in Ni-base superalloys

Transcription

1 Prof. Dr. Gerhard Inden Max-Planck-Institut für Eisenforschung Düsseldorf B enrichments at the γ / M23C6 interface in Ni-base superalloys Thermo-Calc Anwendertreffen September 2011

2 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 for Babcock- Hitachi Europe GmbH, 27-May-2003

3 Alloy 617B, Database TTNI8 Ni+ Cr Co Mo Al Fe Ti C Si N B at% Temperature 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.

4 Constrained equlibrium at 1448 K T=1448K M6C and all borides suspended FCC_A1#1 Status ENTERED Driving force E+00 Moles E-01, Mass E+01, Volume fraction E+00 Mole fractions: NI E-01 MO E-02 SI E-03 B E-04 CR E-01 AL E-02 TI E-03 N E-06 CO E-01 FE E-02 C E-03 M23C6 Status ENTERED Driving force E+00 Moles E-03, Mass E-01, Volume fraction E+00 Mole fractions: CR E-01 MO E-02 B E-04 N E+00 C E-01 CO E-02 TI E-07 SI E+00 NI E-01 FE E-03 AL E+00 FCC_A1#2 Status ENTERED Driving force E+00 Moles E-03, Mass E-02, Volume fraction E+00 Mole fractions: TI E-01 CR E-03 NI E-08 AL E-12 N E-01 MO E-05 CO E-08 SI E-13 C E-02 B E-06 FE E-08

5 Constrained equlibrium at 973 K T=973K all borides suspended FCC_A1#1 Status ENTERED Driving force E+00 Moles E-01, Mass E+01, Volume fraction E+00 Mole fractions: NI E-01 MO E-02 SI E-03 C E-06 CR E-01 AL E-02 TI E-03 N E-08 CO E-01 FE E-02 B E-05 MU_PHASE Status ENTERED Driving force E+00 Moles E-02, Mass E+00, Volume fraction E+00 Mole fractions: MO E-01 CO E-01 AL E+00 C E+00 NI E-01 SI E-03 N E+00 B E+00 CR E-01 FE E-03 TI E+00 GAMMA_PRIME Status ENTERED Driving force E+00 Moles E-02, Mass E+00, Volume fraction E+00 Mole fractions: NI E-01 CO E-02 SI E-03 C E+00 AL E-01 CR E-02 FE E-03 B E+00 TI E-02 MO E-03 N E+00

6 Constrained equlibrium at 973 K M23C6#2 Status ENTERED Driving force E+00 Moles E-02, Mass E-01, Volume fraction E+00 Mole fractions: CR E-01 NI E-02 FE E-04 N E+00 C E-01 CO E-02 TI E-08 SI E+00 MO E-01 B E-03 AL E+00 M23C6#1 Status ENTERED Driving force E+00 Moles E-03, Mass E-02, Volume fraction E+00 Mole fractions: CR E-01 NI E-02 FE E-03 N E+00 C E-01 CO E-02 TI E-09 SI E+00 B E-02 MO E-03 AL E+00 FCC_A1#2 Status ENTERED Driving force E+00 Moles E-03, Mass E-02, Volume fraction E+00 Mole fractions: TI E-01 CR E-05 AL E-13 NI E-13 N E-01 B E-06 FE E-13 SI E-13 C E-03 MO E-09 CO E-13

7 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

8 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.

9 Experimental results: composition profiles B enrichment at the interface M 23 C 6 / γ

10 DICTRA simulation Database MobNi1

11 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

12 DICTRA simulation: cooling

13 DICTRA simulation: cooling

14 DICTRA simulation: annealing at 700 C Isothermal annealing at 700 C for s

15 DICTRA simulation: annealing at 700 C

16 DICTRA simulation: annealing at 700 C

17 DICTRA simulation: annealing at 700 C

18 DICTRA simulation: annealing at 700 C

19 DICTRA simulation: annealing and cooling Annealing at 700 C for s, followed by cooling for 30s with 10 C / s During cooling, the B- enriched M 23 (B,C) 6 forms again.

20 DICTRA simulation: annealing and cooling

21 DICTRA simulation: annealing and cooling

22 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