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A Transforming Metal Nanocomposite with Large Elastic Strain, Low Modulus, and High Strength

Science  08 Mar 2013:
Vol. 339, Issue 6124, pp. 1191-1194
DOI: 10.1126/science.1228602

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Most metals show elastic strain limits well below 1%, beyond which permanent plastic deformation occurs. Metal nanowires can be elastically stretched to much higher strains, on the order of 4 to 7%. However, when placed inside a metal matrix to form a composite, these nanowires can no longer be stretched to the same extent, even when the nanowires are well distributed and show good bonding with the matrix. Hao et al. (p. 1191; see the Perspective by Zhou) used a shape memory alloy as the matrix material to produce a much better (more elastic) composite.

Abstract

Freestanding nanowires have ultrahigh elastic strain limits (4 to 7%) and yield strengths, but exploiting their intrinsic mechanical properties in bulk composites has proven to be difficult. We exploited the intrinsic mechanical properties of nanowires in a phase-transforming matrix based on the concept of elastic and transformation strain matching. By engineering the microstructure and residual stress to couple the true elasticity of Nb nanowires with the pseudoelasticity of a NiTi shape-memory alloy, we developed an in situ composite that possesses a large quasi-linear elastic strain of over 6%, a low Young's modulus of ~28 gigapascals, and a high yield strength of ~1.65 gigapascals. Our elastic strain-matching approach allows the exceptional mechanical properties of nanowires to be exploited in bulk materials.

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