Size effect on the strength of materials

Sample size has significant effect on the strength of materials. For instance, the tensile strength of Cu whiskers increases with decreasing sample diameter. This “smaller is stronger” trend has been found in all kinds of materials. And in micro-nanoscale materials, elastic limit and theoretical strength can be reached. The size-strength relationship in micro-nanoscale materials is studied using in-situ quantitative mechanical testing technique inside TEM or SEM. Models are proposed to understand the underlying mechanism for the size effect.

Sample size dependence of materials’ strength

Deformation mechanism of materials

The study of deformation mechanism of materials using in-situ straining techniques provide us enormous details which are unimaginable before. Deformation mechanism and defects evolution are investigated in various materials including crystalline metals, metallic glasses, and covalent materials. In-situ observation of the deformation process can verify theories, eliminate controversies and reveal new deformation mechanisms.

A new deformation mechanism discovered in Magnesium

FCC metals

Z. J. Wang, Q. J. Li, Z. W. Shan, J. Li, J. Sun and E. Ma, Sample size effects on the large strain bursts in submicron aluminum pillars, Applied Physics Letters, Feb. 2012, Vol. 100, issue 7, 071906.

Z. J. Wang, Z. W. Shan, J. Li, J. Sun and E. Ma, Pristine-to-Pristine Regime of Plastic Deformation in Submicron-Sized Single Crystal Gold Particles, Acta Materialia, Feb. 2012, Vol. 60, issue 3, 1368-1377.

BCC metals

L. Huang, Q. J. Li, Z. W. Shan, J. Li, J. Sun and E. Ma, A new regime for mechanical annealing and strong sample-size strengthening in body-centred cubic molybdenum, Nature Communications, Nov. 2011, Vol 2, 547.

R. Huang, Q. J. Li, Z. J. Wang, L. Huang, J. Li, E. Ma and Z. W. Shan, Flow Stress in Submicron BCC Iron Single Crystals: Sample-size-dependent Strain-rate Sensitivity and Rate-dependent Size Strengthening, Materials Research Letters, Feb. 2015.

W. Z. Han, L. Huang, S. Ogata, H. Kimizuka, Z. C. Yang, C. Weinberger, Q. J. Li, B. Y. Liu, X. Y. Zhang, J. Li, E. Ma and Z. W. Shan, From "smaller is stronger" to "size-independent strength plateau": towards measuring the ideal strength of iron, Advanced Materials, 2015, DOI:10.1002/adma.201500377.

HCP metals

Q. Yu, Z. W. Shan, J. Li, X. Huang, L. Xiao, J. Sun and E. Ma, Strong crystal size effect on deformation twinning, Nature, Jan. 2010, Vol. 463, 335-338.

B. Y. Liu, J. Wang, B. Li, L. Lu, X. Y. Zhang, Z. W. Shan, J. Li, C. L. Jia, J. Sun and E. Ma, Twinning-like lattice reorientation without a crystallographic twinning plane, Nature Communications, Feb, 2014, Vol. 5, 3297.

B. Y. Liu, L. Wan, J. Wang, E. Ma and Z. W. Shan, Terrace-like morphology of the boundary created through basal-prismatic transformation in magnesium, Scripta Materialia, 2015.

Glassy materials

K. Zheng, C. Wang, Y. Q. Cheng, Y. Yue, X. Han, Z. Zhang, Z. W. Shan, S. X. Mao, M. Ye, Y. Yin and E. Ma, Electron-beam-assisted superplastic shaping of nanoscale amorphous silica, Nature Communications, Jun. 2010, Vol. 1, 24. 

C. C. Wang, J. Ding, Y. Q. Cheng, J. C. Wan, L. Tian, J. Sun, Z. W. Shan, J. Li and E. Ma, Sample size matters for Al88Fe7Gd5 metallic glass: Smaller is stronger, Acta Materialia, Aug. 2012, Vol. 60, issue 13-14, 5370-5379.

L. Tian, Z. W. Shan and E. Ma, Ductile necking behavior of nanoscale metallic glasses under uniaxial tension at room temperature, Acta Materialia, Aug. 2013, Vol. 61, issue 63, 4823–4830.

C. C. Wang, Y. W. Mao, Z. W. Shan, M. Dao, J. Li, J. Sun, E. Ma and S. Suresh, Real-time, high-resolution study of nanocrystallization and fatigue cracking in a cyclically strained metallic glass, Proceedings of the National Academy of Sciences of the United States of America, Dec. 2013, Vol. 110, issue 49, 19725-19730.

Reviews and others

Z. W. Shan, In Situ TEM Investigation of the Mechanical Behavior of Micronanoscaled Metal Pillars, JOM, Oct. 2012, Vol.64, issue 10, 1229-1234.

田琳 付琴琴 单智伟, 聚焦离子束在微纳尺度材料力学性能研究中的应用, 《中国材料进展》2013年 第12期.

L. Tian, J. Li, J. Sun, E. Ma and Z. W. Shan, Visualizing size-dependent deformation mechanism transition in Sn, Scientific Reports, Jul. 2013, Vol. 3, 2241.

L. F. Liu, X. D. Ding, J. Li, T. Lookman and J. Sun, Direct observation of hierarchical nucleation of martensite and size-dependent superelasticity in shape memory alloys, Nanoscale, Apr. 2014, issue 6, 2067–2072.

Y. C. Wang, D. G. Xie, X. H. Ning, and Z. W. Shan,Thermal treatment-induced ductile-to-brittle transition of submicron-sized Si pillars fabricated by focused ion beam, Applied Physics Letters, 2015,Vol. 106.