Oregon Health & Science University
A novel combinatory on-line technique coupling Electrochemistry (EC) with Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) for in-situ quantitative determination of the corrosion mechanism in magnetic thin film structures has been developed in this research. Detailed construction of a system and a comprehensive methodology was described in this dissertation. Uniformly coated multi-layer magnetic thin film samples with multi-elemental alloys containing CoCrPtB and CrMo/Cr on the Ni/P substrate were used in this research for demonstrations. In-situ quantifications conducted in a series of experiments revealed that elemental dissolution was a predominant mechanism during corrosion courses of metallic thin film materials. At the microscopic scale, using results from depletion rate determination as well as cross-sectional analyses of microstructures and magnetic features, elemental passivity was observed to occur, depending on corrosion conditions. Without external influences, surface topographic measurements indicated that passive film could be produced at the macro-scale. The dependence of the dissolution rate of each metallic ion of alloys on electrolyte concentration, potential bias, scanning rate, and corrosion duration suggested that the most critical influential factor in corrosion mechanisms was epitaxial microstructures with strongly-oriented arrangements of grains and grain boundaries. Through the use of cross-sectional microstructural analysis, including high resolution TEM micrography, electron FFT diffraction, and nano-probe with EDS profiling, variations of elemental spatial distributions at grains and grain boundaries due to the corrosion phenomena were discovered, which provided a comprehensive understanding of occurrences of micro-corrosion in thin film structures. Because of the unique magnetic property of magnetic thin films, extensive studies of field strengths from the surface were also performed in this research. Important magnetization variations were noticed when cross-sectional images were obtained. Finally, models of corrosion kinetics in the multiple layers of magnetic thin film structures were proposed.
OGI School of Science and Engineering
Xu, Danhua, "A study of magnetic thin film corrosion mechanisms with the development of a novel on-line coupling technique and with microstructural and magnetic cross-sectional profiling techniques" (2008). Scholar Archive. 328.