Papers by Author: Jung Gu Kim

Abstract: Aqueous corrosion behaviors of Fe3Al-based iron aluminides were investigated. From the result of cyclic anodic polarization tests conducted in 3.5 wt.% NaCl solution at 25, 48, 72 and 95°C, as the temperature increased, the resistance to pitting corrosion decreased significantly, especially over the range of 25~48°C. From the result of crevice corrosion tests, no crevice corrosion occurred on FAL-Mo in the lower chloride-containing solution (200 ppm Cl-), however, FAL-Mo did not perform as well as the 304L SS in the higher chloride-containing solution (3.5 wt.% NaCl). From the result of anodic polarization tests performed in sulfur-compound solutions, additions of Cr and Mo to the Fe3Al-based iron aluminides tend to improve the aqueous corrosion resistance. Aqueous corrosion behaviors with different Al content evaluated by cyclic anodic polarization test in the chloride-containing solution exhibited the more stable passive behavior and the higher pitting resistance as Al contents increased.

Abstract: This work focused on the effect of Co content on the corrosion resistance of high pitting resistance equivalent (PRE), super ferritic, Ni-free stainless steels in simulated biosolutions. The effect of Co in Ni-free alloys was evaluated by cytotoxicity test. Anodic polarization test and AC impedance measurement were performed to evaluate the effect of Co on corrosion resistance of the alloys. The cytotoxicity test result for 4 experimental alloys shows non-cytotoxic but mild cytotoxic for 316L stainless steel due to relatively poor corrosion resistance. However, the effect of Co on the passivity was positive in bio-solution but it was negative in acidic chloride solution.

Abstract: The aim of this work is to evaluate the difference in the corrosion resistance between unleaded containing bismuth automotive epoxy primers and leaded one. It was also discussed the effect of zinc phosphate pretreatment. The specimen coated unleaded epoxy primer showed 0.5V higher corrosion potential than that of bare steel. The result of salt spray test did not indicate remarkable difference of corrosion resistance in all specimens above 10
thickness up to 1200 hours. In the cyclic corrosion test, unleaded epoxy primers on phosphated substrate performed good corrosion properties until 800 hours. The lead free primer performed the equivalent corrosion resistance as leaded coating on phosphated steel, but slightly inferior to that of leaded on bare steel. These results show that the pre-treatment of zinc phosphating is effective as well as pigment changing in performing anti-corrosion properties in automotive bodies.

Abstract: The anti-corrosion properties of and catalytic effect of crosslinking on Bi2O3 were investigated in this study. The results of double rubs test with methyl ethyl ketone, cyclic corrosion test and FT-IR with ATR show that Bi2O3 performs anti-corrosion property and catalytic effect of crosslinking of resin.

Abstract: Multilayered coatings of WC-Ti and WC-Ti1-xAlxN were deposited to form a wear- and corrosion-resistant surface. The cathodic arc deposition (CAD) method was used to deposit WC-Ti1- xAlxN coatings with variable Al content onto high speed steel (HSS). Three kinds of WC-Ti1-xAlxN coatings, each with and without interlayer (Ti/TiN), were prepared. The corrosion behaviors of WCTi1- xAlxN coatings in a deaerated 3.5% NaCl solution were investigated by galvanic corrosion test and potentiodynamic polarization test. The porosity of the coatings, both with and without interlayer, generally decreased with increasing Al content. The multilayer coating with a Ti/TiN interlayer was responsible for the increased corrosion resistance due to its lower porosity and higher adhesion strength than the multilayer coatings without interlayer.

Abstract: The microstructure and mechanical properties of spot friction stir welded A 5052 alloy were investigated with insertion depth of welding tool. As the insertion depth of welding tool increased, the size of stirring zone increased and the thickness of upper sheet decreased. The value of shear load was the lowest at the shallowest insertion depth and increased to the highest value of 3.35 kN at a 1.6mm of insertion depth. An increase in the pin insertion depth beyond 1.6mm did not result in further increase in the lap shear load. Spot friction stir welded joints showed shear fracture mode at shallower insertion depths and fracture mode changed to plug fracture mode as the insertion depth was deeper.

Abstract: Four different multilayered coatings with different Al concentrations were deposited on AISI D2 steel. The prepared coating samples were designated as WC-Ti0.6Al0.4N, WC-Ti0.53Al0.47N, WC-Ti0.5Al0.5N and WC-Ti0.43Al0.57N. The multilayered coatings were investigated with respect to coating surface and cross-sectional morphology, roughness, adhesion, hardness, porosity and tribological behavior. Especially, wear tests of four multilayered coatings were performed by using a ball-on-disc configuration with a linear sliding speed of 0.017 m/sec and a load of 5.38N. The tests were carried out at room temperature in air by employing AISI 52100 steel ball (HR = 66) with a diameter of 10mm. The surface morphology and topography of the wear scars of samples and balls have been determined by using scanning electron spectroscopy (SEM). Results have showed an improved wear resistance of the WC-Ti1-xAlxN coatings with increasing Al concentration.