A novel non-contact strain-measurement technique was used to measure the tensile properties of extremely small samples of pure high-density nanocrystalline material. The micro-sample tests confirmed the absence of Young’s modulus variations for metals with grain sizes which approached 25nm. Significant strength enhancements were associated with nanocrystalline specimens. The tensile stresses which were attained in these micro-sample tests were found to be an appreciable fraction of the theoretical shear strength of the metal. Transmission electron microscopic investigations of deformed nanocrystalline Ni failed to produce any evidence of dislocation activity. In the absence of dislocation motion, the tensile strength of truly nanocrystalline metals was markedly high but the properties of samples tended to be undermined by intrinsic porosity and mesoscale micro-crack coalescence.

Microsample Tensile Testing of Nanocrystalline Metals. M.Legros, B.R.Elliott, M.N.Rittner, J.R.Weertman, K.J.Hemker: Philosophical Magazine A, 2000, 80[4], 1017-26