Pralav Shetty1 2 Caelin Muir1 Jessica Krogstad1 2

1, Materials Science and Engineering, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
2, Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States

Solute segregation in nanocrystalline metals has been widely explored as a route to improve the thermal stability of fine grain microstructures. Efforts have revealed that segregation may not always be uniform or subtle, thereby shifting the microstructural stabilization mechanism [1,2]. Delineating the subtle differences between these two mechanisms maybe be possible through improved understanding of mass transport along solute decorated grain boundaries. In this work, we present very recent observations of grain boundary diffusion with concomitant microstructural evolution by employing a thin film diffusion triple configuration. A 10nm layer of pure Al then a 500nm layer of a nanocrystalline, highly textured Ni-Cr alloy are deposited via DC magnetron sputtering on to a coarse-grained Ni-Cr alloy substrate of the same nominal composition. These diffusion triples are annealed under flowing Ar at 600C and the asymmetric diffusion profile is extracted via STEM EDX and APT characterization. Comparison of these diffusion data are presented against similar thin film diffusion triples containing <1at% Y in the nanocrystalline films. Despite nearly identical initial microstructures, there are significant differences between these diffusion profiles, with implications for microstructural stability as well as environmental resistance.

[1] Darling, K. A., M. Rajagopalan, M. Komarasamy, M. A. Bhatia, B. C. Hornbuckle, R. S. Mishra, and K. N. Solanki. "Extreme creep resistance in a microstructurally stable nanocrystalline alloy." Nature 537, no. 7620 (2016): 378.
[2] Abdeljawad, Fadi, Ping Lu, Nicolas Argibay, Blythe G. Clark, Brad L. Boyce, and Stephen M. Foiles. "Grain boundary segregation in immiscible nanocrystalline alloys." Acta Materialia 126 (2017): 528-539.