J.G. Kim

A study on corrosion resistance characteristics of PVD Cr-N coated steels by electrochemical method

The corrosion behavior of Cr-N coated steels with different phases (α-Cr, CrN and Cr2N) deposited by cathodic arc deposition on AISI H13 steel was investigated in a 3.5% NaCl solution at ambient temperature. Potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were the techniques applied to characterize the corrosion behavior. It was found that the CrN coating had a lower current density from potentiodynamic polarization tests than others. The porosity, corresponding to the ratio of the polarization resistance of the uncoated and the coated substrate, was higher in the Cr2N coating than in the other Cr-N coated steels. EIS measurements showed, for most of the Cr-N coated steels, that the Bode plot presented two time constants. Also, the Cr2N coating represented the characteristic of Warburg behavior after 72 h of immersion. The coating morphologies were examined in planar view and cross-section by SEM analysis and the results were compared with those of the electrochemical measurement. The CrN coating had a dense, columnar grain-sized microstructure with minor intergranular porosity. From the above results, it is concluded that the CrN coating provided a better corrosion protection than the other Cr-N coated steels.

Localized corrosion mechanisms of the multilayered coatings related to growth defects

Abstract Multilayered WC–Ti 1− x Al x N coatings were deposited on AISI D2 steel using cathodic arc deposition method. These coatings contain structural defects such as pores or pinholes. Thus, the substrate is not completely isolated from the corrosive environment. These growth defects in the coatings are detrimental to corrosion resistance of the coatings used in severe corrosion environments. The localized corrosion of the coatings was studied in deaerated 3.5 wt.% NaCl solution using classical electrochemical technique (potentiodynamic polarization test). Coating characteristics were examined by means of glow discharge optical emission spectroscopy, scanning electron microscopy, auger electron spectroscopy and transmission electron spectroscopy. The porosity was calculated from a result of potentiodynamic polarization test of the uncoated and coated specimens. The calculated porosity is higher in the WC–Ti 0.6 Al 0.4 N than others, which is closely related to the packing factor. The positive effects of greater packing factor act on inhibiting the passage of the corrosive electrolyte to the substrate and reducing the localized corrosion kinetics. From the electrochemical tests and surface analyses, the major corrosion reaction of coatings is caused by defects (pores, pinholes and crevices), coating delamination and galvanic effect between the droplet and the coating.

Corrosion behavior of PVD-grown WC–(Ti1−xAlx)N films in a 3.5% NaCl solution

Abstract WC–(Ti 1− x Al x )N coatings of stepwise changing Al concentration (WC–Ti 0.86 Al 0.14 N, WC–Ti 0.72 Al 0.28 N, and WC–Ti 0.58 Al 0.42 N) were deposited on AISI 1045 substrate by high-ionization sputtered PVD method. The Al concentration could be controlled by using evaporation source for Al and fixing the evaporation rate of the metals (WC alloy and Ti). The corrosion behavior of WC–(Ti 1− x Al x )N coatings in deaerated 3.5% NaCl solution was investigated by electrochemical corrosion tests and surface analyses. Particular attention was paid to the effects of Al target power density on the film properties related to the corrosion behavior. The measured galvanic corrosion currents between coating and substrate indicated that WC–Ti 0.72 Al 0.28 N coating showed the best resistance of the coating tested. The results of potentiodynamic polarization tests showed that this coating had passivation and lower porosity. This indicated that this coating is effective in improving corrosion resistance. In electrochemical impedance spectroscopy, the WC–Ti 0.72 Al 0.28 N coating showed one time constant loop and the increased polarization resistance of coating relative to other samples. The better corrosion performance of WC–Ti 0.72 Al 0.28 N coating is due to the modified compactness, porosity and adhesion of the coating layer.

On the corrosion behavior of multilayered WC–Ti1−xAlxN coatings on AISI D2 steel

In the present work, multilayered coatings with alternate layers of WC-Ti and WC-Ti 1-x Al x N were deposited for use as wear-resistant and corrosion-resistant surfaces. Ti and TiN base layers were deposited on the substrate prior to the multilayers. WC-Ti 1-x Al x N coatings with variable Al content (i.e., Al target power density) were deposited onto a steel substrate (high-speed steel; HSS) by the cathodic arc deposition method. The Al content could be controlled using an evaporation source for Al and fixing the evaporation rate of the other target sources. Four kinds of WC-Ti 1-x Al x N coatings were prepared (WC-Ti 0.6 Al 0.4 N, WC-Ti 0.53 Al 0.47 N, WC-Ti 0.5 Al 0.5 N and WC-Ti 0.43 Al 0.57 N). The corrosion behavior of WC-Ti 1-x Al x N coatings in deaerated 3.5% NaCI solution was investigated by electrochemical corrosion tests and surface analyses. Particular attention was paid to the effects of Al content on the coating properties related to the corrosion behavior. The galvanic corrosion current measured between the coating and substrate showed a low value. The results of potentiodynamic polarization tests indicated that the WC-Ti 0.43 Al 0.57 N coating with lower porosity enhanced the corrosion resistance. In electrochemical impedance spectroscopy measurements, the WC-Ti 0.43 Al 0.57 N coating showed two time constants and decreased the charge transfer resistance of the coating (R et ). Multilayered coatings were analyzed by EDS and XRD techniques to evaluate the crystal structure and compound formation behavior. Surface and cross-sectional morphology of the films was observed using SEM. In addition, scratch tests were performed to measure film adhesion strength.

Effects of Flow Velocity, pH, and Temperature on Galvanic Corrosion in Alkaline-Chloride Solutions

Abstract The aqueous corrosion characteristics of a carbon steel (CS) coupled to Type 304 (UNS S30400) stainless steel (SS) were studied in deaerated alkaline-chloride solutions with velocity (0, 0...

A Galvanic Sensor for Monitoring the Corrosion Damage of Buried Pipelines: Part 1—Electrochemical Tests to Determine the Correlation of Probe Current to Actual Corrosion Damage in Synthetic Groundwater

Abstract In order to develop a new corrosion sensor for detecting and monitoring the corrosion of buried pipelines, sensor element design and the correlation of its output to the corrosion rate of ...

A Galvanic Sensor for Monitoring the Corrosion Damage of Buried Pipelines: Part 2—Correlation of Sensor Output to Actual Corrosion Damage of Pipeline in Soil and Tap Water Environments

Abstract To develop a new corrosion sensor for detecting and monitoring the external and internal corrosion damage of buried pipeline, the correlation of its output to the corrosion rate of steel p...

Stress corrosion cracking and hydrogen embrittlement cracking of welded weathering steel and carbon steel in a simulated acid rain environment

Abstract The stress corrosion cracking (SCC) and hydrogen embrittlement cracking (HEC) characteristics of welded weathering steel and carbon steel were investigated in aerated acid chloride solution. The electrochemical properties of welded steels were investigated by polarisation and galvanic corrosion tests. Neither weathering steel nor carbon steel showed passive behaviour in this acid chloride solution. The results indicated that weathering steel had better corrosion resistance than carbon steel. Galvanic corrosion between the weldment and the base metal was not observed in the case of weathering steel because the base metal was anodic to the weldment. However, the carbon steel was susceptible to galvanic corrosion because the weldment acts as an anode. Slow strain rate tests (SSRT) were conducted at a constant strain rate of 7.87 × 107 s-1 at corrosion potential, and at potentiostatically controlled anodic and cathodic potentials, to investigate the SCC and HEC properties in acid chloride solution. The welded weathering steel and carbon steel were susceptible to both anodic dissolution SCC and hydrogen evolution HEC. However, weathering steel showed less susceptibility of SCC and HEC than carbon steel at anodic potential because of Cr and Cu compounds in the rust layer, which retarded anodic dissolution, and at cathodic potential due to the presence of Cr, Cu, and Ni in alloy elements, which inhibit the reduction of hydrogen ions. SEM fractographs of both steels revealed a quasicleavage fracture in the embrittled region at applied anodic and cathodic potentials.

Effect of Aluminum on the Corrosion Characteristics of Mg-4Ni-xAl Alloys

Abstract Corrosion properties of Mg-4Ni-xAl alloys were investigated using electrochemical techniques, pH measurement, hydrogen evolution test in acid-chloride solution (pH 5.4, 200 ppm Cl−), and s...

Corrosion Resistance of Ferritic Stainless Steel in Exhaust Condensed Water Containing Aluminum Cations

Stainless steel substrates of exhaust mufflers made of aluminized stainless steel can be exposed to solutions containing Al3+ ions long after the dissolution of their Al coating. This study examined the corrosion behavior of stainless steel in synthetic condensed water that contained different amounts of Al dissolution. The corrosion resistance of stainless steel in the solution containing dissolved Al3+ ions decreased. The unstable passive film contained Al oxides (or hydroxides), which decreased the protective properties of the stainless steel. The dissolved Al3+ ions in the exhaust condensed solution had a negative effect on the corrosion resistance of the stainless steel.