Skip to main content Accessibility help

Size effects of micrometer-scaled metals—the search continues for materials containing real microstructures

  • A. H. W. Ngan (a1), X. X. Chen (a1) (a2), P. S. S. Leung (a1) (a2), R. Gu (a1) (a3) and K. F. Gan (a1)...


Recent observations on strength and deformation of small metals containing microstructures, including dislocation patterns, grain boundaries, and second-phase precipitates are reviewed. These microstructures impose an internal length scale that may interplay with the extrinsic length scale due to the specimen size to affect strength and deformation in an intricate manner. For micro-crystals containing pre-existing dislocations, Taylor work-hardening may dictate the dependence of strength on specimen size. The presence of grain boundaries in a small specimen may lead to effects far from the conventional Hall–Petch behavior. Precipitate–dislocation interactions in a small specimen may lead to an interesting weakest-size behavior.


Corresponding author

Address all correspondence to A. H. W. Ngan at


Hide All
1. Dou, R. and Derby, B.: A universal scaling law for the strength of metal micropillars and nanowires. Scr. Mater. 61, 524 (2009).
2. Greer, J.R. and De Hosson, J.T.M.: Plasticity in small-sized metallic systems: intrinsic versus extrinsic size effect. Prog. Mater. Sci. 56, 654 (2011).
3. Ngan, A.H.W., Zuo, L., and Wo, P.C.: Size dependence and stochastic nature of yield strength of micron-sized crystals: a case study on Ni3Al. Prof. R. Soc. Lond. A462, 1661 (2006).
4. Zuo, L. and Ngan, A.H.W.: Molecular dynamics study on compressive yield strength in Ni3Al micro-pillars. Phil. Mag. Lett. 86, 355 (2006).
5. Greer, J.R., Oliver, W.C., and Nix, W.D.: Size dependence of mechanical properties of gold at the micron scale in the absence of strain gradients. Acta Mater. 53, 1821 (2005).
6. Greer, J.R. and Nix, W.D.: Nanoscale gold pillars strengthened through dislocation starvation. Phys. Rev. B 73, 245410 (2006).
7. Shan, Z.W., Mishra, R.K., Asif, S.A.S., Warren, O.L., and Minor, A.M.: Mechanical annealing and source-limited deformation in submicrometre-diameter Ni crystals. Nat. Mater. 7, 115 (2008).
8. Parthasarathy, T.A., Rao, S.I., Dimiduk, D.M., Uchic, M.D., and Trinkle, D.R.: Contribution to size effect of yield strength from the stochastics of dislocation source lengths in finite samples. Scr. Mater. 56, 313 (2007).
9. Norfleet, D.M., Dimiduk, D.M., Polasik, S.J., Uchic, M.D., and Mills, M.J.: Dislocation structures and their relationship to strength in deformed nickel microcrystals. Acta Mater. 56, 2988 (2008).
10. Ng, K.S. and Ngan, A.H.W.: Stochastic nature of plasticity of aluminum micro-pillars. Acta Mater. 56, 1712 (2008).
11. Cui, Y., Po, C., and Ghoniem, N.: Controlling strain bursts and avalanches at the nano- to micrometer scale. Phys. Rev. Lett. 117, 155502 (2016).
12. Rao, S.I., Dimiduk, D.M., Parthasarathy, T.A., Uchic, M.D., Tang, M., and Woodward, C.: Athermal mechanisms of size-dependent crystal flow gleaned from three-dimensional discrete dislocation simulations. Acta Mater. 56, 3245 (2008).
13. El-Awady, J.A., Wen, M., and Ghoniem, N.M.: The role of the weakest-link mechanism in controlling the plasticity of micropillars. J. Mech. Phys. Solids 57, 32 (2009).
14. Motz, C., Weygand, D., Senger, J., and Gumbsch, P.: Initial dislocation structures in 3-D discrete dislocation dynamics and their influence on microscale plasticity. Acta Mater. 57, 1744 (2009).
15. Akarapu, S., Zbib, H.M., and Bahr, D.F.: Analysis of heterogeneous deformation and dislocation dynamics in single crystal micropillars under compression. Int. J. Plast. 26, 239 (2010).
16. Huang, M., Zhao, L., and Tong, J.: Discrete dislocation dynamics modelling of mechanical deformation of nickel-based single crystal superalloys. Int. J. Plast. 28, 141 (2012).
17. Cui, Y., Lin, P., Liu, Z.L., and Zhuang, Z.: Theoretical and numerical investigations of single arm dislocation source controlled plastic flow in FCC micropillars. Int. J. Plast. 55, 279 (2014).
18. Yu, Q., Legros, M., and Minor, A.M.: In situ TEM nanomechanics. MRS Bull. 40, 62 (2015).
19. Imrich, P.J., Kirchlechner, C., Kiener, D., and Dehm, G.: In situ TEM microcompression of single and bicrystalline samples: insights and limitations. JOM 67, 1704 (2015).
20. Maaß, R., Meza, L., Gan, B., Tin, S., and Greer, J.R.: Ultrahigh strength of dislocation-free Ni3Al nanocubes. Small 8, 1869 (2012).
21. Chen, L.Y., He, M.-R., Shin, J., Richter, G., and Gianola, D.S.: Measuring surface dislocation nucleation in defect-scarce nanostructures. Nature Mater. 14, 707 (2015).
22. Bei, H., Shim, S., Pharr, G.M., and George, E.P.: Effects of pre-strain on the compressive stress-strain response of Mo-alloy single-crystal micropillars. Acta Mater. 56, 4762 (2008).
23. Weinberger, C.R. and Cai, W.: Surface-controlled dislocaiton multiplication in metal micropillars. Proc. Nat. Acad. Sci. USA 105, 14304 (2008).
24. Zhu, T.T., Bushby, A.J., and Dunstan, D.J.: Materials mechanical size effects: a review. Mater. Technol. 23, 193 (2008).
25. Ngan, A.H.W.: An explanation for the power-law scaling of size effect on strength in micro-specimens. Scr. Mater. 65, 978 (2011).
26. Gu, R. and Ngan, A.H.W.: Dislocation arrangement in small crystal volumes determines power-law size dependence of yield strength. J. Mech. Phys. Solids 61, 1531 (2013).
27. Schneider, A.S., Kiener, D., Yakacki, C.M., Maier, H.J., Gruber, P.A., Tamura, N., Kunz, M., Minor, A.M., and Frick, C.P.: Influence of bulk pre-straining on the size effect in nickel compression pillars. Mater. Sci. Eng. A 559, 147 (2013).
28. El-Awady, J.A., Uchic, M.D., Shade, P.A., Kim, S.-L., Rao, S.I., Dimiduk, D.M., and Woodward, C.: Pre-straining effects on the power-law scaling of size-dependent strengthening in Ni single crystals. Scr. Mater. 68, 207 (2013).
29. Phani, P.S., Johanns, K.E., George, E.P., and Pharr, G.M.: A simple stochastic model for yielding in specimens with limited number of dislocations. Acta Mater. 61, 2489 (2013).
30. El-Awady, J.A.: Unravelling the physics of size-dependent dislocation-mediated plasticity. Nat. Commun. 6, 5926 (2015).
31. Gu, R. and Ngan, A.H.W.: Effects of pre-straining and coating on plastic deformation of aluminum micropillars. Acta Mater. 60, 6102 (2012).
32. Ehrler, B., Hou, X.D., Zhu, T.T., Png, K.M.Y., Walker, C.J., Bushby, A.J., and Dunstan, D.J.: Grain size and sample size interact to determine strength in a soft metal. Phil. Mag. 88, 3043 (2008).
33. Chen, X.X. and Ngan, A.H.W.: Specimen size and grain size effects on tensile strength of Ag microwires. Scr. Mater. 64, 717 (2011).
34. Keller, C., Hug, E., and Feaugas, X.: Microstructural size effects on mechanical properties of high purity nickel. Int. J. Plast. 27, 635 (2011).
35. Chen, X.X. and Ngan, A.H.W.: Tensile deformation of silver micro-wires of small thickness-to-grain-size ratios. Mater. Sci. Eng. A 539, 74 (2012).
36. Leung, P.S.S. and Ngan, A.H.W.: Size effect on the strength of micron-sized polycrystals—a dislocation dynamics simulation study. Scr. Mater. 69, 235 (2013).
37. Gu, R. and Ngan, A.H.W.: Size effect on the deformation behavior of duralumin micropillars. Scr. Mater. 68, 861 (2013).
38. Gan, K., Gu, R., and Ngan, A.H.W.: The weakest size of precipitated alloys in the micro regime: the case of duralumin. Submitted to J. Mater. Res.
39. Gu, R., Leung, P.S.S., and Ngan, A.H.W.: Size effect on deformation of duralumin micropillars—a dislocation dynamics study. Scr. Mater. 76, 73 (2014).
40. Zhou, C., Beyerlein, I.J., and LeSar, R.: Plastic deformation mechanisms of fcc single crystals at small scales. Acta Mater. 59, 7673 (2011).

Size effects of micrometer-scaled metals—the search continues for materials containing real microstructures

  • A. H. W. Ngan (a1), X. X. Chen (a1) (a2), P. S. S. Leung (a1) (a2), R. Gu (a1) (a3) and K. F. Gan (a1)...


Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed