| Summary: | 碩士 === 大葉大學 === 機械工程研究所 === 90 === The relationship of " processing / microstructure / mechanical- properties " of the electrodeposited Co-Cu alloy was established to achieve better understanding of the microstructure and mechanical properties of the Co, Cu and Co-Cu deposits plated at various current densities. 35μm-thick Co, Cu and Co-Cu coatings were electrodeposited onto copper plates using direct current. The electroplating parameters studied include current density, electroplating time and the type and extent of agitation. Then, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the microstructure of the various deposits, particularly the grain structure and lattice defects. Finally, the hardness of the deposit was measured using a Vickers hardness tester.
When air was pumped into the bath for agitating the electrolyte and removing the hydrogen bubbles formed on the cathode surface, the cathodic current efficiency was approximately 10 %. SEM observations further identified the surface of the copper plate was dotted with metal oxide powders. Conversely, when nitrogen gas was pumped into the bath, the coatings with rather uniform thickness were free of pin holes and exhibited a lustrous surface. Additionally, the cathodic efficiency was close to 100 %.
Experimental results indicate that the hardness of the Co-Cu alloy could be divided into two categories; that is, the deposits plated at current densities less than 2 A/dm2 was softer than those plated at current densities exceeding 2 A/dm2. The maximum hardness of the deposit was approximately 10% higher than the minimum hardness, indicating the current density slightly affected the hardness of the deposit. The Co-Cu alloy deposited at 0.3~5 A/dm2 exhibited a columnar grain structure. Cross-sectional TEM further revealed that the deposits had a bimodal grain structure, i.e., relatively-small equiaxed grains were occasionally observe to disperse in the coarse columnar grains. Moreover, with increasing current densities, the defect density of the deposits increased and their resulting hardness increased.
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