Simultaneous effect of surface roughness and passivity on corrosion resistance of metals

Abstract

Unidirectional surface roughness of varying magnitudes were created on both nickel and mild steel by grinding on SiC papers with grit sizes from G60 (roughest) to G1200 (smoothest) and the corrosion resistance in 0.5M H 2 SO 4 solution was determined using a potentiodynamic polarization technique. A different trend of corrosion rate versus roughness was seen for the active-passive metal (nickel) and non-active-passive metal (mild steel). For nickel there was an increase in corrosion rate with increasing roughness, whereas for mild steel the corrosion rate decreased with increasing surface roughness. Furthermore, through a detailed examination of the surface before and after corrosion using techniques including profilometry, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), it was established that different corrosion mechanisms were operative for nickel and mild steel. For both metals, the smaller grit sizes produced a rougher surface with wider and deeper grooves. In the case of nickel, the higher roughness provided a greater contact area between the corrosive medium and metal and there was trapping of the corrosive ions in the deep grooves. Both of these factors would lead to an increase in corrosion rate. Also, for the smoother nickel surfaces, it is easier to form a stable passive film. For mild steel, which does not form a passive film, corrosion rates are generally much higher than for nickel. For the rougher surfaces with the deeper grooves, the corrosion product, FeSO4, can fill the grooves thereby acting as a barrier to further ingress of the corrosive ions to the un-corroded metal.

Experimental Investigation on Roughness Parameters of 42CrMo4 Steel Surface During Nitrocarburizing Treatment

“…There is a relationship between high peaks and the two phenomena of friction and wear, according to studies [24,25]. Additionally, deeper grooves and valleys in the surface texture might cause crack propagation [26,27] and corrosion [28,29]. It can be seen from the table 1 and the Fig.…”

Evaluation of the biocompability and corrosion activity of resorbable CaMgZnYbBAu alloys

“…However, the lowest roughness values were obtained for the Ca 32 Mg 12 Zn 38 Yb 15 B 3 and Ca 32 Mg 12 Zn 38 Yb 18 alloys. These may suggest that these alloys were more corrosion resistant, because the lower the roughness values, the higher the corrosion resistance 29 , 30 . It should also be noted that corrosion resistance is dependent not only on the surface roughness but also on the ability of the alloy to form a protective passive film on its surface 30 .…”

“…These may suggest that these alloys were more corrosion resistant, because the lower the roughness values, the higher the corrosion resistance 29 , 30 . It should also be noted that corrosion resistance is dependent not only on the surface roughness but also on the ability of the alloy to form a protective passive film on its surface 30 . Mitchell et al 27 studied the effect of surface roughness on the corrosion behavior of AZ31 Mg alloys for 672 h of immersion in a solution of 3.5 wt.% NaCl.…”

Effect of the electrochemical characteristics of titanium on the adsorption kinetics of albumin

“…It is probably caused by the differences in surface roughness between the two samples (attributed to a larger true surface area) as has been shown in previous studies. 30,31 This is shown in Fig. 2, where the QCM surface has a larger average surface roughness (R a ) than bulk titanium (R a ¼ 8.78 nm for titanium-coated QCM sensor versus R a ¼ 1.27 nm for bulk titanium).…”