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Advanced High Temperature Alloys

Advanced High Temperature Alloys
Advanced High Temperature Alloys Prof. Dr.Ing. Uwe Glatzel Metals and Alloys University Bayreuth SS 2015 1 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysLecturer: Prof. Dr.Ing. habil. Uwe Glatzel • born Dez. 1960 • PhysikDiplom (B.Sc. and M.Sc) in Tübingen (exchange year in Corvallis, Oregon, USA) • PhD thesis at the Institute for Metals Research, Technical University Berlin, Prof. Monika FellerKniepmeier • postdoc (1 Jahr) at Stanford University • Habilitation TUBerlin • GerhardHess award of the German Science Foundation (DFG) for young scientist (400.000 €) • 19962003 full professor for Metals and Alloys, Jena • since April 2003 Bayreuth (Chair for Metals and Alloys) postal address: LudwigThomaStr. 36b phone: +49 (0) 921 555555 D95447 Bayreuth, Germany email: uwe.glatzelunibayreuth.de 2 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysLiterature • R. Bürgel, Handbuch HochtemperaturWerkstofftechnik, Vieweg • R.C. Reed, The Superalloys Fundamentals and Applications, Cambridge Univ. Press • M.J. Donachie, S.J. Donachie, Superalloys A Technical Guide, ASM International • H. Frost, M.F. Ashby, DeformationMechanism Maps, Pergamon Press • M.F. Ashby, Materials Selection in Mechanical Design, Elsevier • G. Meetham, M. Van der Voorde, Materials for High Temperature Engineering Applications, Springer • J. Betten, Creep Mechanics, Springer • R.E. ReedHill, Physical Metallurgy Principles, PWSKENT Publishing • D.R. Askeland: Materialwissenschaften, Spektrum Lehrbuch; 1994 • W.D. Callister: Materials Science and Engineering An Introduction, Wiley, New York, 1999 • H. Schumann, Metallographie, Deutscher Verlag für Grundstoffindustrie, Leipzig • F. Vollertsen, S. Vogler, Werkstoffeigenschaften und Mikrostruktur, Hauser Verlag • P. Haasen, Physikalische Metallkunde, SpringerVerlag, Berlin • H.J. Bargel, G. Schulze, Werkstoffkunde, VDIVerlag, Düsseldorf • P. Sarrazin, A. Galerie, J. Fouletier, Mechanisms of High Temperature Corrosion, Trans. Tech. Publ. •N. Cumpsty, Jet Propulsion, Cambridge Univ. Press lecture notes: http://www.metalle.unibayreuth.de then "Lehre" then "Vorlesungen", you will find the link to this lecture notes and three review talks we will do at the end. 3 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysWhat You Should Know: • basic thermodynamics • introduction to diffusion • introduction to dislocations • phase diagrams • theory of elasticity • ... • basic materials science courses 4 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysContent 1. Introduction, Basics 2. Stability of Microstructure 3. Mechanical Properties a) Static b) Cyclic (Fatigue) 4. High Temperature Corrosion 5. High Temperature Alloys 6. Lost Wax Investment Casting 7. Depending on Time: Lectures on a) SX NiBase Superalloys b) LEK 94 c) PtBase Superalloys 5 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysIntroduction • only alloys will be looked at (no ceramics, no polymers). • no coatings (BUT : practically all high temperature systems are coated), simply not enough time. 6 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysMotivation for High Temperature Alloys T T max min η • efficiency of Carnot heat enging T max (with hot and cold temperatures). Several research projects related to jet engines, stationary gas turbines and wastetoenergy plant are carried out within my group with the goal to increase T . max • melting processes (glass, metal, ... ). • chemical process (PTFE, ... ). • many other applications ... • jet engines, see Single Crystal NiBase Superalloys 7 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysMaximum Temperatures for Applications of Different Materials maximum service temperature Group deformation/damage mechanism °C Polymer up to 300 melting, decomposing (pyrolyze) Glass up to 800 viscous flow FeBasis (coated) up to 1100 FeODS up to 1300 Ni and Cobase up to 1200 creep, dislocation climb, Metals Ptbase up to 1600 grain boundary sliding refractory metals in inert atmosphere above 1600 MoSi up to 1800 2 viscous flow, glass transition Ceramics SiC up to 1600 temperature, grain boundary sliding Composits (SiC/C) up to 1600 complex 8 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysOverview Materials source: Plansee AG, Reutte, Tirol, Austria 500 1500 2000 temperature °C 9 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys usable strengthTaking Density into Account 500 1500 2000 temperature °C 10 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys usable strengthOxidation Resistance 500 1500 2000 temperature °C 11 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys usable strengthRefractory Metals: wider definition Most common definition of of refractory metals (refractory = refractory metals widerspenstig, halsstarrig): two elements of the 5. and three elements of the 6. period with melting points higher than Pt. Processing in general T of platinum m by powder metallurgy. 12 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysDensity Os, Ir Pt Re W Au Ta Hf Ru, Rh, Pd Tc Pd Mo Ag Nb Ni 13 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysAbundance of Elements in Earth's Upper Continental Crust to find 1 Rh atom within a bunch of Siatoms is comparable to find one individual person within the word population © U.S. Geological Survey Fact Sheet 08702 (2002) 14 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysMaterial Choice • temperature • environment • moving/nonmoving part • design complexity (how to manufacture) • price constrictions (depending on application of system). Reduction of 1 kg in weight: – car 0 5 € – plane 100 – 500 € – aerospace 100.000 500.000 € 15 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysInfluence of ... on ... • temperature: – phase transitions, volume fractions, ... – diffusion ( recrystallization, dislocation climb, diffusional creep, ... ) – thermal fatigue (TF) • mechanical: – creep – fatigue (low cycle, LCF, high cycle fatigue, HCF) • environment: – oxidation – corrosion • combinations: – thermomechanical fatigue (TMF) – stress corrosion cracking, stress oxidation, ... 16 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysBasics Thermodynamics ↔ Kinetics Boltzmannstatistics: energy of movement increases with temperature 3 u kT kin B atom 2 3 Q u 2 u 2 kT 3kT  total kin B B atom atom RT 2  e 0  0,33 eV, bzw. 32 kJ/mol bei 1000°C Arrheniusplot U 3 RT total mol 17 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysVacancy Concentration F = U T·S  nonzero vacancy concentration is in thermodynamic equilibrium Q vac  nickel Q = 1,36 eV (energy necessary to create one vacancy) RT vac c e v T°C 20 300 450 800 1000 1200 1454 T/T 0.17 0.33 0.42 0.62 0.74 0.85 1.00 m 23 12 9 6 5 5 4 c 10 3·10 10 10 10 7·10 3·10 v equilibrium vacancy concentration for nickel 18 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysNickel Vacancy Concentration Q vac  0 kT 10 B c e v T /2 m 5 10 with: nickel 10 Q = 1,36 eV 10 vac 5 k = 8.60210 eV/K B 15 10 1,00 20 10 0,75 Nickel Vacancy Concentration Nickel Vacancy Concentration 0,50 25 10 0,25 0 200 400 600 800 1000 1200 1400 1600 0,10 T m temperature °C 0 200 400 600 800 1000 1200 1400 1600 T m temperature °C 19 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys vacancy concentration 4 vacancy concentration 10 Diffusion  jDc 1. Fick's law 2 1 j = (atoms) · m · s 2 1 D = m · s 3 c = (atoms) · m vacancy diffusion or volume diffusion 20 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCoefficient of Diffusion Q energy to create a vacancy vac Q activation energy to migrate a vacancy migration Q activation energy for volume diffusion sd Q = Q + Q sd vac migration (QQ ) Q vac migration sd kT kT D De De 0 0 nickel Q≈ 17 ·k ·T Q≈ 2.5 eV = 244 kJ/mol sd B m sd (for a perfect crystal; defects will lower the activation energies) 21 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysQ versus T sd m 600 kJ/mol 500 kJ/mol 400 kJ/mol 300 0.137 kJ/(mol·K) ≈ 17 · k ·NT B A m T (K) m 22 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysDependence Melting Point and Enthalpy of Vacancy Creation T 17·R·T Q crystal m m vac element °C eV eV structure Pb 327 0.88 0.57 fcc Al 660 1.36 0.68 fcc Cu 1 085 1.99 1.29 fcc Ag 1 235 2.21 1.12 fcc Ni 1 455 2.53 1.78 fcc Pt 1 768 2.98 1.32 fcc Mo 2 623 4.23 3.00 bcc W bcc 3 422 5.40 4.00 23 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCoefficient of Diffusion Steep slope indicates a high activation energy. fcc Small elements diffuse γiron bcc faster. αiron Diffusion in fcc crystals slower than in bcc crystals. 24 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCoefficient of Diffusion with Defects surface diffusion Coefficient of diffusion of Th in W. grain boundary diffusion Overall velocity for diffusion depending on grain boundary volume diffusion thickness, grain size and pipe dislocation density. diffusion 25 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysPipe Diffusion D = D + a · ρ · D eff sd disl. disl. disl. a area of dislocation core disl. 2 2 ( ≈ 5 b≈ 0.3 nm ) volume diffusion dominant ρ dislocation density pipe diffusion dominant D pipe diffusion along disl. dislocation core disl. increasing sd atom flux D·area decreasing atoms  2 atoms  2 Dd  sd grain Dbn  disl. time  grain time  disl. dashed line: diffusion in crystal by the velocity of pipe diffusion 2 D b 2 2 sd Dd Dbn  identical atom fluxes if: sd grain disl. D d disl. grain 26 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysGrain Boundary Diffusion D = D + π ·  / d · D eff sd grain bound. gb volume diffusion dominant with: grain boundary diffusion dominant  effective grain boundary fine grain thickness ( ≈ 2 b ≈ 0.5 nm) gb coarse d grain size grain sd D pipe diffusion along dislocation disl. core dashed line: diffusion in crystal by the velocity of grain boundary diffusion D 2 sd Dd Dd identical atom fluxes if: sd grain gb grain D d gb grain 27 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysDiffusional Creep • NabarroHering creep (pure volume diffusion) D  self diffusion   2 NH 2 d kT grain Cc • Coble creep (grain boundary diff.) NHc D  grain boundary   2 C 3 d kT grain  thickness of grain boundary, Ω atomic volume 28 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCombined NH and Coble Creep:  DD  D self diffusion grain boundary eff    2  diffusion creep NH C 2 3 2  kT d d kT d grain grain grain  D grain boundary D D eff self diffusion d grain for real geometry (noncuboidal grains) D D gb sd D identical creep rates if: sd d D d grain gb grain 29 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysActivation Energies Indicating Mechanism Changes 150 kJ/mol Q sd 100 kJ/mol 50 K temperature 0 200 400 °C 600 Single crystal aluminium, oriented such that 110111 slip is activated. Lytton, Shepard and Dorn, Trans. AIME 212 (1958) 220 30 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysDiffusion in Ordered Structures (Intermetallic Phases) • High binding energies  high activation energies  low coefficient of diffusion • Example NiAl: very high enthalpy of ordered B2 structure  high enthalpy outweighs low entropy  ordered up to T m Ni T = 1,455°C m Al T = 660°C m NiAl T = 1,638°C m 31 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysSummary: Effects of Diffusion on High Temperature Alloys • fcc preferred: lower coefficient of diffusion (D factor of close to T m 13 2 1 12 2 1 10 lower than bcc (D = 210 m s , D = 210 m s ). Ni Cr • Grain size as large as possible (→ directionally solidified or single crystal parts) • intermetallic phases helpful: at least a factor 2 lower coefficient of diffusion. At 1000°C: 16 2 1 Ni in Ni: 2.210 m s 16 2 1 Ni in NiAl and Ni in Ni Al: 110 m s . 3 • low dislocation density helpful (implies lower stress levels, which is helpful in general) 32 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysSecond Fick's Law Can be concluded directly from first Fick's law.  c  Dc  t Similar in heat transfer systems, electrical potential, ... . f (x)1x 1 1  x f (x)1  0.8 2 0.5  0.6 f (x) 1  x 0.4 f (x)1  3 f (x) 0.05  2 0.2 f (x)  3 x solution to these  c(x, t) c c c 0.5 1 1.5 2 1 1 0  2 D t boundary conditions:  33 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysThermal Conductivity The most simple, stationary case: no heat radiation, constant temperatures in front and back of component. λ … coefficient of heat (or thermal) conductivity: λ = a · c · ρ p a … coefficient of temperature conductivity c … heat capacity p ρ … density  ... coefficient of heat transfer compare:    jDc qλT  c T  Dc aΔT  t t 34 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysTemperature Distribution with Thermal Barrrier Coating (TBC) cooling air hot air Wärmedämm Haftvermittlerschicht Grundwerkstoff TBC bond coat substrate schicht In case of transients, the temperature should reach a stable distribution as fast as possible in order to reduce thermal stresses ( temperature conductrivity as high as possible). In case of stationary circumstances, heat conductivity leads to heat flow into the solid. 35 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysMaterial Parameters at RT heat cond. heat cap. density temp. cond. λ cρ a p material/property 2 W  J m g 6 10   3 m K  kg K s cm  ferritic steel 45 460 7.8 13.0 austenite steel 15 500 8.0 3.8 Nibase alloys 11 450 8.2 3.0 Mo 145 240 10.2 59.0 Ti alloys (rich) 7 530 4.5 2.9 Al 210 890 2.7 87.0 Al O bei RT 25 800 3.9 8.4 2 3 ( Al O bei 1000°C ) ( 6) 2 3 source: Bürgel Attention: Heat conductivity strongly depends on alloy composition, see steels and pure Ni with 91 W/(mK) in comparison to Nibase alloys with 11 W/(mK) 36 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysContent 1. Introduction, Basics 2. Stability of Microstructure 3. Mechanical Properties a) Static b) Cyclic (Fatigue) 4. High Temperature Corrosion 5. High Temperature Alloys 6. Lost Wax Investment Casting 7. Depending on Time: Lectures on a) SX NiBase Superalloys b) LEK 94 c) PtBase Superalloys 37 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysMicrostructure is NOT stable annealed deformed stressrelieved recrystallized 38 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysRecrystallization fully recrystallized time dependence of recrystallization can be approximated by AvramiJohnsonMehl function: partly recrystallized n  t   t  0 f1 e r , deformed 39 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysGrain Coarsening • driving force: reduction of grain boundary energy • T 0.7 · T m • no predeformation necessary • selfsimilar system 1/3 • Ostwald ripening d t (big grains eat up small grains) • new grains have low dislocation density 40 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysGrain Coarsening monomodal bimodal (some grain boundaries are pinned, e.g. by precipitates) 41 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysPrecipitate Hardening Requirements: • solid solution at higher temperatures (ability to homogenization heat treatment) • during cooling a twophase region should be reached solution heat treatment • in general: cooling rate as high as possible, thereafter quenching annealing (in the twophase annealing region) to let grow the furnace cooling precipitates 42 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysThermodynamic ↔ Kinetic 43 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysExample: AlCu Alloy GuinierPreston solution heat treatment Zones leading to θPrecipitates quenching (Al Cu) have 2 paved the way annealing annealing to the success of quenching Alalloys supersaturated solid solution 44 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysOther Examples of precipitate hardening: Al Cu in AlCu alloy: 2 platinumbase superalloy nickelbase superalloy 45 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysTime Dependence of Precipitation Hardening nucleation, growth, coarsening T = const. d precipitate sizeλ distance between precipitates T T f volume fraction of precipitates T 46 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCoherent Semicoherent Incoherent (mit Orientierungsbezug) (ohne Orientierungsbezug) a a a a a a a p m p m p m misfit  : 1  a a a a a 2 p m m p 47 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysEnergy Consideration for Precipitate Hardening G =G +G +G +G total vol boundary strain defect total change in free enthalpy strain enthalpy (elastic energy + dislocation line energy) reduction of enthalpy by precipitation coupled with a defect enthalpy of phase boundary (scales with surface) enthalpy of formation of matrix to precipitate (scales with volume) 48 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysHeterogeneous Nucleation dislocations subgrain grain boundaries boundaries surface (internal and external) vacancy cluster stacking faults incoherent coherent precipitates twin boundaries 49 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysTEMMicrograph of TiC Precipitates at Dislocations in an Austenitic Steel 50 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysOstwaldRipening of Precipitates 3 3 d d Dt here for T/T 0.74 0 m 1 year ' particle size in IN 738 LC at T = 920°C. particle coarsening constant of 1/3 50 nm · h +0,5 µm after 1.000 h +1 µm after 8.000 h 51 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysContent 1. Introduction, Basics 2. Stability of Microstructure 3. Mechanical Properties a) Static b) Cyclic (Fatigue) 4. High Temperature Corrosion 5. High Temperature Alloys 6. Lost Wax Investment Casting 7. Depending on Time: Lectures on a) SX NiBase Superalloys b) LEK 94 c) PtBase Superalloys 52 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysRoom Temperature (RT) versus High Temperature (HT) Deformation • most alloy properties at room temperature are time and rate independent (elastic constants, tension stress, ... ), tension stress experiment. • For T 0.4 · T the properties (deformation) will be time m temperature and rate dependent, creep experiment. solid solution precipitate deformation hardening fine grain hardening strengthening hardening cold deformation (RT) strong medium medium to strong medium to strong temporary hardening, reduced strength with reduced creep rupture fine grain material creep (HT) medium medium to strong strength, may lead to  coarse grain, recrystallization better single crystal 53 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysElastic (E)Modulus and Poisson's Ratio Nibase superalloys 120 115 110 105 0,39 0,41 85 1000°C E G shear modulus G 2(1) 54 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysChange in Materials Properties with Temperature Material properties of steel and Nialloys at elevated temperatures. Comparison between shortterm and long term parameters. 55 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysTension ↔ Creep Experiment (UTS) (YS) design by t 1 design by YS or UTS 56 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysHigh Temperature Deformation • dislocation glide (Peierls stress, in fcc and hcp very small and for T 0.15 T negligible) m • cross slip of screw dislocations and dislocation interactions (for a low stacking fault energy  larger dislocation spacing  thermal activation necessary, T 0.2 T , influence on deformation rate) m • climb of edge dislocations to overcome obstacles: diffusion at complete dislocation line  T 0.4 T m 57 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysDislocation Climb climb of edge dislocations to annihilate each other. arrangement in low energy configurations (subgrain boundaries), climbing around abstacles (leaving the glide plane) movement of screw dislocations with kink 58 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys59 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysInternal Back Stress Dislocations climb allows annihilation of dislocations and to establish a constant dislocation density, resulting in an internal back stress of: Gb int. G b 1 1    = and dislocation r 2 r G shear modulus, α constant 0.3 1, b magnitude of Burgers vector 60 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCreep Experiment behavior of pure metals: primary secondary tertiary: 61 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCreep Experimental Setup up to 1400°C Constant temperature and stress or load 62 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCreep Experimental Setup for Electrical Conductivity Material up to Melting Temperature Pyrometer from left, optical strain measurement from right, both contactfree. 63 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysInterrupted creep tests single crystal (SX) nickel base superalloy (habilitation thesis Glatzel) 7 6 8x10 6 001 orientation, 1123K, 650MPa 6 6x10 5 001 orientation, 1123K, 650MPa 4 6 4x10 3 2 6 2x10 1 0 0 0 10203040506070 0 10203040506070 time h time h 5 10 1123K, 650 MPa logarithm of strain rate versus strain 6 10 (most valuable information for materials scientist) 7 10 01 2345 6 64 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys strain strain strain rate 1/s strain rate 1/sDifferent Creep Stages • primary creep: strain rate dε/dt decreases  material hardens • secondary creep stage: strain rate constant  hardening and softening are in equilibrium  dislocation multiplication and annihilation in equilibrium  disl. density ρ = const. • tertiary creep: necking (creep pores) develop  local stress and strain rate increases drastically. 65 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysWorld Record Japan, Germany NIMS: 14.853 days on 24. Feb. 2012, probably still running (started in 06/1969) Siemens: 14,852 days terminated in 2000 http://www.nims.go.jp/eng/news/press/2011/02/p201102240.html 66 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysModelling of Primary and Secondary Creep Stage  velocity density    bv and: Preußner et al. Int. J. Plasticity 25 (2008) 973 67 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysProblem with Low Creep Rates Life time of stationary gas turbines 20 years and  = 3 max. 11 1 ≈ 5·10 s   steady state 9 1 Reliable data in lab down to 1·10 s : Δl= 1 μm with l = 25 mm after 10 h 0 ≈ 3.5 strain per year Within university labs we are two orders of magnitude too fast compared to real life of a stationary gas turbine 68 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysEngineering Creep Curves raw data creep curves: time to failure:  time – strain (e.g. 1)  isochrone strain isochrone time to failure: 69 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysNatural Creep Law   b v steady state 2   external   G b  1 v  external 3  external   natural creep law  2 G b 70 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysNorton Creep Law (Empirical) Q creep with Norton creep exponent "n" n RT  ε Aσe steady state external and Q≈ Q creep self diffusion power law break stress dependence down (plb) of the stationary T = const. creep rate of the austenitic steel 800 dislocation H at 900°C and climb 1000°C: diffusional creep 71 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysTemperature Dependence of Stationary Creep Rate fcc alloys:  = 28 MPA = const. Ni Q≈ 244 kJ/mol sd Fe Q≈ 290 kJ/mol sd n Qc   3,5 RT   A e  s SF E  this equation used in: Fleischmann et al., Acta Mat. 87 (2015) 350 Austenitischer Stahl 800H 72 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysActivation Energy for Creep slope = 1 73 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysConstant Load ↔ Constant Stress n n  F F(1)  n n n   1  0 0 0 0 0  A A   0 failure in case the gauge length deforms uniform with constant volume This method is applicable to determine the stress exponent "n" only, if the secondary creep state lasts to at least 10  ln = ln + n · ln + n · ln (1+ε) = const. + n · ln (1+ε) 0 0 74 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysAshby Deformation Mechanism Maps n = 3 75 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysAshby Deformation Mechanism Maps Versetzungsklettern dislocation climb 76 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysDeformation Mechanisms: Elastic Deformation: Spontaneous and reversible deformation. In the elastic region:  = E· (rule of 3 thumb: ≈10 , but definitely 1). Plastic or nonreversible deformation achieves way higher e, max strains. Coblecreep (grain boundary diffusion) is in theory possible even at 0 K. Dislocation Glide: … without significant time dependent recovery (climb). Is dominant in the complete temperature regime from 0 K up to the melting point T at moderate and higher stress levels. At low m temperatures ( 0.4T ) dislocation glide has the lower boundary in the range of the elastic stress limit m 3 (typically 10E). Dislocation Climb: At higher temperatures ( 0.4T ) and lower stress levels dislocation climb plays the m n major role = time dependent constant strain rate (d/dt)  , with a Norton stress exponent inbetween ss 3 und 8. Diffusional Creep: In principle over the complete temperature regime (0 K T ). Relevance only at very m low stress levels and T close to T : Coblecreep (grain boundary diffusion). For geological times a time m dependent deformation can be determined. Transition to NabarroHerring creep (volume diffusion) is dependent on grain size and grain boundary thickness. The transition temperature from coble to Nabarro Herring creep can be explained by the different activation energies of volume and grain boundary diffusion. 77 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCreep of Alloys (assuming solid solution, no precipitates) a) interaction dislocation Gb i solid solution and impurity (low temp.) b) stationary dislocation pinned by impurities (Cottrell clouds) c) pulled off Cortrell clouds (Lüders bands) d) gliding dislocation trails impurities behind (viscous glide) e) impurities faster than dislocation (very high temp., no hardening) f) annihilation due to dislocation climb 78 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysPrecipitate Hardening Gb i solid solution precipitate threshold stress concept (with n ≈ 3 4 and Q = Q ): creep self diffusion n Qc   0 RT   A e  ss E  coherent and semi incoherent phase mechanism temperature coherent phase boundaries boundaries cutting 0 K up to T yes no s bypass by Orowan 0 K up to T yes yes s climb over obstacles 0.4T yes no s 79 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysOrowan Stress Line tension leads to a back stress, the Orowan stress, due to obstacles L (in most cases precipitates) with an average distance L between these 2r Tsin precipitates.  T T r  G b σ Orowan L 80 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysHardening Mechanisms as Function of Precipitate Size d initial precipitate size T0  and  arbitrary external stress levels 1 2 = cutting   d passing by: T 1   climbing: 2 d T Cutting is relevant only for coherent precipitates  Dependence of stationary creep rate on initial precipitate size for two different external stress levels 81 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysPinning of Dislocations by Carbides in Austenitic Steel T = 1000°C, σ = 25 MPa, carbides of the type TiC und M C 23 6 82 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysVery High Volume Fractions Volume fractions of 70 are only achievable with nonspherical precipitates. Spacing between precipitates is getting smaller  Orowan stress ≈ G·b/L necessary. For small strains precipitates are not cut by Orowan dislocations. With G = 90 GPa, b = 0.25 nm, L ≈ 75 nm = ≈ 300 MPa Orowan nickel base superalloys ODS alloys: 3 G b f γ' ≈ Orowan d part. 83 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysDispersion Hardening (oxide dispersion strengthened alloys (ODSalloys)) yield precipitate strengthened stress dispersion strengthened temperature T m temperature regime for backside pinning of dislocation by dissolution of precipitates ODSparticle (Rössler + Arzt) 84 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysSummary: Hardening Mechanisms Gb Internal back stress in steady state regime: i Orowan stress in case of precipitates or particles: ≈ G·b/L Orowan Δ r σ const. Solid solution strengthening: solid solution r Δa σ Eε E coherency misfit In case of coherent precipitates: a Size effects, see paper E. Arzt (Acta mat. 46 (1998), 56115626) 85 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCreep Damage creation of a creep pore in poly crystalline material due to disloction glide: a) cracks at grain boundaries b) cavities (micropores) at grain boundaries 86 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysCreep Damage fracture nucleation, not detectable with OM micropore, difficult to detect micro cracks pear necklace like chain of micropores (easy detectable) 87 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysExtrapolation of TimetoFracture Data (LarsonMiller plot, LarsonMiller parameter) MonkmannGrant relation with constant K and exponent m ≈ 1: K t  ln(t ) K mln f m↔ f ss   ss Q Q creep creep 1  n  ln( ) B B RT RT ↔  ss 1 2 ε Aσ e B e ss 0 T 1 1 ln(t ) K m B m B C P f 1 2 1952 GE T T with material dependent constants C and P. 3 Nibase → LarssonMiller plot: P = TC + ln(t )10 , with C = 20, T in K, t in h f f Example: t =100 h, T = 1273 K → P = 31.3 (relation t with T atσ = const.) f f 88 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysLarsonMillerPlot stationary gas turbine, about 20 years of service 130.000 h Comparison of CMSX6, LEK 94 and CMSX4, patent Wöllmer, Glatzel, 3 Mack, Wortmann P=T20 + ln(t )10 (T in K, t in h) f f 89 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysComparison LEK 94 with CMSX4 and CMSX6 3 CMSX6 Wortmann 88 8.0 g/cm 3 CMSX4 Erickson 94 8.7 g/cm 500 3 CMSX4 Frasier 90 8.7 g/cm 3 LEK2 8.5 g/cm 3  K LEK4 8.2 g/cm 3 LEK5 8.2 g/cm 3 LEK3 8.1 g/cm 3 LEK6 8.3 g/cm 3 LEK1C 8.4 g/cm 230 3 LEK1B 8.3 g/cm 3 LEK1A 8.2 g/cm T = 10 K  K 120 Not corrected 10 K regarding density 25 26 27 28 29 30 31 32 LarsenMillerparameter 3 P = T (20+log t ) 10 f 90 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys stress MPaContent 1. Introduction, Basics 2. Stability of Microstructure 3. Mechanical Properties a) Static b) Cyclic (Fatigue) 4. High Temperature Corrosion 5. High Temperature Alloys 6. Lost Wax Investment Casting 7. Depending on Time: Lectures on a) SX NiBase Superalloys b) LEK 94 c) PtBase Superalloys 91 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysTime Dependent Variation of Stress and/or Temperature and/or ... Wöhler diagram for T 0.4·T . Z time fatigue limit, D endurance m fatigue limit 7 a) type I metal (bcc) b) type II metal (fcc) endurance limit at 2·10 92 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysChange in Wöhler Diagram with Temperature and Holding Time 10 CrMo910 93 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysThermal Fatigue Thermal breathing of turbine blade: a) heating phase: edges reach high temperatures faster than interior b) cooling phase: edges cool faster than interior c) repeated thermal cycles lead to thermal fatigue cracks at edges 94 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysThermal Strains and Stresses : ε = α · ΔT, or: σ = E · ε thermal thermal thermal thermal  = E · α · ΔT thermal thermal 95 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysLower EModulus is Helpful: 111 001  orientation of single crystals in 100 direction reduces thermal stresses Siebörger et al., Mat. Sci. Eng. A298 (2001) 26–33 96 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysAnisotropy and Temperature Dependence of Elastic Constants in Nibase Superalloys D. Siebörger, H. Knake, U. Glatzel, Mat. Sci. Eng. A298 (2001) Orientation dependence of Young’s modulus E of matrix phase. Distance from the center to the surface indicates the magnitude of the Young’s modulus in this direction. 97 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysTMF and many other Time Dependent Test Techniques Can not be covered in this lecture 98 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysContent 1. Introduction, Basics 2. Stability of Microstructure 3. Mechanical Properties a) Static b) Cyclic (Fatigue) 4. High Temperature Corrosion 5. High Temperature Alloys 6. Lost Wax Investment Casting 7. Depending on Time: Lectures on a) SX NiBase Superalloys b) LEK 94 c) PtBase Superalloys 99 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysHigh Temperature Corrosion • oxidation: external and internal, passivation • carburization (internal carbides) • nitration: internal, seldom nitrite passivation • sulfurization: external (sometimes passivation), seldom internal Worldwide 1 ton iron per minute corrodes to rust (low temperature aqueous corrosion). 100 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysEllinghamRichardsonDiagram right hand and lower axes air  O partial pressure at T = 0. 2 As an example p of O 2 15 20 17 10 Pa = 10 bar = 10 mbar HV is shown as a dashed line. UHV only the oxides below this line are thermodynamic stable. 101 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysTime Dependent Oxidation 102 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysOxidation Mechanisms • logarithmic (not shown)  low temperature oxidation which eventually comes to a stop or no measurable increase in oxide scale thickness (e.g. Al, Cr, Mg). 2 • parabolic mass change (Δm/A) t. Diffusion through oxidation layer either oxygen or metal. Most favorable oxidation behavior (Al passivation at high temperatures). • linear mass change: oxide layer with cracks  continuous contact with metal (e.g. Ta, Nb). • mass loss: volatile oxides  catastrophic oxidation (e.g. V, Mo, W, Cr, Pt). You can see it inside a broken light bulb. 103 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysPillingBedworth Ratio PB = (volume of oxide of one metal atom)/(volume of metal atom) Oxide TiO MgO Al O MgO Ti O ZrO Ti O NiO FeO TiO CoO 2 3 2 2 3 2 3 5 2 PB 0.70 0.81 1.28 1.34 1.50 1.56 1.65 1.65 1.70 1.73 1.86 Oxide Cr O FeCr O Fe O Fe O SiO Ta O Nb O W 2 3 2 4 3 4 2 3 2 2 5 2 5 PB 2.05 2.10 2.11 2.15 2.15 2.50 2.68 3.40 ideal is 1.1 to 1.3 Of course thermal expansion coefficients also play a major role for the stability of oxide scales. 104 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysAlloying Effects: different elements have different oxygen affinity concentration changes diffusion rates are different oxide layer contains other metals 105 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysExample NiCrAl  Ni Cr 10 Al 5 oxide layer and internal oxidation occurs 1000°C 106 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysObservations for the Superalloy Rene N5 Bensch et al., Acta Mat. 2010 and Acta Mat. 2012 layer number layer composition properties 1 cover oxide layer NiO, CoO thick and porous monophase layer 2 interlayer of oxides NiAl O , NiTa O , Cr O thick and porous layer consisting of two fractions 2 4 2 6 2 3 3 third oxide layer Al O dense and thin monophase layer 2 3 4γ’free layer see Tab. 1 Alcontent of 2.2 wt. 5γ’ reduced layer composition inbetween layer number 4 and 6 reduced Al content, γ’ morphology change 6 twophase centre region nominal composition of René N5 (Tab. 1) regular γ’/ γ structure, see Fig. 6 f) 107 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysContent 1. Introduction, Basics 2. Stability of Microstructure 3. Mechanical Properties a) Static b) Cyclic (Fatigue) 4. High Temperature Corrosion 5. High Temperature Alloys 6. Lost Wax Investment Casting 7. Depending on Time: Lectures on a) SX NiBase Superalloys b) LEK 94 c) PtBase Superalloys 108 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysHigh Temperature Alloys T 500°C, Application in: • energy generation • engines (cars, trains, airplanes, ships, ... ) • chemical industry • metallurgy • mechanical engineering 109 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysOverview Metals ele struc T T max. Osolubility advantages/disadvantages trans. m 3 m. ture °C g/cm at. Ti 882 4.5 31.9 + low density  hdp  krz 1855 4.5 8 + high melting point + abundant available 5 1 +low  ( 10 K ) th.  no alloy known with adequate strength for temperatures 600°C  high oxygen and nitrogen solubility 700°C, increased brittleness  linear oxidation 800°C  low thermal conductivity  ignition hazard V krz 1910 6.1 17 catastrophic oxidation; T (V O ) = 658°C m 2 5 Cr krz 1863 7.2 0.0053 very brittle at RT; conventionally not processable Mo krz 2623 10.2 0.03 + very high creep strength +low , high thermal conductivity, good thermal fatigue strength th  very brittle at RT  catastrophic oxidation; T (MoO ) = 795°C m 5  no long lasting coating available W krz 3422 19.3 0 + highest melting point of metals (only C with even higher T ) m + very high creep strength +low  , high thermal conductivity, good thermal fatigue strength th  very brittle at RT  catastrophic oxidation 1000°C durch hohe WO Abdampfrate 3  no long lasting coating available  very high density 110 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysOverview Metals elem. structure T max. O advantages/disadvantages trans. 3 T g/cm solubility m °C at.  krz 912 7.9 0.0008 + very good corrosion resistance by alloying with Cr or (Cr + Al)  kfz 1395 7.7 0.0098 +structure can be stabilized down to RT (by Ni) Fe  krz 1538 7.4 0.029 + very good processable and weldable + low cost ( 1 €/kg)  strength at high temperatures ( 700°C) limited Co hdp 422 8.8 0 + very good corrosion resistance by alloying with Cr or (Cr + Al)  kfz 1495 8.7 0.048 + Coalloys castable in air good weldability  only moderate hardening available  Niadditions necessary to stabilize fcc structure, reduces strength Ni kfz 1455 8.9 0.05 + broad possibilities for alloying, high strength increase possible by alloying with Al, leading to 'phase (Ni Al) 3 + very good corrosion resistance by alloying with Cr or (Cr + Al) + processable  relatively low melting point  high, low thermal conductivity th. Pt kfz 1772 21.5 0 + high corrosion and oxidation resistance + high melting point  very high density  very expensive ( 33 €/g) 111 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysEvolution of materials used in aeroengines The earlier approach of technology transfer from military to civil is tending to switch direction. © www.azom.com 112 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysExample of Intermetallic Phases (NiAlSystem) 113 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysNiAl Intermetallic Phases phase structure T advantages/disadvantages  trans. 3 T g/cm m °C Ni Al L1 1383 7.5 + anomalous temperature dependence of strength 3 2 + same structure base than Ni matrix (fcc) + stable for larger Al variations 1 wt. Al + ductile as single crystal  high density  brittle as polycrystal (can be hindered by boron doping (grain boundary strengthener) Alcontent not sufficient to build stable Al O layer  reduced high 2 3 temperature oxidation resistance NiAl B2 1638 5.85 + very good oxidation resistance, since 30 wt. Al + high melting point + low density + ordered structure up to melting point + high thermal conductivity + low coefficient of thermal expansion  extremely brittle at temperatures below 500°C (von Mises criterion not fulfilled)  low strength at high temperatures 114 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysNiAl, B2 Ordered Intermetallic Phase • At a first sight very interesting (see advantages) but despite many efforts and many 100 Mio. US research money spent, up today no bulk usage of NiAl has been achieved. • BUT: aluminum coatings leading to NiAl layers is heavily used. 115 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysContent 1. Introduction, Basics 2. Stability of Microstructure 3. Mechanical Properties a) Static b) Cyclic (Fatigue) 4. High Temperature Corrosion 5. High Temperature Alloys 6. Lost Wax Investment Casting 7. Depending on Time: Lectures on a) SX NiBase Superalloys b) LEK 94 c) PtBase Superalloys 116 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysMTSFactory in Bayreuth groundbreaking ceremony: 20.02.2008, toppingout ceremony: 06.06.2008 start of production: 12/2008 117 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysMTSFactory, June 2008 118 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysMTSFactory, June 2008 119 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysMTSFactory, June 2008 120 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysProcessing of a Turbine Blade FPI XRay Turbine Casting Feinguss, Wachsausschmelzverfahren, lost wax investment casting, ... Additionally: hollow geometries possible (core insertion) 121 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysArchaeological Evidence (Bibracte) 50 B.C. Turbine Casting ceramic mould filled with wax cloth clip 122 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and AlloysSingle Crystal Casting Metals and Alloys, Bayreuth 20 s 0,8...400 mm/min University Bayreuth, Advanced High Temperature Alloys 123 Uwe Glatzel, Metals and AlloysContent 1. Introduction, Basics 2. Stability of Microstructure 3. Mechanical Properties a) Static b) Cyclic (Fatigue) 4. High Temperature Corrosion 5. High Temperature Alloys 6. Lost Wax Investment Casting 7. Depending on Time: Lectures on a) SX NiBase Superalloys b) LEK 94 c) PtBase Superalloys 124 University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys