On Local Phase Equilibria and the Appearance of Nanoparticles in the Microstructure of Single-Crystal Ni-Base Superalloys

0464788 - ÚFM 2017 RIV DE eng J - Journal Article
Yardley, V. - Povstugar, I. - Choi, P.-P. - Raabe, D. - Parsa, A. B. - Kostka, A. - Somsen, Ch. - Dlouhý, Antonín - Neuking, K. - George, E. P. - Eggeler, G.
On Local Phase Equilibria and the Appearance of Nanoparticles in the Microstructure of Single-Crystal Ni-Base Superalloys.
Advanced Engineering Materials. Roč. 18, č. 9 (2016), s. 1556-1567. ISSN 1438-1656. E-ISSN 1527-2648
R&D Projects: GA ČR(CZ) GA14-22834S
Institutional support: RVO:68081723
Keywords : atom-probe tomography * gamma/gamma-interfaces * creep * stress * alloy
Subject RIV: JG - Metallurgy
Impact factor: 2.319, year: 2016

High-resolution characterization techniques are combined with thermodynamic calculations (CALPHAD) to rationalize microstructural features of single crystal Ni-base superalloys. Considering the chemical compositions of dendritic and interdendritic regions one can explain differences in γ′-volume fractions. Using thermodynamic calculations one can explain, why γ-nanoparticles are observed in the central regions of large cuboidal γ′-particles and why tertiary γ′-nanoparticles form in the γ-channels. The chemical compositions of the γ-channels and of the newly formed γ-particles differ because of the Gibbs–Thomson pressure which acts on the small particles. With increasing size of secondary γ′-particles, their shape changes from spherical to cuboidal. Some general thermodynamic aspects including the temperature dependencies of the Gibbs free energy G, the enthalpy H, and the entropy S and site occupancies in the ordered L12 (γ′) phase are considered. The importance of cooling rate after homogenization is discussed.
Permanent Link: http://hdl.handle.net/11104/0263577