General corrosion of B-strengthened Ni- and Fe-based microcrystalline alloys in de-aerated 1 M HCI solution

Abstract

The general corrosion characteristics of four boride-strengthened microcrystalline alloys, two Ni-based and two Fe-based, were studied in de-aerated 1 M HCI solution at room temperature in a rotating cylinder system at three rotation speeds (600, 1200 and 1800 rpm), using electrochemical small amplitude cyclic voltammetry and AC impedance techniques. For comparison, two commercial materials, namely Alloy 600 and AISI Type 316 SS, were studied too. Good agreement was obtained between small amplitude cyclic voltammetry and AC impedance measurements of the polarization resistance. Both the corrosion potential and corrosion rate became independent of time after log exposures. In the case of Ni-based materials and in that of 316SS, both the corrosion potential and rate were not affected by changes in the speed of rotation. In the case of Fe-based microcrystalline alloys, the corrosion rate decreased while the corrosion potential increased with Re. This finding was explained by corrosion-induced surface enrichment in Mo, the extent of which increased with increasing speed of rotation. Within the range of rpm tested, the corrosion rates measured for the Fe-based materials were generally higher than those measured for the Ni-based materials and the corrosion rates decreased with increasing Ni contents in the alloy. No extraordinary resistance to general corrosion in 1 M HCl at room temperature was found for the four boride-strengthened microcrystalline alloys tested.