Iron aluminides (Fe3Al) are being considered for high temperature applications due to their attractive properties such as high strength, low density, excellent oxidation, sulfidation and corrosion resistance. Another advantage is its low cost as it does not contain any strategic elements like Ni, Co, etc and is made up of Fe and Al which are abundant. These virtues of Fe3Al make it an alternative to high-alloyed stainless steels and nickel-based super-alloys. However, iron aluminides suffer from poor room temperature ductility and high temperature strength, which limit their commercial applications. Many attempts have been made to improve the strength and ductility by alloying with solid solution strengtheners like Cr, Mn, Ti, Cu, Ni, Si, Co, C and Mo, precipitation hardening elements like Re, Hf, C, Zr, Nb, Ta, B and Ti, and grain refinement with the addition of B along with Zr/ Ti/ C. Even though, ductility of iron aluminides was improved but yield and tensile strengths wer e reduced. Oxide dispersion strengthening is one of the promising method in which, the presence of nano-sized dispersoids promotes grain refinement by effective pinning of grain boundaries and also strengthens the grain boundaries. Oxide dispersion strengthened (ODS) Fe3Al is expected to have improved ductility, creep resistance and fracture toughness due to the beneficial action of stable nano-sized dispersoids in retaining the fine grained structure developed during the processing.
In the present research, oxide dispersion strengthened ordered iron aluminides (ODS Fe3Al) was produced by mechanical alloying and hot extrusion. The atomized pre-alloyed powder, milled powder as well as extruded and heat treated samples were characterized for composition, morphology, particle size, microstructure, hardness and room temperature tensile properties. The extruded and heat treated ODS Fe3Al exhibited both elongated and fine equi-axed grain structure in longitudinal direction, whereas equi-axed grain structure was observed in transverse direction. The average grain size of ODS Fe3Al was about 1 µm. Eventhough, both prealloyed as well as milled powder showed only FeAl phase, D03 structured Fe3Al along with Y3Al5O12 and TiO phases exisited in ODS Fe3Al. Dispersoids of two distinct sizes and phases were observed. The fine spherical (7- 25 nm) particles were of Y3Al5O12 and the coarser spherical particles (> 25 nm) were of TiO type. At room temperature the yield s trength and elongation of ODS Fe3Al were measured to be 1104 MPa and 8 % respectively. The enhancement in strength and ductility was due to the nano-sized dispersoids and fine grained structure. Efforts are being made to enhance the ductility further.