Microstructural evolution of a Ni-based superalloy (617B) at 700 ¡ãC studied by electron microscopy and atom probe tomography

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• 作者：Darius Tytko^a ; ^{d.tytko@mpie.de} ; Pyuck-Pa Choi^a ; ^{p.choi@mpie.de} ; Jutta Klö ; wer^b ; Aleksander Kostka^a ; Gerhard Inden^a ; Dierk Raabe^a
• 关键词：Atom probe tomography ; Ni-based superalloy ; Alloy 617B ; M23C6 ; Boron enrichment
• 刊名：Acta Materialia
• 出版年：2012
• 出版时间：February 2012
• 年：2012
• 卷：60
• 期：4
• 页码：1731-1740
• 全文大小：2309 K

文摘

We report on the microstructural evolution of a polycrystalline Ni-based superalloy (Alloy 617B) for power plant applications at a service temperature of 700 ¡ãC. The formation of secondary M₂₃C₆-carbides close to grain boundaries (GBs) and around primary Ti(C,N) particles is observed upon annealing at 700 ¡ãC, where ¦Ã?is found to nucleate heterogeneously at M₂₃C₆ carbides. Using atom probe tomography, elemental partitioning to the phases and composition profiles across phase and grain boundaries are determined. Enrichments of B at ¦Ã/M₂₃C₆ and ¦Ã?M₂₃C₆ interfaces as well as at grain boundaries are detected, while no B enrichment is found at ¦Ã/¦Ã?interfaces. It is suggested that segregation of B in conjunction with ¦Ã?formation stabilizes a network of secondary M₂₃C₆ precipitates near GBs and thus increases the creep rupture life of Alloy 617B. Calculations of the equilibrium phase compositions by Thermo-Calc confirm the chemical compositions measured by atom probe tomography.