Effect of Cr, Nb and Zr additions on the aqueous corrosion behavior of iron-aluminide

Detailed electrochemical analysis in moderate corrosive environment and the microstructures examination have been conducted for different iron-aluminide Fe-28% Al alloys prepared from Cr, Nb and Zr additions. The electrochemical corrosion tests performed in a low chlorinated medium (Na2SO4 0.05 mol L−1 + NaCl 0.5 g L−1) showed an increasing protective effect against corrosion attack for 2% and 5% Cr and for 0.5% and 2% Nb alloys. In contrast addition of 0.5% and 2% Zr to Fe-28% Al leads to a generalized corrosion phenomenon, which decreases after the addition of Cr and Nb. The examination by a dispersive energy spectrometer in scanning electron microscope of corroded samples reveals the origin of pits initiation, which are developed around Fe2AlCr, Fe3Nb(Al), Fe2(AlZr) phases and are also present around Fe3AlC0.69,Cr23C6, NbC, and ZrC carbide precipitates. It is noted that these carbides are formed at the grain boundaries and inside grain of Fe3Al matrix. Details microstructural study of these phases were confirmed by X-ray diffraction analysis and present the driving main cause of the embrittlement and pitting corrosion of these alloys.

► Fe-28% Al with Cr, Nb and Zr additions were prepared in well ordered DO3 structure.
► 2% and 5% Cr additions enhance the corrosion resistance with low density pitting.
► 0.5% and 2% Nb additions to Fe-28Al-5Cr exhibits the best resistance against corrosion.
► 0.5% and 2% Zr additions to Fe-28Al-5Cr leads to a generalized corrosion by pitting.
► The pits are developed around the second phases and carbides precipitates in the matrix.