Kyu Young Kim

Al+Y codeposition using EB-PVD method for improvement of high-temperature oxidation resistance of TiAl

Abstract An “Al+Y codeposition” on TiAl by the single EB-PVD method has been developed to improve the oxidation resistance of TiAl. To determine the optimum codeposition condition, the Al+Y codepositions with various ratios of Al and Y are evaluated through the isothermal and cyclic oxidation tests. The oxidation resistance of TiAl can be improved extensively by the Al+Y codeposition due to the formation of a gradient coating of Al and Y. The Al+Y codeposition with the ratio of Al:2Y for evaporation source material is proved to be the best. With a proper ratio of Al:Y, the Al+Y codeposition forms two distinctive layers of the oxides during high-temperature oxidation; Al 2 O 3 in the inner layer and (Y, Al)O type oxide in the outer layer. In addition to the inner Al 2 O 3 layer, the formation of the outer (Y, Al)O type oxide layer further improves the stability of the coatings. The stability of the Al+Y codeposition greatly depends upon the alloying element of TiAl substrate or oxidation resistance of the TiAl substrate alloy. The non-alloyed TiAl shows a poor coating stability, whereas TiAl–2.8Nb and Alloy K5 show a good coating stability under severe thermal stresses during cyclic oxidation since a stable Al 2 O 3 can form on the surface of these alloys.

Actuator Performance Degradation of Piezo-Composite Actuator LIPCA under Cyclic Actuation

This paper is concerned with the fatigue characteristics of LIPCA (LIghtweight Piezo-Composite Actuator) device system. LIPCA device system is composed of a piezoelectric ceramic layer and fiber reinforced light composite layers, typically a PZT ceramic layer is sandwiched by a top fiber layer with low CTE (coefficient of thermal expansion) and base layers with high CTE. The advantages of the LIPCA design are using the lightweight fiber reinforced plastic layers without compromising the generation of high force and large displacement and to have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use resin prepreg system. To investigate the degradation of actuation performance of LIPCA due to the repeated fatigue loading, the repeated loading tests up to several million cycle were performed and the actuation displacement for a given excitation voltage was measured during the test. The fatigue characteristics was measured using an actuator test system consisted of an actuator supporting jig, a high voltage actuating power supplier, and a non-contact laser measuring system and evaluated.

Nondestructive evaluation of corrosion beneath organic coatings by synchrotron X-rays

An application of X-ray techniques including X-ray scattering and X-ray absorption spectroscopy for a nondestructive evaluation of corrosion of steels beneath an organic coating is discussed. The capability of the X-ray techniques for the nondestructive evaluation has been demonstrated, and chemical species of Fe oxides beneath the corroded organic coating is identified by the X-ray techniques.

Correlation of Microstructure with Hardness and Corrosion Resistance of Surface Alloyed Materials Fabricated with Fe-Based Metamorphic Powders by Accelerated Electron Beam Irradiation Method

This study aims at correlating microstructure with hardness and corrosion resistance of surface alloyed materials fabricated with Fe-based metamorphic powders by an accelerated electron beam irradiation method. The surface alloyed materials contained 48 vol.% of hard Cr2B crystalline phases in the Cr0.19Fe0.7Ni0.11 matrix, and thus its hardness was 2.5 times greater than that of the steel substrate. The corrosion resistance of the surface alloyed materials was better than that of an STS304 stainless steel or coatings fabricated by high-velocity oxygen fuel spraying of Fe-based metamorphic powders because the Cr0.19Fe0.7Ni0.11 matrix of the surface alloyed layers and coating was selectively corroded, while Cr2B borides were retained inside pits. These findings suggested that the fabricated surface alloyed materials presented good application possibilities as excellent wear- and corrosion-resistant materials.

Non-Destructive Visualization of Two-Phase Fields by the Electrical Impedance Tomography with an Adaptive Mesh Grouping Scheme

The electrical impedance tomography (EIT) has a strong potential for none-destructive visualization of objects existing inside a none-transparent container. Although the EIT has an inherent advantage of high speed data acquisition, the poor spatial resolution of the reconstructed image remains as challenging problem to be solved. In this paper, we propose a novel method that can enhance the spatial resolution but reduce the computational burden. The method is based on adapting a mesh-grouping scheme to the Gauss-Newton algorithm in the inverse procedure. To test the effectiveness of the method, we have applied the method to hypothetical two-phase fields. We present some of the computer simulation results which show significantly enhanced spatial resolution in the reconstructed images of the two-phase fields with less computation time.

Nondestructive Mapping of Corrosion of Steel beneath Paint Coating by Synchrotron X-Ray Absorption Spectroscopy

An application of synchrotron X-ray absorption spectroscopy (XAS) for a nondestructive evaluation of corrosion of steel beneath an organic paint coating is discussed. The XAS technique is applied to map out the corrosion beneath paint coating for the nondestructive evaluation, and to identify chemical species of corrosion products. Introduction Organic paint coatings are widely used to control corrosion of steel structures, both to maintain an appearance and to prevent the loss of a structural integrity. The anti-corrosive organic coatings cover about 50 % among corrosion protections of the steel structures [1]. However, the organic coatings may be degraded under various service conditions, and their degradation may result to a reduction of their anti-corrosive effectiveness. Since the undercoating corrosion can lead to a failure of the steel structures if not detected at an early stage, the detection of corrosion under the organic coatings at the earliest stage is an important issue toward improving a safety and reducing a cost. As an alternative way to predict the corrosion under the organic coatings, protective properties of the organic coatings have been evaluated by an inspection of discoloration or gloss, an adhesion test, and a mechanical test. But these methods have a poor reliability. Recently several methods, such as electrochemical tests including a corrosion potential, a polarization resistance and a current interrupter [2], an electrochemical impedance spectroscopy [3-6], an acoustic emission [7,8], a scanning vibrating electrode technique [9], a Fourier transform infrared spectroscopy [10], an X-ray photoelectron spectroscopy [11,12], and an electron spin resonance [13,14], are proposed to investigate the corrosion under the organic coatings. However, these methods also seem to have a limited capability and sensitivity. In the present study, X-ray technique of X-ray absorption spectroscopy (XAS) using synchrotron light source was applied for a nondestructive evaluation of corrosion of steel beneath an organic coating. X-rays can be used to investigate the corrosion beneath the organic coating layer, as they are able to penetrate a few tens of microns into organic coating materials. Furthermore, the X-ray technique can give precise information on a chemical composition and a formula of corrosion products. It is also noted that so far the X-ray technique using synchrotron X-rays is a laboratory analysis tool rather than field technique. Experimental Sample preparation. An alkyd resin formulated with zinc potassium chromate was used as coating material. A carbon steel substrate was pre-treated by a sand blast, degreasing in acetone and rinsing with methyl alcohol. After application of the coating material on the steel substrate, the coating was dried in a Temp/humidity chamber at 20 °C and 60 % R.H. for one week. The thickness of the dried Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 950-953 doi:10.4028/www.scientific.net/KEM.270-273.950