Abstract:
Even the slightest content of species segregating at the grain boundaries (GBs) of a polycrystalline material can dramatically change its physical (mechanical, thermal, electrical, optical) features and its lifetime. While some nonmetallic species may improve its mechanical properties, sulfur segregating in nickel GBs yields its embrittlement, when the S-content reaches a critical concentration specific of a ductile-brittle transition [1]. Recent observations of different GBs using the NanoSIMS device revealed that one has to account for the atomic-scale structure of the GB to understand its S content, as different GBs with different orientations display different enrichments [2]. But the expected small thickness of the segregated layers prevent a straightforward observation and requires complementary atomic-scale models.<br />Literature abounds with first-principles computations on the Ni-S, but only very few and specific GBs can be handled for tractability reasons. While many very efficient interatomic potentials can deal with pure metals and metallic alloys, up-to-date only the ReaxFF approach allows to account for Ni-S at the atomic scale [3]. We discuss its use to reach an atomic-scale description of a given GB (chemistry-structure coupling) and the challenges to solve both from computational and experimental developments to describe the interface of Ni-S GBs.<br />[1] J. K. Heuer, P. R. Okamoto, N. Q. Lam and J. F. Stubbins, Applied Physics Letters 76 (23), 3403-3405 (2000)<br />[2] F. Christien, C. Downing, K.L. Moore, C.R.M. Grovenor, Surface and Interface Analysis 44, 377-387 (2012)<br />[3] H.-P. Chen, R. K. Kalia, E. Kaxiras, G. Lu, A. Nakano, K. Nomura, A. C. T. van Duin, P. Vashishta, and Z. Yuan, Phys. Rev. Lett. 104, 155502 (2010)
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