Development of novel aluminium matrix nanocomposites

Novel Al matrix nanocomposites have been produced and studied based on a high strength nanoquasicsytalline (NQX) Al93Fe3Cr2Nb2 (at%) alloy. Two types of metallic materials including pure metals (such as Nb or Ti) and amorphous Ti50Cu25Ni25 (at%) alloy ribbons have been used as reinforcements. The constituent materials, extruded alloy/composites bars have been characterised using various techniques including electron microscopy, X-ray diffraction, differential scanning calorimetry, and X-ray computed tomography. The mechanical properties of the extruded alloy/composites bars have been studied by Vicker’s hardness tests, compression tests at room temperature and elevated temperature, and split Hopkinson pressure bar tests. The microstructure of the alloy/composites contains i-phase particles embedded in α-Al, mostly with diameters under 1µm, along with some possible intermetallic precipitates. NQX/Ribbons composite also contains amorphous phase and a crystalline Ti2(Cu, Ni) phase. Compression strength of the alloy/composites at room temperature and elevated temperature are superior to conventional high strength Al alloys and corresponding Al matrix composites. The elastic (non-plastic) reinforcements (the melt-spun amorphous Ti-based alloy ribbons) contributes to an increase of the strength but a reduced ductility, which leads to a lower toughness material respect to the alloy matrix. However, the elastic-plastic reinforcements (pure Nb or pure Ti) contributes to an increased strength and maintain the ductility, which leads to a higher toughness material respect to the alloy matrix. From the tomography results of the NQX/Ribbons composite and Al-QC/Nb composite, their plastic deformation has been visualised and localised strain at the shear stress plane has been identified. The strength of NQX alloy have been attributed to grain boundary and Orowan’s strengthening mechanisms, while solid solution and dislocation strengthening have also contributed to the strength in a minor fraction. Strengthening from the reinforcements in the composites have been explained by composite models such as Rule of Mixture and Shear Lag model which fit well with the experimental results.