Texture Evolution in Nanocrystalline Nickel: Critical Role of Strain Path
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INTRODUCTION
NANOCRYSTALLINE (nc) materials have received significant attention of researchers in the recent decades owing to their distinct physical and mechanical properties from the respective microcrystalline counterparts.[1] The reduction of grain sizes to less than 100 nm introduces a combination of deformation mechanisms involving grain boundary-mediated processes, in addition to the normal crystallographic slip and twinning.[2,3] For grain sizes below a certain threshold value, grain boundaries play a major role in accommodating plastic deformation.[4–7] The atomistic simulations provide a valuable insight in understanding the active deformation mechanisms in the smallest grain size regime, which, otherwise, is below the resolution limit of many advanced microscopic techniques.[8–10] Depending on the stacking fault energy (SFE) of materials, the transition from perfect slip (for high SFE materials) or extended partial dislocation slip (in the case of low SFE) to GB-mediated deformation processes occurs. Large strain plastic deformation is generally associated with the development of unique crystallographic texture. The evolution of characteristic rolling texture in microcrystalline FCC metals and alloys is strongly dependent on the SFE of the material. Materials having high SFE exhibit copper (Cu)-type texture (a combination of Cu {112}h111i, S {123}h634i, Bs {110}h112i components), whereas materials of low SFE show brass (Bs)-type texture which comprises a strong Goss {110}h001i and Bs components, in comparison to Cu and S components. The mechanisms that could lead to R. MADHAVAN, Post-doctoral Fellow, and SATYAM SUWAS, Associate Professor, are with the Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, Karnataka, India. Contact e-mail: [email protected] S. NAGARAJU, formerly summer intern with the Department of Materials Engineering, Indian Institute of Science, is now Trainee Scientific Officer with the Bhabha Atomic Research Center, Trombay, India. Manuscript submitted July 6, 2014. Article published online December 3, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
the formation of these two types of textures have been widely discussed.[11] Based on the understanding of nc materials, it is quite natural to believe that texture evolution in these materials will be influenced by the mechanisms exclusive of grain size in addition to wellknown effect of SFE. However, very few experimental studies have addressed the deformation mechanisms and subsequent evolution of deformation texture in nc metals. Markmann et al.[12] studied the development of rolling texture in inert gas-condensed Pd and reported the absence of characteristic rolling texture and the retention of initial fiber texture, which has been attributed to grain boundary (GB)-mediated processes. On the other hand, Yang et al.[13] reported the evolution of Goss and Cu components at a very early stage of rolling in nc Ni-18 pct Fe alloy, which is an indicative of dislocation-assisted plasticity. The st
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