Tribochemical Effect Of The Blended Powder Mixtures Based On Fe₃(Si_x,Al_1-x) Ordered Alloy During Milling

Fe3(Si_xAl_1x) ordered intermetallic compound can be used not only as a kind of attractive soft magnetic materials, but as a kind of potential hig-temperature materials. In this work, the tribochemical effects of 3Fe/(xSi,(l-x)Al) blended powder mixtures in ball milling have been studied using Fritsch Pulversitte 5 planet ball mill, X-Ray diffractometer(XRD) and scanning electron microscope(SEM). The as milled powders have been annealed and hot-pressure sintered. The phase of the annealed powders and the hot-pressure sintered products, the scanning electron micrographs and the density of the hot-pressure products have been analysed.It was found that during the process of the milling, the changes of the tribochemical effects of 3Fe/xSi/(l-x)Al blended powder mixtures are as follows:1. The crystalline size decreases with milling time. It changes very fast at the first stage of the ball milling. 5 hours later, the crystalline size reaches to less than 20nm. Then the decreases of the crystalline size time become slow.2. The lattice strain increases with milling time. It changes fast when the deformation of the powder is easy. When the density of the lattice defect reaches to a certain extent, the increases of the lattice strain with become slow. It reaches to its limitation when the milling time is long enough.3. The effective temperature factor increases with milling time which is very similar to the lattice strain. It changes fast at the first stage of the balling milling, and reaches to its limitation at the last stage.It was also found that supersaturated solid solution ofa-Fe(Si,Al) was formed during the ball milling of the 3Fe/xSi/(l-x)Al blended powder mixtures. Based on the result of the experiment and Miedema's semi-empirical theory, the thermodynamic model for binary system is established to calculate the free energy and the enthalpy of the Fe75Si25 and Fe75A125 alloy. When the component are Fe75Si25 and Fe75A125, the free energy of Fe₃Si and Fe₃Al are the lowest. Mechanical milling introduces high energy into the material being processed. This energy can be stored in crystalline boundary and the dislocations of the alloy, which make the free energy of Fe3(Si,Al) higher than in the a-Fe(Si,Al) solid solution. So, the ordered intermetallic Fe3(SixAll-x) powder can be prepared by annealing using the as-milled powders.