Characteristics and mechanism of the synergistic effect between erosion and corrosion

The characteristics and mechanism of synergistic effect between the erosion and corrosion were investigated by means of erosion and corrosion testing, electrochemical measurements and microstrain measurement by XRD broadening. The investigations were carried out on heat-treated (as-received, annealed, quenched and tempered) AISI 52100 and AISI 1020 steels eroded with varying amounts of erodent (10g, 50g and 100g SiC particles) and/or at varying erosion angles (30°, 45° and 60°). The variation of selected electrochemical parameters i.e. open-circuit potential, linear polarization and polarization curves, corrosion potential, polarization resistance and calculated corrosion rate, was measured as a function of the amount of erodent, erosion angle and heat treatment.; A synergistic effect was shown to exist between erosion and corrosion, i.e. the material loss due to the combined erosion-corrosion is much greater than the summation of those components due to erosion and corrosion separately. Synergistic effect between erosion and corrosion for AISI 52100 steel contributes 80% of the total material loss whereas that for AISI 1020 steel contributes 60% of the total material loss. The synergistic effect is a result of the accelerated corrosion rate, whereby erosion both thermodynamically and kinetically facilitates the corrosion reaction.; As a result of the impacting erodent, the open-circuit potential and corrosion potential decreased negatively, the polarization resistance increased positively, and thus the corrosion rate is correspondingly increased. In addition to the effect of the amount of erodent, the erosion angle also affects the electrochemical behavior. There is a minimum negative open-circuit potential and corrosion potential, a minimum polarization resistance and a maximum corrosion rate at an erosion angle of 45°.; The microstrain induced in the steels due to impact was determined using XRD peak broadening. The microstrain increases with increasing amount of erodent and is a maximum at an erosion angle of 45°. The calculated stored strain energy increases with increasing amount of erodent and is a maximum at an erosion angle of 45°.; A theoretical relationship is developed to describe the correlation between corrosion rate, potentials, stored strain energy, polarization behavior and the mechanism of synergistic effect. This mathematical kinetics equation is considered to be valid since the calculated corrosion rate agrees very well with the measured corrosion rate. Thus the mechanism of synergistic effect is a mechano-electrochemical effect due to the erosive action causing a decrease in corrosion potential and an increase in stored strain energy.