Microstructures And Mechanical Properties Of Nanocrystalline Fe₃Al Matrix Fabricated By Vacuum Hot-pressing

Fe-Al intermetallic compounds have potential applications in high temperature structural materials due to their better properties compared with other traditional structure materials such as stainless steels. However, two problem which still restrict their application are brittleness at room temperature and reduction of creep resistant above 600°C. Methods such as grain refinement by mechanical alloying and adding reinforcing agents are usually considered to improve its properties at both room and high temperature.In this paper, nanocrystalline Fe₃Al powders with variable Ti,B compositions were prepared by mechanical alloying(MA), and then Fe₃Al matrix bulk materials with different Ti,B content were fabricatied using vacuum hot-pressing technique. Microstructures of the mechanically alloyed powders and hot pressed bulks were analyzed using XRD,TEM and SEM,respectively. The mechanical properties and the fractographies of the bulks were also investigated. Fianally, the influences of microstructures and the Ti, B compositions on the mechanical properties of Fe₃Al based bulks were discussed.The supersaturated Fe(Al) solid solution is formed during milling the Fe₇₂Al₂₈ mixed powder. The supersaturation Fe(Al,Ti,B) solid solution is formed during milling the Fe-Al-Ti-B mixed powder , which are then transformed into an amorphous state during prolonging the milling time.The crystalline size are decreased and the lattice parameter increased rapidly with increasing the milling time at the initial stage, and then slow down when prolonging the milling time. Finally, the microstructures remain to be stable, and nanocrystalline powders are formed.After the powders vacuum hot-pressed at 1200°C for 1h, the bulk Fe₃Al based materials were fabricatied. The crystalline size remains in nanometeric scale, although grain growth was happened during sintering.The Fe₇₂Al₂₈ sintered bulk is compose of ordered DO3-Fe₃Al and a little Fe₃AlC0.5. In the Fe-Al-Ti-B sintered bulks, some TiB2 and Fe2B are formed in the Fe₃Al matrix. The matrix contains some larger micron particles and submicron particlesd. The bulk materials fabricatied by MA and vacuum hot-pressing are much better than casting Fe₃Al materials in intensity and hardness. And, the boride particles reinforced materials have even higher properties than the nanocrystalline Fe₃Al materials. The bulk Fe₃Al matrix nanocomposite of 5 at%(Ti₃₃B₆₇) has the highest bending strength (1440 MPa) and a hardness value (461.3Hv).The fractural mechanism of the nanocrystalline Fe₃Al materials is brittle in general. Otherwise, it is of a little plastic fractural composition.