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Seminar in Computational Thermodynamics & Kinetics             with Thermo-Calc Software               Madrid, 1-2 June, 2...
Outline • The fundamentals: assessments • Composition tuning of a high speed steel • Development of master alloys for powd...
THE FUNDAMENTALS:ASSESSMENTST. Gómez-Acebo, "Thermodynamic Assessment of the Ag-Zn System", CALPHAD22 (2), 203-220 (1998)d...
Thermodynamic assessment                                • Review of literature                                  data:     ...
Thermodynamic models: Gibbs energy                                                                                    E Gm...
Summary of Ag-Zn assessment • 50 literature sources (papers) • 700 experimental points • Model 7 phases: L, , , , , ,   – ...
COMPOSITION TUNING OF AHIGH SPEED STEELV. Trabadelo, S. Giménez, T. Gómez-Acebo and I. Iturriza, “Critical assessment ofCo...
Sintering of high speed steels • Complex chemistry:    – Fe-Cr-Mo-Co-V-W-C-N    – High C content: carbides • Optimum Sinte...
M2 HSS: validation of database (SSOL2)  Experimental DT analysis        Reported OST
M35MHV: identification of the stablephases      All phases in SSOL        Only observed phases: L, bcc ( ), Including gas,...
M35MHV: effect of C and NFe–1.80C–4.0Cr–5.4Mo–5.5Co–0.035N–4.2V–6.0W–0.06O, with C additions, sintered in90N2-9H2-1CH4    ...
M42HVIG vs M35MHV • New experimental HSS: M42HVIGHSS       C    N*    O*    Cr   Co   Mo   V    W    Si   FeM35MHV    1.82...
M42HVIG with 1.1 wt.% NSintered in 90N2-9H2-1CH4                            • Discrepancies in Solidus                    ...
Change in carbide morphology with Ccontent    M42HVIG + 0.4% C         M42HVIG + 0.7% C • Higher C content -> change in mo...
Carbides composition in M42HVIG
Recalculated diagram for M42HVIG                       • Solidus temperature:                           – Calculated old: ...
Recalculate phase diagram for M35MHVconsidering M2C     Original isopleth       New isopleth, with M2C
Why is M2C observed in M42HVIG andnot in M35MHV?• Mo and W have a similar role in  HSS: formation of M6C carbide• Equivale...
Conclusions • For well-known systems: calculations with   few phases • Computer-aided design of HSS: accurate   selection ...
DEVELOPMENT OF MASTERALLOYS FOR P/MT. Gómez-Acebo, M. Sarasola and F. Castro, “Systematic search of low meltingpoint alloy...
Master alloys • Pre-alloyed powders added to promote   densification • In liquid phase sintering: liquid formation at   “l...
Projections of liquidus monovariantlines                                            “Top” view                            ...
Ternary Al-Mg-Zn                                  Red arrow:                                  lowest eutectic             ...
Ternary Al-Mg-Zn                  0                                   340ºCHEAT FLOW (W/g)                  -1            ...
Ternary Al-Cu-Mg                                                           Projections of the liquidus monovariant lines. ...
Quaternary Al-Cu-Mg-ZnProjections of the liquidus monovariant lines onto the temperature-composition planes for part of th...
Ternary Fe-Mn-C
Ternary Fe-Mn-C
Ternary Fe-Mn-CDSC and TG analyses of an                Optical micrograph of the C-Fe-Mnexperimentally obtained alloy wit...
Quinary C-Cr-Fe-Mn-Mo system                               • Quaternary C-Fe-                                 Mn-Mo system...
Note on calculation of liquidusmonovariant lines in multicomponentsystems • With Thermo-Calc, currently a 5-dimension diag...
Binary Mn-Ni • Intermediate phases not included in databases
Conclusions • Calculation like those presented here allow   the systematic search of liquid phases in the   whole composit...
LIFE ESTIMATION OF GASTURBINE OVERLAY COATINGST. Gómez-Acebo, B. Navarcorena and F. Castro, “Interdiffusion in multiphase,...
Introduction • GT blades: coatings of   oxidation-resistant alloys:    – MCrAlY: M=Ni,Co,Fe    – Pt-Aluminides • Life of t...
Introduction • Coating: -fcc + -B2    –    : bond coat (diffusion)    –    : Al reservoir • Loss of oxidation resistance: ...
Objectives • Diffusion in ternary and multicomponent Al-   Co-Cr-Ni-Ti alloys • Review of thermodynamic and kinetic data •...
Materials and experimental procedure          Alloy Preparation                      Diffusion couples •   Mixture of high...
Thermodynamic description • TCNI1 database [N. Dupin and B. Sundman, "A thermodynamic   database for Ni-base superalloys",...
Thermodynamic data of Al-Co-Cr                                 Calculations from                                  the thr...
Al-Co-Cr alloys                                   Co-5.0Al-25.7Cr                                   f =0.06 (meas.)       ...
Kinetic description • Ni-database [C. E. Campbell, W. J. Boettinger, and U. R.   Kattner, "Development of a diffusion mobi...
Kinetic description (fcc phase)                                M i0      Qi               1                    Qi* • Atomi...
Diffusion in Al-Co-Cr ( / couples)     C1: Co-4.2Al / Co-8.9Cr   C2: Co-4.0Al / Co-14.1Cr          1100 ºC, 72 h          ...
Diffusion in Al-Co-Cr ( + / couples)C3: Co-8.2Al / Co-11.1Cr   C4: Co-9.1Al / Co-17.0Cr   C5:Co-10.0Al / Co-30.0Cr     110...
Diffusion in Al-Co-Cr ( + / couples)                                               Original interface                     ...
Diffusion in Al-Co-Ni ( / + ’ couples)                        C6: Ni-5Al-30Co / Ni-10Al-23.3Co                            ...
Diffusion in Al-Co-Cr-Ni ( + / couples)  C9: Co-5Al-25.7Cr / Ni-6.5Al-40.8Co             1100 ºC, 72 h                 + <...
Diffusion in Al-Co-Cr-Ni ( + / couples) C9: Co-5Al-25.7Cr   C10: Co-6Al-27.9Cr   C11: Co-7.7Al-32Cr / Ni-6.5Al-40.8Co    /...
Diffusion in Al-Co-Cr-Ni ( + / couples) C9: Co-5Al-25.7Cr / Ni-6.5Al-40.8CoC10: Co-6Al-27.9Cr / Ni-5.5Al-39.8Co           ...
Diffusion in Al-Co-Cr-Ni-Ti ( + / )                            Original interfaceC13: Co-6.5Al-28Cr / Ni-5.5Cr-8.9Ti-1.4Al...
Diffusion in Al-Co-Cr-Ni-Ti ( + / )                                      C13: Co-6.5Al-28Cr /                             ...
Lifetime estimation of GT coatings • Al loss is due to three factors:    – Interdiffusion    – Oxidation    – Spallation (...
Lifetime estimation of GT coatings             Depletion of -phase                                                      11...
Conclusions • Review of thermodynamic and kinetic data    – Al-Co-Cr: good predictions from the binaries    – Kinetic data...
Future CALPHAD conferences
Thermo-Calc Workshop Madrid 2010
Thermo-Calc Workshop Madrid 2010
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Thermo-Calc Workshop Madrid 2010

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Seminar in Computational Thermodynamics & Kinetics with Thermo-Calc Software
Madrid, 1-2 June, 2010

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Thermo-Calc Workshop Madrid 2010

  1. 1. Seminar in Computational Thermodynamics & Kinetics with Thermo-Calc Software Madrid, 1-2 June, 2010 Computational Thermodynamics applied to powder metallurgy Dr. Tomás Gómez-Acebo
  2. 2. Outline • The fundamentals: assessments • Composition tuning of a high speed steel • Development of master alloys for powder metallurgy • Life of Gas Turbine coatings
  3. 3. THE FUNDAMENTALS:ASSESSMENTST. Gómez-Acebo, "Thermodynamic Assessment of the Ag-Zn System", CALPHAD22 (2), 203-220 (1998)doi:10.1016/S0364-5916(98)00024-8
  4. 4. Thermodynamic assessment • Review of literature data: – Phase diagram: compositions, T, solu bility… – Chemical thermo: , a, cp, H, … – Crystallography • Thermodynamic model of each phase • Reproduce experimental dataThe natural way of understanding thermodynamic models
  5. 5. Thermodynamic models: Gibbs energy E Gm xAg GAg x Zn GZn RT xAg ln xAg x Zn ln x Zn Gm Gref (mechanical Sid (configurational mixture) entropy) Gid (ideal solution) Excess Gibbs energy: Redlich-Kister polynomials 2 E 0 1 2 Gm xAg x Zn LAg,Zn LAg,Zn xAg x Zn LAg,Zn xAg x Zn  Each phase is modelled separatedly
  6. 6. Summary of Ag-Zn assessment • 50 literature sources (papers) • 700 experimental points • Model 7 phases: L, , , , , , – Liquid: 0L=a+bT; 1L=a – (fcc): 0L=a+bT; 1L=0 – (bcc): 0L=a+bT; 1L=a – (hcp-Zn): 0G; 0L=a – (hcp): 0G; 0L=a+bT; 1L=a; 2L=a – (Zn)1(Ag,Zn)2: 0G; 0L=a – (Ag,Zn)2(Ag)2(Ag,Zn)3(Ag,Zn)6: 0G
  7. 7. COMPOSITION TUNING OF AHIGH SPEED STEELV. Trabadelo, S. Giménez, T. Gómez-Acebo and I. Iturriza, “Critical assessment ofComputational Thermodynamics in the alloy design of PM high speed steels”.Scripta Materialia, 53 (3) 287-292 (2005). doi:10.1016/j.scriptamat.2005.04.017
  8. 8. Sintering of high speed steels • Complex chemistry: – Fe-Cr-Mo-Co-V-W-C-N – High C content: carbides • Optimum Sintering Temperature (OST) – Effect of C, N and sintering atmosphere – L+fcc+carbides – Avoid cementite – Liquid phase sintering
  9. 9. M2 HSS: validation of database (SSOL2) Experimental DT analysis Reported OST
  10. 10. M35MHV: identification of the stablephases All phases in SSOL Only observed phases: L, bcc ( ), Including gas, MC=(Mo,W)C fcc ( and MX), M6C, M3C, Fe2MoC ( )
  11. 11. M35MHV: effect of C and NFe–1.80C–4.0Cr–5.4Mo–5.5Co–0.035N–4.2V–6.0W–0.06O, with C additions, sintered in90N2-9H2-1CH4 100 ppm N 7000 ppm N Narrow sintering window Wider sintering window
  12. 12. M42HVIG vs M35MHV • New experimental HSS: M42HVIGHSS C N* O* Cr Co Mo V W Si FeM35MHV 1.82 350 600 4.00 5.50 5.40 4.20 6.00 - Bal.M42HVIG 1.48 221 484 4.08 8.50 10.1 5.29 - 0.41 Bal. wt.-%, * ppm • Reasonable to consider the same set of phases, rejecting the remaining phases: – L, bcc ( ), fcc ( and MX), M6C, M3C, Fe2MoC ( )
  13. 13. M42HVIG with 1.1 wt.% NSintered in 90N2-9H2-1CH4 • Discrepancies in Solidus temperature: – Calculated: 1136 ºC – Experimental: 1156 ºC • Correct prediction of microstructure (sintering at OST=1210 ºC): carbides Measured N: 1.14 wt.%
  14. 14. Change in carbide morphology with Ccontent M42HVIG + 0.4% C M42HVIG + 0.7% C • Higher C content -> change in morphology of bright carbides • Evolution from cubic M6C to hexagonal M2C
  15. 15. Carbides composition in M42HVIG
  16. 16. Recalculated diagram for M42HVIG • Solidus temperature: – Calculated old: 1136 ºC – Calculated new: 1158 ºC – Experimental: 1156 ºC • 1: intersection liquidus/M2C • 2: peritectic L+M6C = M2C • 1 to 2: increase in C content: – Increases M2C, not C in fcc – No reduction in Tsol • Mo stabilizes M2C
  17. 17. Recalculate phase diagram for M35MHVconsidering M2C Original isopleth New isopleth, with M2C
  18. 18. Why is M2C observed in M42HVIG andnot in M35MHV?• Mo and W have a similar role in HSS: formation of M6C carbide• Equivalent Mo content: M Mo we (Mo) w(Mo) w( W ) MW• Driving force for precipitation of M2C at 1150 ºC• Constant equivalent Mo: we(Mo) = 10%• High positive value: less stable
  19. 19. Conclusions • For well-known systems: calculations with few phases • Computer-aided design of HSS: accurate selection of phases involved • Sintering behaviour of well-studied systems should not be automatically extrapolated for new compositions
  20. 20. DEVELOPMENT OF MASTERALLOYS FOR P/MT. Gómez-Acebo, M. Sarasola and F. Castro, “Systematic search of low meltingpoint alloys in the Fe-Cr-Mn-Mo-C system”. Calphad, 27 (3) 325-334 (2003).doi:10.1016/j.calphad.2003.12.001
  21. 21. Master alloys • Pre-alloyed powders added to promote densification • In liquid phase sintering: liquid formation at “low” temperatures • Enhances diffusion of chemical elements • Alloy design: systematic search of low melting point alloys • Study of liquidus surface, liquidus monovariant lines
  22. 22. Projections of liquidus monovariantlines “Top” view “Side” view
  23. 23. Ternary Al-Mg-Zn Red arrow: lowest eutectic temperature Liquidus surface: Two projections of the liquidus monovariant projection onto the lines of the Al-Mg-Zn system onto composition axis. temperature-composition planes. Minimum liquidus temperature: 338 ºC for 3.97Al- 49.0Mg-47.0Zn (in wt-%).
  24. 24. Ternary Al-Mg-Zn 0 340ºCHEAT FLOW (W/g) -1 -phase and MgZn -2 Mg -3 250 300 350 400 450 T (ºC) DSC analysis of an SEM micrograph of the Al-Mg-Zn experimentally obtained alloy alloy with minimum liquidus with composition close to that temperature, showing the with minimum liquidus identified phases. temperature.
  25. 25. Ternary Al-Cu-Mg Projections of the liquidus monovariant lines. Liquidus surface 0 Minimum liquidus temperature: 425 ºC for 428ºC 32.5Al-4.29Cu-63.2Mg (in wt-%). HEAT FLOW (W/g) -1 AlMg- hcp(Mg) -2 Q-phase -3 350 400 450 500 T (ºC)DSC analysis alloy withcomposition close to that withminimum liquidus temperature.
  26. 26. Quaternary Al-Cu-Mg-ZnProjections of the liquidus monovariant lines onto the temperature-composition planes for part of the quaternary Al-Cu-Mg-Zn system. Cuadditions to the ternary do not reduce the liquidus temperature of the Al-Mg-Zn eutectic.
  27. 27. Ternary Fe-Mn-C
  28. 28. Ternary Fe-Mn-C
  29. 29. Ternary Fe-Mn-CDSC and TG analyses of an Optical micrograph of the C-Fe-Mnexperimentally obtained alloy with alloy with minimum liquiduscomposition close to that with minimum temperature, showing eutecticliquidus temperature structure of fcc+M3C.
  30. 30. Quinary C-Cr-Fe-Mn-Mo system • Quaternary C-Fe- Mn-Mo system. • “1”: eutectic with lowest T: – 1309 K (1036 ºC) – Fe-4C-21Mn- 10Mo • Quinary C-Cr-Fe-Mn-Mo system. • Cr additions to the quaternary do not reduce the liquidus temperature of the eutectic.
  31. 31. Note on calculation of liquidusmonovariant lines in multicomponentsystems • With Thermo-Calc, currently a 5-dimension diagram can be calculated. – The first two axis variables can be any property considered as a condition (i.e. composition of two components) – The other axes have to be potentials (temperature and activity of the other components). • The calculation proceeds when the diagram is calculated starting from an invariant point. • Extremely sensitive to starting point of calculation.
  32. 32. Binary Mn-Ni • Intermediate phases not included in databases
  33. 33. Conclusions • Calculation like those presented here allow the systematic search of liquid phases in the whole composition range. • Projections onto a temperature vs composition plane allow easy identification of multicomponent eutectic points. • Experimentally obtained alloys in the Al-Mg- Zn, Al-Cu-Mg and Fe-Mn-C ternary systems have allowed verification of the theoretical predictions for the eutectic temperatures.
  34. 34. LIFE ESTIMATION OF GASTURBINE OVERLAY COATINGST. Gómez-Acebo, B. Navarcorena and F. Castro, “Interdiffusion in multiphase, Al-Co-Cr-Ni-Ti diffusion couples”. Journal of Phase Equilibria and Diffusion, 25 (3) 237-251 (2004). http://dx.doi.org/10.1007/s11669-004-0112-y
  35. 35. Introduction • GT blades: coatings of oxidation-resistant alloys: – MCrAlY: M=Ni,Co,Fe – Pt-Aluminides • Life of the coating: loss of oxidation resistance
  36. 36. Introduction • Coating: -fcc + -B2 – : bond coat (diffusion) – : Al reservoir • Loss of oxidation resistance: Al – Oxidation: growth of oxide layer – Spallation: loss of oxide layer – Inward diffusion of Al – Outward diffusion of Ni etc: depletion of .
  37. 37. Objectives • Diffusion in ternary and multicomponent Al- Co-Cr-Ni-Ti alloys • Review of thermodynamic and kinetic data • Lifetime estimation of MCrAlY coatings
  38. 38. Materials and experimental procedure Alloy Preparation Diffusion couples • Mixture of high-purity metals: • Al-Co-Cr / Al, Co, Cr, Ni, Ti. + / • Uniaxially pressed at 400 MPa. • Al-Co-Ni / + ’ • Furnace melt at Tliq+200 K in Ar. • Al-Co-Cr-Ni + / • Homogenisation 3h, 1100 ºC in • Al-Co-Cr-Ni-Ti + / Ar. + / +Ni3Ti • Diffusion annealing: 1100 ºC, 24-72 h • Diffusion profiles: EDAX
  39. 39. Thermodynamic description • TCNI1 database [N. Dupin and B. Sundman, "A thermodynamic database for Ni-base superalloys", Scan. J. Metall., 30, 184-192 (2001)]. • All binaries assessed • Assessed ternaries: – Al-Co-Ni – Al-Cr-Ni – Al-Cr-Ti – Al-Ni-Ti – Cr-Ni-Ti • Non-assessed ternaries: – Al-Co-Cr – Al-Co-Ti – Co-Cr-Ni – Co-Cr-Ti – Co-Ni-Ti
  40. 40. Thermodynamic data of Al-Co-Cr Calculations from the three binaries (no ternary parameters) Experimental data [K. Ishikawa et al, "Phase equilibria and stability of the BCC aluminide in the Co-Cr-Al system", Ber. Bunsenges. Phys. Chem., 102, 1206- 1210 (1998)]. Unrealistic data for solvus line / +
  41. 41. Al-Co-Cr alloys Co-5.0Al-25.7Cr f =0.06 (meas.) f =0.03 (calc.) Co-6.0Al-27.9Cr f =0.24 (meas.) f =0.23 (calc.) Calculations from the binaries (no ternary parameters) Good agreement for + region Co-7.7Al-32.0Cr GT29: a commercial MCrAlY f =0.59 (meas.) coating: Co-6Al-29Cr-[0.5Y] f =0.51 (calc.)
  42. 42. Kinetic description • Ni-database [C. E. Campbell, W. J. Boettinger, and U. R. Kattner, "Development of a diffusion mobility database for Ni- base superalloys", Acta Mat., 50, 775-792 (2002)]. • Assessed sub-systems: – Al-Cr  Non assessed sub-systems: – Al-Ni • Al-Co • Co-Cr – Al-Ti • Co-Ti – Co-Ni • Cr-Ti – Cr-Ni • Other ternary sub-systems – Ni-Ti – Al-Cr-Ni  Diffusion only in -fcc phase – Al-Ni-Ti
  43. 43. Kinetic description (fcc phase) M i0 Qi 1 Qi* • Atomic mobilities: Mi exp exp RT RT RT RT Qi* Qi RT ln( M i0 ) • Redlich-Kister polynomials: Qi* x j Qi j xp x j k Aipj ( x p x j )k j p j p k Ti Ni • Accepted approximations: QAl QAl Cr Cr QCo Q Ni Ti Co QCo QCo Ti Ni QCr QCr Al Co Ti Ni QTi QTi QTi QTi Cr Cr QTi QAl Ti Ni Q Ni Q Ni Co Fe QAl 5QFe
  44. 44. Diffusion in Al-Co-Cr ( / couples) C1: Co-4.2Al / Co-8.9Cr C2: Co-4.0Al / Co-14.1Cr 1100 ºC, 72 h 1100 ºC, 72 h
  45. 45. Diffusion in Al-Co-Cr ( + / couples)C3: Co-8.2Al / Co-11.1Cr C4: Co-9.1Al / Co-17.0Cr C5:Co-10.0Al / Co-30.0Cr 1100 ºC, 72 h 1100 ºC, 72 h 1100 ºC, 72 h
  46. 46. Diffusion in Al-Co-Cr ( + / couples) Original interface C4: Co-9.1Al / Co-17.0Cr Regression of phase + <
  47. 47. Diffusion in Al-Co-Ni ( / + ’ couples) C6: Ni-5Al-30Co / Ni-10Al-23.3Co 1100 ºC, 48 h > + ’ Original interface
  48. 48. Diffusion in Al-Co-Cr-Ni ( + / couples) C9: Co-5Al-25.7Cr / Ni-6.5Al-40.8Co 1100 ºC, 72 h + < C10: Co-6Al-27.9Cr / Ni-5.5Al-39.8Co 1100 ºC, 72 h + < C11: Co-7.7Al-32Cr / Ni-5Al-38Co 1100 ºC, 72 h + <
  49. 49. Diffusion in Al-Co-Cr-Ni ( + / couples) C9: Co-5Al-25.7Cr C10: Co-6Al-27.9Cr C11: Co-7.7Al-32Cr / Ni-6.5Al-40.8Co / Ni-5.5Al-39.8Co / Ni-5Al-38Co
  50. 50. Diffusion in Al-Co-Cr-Ni ( + / couples) C9: Co-5Al-25.7Cr / Ni-6.5Al-40.8CoC10: Co-6Al-27.9Cr / Ni-5.5Al-39.8Co Regression of phaseC11: Co-7.7Al-32Cr / Ni-5Al-38Co
  51. 51. Diffusion in Al-Co-Cr-Ni-Ti ( + / ) Original interfaceC13: Co-6.5Al-28Cr / Ni-5.5Cr-8.9Ti-1.4Al C12: Co-6.7Al-29.4Cr / Ni-20Cr-6Ti 1100 °C, 72 h 1100 °C, 72 h + < + ’] + < + Ni3Ti]
  52. 52. Diffusion in Al-Co-Cr-Ni-Ti ( + / ) C13: Co-6.5Al-28Cr / Ni-5.5Cr-8.9Ti-1.4Al 1100 ºC, 72 h + < + ’] C12: Co-6.7Al-29.4Cr / Ni-20Cr-6Ti 1100 ºC, 72 h + < + Ni3Ti]
  53. 53. Lifetime estimation of GT coatings • Al loss is due to three factors: – Interdiffusion – Oxidation – Spallation (only in discontinuous operation) • Highest rate: interdiffusion • Possible criteria for lifetime estimation of the coating: – Loss of phase in the coating – Depletion of phase in the coating surface – Depletion of Al in the coating surface: formation of a stable oxide
  54. 54. Lifetime estimation of GT coatings Depletion of -phase 1150 GT29 100/200 m 1100 Temperature (ºC) 1050 CMSX-4 4 mm 1000 950 900 100 m 200 m 850 1 month 1 year 10 years 800 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 time (s)
  55. 55. Conclusions • Review of thermodynamic and kinetic data – Al-Co-Cr: good predictions from the binaries – Kinetic data needed for Co • Analysis of the diffusion paths: – Good prediction for Al – Good prediction for depletion of -phase – Other elements (Cr, Ni): not satisfactory predictions • Lifetime estimation of the coatings: interdiffusion
  56. 56. Future CALPHAD conferences

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