Papers by Author: Sung Duk Kwon

Abstract: Chemical vapor deposit (CVD) diamond coating layer is expected to extend the lifetime of mechanical parts that are used severely abrasive conditions. However, one of the most severe problems is that the delamination between the CVD diamond coating layer and the silicon substrate occurs frequently due to large difference in the material properties. Therefore, the nondestructive evaluation of adhesive property of CVD diamond coating layer is needed. To address such a need, back-scattered Rayleigh surface wave is currently applied. However, the interpretation of the acquired signal is not easy at all. To take care of such a difficulty, we proposed the time trace angular scan (TTAS) plot and the frequency spectrum angular scan (FSAS) plot that can make possible of the systematic interpretation of the back-scattered signals from the diamond coating layer. In this paper, the concept of the TTAS and FSAS plots and the experimental results presented to demonstrate the effectiveness of the proposed approach.

Abstract: Titanium-nitride (TiN) ceramic coatings are widely utilized to extend the lifetime of mechanical parts under severely abrasive conditions and in lubrication environment. Since ceramic layers coated on machinery components inevitably experience the changes in their properties, it is necessary to evaluate the characteristics of ceramic coating layers nondestructively for the reliable use of coated components and the remaining life prediction. For this purpose, in the present study, the ultrasonic backward radiation technique is applied to evaluate very thin TiN ceramic layers coated on AISI 1045 steel and austenitic 304 steel substrates. In this study, very interesting behaviors are revealed from the interrogated TiN ceramic coated specimens. The sliding loading in the abrasive wear regime increases the peak amplitude of the profile. However, the sliding loading large enough to produce scuffing finally decreases the peak amplitude of the profile while the peak angle increases.

Abstract: The propagation characteristics of the back-reflected Rayleigh surface wave in chemical vapor deposit (CVD) diamond coated specimens were investigated experimentally using the ultrasonic backward radiation measurement. The deliberated delaminations produced between the coating layer and the substrate decreased Rayleigh surface wave velocity. This initial experimental result obtained in the present study demonstrates the high potential of the backward radiated ultrasound as a tool for nondestructive evaluation of very thin CVD diamond coating layer.