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Nickel-based Superalloys

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Title: Nickel-based Superalloys


1
Nickel-based Superalloys
2
  • 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.

3
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.
4
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.

5
  • 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 phase With ß (NiAl) primary
    solidification phase Near eutectic Ni-Al-Cr-Fe
    alloy.

6
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  
  •  

7
  •                         (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.

8
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.

9
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

10
Nickel-based superalloy TMS82 during the early
stages of primary creep showing andislocation
ribbon passing through both precipitates and
matrix.
11

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.

12
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.

13
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.

14
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.

15
The yield stress of ?increases with
increasing temperature (up to about 700ºC)
16
Microstructure must be stable Any finely divided
precipitate distribution will tend to coarsen
driving force is lowering of interfacial
energy. ? is nearly exactly lattice-matched to
the Ni matrix. Interfacial energy is nearly zero.
17
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

18
  • 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.

19
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
20
  • 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

21
Yield strength, UTS, fracture strain, etc, rather
less important than creep behaviour and
fatigue behaviour.
22
  • 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.

23
  • 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.

24
  • 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).

25
  • 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.

26
  • 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.

27
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 .
28
  • 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 .

29
Comparison of creep response in air versus
helium. Top 820oC. Bottom 920oC.
30
  • 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
31
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
Waspaloy Nitinol alloys Electroformed Nickel
Foil INCOTHERM alloy TD INCOBAR
DEPOLARIZED nickel 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.
32
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