Effect of Varying Test Parameters on Elastic–plastic Properties Extracted by Nanoindentation Tests
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A systematic experiment was performed in an effort to investigate how the levels of certain test parameters affect the values of elastic modulus, hardness, yield stress, and strain hardening constant obtained using nanoindentation test. Maximum applied load, loading (unloading) rate, and hold time at maximum load were varied at three levels. The effects of these testing parameters were investigated through a three-level, full factorial design of experiment. The experiments were conducted on ultrafine Al-Mg specimens that were mechanically extruded. Both longitudinal and transverse extrusion directions were examined to investigate effects of anisotropy on mechanical properties and evaluate the persistence of observed variations due to test parameters on different materials orientations. An indentation size effect (ISE) was observed demonstrating that maximum load—and thereby maximum indentation depth—can have a significant effect on values of hardness and elastic modulus. Hardness values decreased with higher loading rates, and higher rates of unloading resulted in higher values of elastic modulus (5–10 GPa increases). Strain-hardening exponent showed a decreasing trend with increasing loading rate while yield stress exhibited a consistent correlation to hardness across all studied parameters. The material exhibited very little creep during the hold period, and values of the calculated properties were not significantly altered by varying the length of the hold time. Anisotropy effect was observed, particularly in the values of yield strength. This is attributed to the preferred grain orientation due to extrusion.
KeywordsNanoindentation Ultrafine grain Plastic behavior Al-Mg Strain hardening exponent Yield strength Hardness p-h curve
The authors would like to acknowledge the National Science Foundation for support of this research. This material is based upon work supported by the National Science Foundation under Grant No. 1053434. This work used resources in the Center for Materials for Information Technology which is supported by The University of Alabama.
- 18.Harvey E, Ladani L, and Weaver M (2012) “Complete Mechanical Characterization of Nanocrystalline Al-Mg Alloy Using Nanoindentation,” Mech Mater 52:1–11. doi: 10.1016/j.mechmat.2012.04.005
- 23.Han L, Hu H, Northwood DO, and Li N (2008) “Microstructure and nanoscale mechanical behavior of Mg-Al and Mg-Al-Ca Alloys” Mater Sci Eng A 473: 16–27Google Scholar
- 24.Li J, Li F, Xue F, Cai J, and Chen B (2012) “Micromechanical behavior study of forged 7050 aluminum alloy by microindentation” Mater Des 37: 491–499Google Scholar
- 25.Xue F, Li F, Cai J, Yuan Z, Chen B, Liu T (2012) Characterization of the elasto-plastic properties of 0Cr12Mn5Ni4Mo3Al steel by microindentation. Sustain Mater Des Appl 36:81–87Google Scholar
- 26.Bolshakov A and Pharr G (1998) “Influences of pileup on the measurement of mechanical properties by load and depth sensing indentation techniques”, J Mater Res 13(4): 1049–1058Google Scholar
- 27.Giannakopoulos A and Suresh S (1999) “Determination Of elastoplastic properties by instrumented sharp indentation” Scr Mater 40(10): 1191–1198Google Scholar
- 28.Tabor D (1951) The hardness of metals. Oxford University Press Inc., New YorkGoogle Scholar
- 31.Vlassak JJ, Nix WD (1993) “Indentation modulus of elastically anisotropic half spaces,” Phil Mag A 67:1045–1056Google Scholar
- 33.Han B, Lee Z, Witkin D, Nutt S, and Lavernia E (2005) “Deformation Behavior of Bimodal Nanostructured 5083 Al Alloys” Metall Mater Trans A 36: 957Google Scholar
- 34.Joshi S, Ramesh K, Han B and Lavernia E (2006) “Modeling the Constitutive Response of Bimodal Metals”, Metall Mater Trans A 37: 2397–2404Google Scholar
- 35.Magee A, Ladani L, Topping T and Lavernia E (2012) “Effects of tensile test parameters on the mechanical properties of a bimodal Al–Mg alloy,” Acta Mater 60: 5838–5849Google Scholar