Stability of nanosized alloy thin films: Faulting and phase separation in metastable Ni/Cu/Ag-W films

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• 作者：G. Csiszá ; r^a ; ^{g.csiszar@is.mpg.de" class="auth_mail" title="E-mail the corresponding author} ; S.J.B. Kurz^a ; ^{s.kurz@is.mpg.de" class="auth_mail" title="E-mail the corresponding author} ; E.J. Mittemeijer^a ; ^b ;
• 关键词：Thin film ; Nanocrystalline stability ; Solute segregation ; Residual stress ; Faulted structure ; Suzuki-effect
• 刊名：Acta Materialia
• 出版年：2016
• 出版时间：15 May 2016
• 年：2016
• 卷：110
• 期：Complete
• 页码：324-340
• 全文大小：4707 K

文摘

A comparative study of Me(=Ni/Cu/Ag)-based, W-alloyed, nanocrystalline, heavily faulted thin films was carried out to identify parameters stabilizing the nanocrystalline nature upon thermal treatment. The three systems, initially of comparably, heavily twinned (twin boundaries at spacings of 1–5 nm) microstructures showed similarities but also strikingly different behaviours upon annealing, as observed by application of in particular X-ray diffraction (line-broadening) analysis and (high resolution) transmission electron microscopy. During annealing in the range of 30–600 °C, (i) segregation at the planar faults (for Me = Ni) and at grain boundaries (for Me = Ni,Cu,Ag), as well as nanoscale phase separation (for Me = Cu,Ag) take place, (ii) distinct grain growth does not occur and (iii) the twin boundaries either are largely preserved ((Ni(W) and Ag(W)) or disappear totally (Cu(W))), which was ascribed to an altered faulting energy, due to change of the amount of W segregated at the twin boundaries, and to the evolution of nano-precipitates. The nanosized films exhibit very large internal (macro)stresses parallel to the surface, which change during annealing in the range of 1 GPa (tensile) to −3 GPa (compressive) and thus are sensitive to the microstructural changes in the films (decomposition and relaxation) that happen on a nanoscale. The results are discussed in terms of thermodynamic and/or kinetic constraints controlling these processes and thus the thermal stability of the systems concerned.