Document Type

Thesis

Date of Award

Spring 5-31-2017

Degree Name

Master of Science in Materials Science and Engineering - (M.S.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

N. M. Ravindra

Second Advisor

Michael Jaffe

Third Advisor

S. Basuray

Fourth Advisor

Alex Stein

Abstract

Corrosion is a subject of interest to interdisciplinary research communities that includes fields of materials science, chemistry, physics, metallurgy and chemical engineering. In order to understand the mechanisms of corrosion and the function of corrosion inhibitors, the reactions at the interfaces between the corrosive electrolyte and a steel surface, particularly at the initial stages of the corrosion process, need to be described. Naturally, these reactions are strongly affected by the nature and properties of the steel surfaces. It is however seen that the majority of recent corrosion and corrosion-inhibition investigations are limited to electrochemical testing, with ex situ analysis of the treated steels (post-exposure analysis). The characterization of materials and their surface properties, such as texture and morphology, are not being considered in most of the studies.

Similarly, in situ investigations of the initial stages of the corrosion reactions, using advanced surface characterization techniques, are scarce. In this thesis, attention is brought to the importance of surface features of carbon steels, such as texture and surface energy, along with defects and dislocation related to mechanical processing of carbon steels. This work is extended to a critical review of surface analytical techniques that are used for characterization of carbon steels in corrosive media with particular focus on examining steel surfaces treated with corrosion inhibitors. Further, emerging surface analysis techniques and their applicability to analyses of carbon steels in corrosive media are discussed.

Due to their good corrosion resistance, favorable mechanical properties, and reasonable price regarding their excellent properties, martensitic stainless steels have, over recent decades, become one of the alloys that are increasingly used in blade manufacturing industry. Architects often design stainless steel exterior elements with higher polished surface, which are resistant to corrosion processes. The aim of this work is to investigate the influence of different types of surface finishes to stainless steel of quality AISI 440 on the corrosion properties of this steel. In order to achieve this goal, tests are performed on surface finishes in two different environments: in an NaCl aqueous solution, and in Acetic Acid. In addition to the methods used, surface roughness is also measured, and SEM-EDS surface analyses are performed. Based on the results of the performed analyses, it is found that, in the NaCl solution, the pitting potential depends strongly on the surface roughness and the surface finish. The evolution of the passive films on Martensitic 440 stainless steel in seawater and in pure 3.5 % NaCl and 3.5% acetic acid is studied using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). This thesis describes and evaluates the comparison of the effects of pure 3.5 % NaCl with acetic acid through surface and corrosion measurements.

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