Comprehensive structural and mechanical characterization of in-situ Al–Al3Ti nanocomposite modified by heat treatment

Abstract

Aluminum-Al3Ti reinforced MMCs were produced with a large amount (up to ~30 vol%) of Al3Ti phase via mechanical alloying, hot extrusion and heat treatment (as a supplementary process) of the Al–Ti elemental powder mixture, respectively. Samples in each stage were studied precise and comprehensive by field emission electron microscope, energy dispersive spectroscopy, X-ray diffraction, differential scanning calorimetry, densitometry, macro and micssro hardness, nanoindentation and tensile tests. The results indicated that after 4-h vibratory milling, the aluminum crystallite size reached 63 nm and Al3Ti phase formed in powder mixture. After hot extrusion, the volume percentage of Al3Ti increased by the formation of new Al3Ti nanoparticles, and a densed structure was achieved. As the milling time increased and crystallite and particle sizes of aluminum and titanium become smaller, the mechanical behavior of the hot extruded nanocomposites was improved. After heat treatments, the amount of Al3Ti phase significantly increased, and by thickening the Al3Ti layers around the titanium microparticles at high temperatures and long time periods, the voids in the structure proliferated. Increase in Al3Ti content can improve the mechanical properties, provided that volume exchanges originating from its formation do not cause widespread formation of voids in the structure. Mechanical properties varied as a function of aluminum and titanium crystallite and particle sizes and amount of Al3Ti phase and voids in the final samples. Aluminum crystallites growth during heat treatment reduces the hardness and increases the matrix ductility, and reinforcement particles growth brings faster failure for the samples.