An investigation of diffusion-mediated cyclic coarsening and reversal coarsening in an advanced Ni-based superalloy

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• 作者：Yiqiang Chen^a ; R. Prasath babu^a ; Thomas J.A. Slater^a ; Mingwen Bai^a ; Robert Mitchell^b ; Octav Ciuca^a ; Michael Preuss^a ; ^{Michael.preuss@manchester.ac.uk" class="auth_mail" title="E-mail the corresponding author} ; Sarah J. Haigh^a ; ^{sarah.haigh@manchester.ac.uk" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Ni based superalloys ; coarsening ; precipitates ; Scanning transmission electron microscopy ; elemental mapping ; energy dispersive X-ray spectroscopy
• 刊名：Acta Materialia
• 出版年：2016
• 出版时间：15 May 2016
• 年：2016
• 卷：110
• 期：Complete
• 页码：295-305
• 全文大小：3081 K

文摘

The anomalous cyclic coarsening behaviour of γ′ precipitates after ageing at 1073 K has been investigated for the low misfit commercial powder metallurgy (PM) Ni-based superalloy RR1000. Using scanning transmission electron microscope (STEM) imaging combined with absorption-corrected energy-dispersive X-ray (EDX) spectroscopy, the elemental segregation as a function of coarsening behaviour has been experimentally observed for secondary γ′ precipitates. Elemental EDX spectrum imaging has revealed nanoscale enrichment of Co and Cr and a depletion of Al and Ti within the γ matrix close to the γ-γʹ interface. Our experimental results, coupled with complementary modelling and synchrotron X-ray diffraction analysis, demonstrate the importance of elastic strain energy resulting from local compositional variations for influencing precipitate morphology. In particular, elemental inhomogeneities, as a result of complex diffusive interactions within both matrix and precipitates, play a crucial role in determining the rate of coarsening. Our findings provide important new evidence for understanding the microstructural evolution observed for advanced superalloys when they are exposed to different heat treatment regimes.