| Summary: | 碩士 === 國立臺北科技大學 === 製造科技研究所 === 92 === The electropolishing method has been using as one of the main technologies in manufacturing components of the semi-conductor and bio-medical materials due to the requirements of extreme smoothness, cleanness, and corrosion resistance on the operation conditions since 1935. In order to prevent surface from the attack of corrosion and have well-biocompatibility, the metallic implants for surgical operation need to be electropolished.
The purpose of this research work is to use electropolishing method to polish the stainless steel AISI 316L, stainless steel SUS 420F, stainless steel SUS 420J2, and the NiTi alloy, and to level and brighten the specimen surface. A passivation layer on the specimen surface was produced which can enhance the corrosion resistance of materials. Some parameters that affect the electropolishing effectiveness are the additives of electrolyte, voltage, time, current density, temperature of the electrolytes, and the original roughness of the prepared specimen. The experimental results also demonstrate the fact of these points of view.
All of the specimens were polished to 600 grit sandpaper with the dimension 11 mm×11 mm×1 mm in square for AISI 316L, diameter of 18 mm and height of 5 mm in the round shape for SUS 420F, 5 mm×40 mm rod for SUS 420J2, and 12 mm×12 mm×1 mm in square for NiTi alloy, individually. It is found that the voltage of 10 volts is suitable for polishing AISI 316L with current density 17 ~ 50 A/dm2 for polishing time 180 seconds, the voltage of 30 volts is suitable for polishing SUS 420F with current density 53 ~ 80 A/dm2 for polishing time 5 seconds, the voltage of 30 volts is suitable for polishing SUS 420J2 with current density 75 ~ 93 A/dm2 for polishing time 5 seconds, and the voltage of 15 volts is suitable for polishing NiTi alloy with current density 89 ~ 115 A/dm2 for polishing time 10 seconds. According to our experimental results, the usage of surface roughness measurement instrument (surface roughness measurement instrument，α-step), scanning electron microscope (Scanning Electron Microscope，SEM), energy dispersive spectrometer (Energy Dispersive Spectrometer，EDS), and electron spectroscopy for chemical analysis system (Electron Spectroscopy for Chemical Analysis，ESCA) are adequent for this research test. And we also establish a systematic criterion in studying the optimization of electropolishing.
The experimental results show that a passivaition layer Cr2O3 is formed for the materials AISI 316L, SUS 420F, and SUS 420J2. On the other hand, TiO2 passivation layer is formed for NiTi shape alloy. The average surface roughness Ra will be decreased from 0.042μm to 0.013μm for AISI 316L, to 0.018μm for SUS 420F, from 0.075μm to 0.052μm for SUS 420J2, and from 0.045μm to 0.020μm for NiTi alloy.
Using the SEMI standards as guidelines, we have developed an environmental protective electrolyte that operates under low temperature without addition of chromic acid. Simultaneously the electrolyte can operate and meet all the requirements of SEMI specification .
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