Segregation and 畏 phase formation along stacking faults during creep at intermediate temperatures in a Ni-based superalloy

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• 作者：T.M. Smith^a ; ^b ; ^{smith.5881@osu.edu" class="auth_mail" title="E-mail the corresponding author} ; B.D. Esser^a ; ^b ; N. Antolin^b ; G.B. Viswanathan^a ; ^b ; T. Hanlon^c ; A. Wessman^c ; D. Mourer^d ; W. Windl^b ; D.W. McComb^a ; ^b ; M.J. Mills^a ; ^b
• 关键词：EDX ; STEM ; HAADF ; HAADF simulation ; DFT ; Atomic resolution EDS ; Ni-based superalloy ; 畏 phase ; SESF ; Segregation ; Single crystal creep ; Phase transformation
• 刊名：Acta Materialia
• 出版年：2015
• 出版时间：November 2015
• 年：2015
• 卷：100
• 期：Complete
• 页码：19-31
• 全文大小：4615 K

文摘

In this paper, the local compositional and structural changes occurring in association with stacking faults in a Ni-base superalloy are characterized and related to the possible rate-controlling processes during creep deformation at intermediate temperatures. These rate-controlling processes are not presently understood. In order to promote stacking fault shearing, compression creep tests on specially prepared single crystals of an exploratory Ni-base superalloy were conducted at 760 °C in the [0 0 1] orientation. Scanning transmission electron microscopy (STEM) imaging was coupled with state-of-the-art energy dispersive X-ray (EDX) spectroscopy to reveal for the first time an ordered compositional variation along the extrinsic faults inside the 纬′ precipitates, and a distinct solute atmosphere surrounding the leading partial dislocations. The local structure and chemistry at the extrinsic fault is consistent with the 畏 phase, a D0₂₄ hexagonal structure. Density Functional Theory (DFT) and high angle annular dark field (HAADF)-STEM image simulations are consistent with local 畏 phase formation and indicate that a displacive–diffusive transformation occurs dynamically during deformation.