• Corrosion Science and Technology
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• v.7 no.6
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• pp.301-306
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• 2008

Surface composite layers of 1.9~2.9 mm in thickness were fabricated by depositing metamorphic powders on a carbon steel substrate and by irradiating with a high-energy electron beam. In the surface composite layers, 48~64 vol.% of $Cr_{2}B$ or $Cr_{1.65}Fe_{0.35}B_{0.96}$ borides were densely precipitated in the austenite or martensite matrix. These hard borides improved the hardness of the surface composite layer. According to the otentiodynamic polarization test results of the surface composites, coatings, STS304 stainless steel, and carbon steel substrate, the corrosion potential of the surface composite fabricated with 'C+' powders was highest, and its corrosion current density was lowest, while its pitting potential was similar to that of the STS304 steel. This indicated that the overall corrosion resistance of the surface composite fabricated with 'C+' powders was the best among the tested materials. Austenite and martensite phases of the surface composites and coatings was selectively corroded, while borides were retained inside pits. In the coating fabricated with 'C+' powders, the localized corrosion additionally occurred along splat boundaries, and thus the corrosion resistance of the coating was worse than that of the surface composite.

• Journal of Surface Science and Engineering
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• v.39 no.1
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• pp.1-8
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• 2006

In this study, effect of sputtering after plasma nitriding and before PVD coating on the microstucture, microhardness, surface roughness and the adhesion strength of CrN thin films were investigated. Experimental results showed that this sputtering process not only removed surface compound layer which formed during a plasma nitriding process but also induced an alteration of the surface of plasma nitrided substrate in terms of microhardness distribution and surface roughness, which in turn affected the adhesion strength of PVD coatings. After sputtering, microhardness distribution showed general decrease and the surface roughness became increased slightly. The critical shear stress measured from the scratch test on the CrN coatings showed an approximately twice increase in the binding strength through the sputtering prior to the coating and this could be attributed to a complete removal of compound layer from the plasma nitrided surface and to an increase in the surface roughness after sputtering.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.10a
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• pp.150-150
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• 2009

• Corrosion Science and Technology
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• v.4 no.2
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• pp.64-68
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• 2005

Various metallic materials are coated on Fe base materials via thermal spraying or welding process to improve both corrosion resistance as well as erosion resistance of the Fe base materials used in buildings and special works. The mechanical properties and corrosion resistance of the coat are estimated by means of hardness measurement and anodic polarization test. In additions, the effect of alloying elements and microstructure of the coatings on the mechanical and chemical properties of the coat is investigated using X- ray diffraction, Optical microscope, Transmission electron microscopy and Auger analysis. The coating deposited by tungsten inert gas (TIG) welding exhibit a good combination of hardness and corrosion properties.

• Korean Journal of Materials Research
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• v.13 no.7
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• pp.420-423
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• 2003

Coatings of TiCrN ion-plated on a steel substrate was oxidized at $800^{\circ}C$ in air, and their oxidation mechanism was presented. During oxidation, substrate elements and Ti and Cr in the coating always diffused outwardly to form the oxide scale. Simultaneously, oxygen from the atmosphere diffused inward1y to react with Ti and Cr to form $TiO_2$and $Cr_2$$O_3$, respectively. Also, the counter-diffusion of cations and oxygen resulted in some oxygen dissolution in the unoxidized TiCrN coating, and Fe dissolution in the oxide scale. When the Ti content in the coating was high, the $TiO_2$-forming tendency was strong, while when the Cr content was high, the $Cr_2$$O_3$-forming tendency was strong.

• Journal of Surface Science and Engineering
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• v.43 no.1
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• pp.31-35
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• 2010

Coatings of Ni-17 at.%W were electroplated on a steel substrate, and their corrosion behavior was investigated between 600 and $800^{\circ}C$ in an Ar-0.2%$SO_2$ atmosphere. They delayed the corrosion of the steel substrate. They were corroded into an outer NiO-rich layer, and an inner ($WO_3+NiO+NiWO_4$)-mixed oxide layer. Below these oxide layers, a sulfide layer gradually formed.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.638-639
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• 2006

Multilayered coatings on tungsten carbide cutting tools are widely used for enhancing cutting performance. In this paper, we review the CVD TiC/TiCN multilayer as a function of the multilayer period. The TiC/TiCN multilayers in initial stage show preferred (220) orientation but shifts to (200) orientation with decreasing multilayer period. The nanohardness of TiC/TiCN multilayers were found to increase with decreasing multilayer period and shows a maximum of 23.8 GPa at a period = 33.5 nm.

• Journal of Surface Science and Engineering
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• v.57 no.4
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• pp.348-354
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• 2024

Nanocrystalline zirconium nitride (ZrN) coatings were deposited by mid-frequency direct current sputtering (mfMS) with varying pulsed plasma parameters such as pulse frequency and duty cycle to understand the effect of pulsed plasma on the microstructure, residual stress and mechanical properties. The results show that, with the increasing pulse frequency and decreasing duty cycle, the coating morphology changed from a porous columnar to a dense structure, with finer grains. Mid-frequency magnetron sputtered ZrN coatings with pulse frequency of 30 kHz showed the highest both nanoindentation hardness of 16.3 GPa, and elastic modulus of 214.4 GPa. In addition, Effect of pulse frequency on a residual stress and average crystal grain sizes was also investigated.

• Journal of the Korean Ceramic Society
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• v.48 no.2
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• pp.160-167
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• 2011

Plasma sprayed ceramic coatings inherently contain pores and usually also cracks. Post-treatment of the plasma sprayed coatings is a way to close the connected pores and cracks. In this study, post-sealing treatment in plasma sprayed $Al_2O_3$ coatings was employed to overcome the reduction of coating properties. $Al_2O_3$ plasma thermal spray coating was made on aluminum alloys plate, $CrO_3$ post coating and heat treatment at $550^{\circ}C$ was carried out in order for final $Cr_2O_3$ to be saturated through phase transformation. Chromia sealing began at the fine defect in coated microstructure, while larger pores were permeated later. The increase in concentration and treatment frequency of sealing solution resulted in the decrease of porosity of coating layer, while cracks occurred partially after the third treatment. After twice treatment of 10M $CrO_3$ solution, microhardness and breakdown voltage of $Al_2O_3$ coatings were found to increase by ${\fallingdotseq}$ 50% and ${\fallingdotseq}$ 390% respectively than without post-treatment.

• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.506-513
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• 2010

The composite coatings of $(ZrO_2-8Y_2O_3)$/(Ni-22Cr-10Al-1Y) were prepared by the air plasma spraying method. They consisted of (Ni,Cr)-rich regions,$(ZrO_2-Y_2O_3)$-rich regions, and $Al_2O_3$-rich regions that were formed by oxidation of Al from (Ni-22Cr-10Al-1Y) during spraying. The coatings corroded at 800 and $900^{\circ}C$ in NaCl-$Na_2SO_4$ molten salts up to 50 hr. Ni, Cr and Al oxidized to NiO, $Cr_2O_3$ and ${\alpha}-Al_2O_3$, respectively. These oxides and $(ZrO_2-Y_2O_3)$ were dissolved off into the molten salts during hot corrosion, which resulted in the ever-lasting corrosion of the composite coatings. Chromium diffused out from the (Ni,Cr)-rich regions and oxidized to $Cr_2O_3$, which was most frequently found as surface scales. Aluminum retained in the (Ni,Cr)-rich regions were similarly diffused out.