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In this study, electroless nickel (EN) plating was performed with stabilizer concentration to improve cavitation erosion resistance of gray cast iron under marine environment. Cavitation erosion tests were carried out in natural seawater solution in accordance with modified ASTM G32 . The change of stabilizer concentration affected the plating rate, P content, and average crystal size of EN coating. The decrease of the plating rate with the stabilizer concentration and the flake-shaped graphite exposed to the gray cast iron surface negatively affected the cavitation erosion and corrosion prevention. In particular, cavitation erosion damage of EN coating was accelerated due to combined galvanic corrosion when the EN coating was destroyed and the substrate was exposed under the cavitation erosion environment.

In this paper, the effect of lead nitrate stabilizer concentration on the electroless nickel (EN) plating properties of gray cast iron was investigated in a sulfuric acid plating bath. The specific critical stabilizer concentration was found to vary the EN coating properties. At the critical stabilizer concentration or more, plating rate and the chemical composition of the EN coating were changed because the deposition of Ni and P was inhibited by excessive stabilizer concentration. The surface morphology of the EN coating was strongly influenced by the plating rate change with the stabilizer concentration and the galvanic coupling effect due to the microstructure of the substrate. The crystallinity of the EN coating tended to increase with increasing stabilizer concentration. As a result, the EN plating properties of gray cast iron were greatly affected by the stabilizer concentration in the plating bath and the microstructure of the substrate.

Electroless nickel plating (ENP) was performed to prevent the cavitation erosion damage of gray cast iron in the marine environment. The effect of the changes in the pH of a plating bath on the ENP coating characteristics, corrosion resistance and the cavitation erosion damage behavior in natural seawater were examined. The results showed that the pH of the plating bath had a significant effect on the plating rate, crystallinity, composition, and microhardness of the ENP coating. The corrosion resistance of ENP coating was greatly affected by the plating rate and the microstructure of the substrate. The cavitation erosion damage behavior depended on the crystallinity of the ENP coating. Once the substrate is exposed by the cavitation erosion of ENP coating, it is accompanied by galvanic corrosion, which accelerates the damage. Furthermore, the cavitation erosion damage mechanism of ENP coating was investigated.

In this study, plasma ion nitriding (PIN) was performed as a measure to prevent the cavitation damage of gray cast iron (GCI) which is a cylinder liner material of diesel engine and evaluated its applicability. GCI treated by PIN presented about 45.2% improvement in surface hardness. In addition, a thickness growth behavior of flake-shaped graphite was observed in the nitrogen diffusion layer. As a result of cavitation erosion test, the maximum surface damage depth increased greatly due to a crater growth behavior along the depth on the flake-shaped graphite distributed on the surface. Furthermore, the weight loss after cavitation test indicated poorer cavitation resistance compared to the as-received specimen. Consequently, the application of PIN to prevent the cavitation erosion damage of GCI requires minimization of defects by flake-shaped graphite.

In this paper, optimum process conditions of electroless Ni-P (EN) coating were identified by Taguchi method to minimize cavitation erosion damage of gray cast iron in seawater. The concentration of complexing agent (lactic acid) and concentration of reducing agent in EN coating process have the greatest influence on cavitation erosion characteristics. The EN coating characteristics for the optimal conditions were analyzed using a scanning electron microscope, an energy dispersive X-ray spectrometer, and X-ray diffraction. The EN coating showed the best cavitation erosion resistance characteristic when the P content was 5.37 wt.%, and it had amorphous-nanocrystalline composite structure. Also, cavitation erosion mechanism was investigated by surface analysis of EN coating after cavitation erosion test.

본 연구는 알루미늄 선체에 적용 가능한 표면처리기술을 확보하기 위해 알루미늄 합금, 방오도료, 우루시올 그리고 양극산화 후 비등수 실링처리된 시편에 대하여 천연해수에서 침적실험 및 유속실험을 실시하여 해양생물 부착 특성을 분석하였다. 침적실험 결과 방오도료를 제외한 모든 시편에서 해양생물이 번식하였으며, 알루미늄 합금과 우루시올 시편은 부식손상이 동반되었다. 한편 부착된 해양생물은 유속실험에 의해 효과적으로 제거되었다.

Copper alloys have widely used for marine plants, ship building equipment, and renewable energy facilities under marine environment due to its excellent castability, durability, and corrosion resistance. In this study, the surface of ALBC3 alloy was modified with shot peening time to improve the strength and cavitation characteristics. For evaluation of cavitation resistance, cavitation experiments for the non-shot peened and shot-peened specimens were performed to investigate the extent of damage and determine the weight loss. As a result, the shot peened ALBC3 alloys improved cavitation resistance. In particular, the shot peening time of 3.5 min was considered to be the optimum shot peening condition since it presented an improvement of 35.7% in cavitation resistance.

In this study, Al and Zn arc thermal spray coatings were carried out onto the substrate of SS400 steel to improve corrosion resistance and durability of hull structural steel for ship in marine environment. Therefore cavitation-erosion test was conducted to evaluate the durability of painted and thermal spray coated specimens. And then the damaged surface morphology and weight loss were obtained to compare with each other, respectively. As a result, the painted specimen was the poorest cavitation resistance characteristics because surface damage behavior appeared to be exfoliated in bulk shape during the cavitation experiment. And Zn thermal spray coating layer presented the significant surface damage depth due to relatively low surface hardness and local cavitation damage tendency. On the other hand, as a result of the weight loss analysis, the painting layer presented the poorest cavitation resistance and the Al thermal spray coating layer relatively showed the best results after cavitation experiment.

In this study, the current density requirements of zinc sacrificial anode for corrosion protection of AA5083-H321 aluminum hull for the ship was determined through various electrochemical tests. Surface observation and chemical composition analysis were performed after the galvanostatic test for various current density requirements determined by the cathodic polarization experiment. As a result, the most appropriate current density requirement range was determined as 3.7 × 10−6–5.8 × 10−6 A/cm2. Excessive current density over 7.6 × 10−6 A/cm2 caused local surface damage due to the effect of Mg-rich and Fe-rich intermetallic phases. In addition, the self-consumption of zinc sacrificial anode was determined through Tafel's extrapolation method.

This study investigated the cavitation erosion resistance of electroless Ni-P (EN) coated gray cast iron (GCI) in seawater solution. Furthermore, the optimum coating design parameters were examined to minimize cavitation erosion damage through analysis of variance (ANOVA) based on the L9 orthogonal array. In this study, four coating design factors were used: concentration of source of nickel (A), concentration of reducer agent (B), deposition temperature (C), and pressure of shot peening (D). In accordance with the regulation of the modified ASTM G32, the cavitation erosion experiment was conducted for 1 hour in a seawater solution to find the optimum design parameters which can minimize the cavitation erosion damage. Besides, ANOVA was performed to verify the contribution of each coating design parameter. As a result, the concentration of reducer agent among the EN process parameters was determined as the most significant factor in the cavitation erosion behavior.

Arc thermal spray coating using Al-3%Mg thermal spray wire was carried out to prevent steel from corrosion damage under the marine environment. Post-sealing was applied to Al-3%Mg spray coating treatment using organic/inorganic composite ceramics in order to improve the corrosion resistance of the as-sprayed coating. The results of various electrochemical experiments with sealing treatment indicated that the improvement in corrosion resistance was observed due to low current density in all applied potential range during anodic and cathodic polarization experiments. Futhermore, the natural potential measurement exhibited severe potential fluctuation due to influence of micro-crack presence on the surface of sealed thermal spray coating layer. In addition, the sealed layer was easily eliminated during anodic polarization. Nevertheless, Al-3%Mg spray coating layer improved corrosion resistance by sealing treatment because the sealed coating efficiency was determined to be 92.11%, indicating the exterior environment barrier effect which is based on the Tafel analysis.

The sustainable development of engineering, mechanical instrument requires higher speed and higher power. It cause a physical damage is excessive damage for underwater rotating system as cavitations and erosion, but also electrochemical corrosion by chloride ion and flow of current in marine environment. In this study, we assessed electrochemical corrosion characteristics of aluminum-bronze that are the material for the underwater rotating system used in the ocean industry and studied the complex behavior of electrochemical corrosion and cavitation corrosion through the hybrid test that also included cavitation corrosion environment. After the cavitation hybrid tests, surface of specimens are observed to measurement damage degree using 3D optical microscope and compared the average of damage depth by immersion time. The observation of the surface micro-structure suggested that the corrosion took place initially in β phase that has poor corrosion resistance in spite of high hardness.