표면 연마 방법에 따른 니티놀 잔류응력 분석

정지선,홍광표,김운용,조명우,Jeong, Ji-Seon,Hong, Kwang-Pyo,Kim, Woon-yong,Cho, Myeong-Woo 한국금형공학회 2017 한국금형공학회지 Vol.11 No.2

Nitinol, a shape memory alloy (SMA), is manufactured from titanium and nickel and it used in various fields such as electrical applications, micro sensors. It is also recommended as a material in medical for implant because it has excellent organic compatibility. Nitinol is intended to be inserted into the human body, products require a high-quality surface and low residual stress. To overcome this problems, explore electrolyte polishing (EP) is being explored that may be appropriate for use with nitinol. EP is a particularly useful machining method because, as a non contact machining method, it produces neither machining heat nor internal stress in the machined materials. Sandpaper polishing is also useful machining method because, as a contact machining method, it can easily good surface roughness in the machined materials. The electrolyte polishing (EP) process has an effect of improving the surface roughness as well as the film polishing process, but has a characteristic that the residual stress is hardly generated because the work hardened layer is not formed on the processed surface. The sandpaper polishing process has the effect of improving the surface roughness but the residual stress remains in the surface. We experimented with three conditions of polishing process. First condition is the conventional polishing. Second condition is the electrochemical polishing(EP). And Last condition is a mixing process with the conventional polishing and the EP. Surface roughness and residual stress of the nitinol before a polishing process were $0.474{\mu}mRa$, -45.38MPa. Surface roughness and residual stress of the nitinol after mixing process of the conventional polishing and the EP were $1.071{\mu}mRa$, -143.157MPa. Surface roughness and residual stress of the nitinol after conventional polishing were $0.385{\mu}mRa$ and -205.15MPa. Surface roughness and residual stress of sandpaper and EP nitinol were $1.071{\mu}mRa$, -143.157MPa. The result shows that the EP process is a residual stress free process that eliminates the residual stress on the surface while eliminating the deformed layer remaining on the surface through composite surface machining rather than single surface machining. The EP process can be used for biomaterials such as nitinol and be applied to polishing of wafers and various fields.

Methodological Consideration on the Prediction of Electrochemical Mechanical Polishing Process Parameters by Monitoring of Electrochemical Characteristics of Copper Surface

Seo, Yong-Jin The Korean Electrochemical Society 2020 Journal of electrochemical science and technology Vol.11 No.4

The removal characteristics of copper (Cu) from electrochemical surface by voltage-activated reaction were reviewed to assess the applicability of electrochemical-mechanical polishing (ECMP) process in three types of electrolytes, such as HNO₃, KNO₃ and NaNO₃. Electrochemical surface conditions such as active, passive, transient and trans-passive states were monitored from its current-voltage (I-V) characteristic curves obtained by linear sweep voltammetry (LSV) method. In addition, the oxidation and reduction process of the Cu surface by repetitive input of positive and negative voltages were evaluated from the I-V curve obtained using the cyclic voltammetry (CV) method. Finally, the X-ray diffraction (XRD) patterns and energy dispersive spectroscopy (EDS) analyses were used to observe the structural surface states of a Cu electrode. The electrochemical analyses proposed in this study will help to accurately control the material removal rate (MRR) from the actual ECMP process because they are a good methodology for predicting optimal electrochemical process parameters such as current density, operating voltage, and operating time before performing the ECMP process.

전해연마를 적용한 미세 마이크로 니들의 표면 향상에 대한 연구

정성택,김현정,위은찬,공정식,백승엽 한국금형공학회 2019 한국금형공학회지 Vol.13 No.3

As the consumer market in the mold, automation and aerospace industries grows, the demand for chemical machining using on electrochemical polishing increases. To enhance the surface roughness and gloss of the micro-needle, we have studied for an electrochemical polishing. Electrochemical polishing requires the chemical reaction of solution and material according to the electrolyte and electrode. In this study, sulfuric acid(30%), phosphoric acid(50%), and DI-water(20%)were used as the electrolytic solution, and the electrolytic solution temperature used 58 ℃. Electrochemical polishing was carried out in experimental conditions, and the micro-needle experiment was carried out from the basic experiment to obtain the experimental conditions. Experimental results show that as the voltage and current increase, the surface roughness improved and the gloss is improved. So, the best result for this experiment was obtained in condition 6, which improved micro-needle.

High‑Quality Surface Finishing of Industrial Three‑Dimensional Metal Additive Manufacturing Using Electrochemical Polishing

김욱수,Jeong Woo Park 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.1

Three-dimensional (3D) additive manufacturing technologies are useful for building various and complicated shapes. Representative technologies include laser metal deposition and selective laser sintering that make metal powders melt in order to form diverse 3D structures. Although numerous well-known advantages of 3D additive manufacturing, they still have some difficulties in surface quality improvement for further applications such as food or biomedical industries because they cause rough surfaces, discoloration, unmelted particles by repeated instant dissolution and solidification of metal particles. This paper introduces an electrochemical polishing (or electropolishing, ECP) process as a possible finishing process for 3D printed parts. Conventional finishing processes including mechanical finishing can hardly polish 3D curved surface readily. In ECP, the tool electrode and the work sample are not in contact with each other. All electrically connected surface exposed to electrolyte are subject to be polished. The printed product performs in a current density region higher than the conventional current density, thereby activating the electrochemical reaction and promoting the dissolution of the metal surface, thereby smoothly polishing a very rough surface. Surface quality including roughness, splashed particle spots, smoothness, brightness, light reflection and corrosion resistance were improved by ECP. Experimental results were analyzed by scanning electron microscopy, optical and detailed atomic force microscopy images according to various ECP electrical conditions.

Electrochemical Surface Evaluation of Copper by Using a Cyclic Voltammetry Method in a NaNO3 Electrolyte for ECMP Applications

서용진,이영균,이우선 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

Recently, electrochemical-mechanical polishing (ECMP) has been suggested as an alternative to the conventional chemical-mechanical polishing (CMP) process. In the ECMP process, Cu ions are electrochemically dissolved by applying an anodic potential to the Cu surface in an electrolyte. In this work, we demonstrate a voltage-activated electrochemical test, such as cyclic voltammetry (CV) and linear sweep voltammetry (LSV), for studying the correlation between the electrochemical surface state of Cu and various process parameters (operating voltage, concentration of electrolytes, current density, operating time, etc.) in an aqueous NaNO3 electrolyte. We also investigated how this chemical electrolyte affected the process of voltage-induced material removal in the ECMP application of a Cu film. In this way, we monitored the oxidation and the reduction process as of the Cu surface caused by a repetition of the anodic and the cathodic potential in a NaNO3 electrolyte.

Voltage-Dependent Electrochemical Removal of Copper in KNO3 Electrolytes for Electrochemical-Mechanical Polishing Applications

서용진,한상준,이우선 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

In this paper, the voltage-activated electrochemical reactions of Cu for electrochemical- mechanical polishing (ECMP) applications were investigated for dierent concentrations of the KNO3 electrolyte. The electrochemical characteristics of Cu, such as active, passive, transient and transpassive states, were evaluated from the current-voltage (I-V ) curve obtained by using linear sweep voltammetry (LSV) and cyclic voltammetry (CV). Finally, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diraction (XRD) analyses were utilized to observe the structural surface states of a Cu disk. The proposed mechanism and analyses were a good methodology for finding suitable electrochemical process parameters for ECMP applications.

Correlation between Process Parameters and Electrochemical Surface State for Electrochemical-mechanical Polishing Application of Copper in Acid- and Alkali-based Electrolyte

이영균,서용진,Jun-Won Yang,김형호,Yeongbong Park,정해도 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.1

We examine the correlation between process parameters and electrochemical surface state for electrochemical-mechanical polishing (ECMP) application of copper (Cu) in alkali-based NaNO3 and acid-based HNO3 elec-trolyte. First, the effects of electrolyte concentration on the electrochemical surface reaction of Cu electrode were evaluated from the current-voltage (I-V) curve obtained by linear sweep voltammetry (LSV) method. Second, we fundamentally studied the chemical states and element composition of the Cu surface according to the concentration of the electrolyte and the potential variation using scanning electron spectroscopy (SEM)and X-ray diffraction (XRD) patterns. The proposed mechanism and analyses were a good methodology in finding suitable electrochemical process parameter for ECMP application.

반도체용 대구경관의 전해 복합연마에 대한 초정밀 가공 특성연구

이정훈(Jung Hun Lee),이은상(Eun Sang Lee) 한국정밀공학회 2004 한국정밀공학회 학술발표대회 논문집 Vol.2004 No.10월

On this study, electrochemical polishing is adapted to ultra-fine surface for semiconductor large radius gas-tube. The system which buffing and electrochemical polishing can be performed simultaneously was constructed in connection with developing exclusive system. Based on existing papers and the research of background, electrode gap and electrolyte flow were fixed. Current density and electrochemical precision time were chosen as variables. On this study, it is objected to find optimal precision condition and precision variables on the in-process electrochemical polishing.

High-Performance Self-Expanding NiTi Stents Manufactured by Laser Powder Bed Fusion

Xiang Li,Shijie Hao,Baopeng Du,Bo Feng,Haohang Li,Ping Qiu,Bingmin Huang,Lishan Cui,Ying Yang 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.5

Laser powder bed fusion (LPBF) is a promising technology for the manufacturing of customized medical implants, due tothe intrinsic potential in the fabrication of components with complex geometries. However, for the LPBF-produced vascularimplants, the dimensional accuracy, forming quality and surface finish are still unable to satisfy the medical requirements. This work provides a systematic study on dimensional accuracy control, relative density, surface polishing, shape memoryfunction, superelasticity property and deployment capability of LPBF-produced self-expanding NiTi stents, aiming at promotingtheir application in the biomedical field. The dimensional deviation of stent struts between designed prototype andas-melted products is reduced to 3% by applying laser beam compensation (LBC) strategy. Meanwhile, the study reveals thatthe LBC parameters have strong influence on the relative density of NiTi stents. 99.89% of relative density is achieved forLPBF-produced NiTi stent as the LBC value is optimized to 120 μm. The incompletely melted powders, balling and rippingstructures on the surface of NiTi stents are observed to exhibit different removal processes during electrochemical polishing. The surface roughness (Ra) of NiTi stent is decreased from 7.17 μm for as-melted stent to 0.34 μm for as-polished one. Basedon high relative density and surface quality, the stents exhibit excellent shape memory function and superelasticity propertyin the process of cyclic deformation. Finally, the deployment capability of the stents is assessed. The results confirm thatLPBF-produced NiTi stents can be successfully crimped and released during the deployment process.

Mechanical effects of polishing pad in copper electrochemical mechanical deposition for planarization?

Sukhoon Jeong,Sangjik Lee,Boumyoung Park,Hyoungjae Kim,Sungryul Kim,정해도 한국물리학회 2010 Current Applied Physics Vol.10 No.1

ECMD (electrochemical mechanical deposition) process consists of a traditional ECP (electrochemical plating) mechanism and a mechanical component. That is, this technique involves both electrochemical plating and mechanical sweeping of the material surface by the polishing pad. The mechanism of the ECMD process may be achieved through two mechanisms. The first mechanism may be the electrochemical plating on the surface where mechanical sweeping of polishing pad does not reach, and the second mechanism may be that the plating rate in the area that is mechanically swept may be reduced by the polishing pad. In this study, the effects of the mechanical component were investigated through various polishing pad types and hole ratios. In comparison to various polishing pad types using the manufactured the ECMD system, the plating rate and WIWNU (within wafer non-uniformity) using the experimental non-pore polishing pad were better than those of the experiments using other polishing pads.