Electrolyte polishing과 MR fluid polishing 공정에서의 Nitinol 형상기억합금의 표면 결함 분석

초록

There are cases applying biomaterials for aged joints and teeth due to aging and development of medical technology. Nitinol is a bio metallic material which requires pure clean surface to meet the surface integrity and without any surface flaw in order to use in safety in human body. When toxicity is generated by metal dissolution through manufacturing process, the creation and corrosion of bacteria is accelerated. To solve this problem, new technology such as ELID, EP(Electrolyte polishing) and MR fluid polishing can be used. EP makes smooth surface, but it cannot obtain nano-level surface roughness. Whereas, MR fluid polishing can obtain nano-level surface, but needs to preprocessing. In this paper, EP is used as preprocessing and MR fluid polishing is final polishing process. As a result, surface roughness is more improved after each polishing process. Through measuring oxidation film thickness, MR fluid polishing cannot eliminate perfectly, but it has a chemical etching effect by increasing surface roughness. Through measuring residual stress, it can be observed that compressive residual stress is measured in all polishing process. Especially after MR fluid polishing, deformed layer and residual stress is eliminated, it can obtain residual stress free nitinol.