Sintered Intermetallic Reinforced 434L Ferritic Stainless Steel Composites
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THE ordered intermetallics based on the aluminides of the transition metals, in particular, nickel, iron, and titanium, have gained the interest of the researchers for their potential use as high-temperature structural parts. They offer the unique combination of oxidation resistance, lower densities, and higher melting points with attractive mechanical properties at higher temperatures that make them cheaper alternatives to the existing superalloys. However, the poor room-temperature ductility of these aluminides restricted their commercial use. Although the high-temperature structural applications are the driving forces for the developments of these intermetallics, their specific strength, wear, and corrosion resistance can be used for some low- or intermediate-temperature applications as well. The ordering influences the chemical activity of the constituent elements and the kinetics of the dissolution processes.[1] Ricker[2] reported the positive effects of ordering in reducing the surface reactivity of Al and Fe atoms in the cases of Ni3Al and Ni3Fe intermetallics respectively. Rao et al.[3] have reported the better corrosion behavior of the Fe3Al samples as compared to the pure Al and Fe samples. Elsewhere, Rao[4] compared the corrosion behavior of the Fe-16Al aluminide with the conventional 430 stainless steels. The study revealed no appreciable difference in the general corrosion behavior between the two samples because the variations in the Icorr and Ecorr values were very minimal. Hence, these A. UPADHYAYA, Associate Professor, and S. BALAJI, Postgraduate Student, are with the Department of Materials and Metallurgical Engineering, Indian Institute of Technology Kanpur, Kanpur-208016, India. Contact e-mail: [email protected] Manuscript submitted April 14, 2008. Article published online January 27, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
alloys are considered for replacing the costlier stainless steels in some of the room-temperature applications. Wolff et al.[5] partially replaced the Cr in the stainless steels with Al and studied their corrosion behavior. They reported negligible difference in general corrosion behavior between the Fe-40Cr and Fe-35Cr-5Al stainless steel samples in 10 pct H2SO4 solution. Velasco et al.[6] reinforced the austenitic 316L stainless steels with intermetallic compounds (Cr2Al, Cr2Ti, and TiAl) in order to improve the mechanical and tribological properties of the sintered stainless steels. Sintered stainless steels possess inferior mechanical and corrosion properties as compared to their wrought and cast counterparts due to the presence of porosity.[7] To enhance the mechanical and tribological properties of the powder metallurgy stainless steels, hard dispersoids such as Al2O3 and Cr3C2 have been used as reinforcements.[8–10] However, the major drawback of these reinforcements is their poor interaction with the matrix stainless steels, which further degrades the densification. In order to improve the densification, the sintering activators such as CrB, B2Cr, BN, and Fe3P were
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