Nanomaterials, Mechanics and MEMS Labratory

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Nanomaterials, Mechanics and MEMS Labratory

Effect of Texture on Mechanical Behavior of Thin Films

Project Status: Active

It is known that the mechanical response of ultrafine-grained (UFG) and Nanocrystalline (NC) metal films depends on the rate at which they are deformed. Strain rate sensitivity (SRS) studies on UFG/NC metals have shown that SRS increases and activation volume decreases as the grain size becomes finer. However, in addition to the mean grain size, texture is also known to significantly influence the deformation behavior of UFG/NC metal films. But the effect of texture on the SRS of metallic films has not been systematically investigated so far.

We have investigated the SRS of nanoscale Al films with nearly identical thickness and mean grain size but substantially different textures. Our results unambiguously show that SRS of UFG Al films is strongly dependent on film texture. Films with a strong (110) out-of-plane texture and composed only of two in-plane grain variants (bicrystalline textured films) show significantly smaller SRS compared to films with a random orientation of grains (non-textured films). The flow stress of the bicrystalline films increased by 14% when the strain rate was increased from 7 x 10-6/s to 5 x 10-3/s. In contrast, the flow stress of non-textured films increased by over 90% over a similar strain rate range. Even within the bicrystalline films, plastic anisotropy induced by crystallographic texture leads to meaningful differences in SRS along different loading directions.

Stress-strain response of a textured and non-textured aluminum film at different strain rates. The two films have a nearly identical thickness (240 nm) and mean grain size (275-285 nm).

Related Publications

1. E. Izadi, S. Opie, H. Lim, P. Peralta and J. Rajagopalan, “Effect of plastic anisotropy on the deformation behavior of bicrystalline aluminum films – experiments and modeling,” Acta Materialia 142, 58-70, 2018 (pdf).

2. E. Izadi, A. Darbal, R. Sarkar, J. Rajagopalan, “Grain rotations in ultrafine-grained aluminum films studied using in situ TEM straining with automated crystal orientation mapping,” Materials and Design 113, 186–194, 2017 (pdf).

3. E. Izadi and J. Rajagopalan, “Texture dependent strain rate sensitivity of ultrafine-grained aluminum films,” Scripta Materialia 114, 65-69, 2016 (pdf).

4. J. Rajagopalan and M. T. A. Saif, “Effect of microstructural heterogeneity on the mechanical behavior of nanocrystalline metal films,” Journal of Materials Research 26, 2826-2832, 2011 (pdf)