Influence of solid solution strengthening on the local mechanical properties of single crystal and ultrafine-grained bin
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hai An Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China; and School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006, Australia
Linlin Li and Zhefeng Zhang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China
Reinhard Pippan Austrian Academy of Sciences, Erich-Schmid-Institute of Materials Science, Leoben A-8700, Austria
Karsten Dursta) TU Darmstadt, Physical Metallurgy, Darmstadt 64287, Germany (Received 23 May 2017; accepted 14 July 2017)
In this work, the influence of Al-solutes on the mechanical behavior of Cu–AlX solid solutions has been studied using indentation strain rate jump tests for single crystalline and ultrafine-grained (UFG) microstructures from high pressure torsion (HPT) processing. Al-solutes in Cu classically lead to a solid solution strengthening, coupled with a decrease in stacking fault energy, which influences also the grain size after HPT processing. For all alloys, a higher hardness is found at lower indentation depths, which can be nicely described by a modified Nix/Gao model down to 100 nm indentation depth. Among the single crystals, the largest size effects are found for the higher solute contents, indicating a stronger work hardening at small length scales for the solid solutions. The dilute UFG solid solutions showed a strong softening after a strain rate reduction test, with a pronounced transient region. Cu–Al15 is, however, quite stable, showing abrupt changes in hardness without strong transients. This indicates that solute solution strengthening does not only influence the indentation size effect and structure formation during HPT processing but also stabilizes the grain structure during subsequent deformation.
I. INTRODUCTION
The deformation mechanism in single crystalline (SX) and ultrafine grained face-centered cubic (FCC) solid solutions have gained much attention in the last decade and particularly, nanoindentation has been used to study different size effects in their mechanical behavior.1 Specifically for ultrafine-grained (UFG) materials, besides the increasing strength, in some cases also the tensile ductility can be increased.2 This paradoxon was already widely investigated in research over the last decade, but it is not fully understood yet.3,4 One important aspect seems to be the enhanced strain rate sensitivity (SRS) of UFG microstructures, which relates
Contributing Editor: Mathias Göken a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.320
to dislocation storage and annihilation mechanism at grain boundaries.4–6 Dislocation storage mechanisms also play an important role during nanoindentation. Specifically for indentation testing of soft annealed single crystals, an increasing hardness is found for smaller indentation depths, referred to as the indentation size eff
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