Fe3Al intermetallic compound has attractive properties as high temperature structural materials, such as high strength, good oxidation resistance, low-cost and so on. However, their commercial application has been limited because of their poor toughness and limited workability. The combination of grain ultra-refinement and phase control is one of the most promising methods to improve their mechanical properties. In this work, we will present the nanostructure and superior mechanical properties of bulk Fe-Al-C nanoalloys made by mechanically alloying (MA) with subsequent spark plasma sintering (SPS).
Four kinds of nanocrystalline Fe-25at%Al-Xat%C (X=1,2,4,6) alloy powder were produced by MA from Fe powder, Al powder and methanol, and were subsequently consolidated by SPS with 32MPa up to 1273K. These compacts have the relative densities of 99.97% (1at%C) to 99.7% (6at%C). The calculations of the relative density variation during the SPS suggest that the compact is consolidated mostly by diffusion, besides the plastic yield and power-law-creep. The structure of most compacts consists of nanocrystalline Fe3Al-phase of about 80nm with nano κ-carbides (Fe3AlC0.5) and small amount of large α-grains of about 1μm with coherently precipitated nano κ-carbides. Their structures were maintained even at 973K. The mechanical properties were measured by the compression test at R.T. to 973K. These bulk nanoalloys perform the superior mechanical properties at R.T. to 973K (e.g. yield strength of 2150MPa and rupture strain of 0.14 for Fe-25Al-2at%C compact at R.T.) when compared with the ordinary Fe3Al (e.g. 380MPa and 0.12 for Fe-28Al). They also show no environmental embrittlement caused by some gaseous species in air, which is one of fatal problems for the ordinary Fe3Al.