| The pitting and general corrosion characteristics of four boride-strengthened microcystalline alloys (Alloys 1 to 4) were investigated. Their potential applications were evaluated by comparisons with commercial Inconel 600 and 316 SS. The materials were divided into two groups: Ni-based materials (Alloy 1, Alloy 2, and Inconel 600) and Fe-based materials (Alloy 3, Alloy 4, and 316 SS).;The general corrosion rate measurements were carried out in deaerated 1N HCl solution at 25(DEGREES)C in the rotating cylinder system at three rotation speeds (rpm = 600, 1200, and 1800) using electrochemical small amplitude cyclic voltammetry (SACV) and AC impedance techniques as well as direct weight loss method. Good agreement was obtained between SACV and AC impedance techniques for measuring the polarization resistance. For the Ni-based materials and 316 SS within the range of rpm (or Re) studied, the corrosion processs is activation-controlled and the rate of corrosion is independent of rpm (Re). For Alloys 3 and 4, the corrosion rate decreases while the corrosion potential increases with increasing Re for the range of Re tested. This phenomenon was explained by the Mo enrichment on the surface of these two alloys.;The pitting corrosion tests were conducted in deaerated 1m NaCl solution at 25, 45, 65, and 80(DEGREES)C. For all the materials studied, the pitting potential (E(,np)) decreases with increasing temperature. Within the temperature range tested, E(,np) increases in the order of Alloy 3 < 316 SS, Inconel 600 < Alloy 2 < Alloy 4 < Alloy 1 with Alloy 1 showing the highest resistance to pitting. This was interpreted in terms of the alloying element and microstructural effects. It was found that Cr is the most effective alloying element in increasing pitting potential. In addition, Alloy 1 as well as Alloy 4, each showing the highest value of E(,np), also shows the largest difference of E(,np)-E(,pp) in each group of materials tested. This behavior was believed to be caused by the shielding effect of the undissolved oxide film covering the pits on these two alloys. |
