High-Entropy Alloys Breakthrough Materials for Aero Engine Applications? By Daniel Svensson, Gothenburg, 13/2 2015
Presentation Outline 1. 2. 3. 4. 5. 6. Introduction High-Entropy Alloys Aero Engine Materials Bridging the Gap Suggested Systems Summary 2
Introduction GKN Aerospace Engine Systems in Trollhättan manufactures engine parts 3 Current superalloys (ρ> 8 g/cm ) High-entropy alloys are potential candidate materials 3
Introduction High-entropy alloys is a new type of metallic materials Exciting properties Good strength Retain strength at elevated temperatures 4
Introduction Review high-entropy alloys Review state-of-the-art aero engine materials Identify problems left to solve Suggest potential highentropy alloy systems 5
Presentation Outline 1. 2. 3. 4. 5. 6. Introduction High-Entropy Alloys Aero Engine Materials Bridging the Gap Suggested Systems Summary 6
High-Entropy Alloys 1. 2. 3. 4. Definition Four core effects Typical properties Processing routes 7
Definition Conventional (low- and medium-entropy) alloys 1-3 principal components with 1 or more minor components Steels, 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 [High-Entropy Alloys - Murty B.S., Yeh J.W., Ranganathan S.] 9
Four Core Effects [Sluggish diffusion in Co Cr Fe Mn Ni highentropy alloys] 2. Sluggish diffusion effect Fluctuating potential energy due to many different elements Much coordination of elements needed Good elevated temperature properties 10
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 [High-Entropy Alloys - Murty B.S., Yeh J.W., Ranganathan S.] 4. Cocktail effect Properties of HEAs not average of those of constituent elements Interaction between constituing elements and lattice distortion will affect properties AlxCoCrCuFeNi 12
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) 13
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 BCC FCC + BCC FCC [Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes] 14
Strength Refractory alloys [Mechanical properties of NbMoTaW and VNbMoTaW refractory high entropy 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 15
Fatigue Limited research One FCC type system [Fatigue behavior of Al0.5CoCrCuFeNi high entropy alloys] Al0.5CoCrCuFeNi One BCC type system Al7.5Cr22.5Fe35Mn20Ni15 Promising results, FCC type slightly better than BCC Scattered results, attributed to microstructural defects 16
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 highentropy alloy systemwith multiprincipal elements] 17
Oxidation [Microstructure and wear behavior of AlxCo1. 5CrFeNi1.5Tiy high-entropy alloys] Not much research Al + (Cr +) Fe AlxCo1.5CrFeNi1.5Tiy 18
Corrosion Varying corrosion properties, in both H2SO4 and NaCl [Alloying and Processing Effects on the Aqueous Corrosion Behavior of High-Entropy Alloys] 19
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 (0 x 2) high-entropy alloys] 20
Processing Casting Most common processing route Vacuum arc melting or vacuum induction melting Copper mold casting Microstructure depends on cooling-rate, heattreatments, forging [High-Entropy Alloys - Murty B.S., Yeh J.W., Ranganathan S.] 21
High-Entropy Alloys Powder metallurgy More homogeneous Good when having a wide range of evaporation temperatures http://what-when-how. com/materialsparts-and- 22
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 ascast alloys, attributed to the fine microstructure http://www.laserstoday.com/2011/05/highperformance-laser-cladding/#more-1035 23
Presentation Outline 1. 2. 3. 4. 5. 6. Introduction High-Entropy Alloys Aero Engine Materials Bridging the Gap Suggested Systems Summary 24
The Aero Engine 1. 2. 3. 4. Suck Squeeze Bang Blow http://en.wikipedia.org/wiki/file:jet_engine.svg 25
Aero Engine Materials Today s 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 [Manufacturing Technology for Aerospace Structural Materials] 26
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 27
Titanium Alloys + + + High strength to weight ratio Good fatigue strength Good corrosion resistance o Not higher temperatures than ~550 C 28
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] 29
Coatings Diffusion coatings (CoAl, NiAl...) Overlay coatings (MCrAlY, WCCo...) Thermal barrier coatings (Y2O3stabilized ZrO2 ) [Tbc experience on ge aircraft engines] 30
Other Exciting New Materials Ceramics (SiC,Al2O3...) Composites (CMC,MMC ) Intermetallics (NiAl,TiAl...) 31
Density Comparison High-entropy alloys Conventional alloys 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 * Calculated using rule-of-mixtures with room temperature data 32
Specific Parts Lower densities than superalloys Elevated temperature strength Hot structural components Turbine Exhaust Case, Mid Turbine Frame, Exhaust Nozzle and Cone 33
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 [Weld sequence optimization:the use of surrogate models 34 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-M247 or Mar-M-509 36
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 37
Presentation Outline 1. 2. 3. 4. 5. 6. Introduction High-Entropy Alloys Aero Engine Materials Bridging the Gap Suggested Systems Summary 38
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 39
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 http://forthillhs.com/students/student% 20subject%20wepages/Welding/index.html 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 Outline 1. 2. 3. 4. 5. 6. Introduction High-Entropy Alloys Aero Engine Materials Bridging the Gap Suggested Systems Summary 42
Suggested Systems Load Carrying Structure Al-Co-Cr-Fe-Ni-Mo Heat Shielding Fairing Al-Co-Cr-Fe-Ni Exhaust Nozzle and Cone AlNbTiV 43
Presentation Outline 1. 2. 3. 4. 5. 6. Introduction High-Entropy Alloys Aero Engine Materials Bridging the Gap Suggested Systems Summary 44
Summary High-entropy alloys: new exciting material Four core effects of high-entropy alloys High mixing entropy Sluggish diffusion Lattice distortion Cocktail effect 45
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 46
Acknowledgements Chalmers Sheng Guo GKN Magnus Hörnqvist Bengt Pettersson Anders Hellgren 47