Nano-TiB 2 reinforced ultrafine-grained pure Al produced by flux-assisted synthesis and asymmetrical rolling
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ng Chenb) and Haowei Wang School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Enrique J. Lavernia Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616, USA
Aidang Shan School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China (Received 13 May 2014; accepted 18 September 2014)
In situ nano-TiB2 reinforced ultrafine-grained (UFG) Al composites were prepared via combined processes of flux-assisted synthesis (FAS) and asymmetrical rolling (ASR). The UFG Al composite with an ASR reduction ratio of 97% exhibits an average matrix grain size of 380 nm and an average TiB2 particulate size of 50 nm. Dislocation density in the composites is higher than that corresponding to the high purity (99.99 wt%) Al under identical processing conditions. The yield and ultimate tensile strength values of the UFG Al composites processed with an ASR reduction ratio of 97% are approximately 9 and 5 times higher relative to those of the initial coarse-grained Al, respectively. Moreover, the UFG Al composite with an ASR reduction ratio of 97% exhibits a higher elongation than that corresponding to the UFG pure Al under identical processing conditions, suggesting that nanoparticulates contribute to the overall plastic deformation when the matrix grains are refined to the UFG regime. Moreover, analysis of the strengthening behavior reveals no clear evidence that Orowan strengthening contributes significantly to the overall yield strength of the Al nanocomposites studied herein.
I. INTRODUCTION
Published studies on the synthesis and behavior of Al-based metal matrix nanocomposites (MMNCs) have been motivated by several factors.1–10 First, from a structural perspective, the physical properties of Al and its alloys (e.g., density) render them an ideal matrix to design light-weight MMNCs.1–5 Second, from a scientific perspective, the face-centered cubic (fcc) crystal structure of Al has been widely studied, and consequently there are well-established fundamental principles that can be used to provide insight into the strengthening mechanisms and deformation behavior of MMNCs.3,6,7 Third, the nanometric particulates, which in principle should strengthen the matrix as a result of interactions with moving dislocation, have become broadly available.3,6 Fourth, it has been demonstrated that severe plastic deformation (SPD) methods can be readily used to Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2014.280 2514
J. Mater. Res., Vol. 29, No. 21, Nov 14, 2014
http://journals.cambridge.org
Downloaded: 15 Mar 2015
refine the microstructure of fcc Al and its alloys to the ultrafine-grained (UFG, 100–1000 nm) and nanostructured (NS, ,100 nm) regimes, providing the opportunity to not only enhance mechanical performance,3,6,8,9 but also to investigate interesting scientific phenomena, such as twinning in fcc Al-based MMNCs.10 In terms of prepari
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