Microstructures and mechanical properties of bulk nanocrystalline Fe-Al-C alloys made by mechanically alloying with subsequent spark plasma sintering

The microstructure and superior mechanical properties of bulk nanocrystalline Fe-Al-C alloys made by mechanically alloying (MA) with subsequent spark plasma sintering (SPS) were investigated. Three kinds of nanocrystalline Fe-24 at% Al-Xat%C (X = 1,2,4) alloy powder were produced by MA from iron and aluminum powder with addition of methanol, and were subsequently consolidated at 1073-1273 K under 64 MPa by SPS. These compacts have the relative densities of 99.97% (1at%C) to 99.5% (4at%C). The structure of compacts with 1at%C is composed of grains of Fe₃Al of 1.5 μm in diameter and nano κ-carbides (Fe₃AlC_0.5) precipitates, while those of compacts with 2 and 4at%C are composed of nanocrystalline Fe₃Al of about 80 nm in diameter, nano κ-carbides and small amount of large α-grains of about 1 μm in diameter. These structures maintain the nanostructure even at 973 K, that is, they have the good thermal stability. The mechanical properties of these compacts were measured by compression tests at room temperature (RT) to 973 K in vacuum. The compacts with 1 and 2at%C of this work perform the superior mechanical properties (e.g. yield strength of 2150 MPa and rupture strain of 0.14 for compact with 2at%C at R.T.) when compared with the ordinary Fe ₃Al casting (e.g. the yield strength of 380 MPa and rupture strain of 0.12).