Prof. Dr. Gerhard Inden Max-Planck-Institut für Eisenforschung Düsseldorf B enrichments at the γ / M23C6 interface in Ni-base superalloys Thermo-Calc Anwendertreffen 8. - 9. September 2011
Experimental data from: Microstructural evolution of a Ni-based superalloy (617B) at 700 C studied by electron microscopy and atom probe tomography D. Tytko a,*, P. Choi a**, J. Klöwer b, A. Kostka a, G. Inden a, D. Raabe a a Max-Planck-Institut für Eisenforschung, Düsseldorf b ThyssenKrupp VDM GmbH, Altena Submitted to Acta Materialia, August 2011 Creep rupture strength from 600 to 750 C (10 5 h) Alloy 617 Alloy 617B (Nicrofer5520Co) (Nicrofer5520CoB) TÜV RheinlandReport 926/W 031029 for Babcock- Hitachi Europe GmbH, 27-May-2003
Alloy 617B, Database TTNI8 Ni+ Cr Co Mo Al Fe Ti C Si N B at% 24.7 11.4 5.2 2.1 1.4.3.3.1.02 Temperature 1448.00 K ( 1175 C) Stable phases: M6C M3B2_TETR FCC_A1#2 FCC_A1#1 Ti(C,N) Metastable phases: M23C6#1 (Cr, Ni, Co, Mo, Fe) 23 (C,B) 6 M23C6#2 (Cr, Mo, Ni, Co, Fe) 23 (B, C) 6 LIQUID CR5B3 SIGMA HCP_A3 BCC_A2 FCC_L10 GAMMA_PRIME M7C3 The carbide M6C and borides are not observed in the microstructure, therefore these phases are suppressed in the following equilibrium calculations.
Constrained equlibrium at 1448 K T=1448K M6C and all borides suspended FCC_A1#1 Status ENTERED Driving force 0.0000E+00 Moles 9.9241E-01, Mass 5.7648E+01, Volume fraction 0.0000E+00 Mole fractions: NI 5.48133E-01 MO 5.18917E-02 SI 3.02294E-03 B 1.97820E-04 CR 2.46347E-01 AL 2.11606E-02 TI 2.78140E-03 N 4.70260E-06 CO 1.14663E-01 FE 1.00655E-02 C 1.73304E-03 M23C6 Status ENTERED Driving force 0.0000E+00 Moles 5.1230E-03, Mass 2.5305E-01, Volume fraction 0.0000E+00 Mole fractions: CR 4.91329E-01 MO 9.79740E-02 B 7.16161E-04 N 0.00000E+00 C 2.06180E-01 CO 4.04811E-02 TI 2.25985E-07 SI 0.00000E+00 NI 1.61204E-01 FE 2.11487E-03 AL 0.00000E+00 FCC_A1#2 Status ENTERED Driving force 0.0000E+00 Moles 2.4644E-03, Mass 7.6277E-02, Volume fraction 0.0000E+00 Mole fractions: TI 5.03044E-01 CR 2.20102E-03 NI 4.42174E-08 AL 3.55948E-12 N 4.03884E-01 MO 2.98563E-05 CO 1.59193E-08 SI 5.05275E-13 C 9.08358E-02 B 4.96399E-06 FE 1.30607E-08
Constrained equlibrium at 973 K T=973K all borides suspended FCC_A1#1 Status ENTERED Driving force 0.0000E+00 Moles 9.0800E-01, Mass 5.2333E+01, Volume fraction 0.0000E+00 Mole fractions: NI 5.68875E-01 MO 3.63552E-02 SI 3.11623E-03 C 6.00221E-06 CR 2.47462E-01 AL 2.00701E-02 TI 1.47515E-03 N 1.93104E-08 CO 1.11729E-01 FE 1.08898E-02 B 2.14503E-05 MU_PHASE Status ENTERED Driving force 0.0000E+00 Moles 5.4021E-02, Mass 3.7424E+00, Volume fraction 0.0000E+00 Mole fractions: MO 3.24466E-01 CO 2.14808E-01 AL 0.00000E+00 C 0.00000E+00 NI 2.35062E-01 SI 1.89723E-03 N 0.00000E+00 B 0.00000E+00 CR 2.22463E-01 FE 1.30394E-03 TI 0.00000E+00 GAMMA_PRIME Status ENTERED Driving force 0.0000E+00 Moles 2.0666E-02, Mass 1.1055E+00, Volume fraction 0.0000E+00 Mole fractions: NI 7.15883E-01 CO 3.15897E-02 SI 3.28876E-03 C 0.00000E+00 AL 1.34340E-01 CR 2.82996E-02 FE 1.28382E-03 B 0.00000E+00 TI 7.97269E-02 MO 5.58822E-03 N 0.00000E+00
Constrained equlibrium at 973 K M23C6#2 Status ENTERED Driving force 0.0000E+00 Moles 1.3180E-02, Mass 6.4147E-01, Volume fraction 0.0000E+00 Mole fractions: CR 6.17286E-01 NI 5.44870E-02 FE 8.89173E-04 N 0.00000E+00 C 2.05312E-01 CO 1.92028E-02 TI 4.55379E-08 SI 0.00000E+00 MO 1.01238E-01 B 1.58454E-03 AL 0.00000E+00 M23C6#1 Status ENTERED Driving force 0.0000E+00 Moles 2.1057E-03, Mass 9.3012E-02, Volume fraction 0.0000E+00 Mole fractions: CR 7.43548E-01 NI 2.34448E-02 FE 1.58783E-03 N 0.00000E+00 C 1.31089E-01 CO 1.89683E-02 TI 4.03949E-09 SI 0.00000E+00 B 7.58075E-02 MO 5.55474E-03 AL 0.00000E+00 FCC_A1#2 Status ENTERED Driving force 0.0000E+00 Moles 2.0255E-03, Mass 6.2657E-02, Volume fraction 0.0000E+00 Mole fractions: TI 5.00068E-01 CR 1.40978E-05 AL 5.00082E-13 NI 5.00082E-13 N 4.93693E-01 B 4.57972E-06 FE 5.00082E-13 SI 5.00082E-13 C 6.22087E-03 MO 5.62865E-09 CO 5.00082E-13
Experimental results: as-received state Grain boundary in the as received state: a) TEM image b) Atom probe image: Ni (green), B (red) c) Composition profiles along the direction of the white arrow The composition at the grain boundary corresponds to the B-rich variant M 23 (C,B) 6
Experimental results: 700 C (a) A dense network of secondary M 23 C 6 carbides has formed close to the primary M 23 C 6 at the GB. (b) These elongated secondary M 23 C 6 carbides are surrounded by γ precipitates HAADF micrograph of the specimen annealed at 700 C for 100h.
Experimental results: composition profiles B enrichment at the interface M 23 C 6 / γ
DICTRA simulation Database MobNi1
DICTRA simulation: cooling M 23 C 6 formed during cooling from 1175 C to 665 with 10K/s In the early stages the high mobility of B compared to C leads to the formation of the B- enriched M 23 (B,C) 6
DICTRA simulation: cooling
DICTRA simulation: cooling
DICTRA simulation: annealing at 700 C Isothermal annealing at 700 C for 360000 s
DICTRA simulation: annealing at 700 C
DICTRA simulation: annealing at 700 C
DICTRA simulation: annealing at 700 C
DICTRA simulation: annealing at 700 C
DICTRA simulation: annealing and cooling Annealing at 700 C for 360000 s, followed by cooling for 30s with 10 C / s During cooling, the B- enriched M 23 (B,C) 6 forms again.
DICTRA simulation: annealing and cooling
DICTRA simulation: annealing and cooling
Conclusions The DICTRA simulations show that the observed effects of B enrichment are due to the considerably higher mobility of B compared to C. The enrichment and depletion of elements observed at grain boundaries after quenching from high temperatures is due to the nucleation of a B-rich M 23 (B,C) 6 during quenching. The DICTRA simulations show that during isothermal annealing the formation of the B- enriched M 23 (B,C) 6 carbide occurs during the early stages of precipitation. This produces a first layer at the interface γ / M 6 C. A second layer is then formed during cooling. End