Hou, X D*; Jennett, N M; Parlinska-Wojtan, M* (2013) Exploiting interactions between structure size and indentation size effects to determine the characteristic dimension of nano-structured materials by indentation. J. Phys. D, Appl. Phys., 46 (26). 265301

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Abstract

Previously Jennett et al. 2009 (Applied Phys. Lett. 95:123102) used uniaxial compression of tungsten single crystal monolithic structures to show that length is the critical dimension determining yield (or flow) stress; wall-like structures exhibiting the same proportional limit as pillars of the same width in each lateral dimension. We have shown that the reciprocal sum of component critical dimensions indentation size, structure size, and dislocation density, combine into a single critical dimension as predicted by slip distance theory (Hou et al. 2012 Acta. Mater. 60:4128). This suggests that 'Length determines strength' and all lengths contribute at all times to the critical value. We have already shown that Cu hardness increases when grain size falls below six times the indentation contact radius (Hou et al. 2008 J. Phys. D, 41:074006). In this paper we test the inverse case (indent size greater than grain size), by indenting two different metallic glasses (NiAl and ZrTiAlCuBe) and comparing results with careful TEM determinations of nano-structure size. We show that the indentation size effect does indeed become observable even when the indent size is larger than the grain size by up to an order of magnitude. The indentation depth (size) at onset of the indentation size effect is proportional to the characteristic structure-size of these nano-structured materials and suggests a novel use of indentation size effect as a determinant of structure size. These findings also have implications for the design of hardness reference blocks and the use of hardness mapping to determine materials property variations.

Item Type:	Article
Keywords:	indentation size effect, structure size effect, metallic glass, nano-crystal
Subjects:	Advanced Materials Advanced Materials > Surface Engineering
Identification number/DOI:	10.1088/0022-3727/46/26/265301
Last Modified:	02 Feb 2018 13:14
URI:	http://eprintspublications.npl.co.uk/id/eprint/5848

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