Corrosion Behaviors of CoCrFeNiX (X = Ga0.75, Mn, Al0.3) High Entropy Alloys Compared with 304 Stainless Steel in 0.5 M H2SO4 Aerated Aqueous Solutions.
| Autor: | Bo-Wei Wu, 吳柏薇 |
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| Rok vydání: | 2019 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 This work investigates the corrosion mechanism of CoCrFeNi HEA, CoCrMo, 304SS and 316L in 0.5 M H2SO4 aerated aqueous. Experimental results show that the first critical current density (icrit1) is related to lower ksp value of Cr(OH)3, the higher the Cr content, the smaller the icrit1. The stable passive current density (ipass) is related to lower ksp values of Fe(OH)3 and Co(OH)3, so that the higher the Fe and Co content, the smaller the ipass. On the other hand, the impedance and compositions of passivation film on CoCrFeNi HEA and 304SS are analyzed by EIS and XPS. As the immersion time increases, the passivation film impedance of CoCrFeNi HEA increases sharply, but the 304SS have not this phenomenon. The difference between the two results that the potentiodynamic curves have 1-Ecorr and 3-Ecorr tendencies, respectively. Furthermore, the fifth elements are added to CoCrFeNi HEA. After adding the elements Mn or Al, the anodic equilibrium potential (Ea) decreases and intersects the cathodic polarization curve at a lower potential, resulting in the lower corrosion potential (Ecorr) and the higher corrosion current density (icorr). This two HEAs have the opportunity to produce the insoluble oxides (MnO2) and hydrargillite (Al2O3∙3H2O) at a higher potential, leading to a decrease in the ipass. Due to the addition of Ga for forming Ga2O3 at the initial polarization, the icrit1 is less than the cathodic current density without cross at the lower potential. They intersect each other until the second passivation region, so the CoCrFeNiGa0.75 has a higher Ecorr and a lower icorr. The CoCrFeNiGa0.75 is two-phase structure before homogenization, resulting in the worse corrosion performance due to Galvanic corrosion. Other HEAs are all FCC one-phase structures before and after annealing and the corrosion behaviors have no significant variations. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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