EFFECT OF Cr, Nb AND Zr ADDITION ON THE CORROSION BEHAVIOUR OF IRON-ALUMINUM ALLOYS (Fe-28at.Al)

摘要

Iron-aluminum alloys (Fe-28at. %Al) containing chromium, niobium and zirconium were prepared in an induction furnace using AISI 1010 steel. Their ordered cubic structure DO_3 type is obtained after annealing treatment of 26 hours at 500°C.The electrochemical corrosion tests performed in a low chlorinated medium (Na_2SO_4 0.05mol.L~(-1)NaCl 0.5g.L~(-1)) show a beneficial effect against corrosion by addition of 2 and 5 at.% chromium and 0.5and 2 at.% niobium designed respectively Al and A3 alloys. While an addition of 0.5 and 2 at. % Zr to the latter leads to a generalized corrosion, this phenomenon decreases with the addition of Chromium and Niobium. The examination by a dispersive energy X (E.D.X) in scanning electron microscope of corroded samples reveals that the pits are initiated and developed around the second phases Fe_3Zr, Fe_3AlC_(0.69) and precipitated as carbides of types Cr_(23)C_6, NbC, ZrC formed at the grain boundaries and in the Fe_3Al base. These phases confirmed by X-ray diffraction (X.R.D) analysis represent the main cause of the embrittlement and pitting corrosion in these alloys.