• Corrosion Science and Technology
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• 제17권3호
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• pp.101-108
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• 2018

AA7010 is an Al-Zn-Mg-Cu alloy containing Zr, developed as an alternate to traditional AA7075 alloy owing to their high strength combined with better fracture toughness. It is necessary to improve the corrosion resistance and surface properties of the alloy by incorporating plasma electrolytic oxidation (PEO) method. AA7010-T7452 aluminum alloy has been processed through the forging route with multi-stage working operations, and was coated with $10{\mu}m$ thick $Al_2O_3$ ceramic aluminina coating using the plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviours were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. The results indicated that the additional thermomechanical treatment during the forging process caused a fully recrystallized microstructure, which lead to the poor environmental cracking resistance of the alloy in 3.5% NaCl solution, despite the overaging treatment. Although the fabricated PEO coating improved general corrosion resistance, the brittle nature of the coating did not provide any improvement in SCC resistance of the alloy. However, the hardness and elastic modulus of the coating were significantly higher than the base alloy.

• 한국표면공학회지
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• 제54권5호
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• pp.238-247
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• 2021

PEO (plasma electrolytic oxidation) was applied to modify the surface of AZ31 magnesium alloy in this study. The mixed solution of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) was used as the electrolyte, and 0 - 0.05 g/L of Ca-GP (Glycerol Phosphate Calcium salt) was added in the electrolyte as an additive. PEO treatment was conducted at a current density of 30mA/cm² for 5 minutes using a DC power supply. The surface properties were identified by SEM, XRD and surface roughness analyses, and the corrosion resistance was evaluated by potentiodynamic polarization and immersion tests. In addition, the biocompatibility was evaluated by immersion test in SBF solution. As the concentration of Ca-GP was increased, the surface morphology was denser and more uniform, and the amount of Ca and the thickness of oxide layer increased. Only Mg peak was observed in XRD analysis due to very thin oxide layer. The corrosion resistance of PEO-treated samples increased with the concentration of Ca-GP in comparision with the untreated sample. In particular, the highest corrosion resistance was identified at the group of 0.04g Ca-GP through potentiodynamic polarization and immersion tests in saline solution (0.9 wt.%NaCl). During the immersion in saline solution, pH rapidly increased at the beginning of immersion period due to rapid corrosion, and then increase rate of pH decreased. However, the pH value in the SBF temporarily increased from 7.4 to 8.5 during the day, then decreased due to the inhibition of corrosion with HA(hydroxyapatite) formation.

• 한국분말재료학회지
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• 제17권2호
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• pp.123-129
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• 2010

The fabrication of interconnect from titanium powders and $TiN_x$ powders is investigated. Corrosion-resistant titanium and $TiN_x$ are used as reinforcement in order to reveal high heat and corrosion resistance at the elevated temperature. We fabricated the plates for interconnect reinforced with $TiN_x$ by mixing titanium powders with 10 wt.% of nano-sized $TiN_x$. Spark Plasma Sintering (SPS) was chosen for the sintering of these composites. The plate made of titanium powders and $TiN_x$ powders demonstrates higher corrosion resistance than that of the plate of titanium powders alone. The physical properties of specimens were analyzed by performing hardness test and biaxial strength test. The electrochemical properties, such as corrosion resistance and hydrogen permeability at high temperature, were also investigated. The microstructures of the specimens were investigated by FESEM and profiles of chemical compositions were analyzed by EDX.

• 해양환경안전학회지
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• 제17권2호
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• pp.155-160
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• 2011

현재 지구온난화 등의 환경문제로 인해 각종 산업분야에서 정량화에 대한 요구가 증대되어 해양산업에도 그 수요가 증가하고 있는 실정이다. 따라서 본 연구에서는 차세대 경량화 재료인 마그네슘이 활용되기 위해서 반드시 극복해야할 가장 중요한 특성인 내식특성에 대하여 고찰하고, 그 내식특성 향상을 위한 마그네슘 박막의 Morphology나 결정배향성의 영향을 해명하고자 하였다. 실험결과로부터 제작한 Mg 박막의 전기화학적 내식특성은 Ar 가스압이 높은 조건에서 제작한 막일수록 내식특성이 우수하였다. 이러한 경향은 표면 및 단면의 Morphology와 결정배향성과의 상관관계를 통하여 설명 가능하였다.

• 한국세라믹학회지
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• 제56권3호
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• pp.317-324
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• 2019

Cr-diamond-like carbon (Cr-DLC) films were deposited using a hybrid method involving both physical vapor deposition and plasma-enhanced chemical vapor deposition. DLC sputtering was carried out using argon and acetylene gases. With an increase in the DC power, the Cr content increased from 14.7 to 29.7 at%. The Cr-C bond appeared when the Cr content was 17.6 at% or more. At a Cr content of 17.6 at%, the films showed an electrical conductivity of > 363 S/cm. The current density was 9.12 × 10^-2 ㎂/㎠, and the corrosion potential was 0.240 V. Therefore, a Cr content of 17.6 at% was found to be optimum for the deposition of the Cr-DLC thin films. The Cr-DLC thin films developed in this study showed high conductivity and corrosion resistance, and hence, are suitable for applications in separators.

• 한국재료학회지
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• 제29권5호
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• pp.288-296
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• 2019

The passivation of AZ91D Mg alloys through plasma anodization depends on several process parameters, such as power mode and electrolyte composition. In this work, we study the dependence of the thickness, composition, pore formation, surface roughness, and corrosion resistance of formed films on the electrolyte temperature at which anodization is performed. The higher the electrolyte temperature, the lower is the surface roughness, the smaller is the oxide thickness, and the better is the corrosion resistance. More specifically, as the electrolyte temperature increases from 10 to $50^{\circ}C$, the surface roughness (Ra) decreases from 0.7 to $0.15{\mu}m$ and the corrosion resistance increases from 3.5 to 9 in terms of rating number in a salt spray test. The temperature increase from 10 to $50^{\circ}C$ also causes an increase in magnesium content in the film from 25 to 63 wt% and a decrease in oxygen from 66 to 21 wt%, indicating dehydration of the film.

• 한국표면공학회지
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• 제56권4호
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• pp.250-258
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• 2023

Ceramic oxide layer was formed on the surface of high silicon aluminum alloy by using PEO (plasma electrolytic oxidation) process. The microstructure of the oxide layer was analyzed using scanning electron microscopy (SEM) and x-ray diffraction patterns (XRD). The high silicon aluminum alloy prior to PEO process consists of Al, Si and Al₂Cu phases in XRD analysis, whereas Al₂Cu phase selectively disappeared after PEO treatment. Considerable decrease of relative intensity in most of peaks in XRD results of the high silicon aluminum alloy treated by PEO process was observed. It may be attributed to the formation of amorphous phases after PEO treatment. The corrosion behavior of the high silicon aluminum alloy treated by PEO process was investigated using electrochemical impedance spectroscopy (EIS) and other electrochemical techniques (i.e., open circuit potential and polarization curve). Electroanalytical studies indicated that the high silicon aluminum alloy treated by PEO process shows greater corrosion resistance than that untreated by PEO process.

• 공업화학
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• 제32권6호
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• pp.653-658
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• 2021

Polyvinylidene fluoride (PVDF)는 우수한 가공성을 가지고 있어 코팅 재료로 유망하지만 다른 불소계 고분자에 비하여 소수성이 약하여 부식 방지 등 그 응용에 제한이 있다. 본 연구에서는 PVDF의 부식방지 특성을 향상시키고자 사불화탄소(CF₄) 가스를 이용하여 플라즈마 불소화를 수행하였고, 유량에 따른 불소 함량 및 소수성 변화를 고찰하고 부식방지 특성을 확인하였다. PVDF 막 표면의 불소 함량은 사불화탄소 유량이 증가함에 따라 46.70%로 증가하였으나 그 표면자유에너지는 불소함량의 증가와 일치하지 않았다. 한편, PVDF 표면의 표면 거칠기는 불소화 유량에 따라 최대 150% 증가하다가 다시 감소하는 경향을 보였다. 이는 플라즈마 불소화는 불소화 기능기 도입 및 표면식각으로 인하여 표면자유에너지에 영향을 주는 것으로 판단된다. 또한, PVDF 코팅된 철판의 부식 정도는 미처리 철판에 비하여 표면 산소 함량이 49.2%에서 19.0% 이하로 크게 개선되었으며, 특히, 불소화 처리된 PVDF의 산소함량은 13.6%으로 불소화 처리되지 않은 PVDF보다 28.4 % 정도 낮아져 우수한 부식방지 특성을 보이는 것으로 관찰되었다.

• Corrosion Science and Technology
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• 제4권6호
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• pp.226-230
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• 2005

Si incorporated diamond-like carbon (Si-DLC) films ranging from 0 to 2 at.% contents were deposited on STS 316L substrates for orthopedic implants by means of r.f. plasma-assisted chemical vapor deposition (r.f. PACVD) technique, using mixtures of benzene ($C_6H_6$) and silane ($SiH_4$) as the precursor gases. This study provides the reliable and quantitative data for assessment of the effect of Si incorporation on corrosion property in the simulated body fluid environment through the electrochemical test. It was found that corrosion to resistance of Si-DLC coatings with increasing Si content are improved owing to high $sp^3$ bonding.

• Corrosion Science and Technology
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• 제5권1호
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• pp.15-22
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• 2006

The introduction of two-grid inside a conventional process system produces a reactive coating deposition and increases metal ion ratio in the plasma, resulting in denser and smoother films. The corrosion behaviors of TiN coatings were investigated by electrochemical methods, such as potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) in deaerated 3.5% NaCl solution. Electrochemical tests were used to evaluate the effect of microstructure on the corrosion behavior of TiN coatings exposed to a corrosive environment. The crystal structure of the coatings was examined by X-ray diffractometry (XRD) and the microstructure of the coatings was investigated by scanning electron microscopy (SEM) and transmission electron spectroscopy (TEM). In the potentiodynamic polarization test and EIS measurement, the corrosion current density of TiN deposited by two grid-attached magnetron sputtering was lower than TiN deposited by conventional magnetron type and also presented higher Rct values during 240 h immersion time. It is attributed to the formation of a dense microstructure, which promotes the compactness of coatings and yields lower porosity.