Date of Award
8-2019
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Civil Engineering
Committee Member
Prof. Amir Poursaee, Committee Chair
Committee Member
Prof. Prasad Rangaraju
Committee Member
Prof. Marian S. Kennedy
Committee Member
Prof. Brandon Ross
Abstract
Corrosion science combines the ability to characterize the composition and structure in atomic scale with the experimental and/or computational modeling to enable technological solutions and service life predictions. However, lack of observations restricts the simulation and service life estimations for all alloys. This dissertation work aims to provide literature, observations and discussion on the influence of microstructure on corrosion of both structural (carbon steel) and advanced alloys (ZK60, a Mg based alloy, and AA6061, a Al based alloy) in range of saline solutions. The solutions were chosen to simulate actual envinment of alloys application.
Based on the relevant research area in department of civil enginieering on degradation of cementitious material and embded steel in concrete, the main focus was the corrosion and passivation of reinforcing carbon steel bars in alkaline solution simulating concrete environment. Scanning electrochemical microscopy was exploited to characterize the kinetics of formation of a passive film and the electrochemical activity of the carbon steel in simulated concrete pore solution. The effect of coupling this carbon steel was also studied and probability of galvanic corrosion was examined. The microstructure and distrobutiona of ferrite and pearlite in the carbon steel was altered, using different heat-treatment procedures, and then the susceptibility to corrosion and chloride threshold values of these steels were evaluated. Post corrosion and electrochemical data revealed that restricting and refining pearlite phase improved corrosion performance of regular reinforcing steel bars in chloride contaminated concrete environment. In addition, the surface microstructure of steel was refined through surface mechanical attrition, i.e. sand blasting. It was found that the dissolution rate of the refined surface was highly dependent on the pH of the environment. Grain refinement provided high defective and energetic zones which preferentially oxidized. Consequently, depending on the environment, the corrosion resistance was improved or exacerbated if the formed oxide component was protective or defective, respectively.
Furthermore, the influence of manufacturing process, and subsequently the microstructure on the corrosion activity of two different alloys, i.e. ZK60 (Mg based alloy) and AA6061 (Al based alloy) were also investigated. Results indicated that uniform microstructure reduced corrosion rate due to formation of integrated and uniform protective oxide film and decreasing galvanic corrosion along the surface.
Recommended Citation
Torbatisarraf, Seyedhamidreza, "Effect of Microstructure on Corrosion of Structural and Advanced Alloys" (2019). All Dissertations. 2652.
https://open.clemson.edu/all_dissertations/2652