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 elements like Ni, Co, etc and is made up of Fe and Al which are abundantly available in India. 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, precipitation hardeners and grain refiners. Even though, ductility of iron aluminides was improved but yield and ultimate tensile strengths were 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. It is known that in the presence of Al, the formation of coarse Y-Al-O complex oxide dispersoids is predominant and the probability of Y-Ti-O formation is relatively low in Ti containing ODS alloys. It is reported that finer Y-Zr-O particles, as compared to Y-Al-O, are formed when Zr is added to ODS alloys containing Al.
In the present research, two ODS Fe3Al alloy systems are produced through powder metallurgy process by adding two types of nano oxide-forming elements viz., one with Ti and the other with Zr to pre-alloyed inert gas atomized powders (Fe-13Al-5.3Cr-0.13Ti). Milling was carried out up to 10 h to optimise the milling time and found that steady state condition was obtained after 7 h. The 10 h milled powders were upset forged and hot extruded at an extrusion ratio of 19:1. Characterization of extruded and heat treated rods with the help of SEM, FESEM, TEM, APT and micro XRD was carried out. Extruded and heat treated rods showed fine grain structure with an average grain size of 540 nm along with uniformly distributed fine complex Y-Al-O, Y-Ti-O and Y-Zr-O oxide particles with an average particle size of 7 nm. It is observed that the stability of Fe3Al phase in these materials increased to 650C from 550C. They exhibited 16% elongation with a yield strength of 1100 MPa at room temperature and 56% elongation with a yield strength of 280 MPa at 700 °C. The presence of nano oxide particles not only inhibited grain growth but also contributed to the enhanced strength up to 700 C. It was found that, the strength of ODS Fe3Al alloys is higher up to 600 C and similar at 700 C when compared to widely used commercial materials like SS-310 and IN617.