel
  based superalloys
• High yield strength in a large temperature range
• Good tensile and compressive yield strength at
  650 1100 C
• Inferior mechanical properties comparing to those
  of recent single crystalline nickel based
  superalloys.

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Industrial applications

• Transfer rolls
• Heat treating trays
• Centrifugally cast tubes
• Rails for walking beam furnaces
• Die blocks
• Nuts and bolts
• Corrosion resistance tool bits
• Single crystal turbine blades

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Nickel-based superalloy TMS82 during the early
stages of primary creep showing andislocation
ribbon passing through both precipitates and
matrix.
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Mechanical Properties and Microstructure

• Over the last 50 years turbine entry
  temperatures (TETs) have risen from 800ºC to
  1600ºC. Materials developments in all turbine
  components, are critical to achieving this, but
  engine designers are looking for a TET of 1800ºC
  to increase engine efficiency and reduce
  environmental impact.
• We focus on understanding the fundamental
  mechanisms determining the mechanical properties
  of turbine materials and use this to produce
  tools and strategies for materials development
  and life prediction.

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Alloy development of fourth-generation
single-crystal alloys

• Nickel-base single-crystal superalloys can be
  strengthened by the addition of tungsten and
  rhenium, but doing so while maintaining
  reasonable density, stability and environmental
  resistance requires careful optimization of the
  composition and microstructure.

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Creep strength comparison of binary NiAl, alloyed
NiAl single crystals, and a first-generation
single-crystal nickel-base superalloy made at
1026oC (1880oF) and a strain rate of 1x10-6
sec-1.

• Microstructure of a creep-resistant
  NiAl-3Ti-0.5Hf single-crystal alloy.

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Nimonics

• Key component of the microstructure is
  precipitates of (Ni,Fe)3Al ?.
• A modern superalloy might be 60 - 85 ?
• - nickel is effectively a glue holding the ?
  together.

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The yield stress of ?increases with
increasingtemperature (up to about 700ºC)
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Microstructure must be stableAny finely divided
precipitate distribution will tend tocoarsen
driving force is lowering of interfacial
energy.? is nearly exactly lattice-matched to
the Ni matrix.Interfacial energy is nearly zero.
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Alloy Additions

• Ti goes into ? - Ni3(Al, Ti) solid soln
  strengthening of ?
• Cr goes into Ni matrix,
• solid soln strengthening, corrosion resistance
• Co goes into both Ni and ? oxidation and
  corrosion resistance lowers solubility of Al in
  Ni, so enhances ? formation, improves g high T
  stability
• C combines with Cr, gives precipitates in Ni

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• Mo, W solid soln strengthening of Ni
• Ta solid soln strengthening of ?
• B improves grain boundary and carbide / matrix
  adhesion, so suppresses cavity formation in creep
• Hf lt0.5, improves high T ductility (scavenges
• impurities?)
• Y improves oxidation resistance
• Re the latest magic dust 3 extends operating
  temperature considerably.

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Typical Ni-based Superalloys

• Nimonic 115
• Ni, 14.5 Cr, 13.3 Co, 3.8 Ti,
• 5.0 Al, 3.3 Mo, 0.15 C, 0.05 Zr, 0.016 B
• - an early wrought alloy
• MAR M200
• Ni, 9 Cr, 10 Co, 1.5 Ti, 5.5 Al, 0.15 C,
• 0.05 Zr, 0.015 B, 10 W, 2.5 Ta, 1.5 Hf
• - standard cast alloy

Nimonic 80A
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• SRR99
• Ni, 8.5 Cr, 5 Co, 2.2 Ti, 5.5 Al, 9.5 W,
  2.8 Ta.
• - Rolls Royce single crystal alloy
• CMSX-4
• Ni, 6.5 Cr, 9 Co, 1 Ti, 5.6 Al, 0.6 Mo,
  6 W, 6.5 Ta, 3 Re, 0.1 Hf
• - advanced single crystal alloy

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Yield strength, UTS, fracture strain, etc, rather
lessimportant than creep behaviour and
fatiguebehaviour.
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• Nickel-based superalloys represent the current
  state-of-the-art for many high-temperature,
  nonnuclear, power-generation applications.
  However, these superalloys have not been tested
  in creep at the combination of high temperatures
  and very long service times anticipated in space
  nuclear power generation. Designers need to know
  the creep resistance of potential impeller
  materials at realistic temperatures, stresses,
  and environments.

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• MAR-M 247LC is a representative of the cast
  superalloys currently used in impellers and
  rotors where the hub and blades are cast as a
  single unit, and was selected for the present
  evaluations at the NASA Glenn Research Center.
  Most creep tests were performed in air using
  conventional, uniaxial-lever-arm constant-load
  creep frames with resistance-heating furnaces and
  shoulder-mounted extensometers.
• However, two tests were run in a specialized
  creep-testing machine, where the specimens were
  sealed within environmental chambers containing
  inert helium gas of 99.999-percent purity held
  slightly above atmospheric pressure.
• All creep tests were performed according to the
  ASTM E139 standard.

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• The cast MAR-M 247LC had irregular, very coarse
  grains with widths near 700 µm and lengths near
  800 to 12,000 µm. The grains were often longer in
  the direction of primary dendrite growth (see the
  photomicrographs).

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• The microstructure was predominated by about 65
  to 70 vol of Ni3Al-type ordered intermetallic ?'
  precipitates in a face-centered cubic ? matrix,
  with minor MC and M23C6 carbides.
• The sizes of the ?' precipitates varied from
  about 0.4 µm at dendrite cores to 3.0 µm between
  dendrites, because of dendritic growth within
  grains.

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• Creep tests in air were designed to determine
  allowable creep stresses for 700o, 820o, and 920
  oC that would give 1-percent creep in 10 years of
  service, a typical goal for this application.
  This service goal represented a target strain
  rate of 0.1 percent/year. Creep strain rate to
  0.2-percent creep is shown versus stress in the
  following graph. Stresses of about 475, 150, and
  70 MPa were estimated to achieve the target
  strain rate at 700o, 820o, and 920 oC,
  respectively.

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Creep stress versus strain rate for MAR-M 247LC,
showing estimated stresses necessary to achieve a
maximum strain rate of 0.1 percent per year.
Additional creep tests and analyses are
necessary, but a preliminary creep analysis using
current test results indicates quite good
potential for an impeller fabricated of MAR-M
247LC for maximum temperatures to 920 oC .
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• Tests to estimate the effects of air versus
  inert environments on creep resistance were also
  initiated. The results of single tests in air at
  1-atm pressure and in helium at slightly above 1
  atm at 820o and 920oC are compared in the
  following graphs. Creep progressed as fast or
  even faster in helium than in air at 820o and
  920oC.
• The creep tests in air reasonably approximate
  response in helium to low creep strain levels
  near 0.1 percent, but not at high strains. More
  tests are needed for confirmation, but this
  suggests that there may be no improvement in
  creep resistance due to the inert environment .

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Comparison of creep response in air versus
helium. Top 820oC. Bottom 920oC.
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• The new nickel-base alloys represent a major
  departure from previous alloy design practices
  used in industry for single-crystal superalloys.
  Advances in past superalloy development for
  turbine blade applications have been accomplished
  with continued increases in the refractory metal
  content, which significantly increase alloy
  density. High alloy densities have limited the
  use of the advanced superalloys to specialized
  applications.

Measured densities of new low-density superalloys
compared with previously developed superalloys.
The most creep resistant, low-density alloys are
shown here for comparison
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BRIGHTRAY Alloys , INCOLOY Alloys , MONEL
Alloys , NILO/NILOMAG Alloys , NIMONIC
Alloys , Nickel/DURANICKEL Alloys ,
UDIMET/UDIMAR Alloys
 Nickel Cobalt Alloys              The
time-tested nickel NI-SPAN-C alloy 902
WaspaloyNitinol alloys Electroformed Nickel
Foil INCOTHERM alloy TD INCOBAR
DEPOLARIZEDnickel anodes RESISTOHM alloys
The time-tested nickel alloys and cobalt alloys
are highly engineered to offer a superior
combination of heat resistance, high temperature
corrosion resistance, toughness and strength for
the most demanding applications.
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