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Influence of light elements on the mechanical properties of interfaces in transition metals

Date: 24.10.2010
Place: 468. Wilhelm und Else Heraeus-Seminar "Ab initio Description of Iron and Steel: Mechanical properties", Ringberg Castle, Tegernsee, Germany

Rebecca Janisch
Sankari Sampath
Andreas Böhner, Department of materials science and engineering, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
Christian Elsässer, Materialmodellierung, Fraunhofer-Institut für Werkstoffmechanik IWM, Freiburg, Germany
Alexander Hartmaier

Interstitial impurities at grain boundaries influence the cohesive properties, for example they can enhance or attenuate grain boundary embrittlement in the body-centred cubic (bcc) transition metals and alloys, and thus the strength of these materials. Furthermore they can also change mechanical properties of grain boundaries by altering the energy barrier for sliding and migration, and thus the deformability of the host metal. Larger concentrations of impurities lead to precipitation and phase transformation at the interface [1].

In this paper we present results of ab-initio electronic structure calculations of mechanical properties of interfaces in bcc metals. We start with the influence of single interstitial impurities on grain boundary structure and cohesion in Nb and Mo [2]. We discuss the origin of the observed trends in terms of element size and bonding chemistry. Then the impurity concentration is increased to investigate the growth mechanisms of carbide precipitates in bcc metals [3]. Our results can be compared to high-resolution transmission electron microscopy pictures. Finally, the properties of Mo-MoCx and Cr-CrCx interfaces as a function of C concentration are discussed [4].

In all parts we will adress the benefits and limitations of ab initio electronic structure calculations for the field of mechanical properties of interfaces. Links to computational methods operating on different length scales will be pointed out in our outlook on ongoing scale-bridging projects at ICAMS.

[1] R. Janisch, C. Elsässer, Interstitital impurities at grain boundaries in metals: insight from atomistic calculations. Int.J. Mat. Res. 100, 1488 (2009).
[2]R. Janisch, C. Elsässer, Segregated Light Elements at Grain Boundaries in Niobium and Molybdenum, Phys. Rev. B 67, 224101 (2003).
[3]R. Janisch and C. Elsässer, Growth and mechanical properties of a MoC precipitate at a Mo grain boundary: an ab initio density functional study, Phys. Rev. B 77, 094118 (2008).
[4] A. Böhner, R. Janisch, and A. Hartmaier, Ab initio investigation of diamond coatings on steel, Scripta Mater. 60, 504 (2009).

Supporting information:

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