Structural And Properties Of The Nanocrystallic Fe₃Al And Its Composites

Mechanical alloying (MA) is the ball milling process where pure element powders or their mixtures are placed in a ball mill and subjected to high energy collision, and solid reactions occur among the powders during the ball milling. Up to now, the technology has been used to prepare supersaturated solid solution, amorphous alloys, intermetallic compound, nanocrystalline, magnetism materials, superconductor materials, and etc.In this paper, Fe₇₂Al₂₈ and Fe₇₂Al₂₈-TiB₂ super-fine powders were prepared by mechanical alloying, then synthesized into nanocrystalline binary Fe-Al (Fe₃Al) or quaternary Fe-Al-Ti-B (Fe₃Al/TiB₂) bulk composite materials by cold-pressing with subsequent sintering technique. The microstructures of MA powders and sintered bulk materials were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectrometer (EDX). The density and micro-hardness of the sintered bulk materials were measured. The structure, morphology and crystalline size of the powder during the process of MA and sintered bulk materials, as well as the mechanical property change of the bulk Fe₃Al and TiB₂/Fe₃ Al composites were studied.The results indicated that Fe-Al powders formed the structure of Fe circular covered with Al at the early stage of the MA process, after MA 25h, the supersaturated Fe(Al) solid solution was formed with lattice parameter and grain size of 0.2905nm and 6.9nm respectively. When Fe₃Al bulk materials were sintered ranging from 800 to 1100 °C, the supersaturated Fe(Al) solid solution was transformed into nanocrystalline Fe₃Al intermetallics. The crystalline size, density and micro-hardness of Fe₃Al bulk material were 38.7nm, 4.41g/cm³ and 460.7HV respectively after sintered at 1100°C for 1 hour. The supersaturated solid solution of Fe(Al,Ti,B) was firstly formed and then transformed into an amorphous state during the milling process. Meanwhile, both order degree and crystalline size decreased continuously. After MA 40h, the crystalline size of Fe(Al,Ti,B) solid solution was 9.6nm. The composite powder was decomposed into nanocrystalline Fe₃Al and TiB₂, and nanocrystalline Fe₃Al/TiB₂ bulk composite was formed with...