Microstructure and thermodynamic analysis of nanostructured Cu-13.2%Al-4%Ni ternary system synthesized by mechanical alloying

Abstract

Thermodynamic analysis of nanostructured Cu-13.2%Al-4%Ni synthesized by mechanical alloying was studied through Miedema's semi-empirical model. The variations of lattice strain, crystallite size and microstructural evolution at various milling times were also measured using X-ray diffraction and scanning electron microscope. The results showed an increase in lattice strain and reduction in crystallite size due to an increase in density of structural defects as a result of high-energy collisions during mechanical alloying. The calculated thermodynamic data suggested that in all binary Cu-Al, Al-Ni and Ni-Cu systems, there is a driving force for solid solution formation over all compositions due to negative Gibbs free energy changes in those compositions, while this value is positive for the formation of amorphous phase over some compositions which can be attributed to the absence of driving force. Additionally, thermodynamic data were in agreement with XRD results which showed solid solution was formed at middle stages of mechanical alloying. Moreover, it is concluded that the formation of solid solution is easier at three corners of ternary diagram, where the concentration of one element is major, whilst amorphous phase formation is more desirable in other compositions.Keywords: thermodynamic properties / nanostructured materials / powder metallurgy / mechanical alloying / shape memory alloys *