TY - JOUR
T1 - Influence of the initial cooling rate from γ′ supersolvus temperatures on microstructure and phase compositions in a nickel superalloy
AU - Li, Muzi
AU - Coakley, James
AU - Isheim, Dieter
AU - Tian, Gaofeng
AU - Shollock, Barbara
N1 - Funding Information:
The authors are grateful to Beijing Institute of Aeronautical Materials Co. , AVIC for the material used in this study and the financial support. Atom-probe tomography measurements were performed at the Northwestern University Centre for Atom-Probe Tomography (NUCAPT) and the LEAP tomograph was purchased and upgraded with funding from the NSF-MRI ( DMR 0420532 ) and ONR DURIP ( N00014-0400798 , N00014-0610539 , N00014-0910781 ) programs. NUCAPT is a Shared Facility of the Materials Research Centre of the Northwestern University, supported by the National Science Foundation's MRSEC program ( DMR-1121262 ). We are also grateful to the Initiative for Sustainability and Energy at Northwestern (ISEN) for grants to upgrade NUCAPT's capabilities.
Publisher Copyright:
© 2017 The Authors
PY - 2018/1/25
Y1 - 2018/1/25
N2 - Different cooling paths from a supersolvus temperature have been applied to FGH96, a polycrystalline nickel base superalloy for turbine disc applications, in order to simulate the different microstructures that exist through the thickness of a disc following an industrial heat treatment. Secondary and tertiary γ′ precipitate size distributions and morphology have been analysed and compared for the different heat treatments using SEM and atom probe tomography (APT). Detailed compositional data for both γ′ precipitate and γ matrix are presented, and compared to equilibrium compositions calculated by Thermo-Calc. For the heat-treatments studied, the secondary γ′ composition indicates a shell of differing composition to that towards the precipitate core. From sequential equilibria compositional calculations, it is suggested that the ‘shell’ forms at a lower temperature than the precipitate core. The fine tertiary precipitates do not show the core-shell compositional differences on continuous cooling. W peaks are noted at the γ/γ′ interfacial region, which is of significance for retarding coarsening. A γ′ depletion zone surrounds the secondary precipitates, within which the γ matrix composition differs significantly to the γ far-field values, Finally, a precipitate nucleation and growth mechanistic model is suggested based on the experimental data and Thermo-Calc calculations.
AB - Different cooling paths from a supersolvus temperature have been applied to FGH96, a polycrystalline nickel base superalloy for turbine disc applications, in order to simulate the different microstructures that exist through the thickness of a disc following an industrial heat treatment. Secondary and tertiary γ′ precipitate size distributions and morphology have been analysed and compared for the different heat treatments using SEM and atom probe tomography (APT). Detailed compositional data for both γ′ precipitate and γ matrix are presented, and compared to equilibrium compositions calculated by Thermo-Calc. For the heat-treatments studied, the secondary γ′ composition indicates a shell of differing composition to that towards the precipitate core. From sequential equilibria compositional calculations, it is suggested that the ‘shell’ forms at a lower temperature than the precipitate core. The fine tertiary precipitates do not show the core-shell compositional differences on continuous cooling. W peaks are noted at the γ/γ′ interfacial region, which is of significance for retarding coarsening. A γ′ depletion zone surrounds the secondary precipitates, within which the γ matrix composition differs significantly to the γ far-field values, Finally, a precipitate nucleation and growth mechanistic model is suggested based on the experimental data and Thermo-Calc calculations.
KW - Atom probe tomography
KW - Nickel base superalloy
KW - Nucleation and growth
KW - Particle size distribution
KW - γ/γ′ composition
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U2 - 10.1016/j.jallcom.2017.10.263
DO - 10.1016/j.jallcom.2017.10.263
M3 - Article
AN - SCOPUS:85032952959
VL - 732
SP - 765
EP - 776
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
SN - 0925-8388
ER -