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Properties and Durability of the Passive Films on a Ni-Cr-Mo Alloy and an Fe-based Bulk Metallic Glass

Pharkya, Pallavi
http://rave.ohiolink.edu/etdc/view?acc_num=case1232857493

Abstract Details

2009, Doctor of Philosophy, Case Western Reserve University, Materials Science and Engineering.
Alloy 22, a Ni-Cr-Mo-W alloy, and SAM1651, an Fe-Cr-Mo-B-Y-C bulk metallic glass are highly corrosion-resistant alloys. The high corrosion resistance of these alloys is due to the formation of tenacious oxide films on their surfaces. This study examines the reformation behavior of the passive films as a function of the corrosion resistance of the alloys and the corrosivity of the environment. The main tasks of this study were (i) to determine the chemical durability of passive films on these highly corrosion-resistant alloys in aggressive environments, (ii) to investigate the durability after mechanically damaging the passive films either locally or over the entire surface area and to study the reformation kinetics, (iii) to compare the durability of the passive films of the aforementioned highly corrosion resistant alloys with an alloy of intermediate corrosion resistance, AL6XN, and an alloy of less corrosion resistance, 316L SS, (iv) to examine the evolution of the electronic properties of the passive films on alloy 22 and SAM1651 under different environmental conditions such as concentrated chloride solution, acidic solution, temperature, potential and oxyanions, and (v) to develop an understanding of the relationship between the passive films’ composition, electronic and electrochemical properties and the performance.A combination of techniques was utilized to meet the above mentioned objectives. Cyclic potentiodynamic polarization (CPP) was used to determine the electrochemical parameters such as freely corroding, breakdown and repassivation potentials. Electrochemical impedance spectroscopy (EIS) was used to determine the electronic properties such as impedance, thickness and capacitance of the passive films. Mott-Schottky (M-S) analysis was used to determine the type and the density of the defects in the passive films. The mechanical durability and reformation kinetics of the passive films was investigated using a scratch-repassivation method. The quality and the protectiveness of the reformed passive films after scribing were examined using EIS, M-S analysis, and AES. The results show that the passive films on alloy 22 and SAM1651 possess high chemical and mechanical durability. The reformed passive films acquired the same electronic and elemental properties as the passive films which were undamaged. The passive films on SAM1651 and alloy 22 showed better corrosion resistance and durability than did the passive films on AL6XN and 316L SS. The results also showed that the passive film behavior depends on the inherent corrosion resistance of an alloy and the corrosivity of the environment. The inherent corrosion resistance depends on the concentration of the passivity-providing elements such as Cr and Mo in the bulk composition of the alloy (and passive film), and the corrosivity of the environment which is influenced by chloride concentration, oxyanions, temperature, pH, and oxidizing potential
Joe H. Payer, PhD (Advisor)
Uziel Landau, PhD (Committee Member)
Mark R. De Guire, PhD (Committee Member)
K. Peter D. Lagerlof, PhD (Committee Member)
Joe H. Payer, PhD (Committee Chair)
306 p.
Materials Science
Ni-Cr-Mo alloy; Amorphous alloy; mechanical durability; passive films

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Citations

  • Pharkya, P. (2009). Properties and Durability of the Passive Films on a Ni-Cr-Mo Alloy and an Fe-based Bulk Metallic Glass [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1232857493

    APA Style (7th edition)

  • Pharkya, Pallavi. Properties and Durability of the Passive Films on a Ni-Cr-Mo Alloy and an Fe-based Bulk Metallic Glass. 2009. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1232857493.

    MLA Style (8th edition)

  • Pharkya, Pallavi. "Properties and Durability of the Passive Films on a Ni-Cr-Mo Alloy and an Fe-based Bulk Metallic Glass." Doctoral dissertation, Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1232857493

    Chicago Manual of Style (17th edition)

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© 2009, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.