Investigation of aluminum-based nanocomposites with ultra-high strength

Previously, we reported ultra-high compressive strength (up to 1065 MPa) for a bulk aluminum-based metal matrix nanocomposite [J. Ye, B.Q. Han, Z. Lee, B. Ahn, S.R. Nutt, J.M. Schoenung, Scr. Mater. 53 (2005) 481-486]. The mechanisms that are responsible for this significant strength increase over conventional materials (∼225 MPa, H. Zhang, M.W. Chen, K.T. Ramesh, J. Ye, J.M. Schoenung, E.S.C. Chin, Mater. Sci. Eng. A: Struct. Mater. Prop. Microstruct. Process. 433 (2006) 70-82) and even over other equivalent nanocrystalline materials (∼470 MPa, R.G. Vogt, Z. Zhang, T.D. Topping, E.J. Lavernia, J.M. Schoenung, J. Mater. Process. Technol., 209 (2009) 5046-5053) have not been studied in detail. The material consists of boron carbide reinforcement in a matrix with both coarse-grained and ultrafine-grained Al 5083; the processing introduces secondary phase dispersoids and dislocations. In this work, we systematically investigate the microstructural origins and the strengthening mechanisms, including Hall-Petch, Orowan and Taylor, as appropriate to each phase constituent. To provide insight into the relative contributions of these mechanisms, we calculate overall strength using rule-of-mixtures, modified shear-lag model, and Mori-Tanaka method.