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Winter 2009 Seminar Series
March 6 at 3:30 p.m.
Room 264 MacQuigg Labs
Fariaty Wong
PhD Candidate advised by Dr. Rudy Buchheit
Department of Materials Science and Engineering
The Ohio State University
The Effect of Alloy Composition on Localized Corrosion Behavior of Ni-Cr-Mo Alloys in Warm to Hot Chloride Solutions
Abstract
Ni-Cr-Mo alloy are known as one of the most versatile Ni-based alloys in resisting corrosion. Additions of Cr and Mo have been proven to be the cause of the good corrosion resistance behavior. The role of Cr and Mo in resisting localized corrosion particularly, pitting corrosion was studied. Ni-Cr-Mo alloys were fabricated with twenty four unique compositions. Polarization experiments were conducted on these alloys in 0.5M NaCl at varying temperatures from 45 to 90°C to obtain corrosion parameters namely, pitting and repassivation potentials. Multiple linear regression analysis was performed to construct a mathematical expression that correlate the pitting and repassivation potentials to the alloying content at each temperature. This expression allows us to roughly predict the corrosion behavior of the Ni-Cr-Mo alloys through Cr and Mo contents only. It appears that Cr content is more critical than Mo content in raising the pitting potential in neutral chloride condition. The effect of both Cr and Mo are quite uniform in affecting the repassivation potential values of the alloys in neutral chloride.
Pitting corrosion is commonly preceded by the occurrence of metastable pitting. Thus, one can better understand the pitting process of an alloy through its metastable pitting behavior. Rigorous metastable pitting study was conducted on Ni-Cr-Mo alloys with Cr content varying from 20 to 29 wt.% and Mo content varying from 12 to 25 wt.%. Potentiostatic experiments were performed in 90°C of 0.5M NaCl to promote the metastable pitting incidence. Analysis was done on the potentiostatic data to better characterize the metastable pitting behavior of the Ni-Cr-Mo alloys. It was observed that a higher Mo content in the Ni-based alloy is responsible for lower peak current values and slowing down the growth rates of the faster growing pits. The Cr content seems to impact the repassivation rates of the metastable pits where higher Cr content increases the repassivation rates. Overall, it can be concluded that both Cr and Mo greatly affect the corrosion behavior of the Ni-based alloys. The role of these elements is found to be beneficial, and some have suggested that they produce synergistic effect when both elements are present.
Bio
Fariaty Wong was born in Rangkasbitung, Indonesia. She came to the United States to pursue her college degree. Fariaty received her Bachelor's degree from the Materials Science and Engineering at The Ohio State University in June of 2003 followed by a Master's degree in March of 2004. She started the Ph.D program in the Fall of 2004. Prof. Buchheit has been served as her advisor for the duration of her graduate studies.
