Daniel Master Thesis Presentation

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High-Entropy Alloys Breakthrough Materials for Aero Engine Applications? By Daniel Svensson, Gothenburg, 13/2 2015

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  • High-Entropy AlloysBreakthrough Materials for Aero Engine Applications?

    By Daniel Svensson, Gothenburg, 13/2 2015

  • Presentation Outline1. Introduction2. High-Entropy Alloys3. Aero Engine Materials4. Bridging the Gap5. Suggested Systems6. Summary


  • Introduction

    GKN Aerospace Engine Systems in Trollhttan manufactures engine parts

    Current superalloys (> 8 g/cm3) High-entropy alloys are potential

    candidate materials3

  • Introduction

    High-entropy alloys is a new type of metallic materials

    Exciting properties Good strength Retain strength at elevated temperatures


  • Introduction

    Review high-entropy alloys Review state-of-the-art aero

    engine materials Identify problems left to solve Suggest potential high-

    entropy alloy systems


  • Presentation Outline1. Introduction2. High-Entropy Alloys3. Aero Engine Materials4. Bridging the Gap5. Suggested Systems6. Summary


  • High-Entropy Alloys

    1. Definition2. Four core effects3. Typical properties4. Processing routes


  • Definition Conventional (low- and medium-entropy) alloys

    1-3 principal components with 1 or more minor componentsSteels, aluminium alloys...

    High-entropy alloys 5-13 principal components (Not the only definition, they can also be defined

    according to their configurational entropy)AlCoCrFeNi, AlMo0.5NbTa0.5TiZr... 8

  • Four Core Effects

    1. High mixing entropy effect Gibbs free energy High configurational entropy can suppress ordered phases Especially at higher temperatures

    9[High-Entropy Alloys - Murty B.S., Yeh J.W., Ranganathan S.]

  • Four Core Effects

    2. Sluggish diffusion effect Fluctuating potential energy

    due to many different elements

    Much coordination of elements needed

    Good elevated temperature properties10

    [Sluggish diffusion in CoCrFeMnNi high-entropy alloys]

  • Four Core Effects

    3. Lattice distortion effect Hinder dislocation movement

    solid solution strengthening Scatter propagating electrons and

    phonons lowered electric and thermal conductivity

    [Solid-Solution Phase Formation Rules for Multi-component Alloys]

  • Four Core Effects

    4. Cocktail effect Properties of HEAs not

    average of those of constituent elements

    Interaction between constituing elements and lattice distortion will affect properties


    [High-Entropy Alloys - Murty B.S., Yeh J.W., Ranganathan S.]

  • Interesting Properties

    Most properties researched has been for some derivations of the Al-Co-Cr-Cu-Fe-Ni system

    Some research on refractory systems (Often melted and cast)


  • Strength The Al-Co-Cr-Cu-Fe-Ni system

    Phase constitution varies with Al content

    Strength dependent on the structure Retain strength at elevated

    temperature, especially fcc type alloys Additional alloying elements (Ti,Mo,Mn,

    Nb,Si) also affect the phase composition


    FCC + BCC



    [Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes]

  • Strength Refractory alloys

    Mostly BCC type, some with ordered phases

    Good elevated temperature strength

    Mostly brittle, though some systems exhibit good compressive ductility

    Also some Al containing systems with relativley low densities


    [Mechanical properties of NbMoTaW and VNbMoTaW refractory high entropy alloys]

  • Fatigue Limited research One FCC type system


    One BCC type systemAl7.5Cr22.5Fe35Mn20Ni15

    Promising results, FCC type slightly better than BCC

    Scattered results, attributed to microstructural defects


    [Fatigue behavior of Al0.5CoCrCuFeNi high entropy alloys]

  • Wear Mainly Al-Co-Cr-Cu-Fe-Ni

    system Not linear with hardness

    as opposed to for ferrous alloys

    Type of wear dependent on constituents (and crystal structure)


    [Mechanical performance of the AlxCoCrCuFeNi high-entropy alloy systemwith multiprincipal elements]

  • Oxidation

    Not much researchAl +(Cr +)Fe -


    [Microstructure and wear behavior of AlxCo1.5CrFeNi1.5Tiy high-entropy alloys]

  • CorrosionVarying corrosion properties, in both H2SO4 and NaCl

    19[Alloying and Processing Effects on the Aqueous Corrosion Behavior of High-Entropy Alloys]

  • Thermal Properties AlxCoCrFeNi

    Thermal conductivity lower than in pure metals Lattice distortion effect Precipitates Nanograins

    Thermal conductivity increase with temperature Lattice distortion Increase in lattice size


    [Microstructure, thermophysical and electrical properties in AlxCoCrFeNi (0x2) high-entropy alloys]

  • Processing

    Casting Most common processing

    route Vacuum arc melting or

    vacuum induction melting Copper mold casting Microstructure depends on

    cooling-rate, heat-treatments, forging 21

    [High-Entropy Alloys - Murty B.S., Yeh J.W., Ranganathan S.]

  • High-Entropy Alloys

    Powder metallurgy More homogeneous Good when having a wide

    range of evaporation temperatures


  • Processing Thin films/coatings

    From vapor state: magnetron sputtering or plasma nitriding

    From liquid state: tungsten inert gas/gas tungsten arc welding or laser cladding

    Additive manufacturing FeCoCrNi from selective laser

    melting Better tensile properties than as-

    cast alloys, attributed to the fine microstructure



  • Presentation Outline1. Introduction2. High-Entropy Alloys3. Aero Engine Materials4. Bridging the Gap5. Suggested Systems6. Summary


  • The Aero Engine

    1. Suck2. Squeeze3. Bang4. Blow



  • Aero Engine Materials Todays aero engines made

    mostly out of four types of alloys Aluminium alloys Steels Titanium alloys Nickel alloys (superalloys)

    Other exciting new materials Ceramics Composites Intermetallics

    26[Manufacturing Technology for Aerospace Structural Materials]

  • Aluminium Alloys and Steels

    Aluminium alloys+ Light-weight (Al density 2.7 g/cm3) Low temperatures Low stiffness

    Steels+ Cheap+ Higher stiffness Not to high temperatures


  • Titanium Alloys

    + High strength to weight ratio+ Good fatigue strength+ Good corrosion resistance Not higher temperatures than ~550o C


  • Nickel Alloys (Superalloys)

    + Able to withstand higher temperatures than Ti alloys

    + High strength+ Good fatigue and creep

    resistance+ Good corrosion and

    oxidation resistance High density


    [Application of alloy 718 in GE aircraft engines: past, present and next ve years, Superalloys 718, 625, 706 and various derivatives]

  • Coatings

    Diffusion coatings (CoAl, NiAl...) Overlay coatings (MCrAlY, WC-

    Co...) Thermal barrier coatings (Y2O3-

    stabilized ZrO2)


    [Tbc experience on ge aircraft engines]

  • Other Exciting New Materials

    Ceramics (SiC,Al2O3...) Composites (CMC,MMC) Intermetallics (NiAl,TiAl...)


  • Density Comparison


    AlCoCrCuFeNi 7.1* g/cm3 Ti-6Al-4V 4.43 g/cm3

    AlCoCrFeNi 6.7* g/cm3 Inconel 718 8.19 g/cm3

    AlMo0.5NbTa0.5TiZr 7.4 g/cm3 Haynes 230 8.97 g/cm3

    VNbMoTaW 12.36 g/cm3 Waspaloy 8.20 g/cm3

    High-entropy alloys Conventional alloys

    * Calculated using rule-of-mixtures with room temperature data

  • Specific Parts

    Lower densities than superalloys Elevated temperature strength

    Hot structural components Turbine Exhaust Case, Mid Turbine Frame, Exhaust

    Nozzle and Cone


  • Turbine Exhaust Case Situated downstream of the

    final turbine Support the low pressure rotor Mount engine to aircraft body Remove angular component of

    outgoing flow Exposed to high temperatures Inconel 718

    34[Weld sequence optimization:The use of surrogate models for solving sequential combinatorial problems]

  • Turbine Exhaust Case

    Separation of functionalities Load Carrying Structure

    Limited by LCF, strength, stiffness, creep/thermo mechanical fatigue and oxidation

    Today Inconel 718 Heat Shielding Fairing

    Limited by temperature capability, formability and oxidation

    Working temperature 670oC, peak temperatures of 760oC

    Solution hardened alloy 35

  • Mid Turbine Frame Situated in between high pressure

    and low pressure turbines Houses the mid turbine bearing,

    supporting low and high pressure rotors

    Similar demands as on the TEC, with a similar separation of functionalities Load carrying structure in Inconel

    718 Heat shielding fairings in Mar-M-

    247 or Mar-M-509


  • Exhaust Nozzle and Cone Integrate with TEC to

    avoid interfaces Limited by creep,

    temperature capability, surface stability and weight

    Today often titanium alloys

    Research into CMCs Boeing


  • Presentation Outline1. Introduction2. High-Entropy Alloys3. Aero Engine Materials4. Bridging the Gap5. Suggested Systems6. Summary


  • Bridging the Gap

    Fatigue and creep Little fatigue research, only two systems Only HCF, not LCF No creep research Good creep resistance can be expected from the sluggish

    diffusion and lattice distortion core effects Conventionally creep resistance is increased by

    coarsening the grains


  • Bridging the Gap

    Oxidation Little research Al and Cr conventionally gives good resistance by forming

    protective layers Property and alloy optimization

    Balancing properties against each other (e.g. strength and ductility)

    Be aware of eventual problems with the used elements (expensive, rare, hazardous etc.) 40

  • Bridging the Gap

    Thermal stability Not well researched Many alloys have been in a metastable

    state Alloys will be exposed to high

    temperatures for extended periods of time

    Manufacturability Materials must be formable and

    possible to join with other materials Property scattering from defects needs

    to be removed/minimized 41


  • Presentation Outline1. Introduction2. High-Entropy Alloys3. Aero Engine Materials4. Bridging the Gap5. Suggested Systems6. Summary


  • Suggested Systems

    Load Carrying StructureAl-Co-Cr-Fe-Ni-Mo

    Heat Shielding FairingAl-Co-Cr-Fe-Ni

    Exhaust Nozzle and ConeAlNbTiV


  • Presentation Outline1. Introduction2. High-Entropy Alloys3. Aero Engine Materials4. Bridging the Gap5. Suggested Systems6. Summary


  • Summary

    High-entropy alloys: new exciting material Four core effects of high-entropy alloys

    High mixing entropy Sluggish diffusion Lattice distortion Cocktail effect


  • Summary

    Potential for low density metallic alloys with good elevated temperature properties

    Candidates for structural components in the hotter parts of aero engines

    Many problems left to solve


  • Acknowledgements

    Chalmers Sheng Guo

    GKN Magnus Hrnqvist Bengt Pettersson Anders Hellgren