Papers by Author: Seung Baek

Abstract: A-C: H (Hydrogenated amorphous carbon) diamond like carbon(DLC) film is the low stabilities of chemical and mechanical properties at high temperatures. Some researchers reported that Raman spectra shown significant conversion of DLC films to nano-crystalline graphite on heating in ambient air at temperatures above 300°C and conversion to nano-crystalline graphite was completed by 450~600°C In this study, DLC films(thickness : 1.5-m) were deposited on p-type (100) silicon films by using C6H6 and C6H14 plasma produced with a 13.6MHz RF source. To investigate the mechanical stability of DLC films below 250°C, we thermally aged the films for different aging temperatures (150°C, 200°C, 250°C) and times (0: virgin, 120, 240, 360 hours). By using indentation test and Raman spectra analyses, it has been found that the H3/E2 decreases with increasing I(D)/I(G) ratio. Also we confirmed that sample-2(precursor gas: C6H14) had better mechanical characteristic and thermal stability than the sample-1(precursor gas: C6H6).

Abstract: In this study, we performed fracture tests on thermally aged DLC thin films by using micro-indentation and nano-indentation and investigated the deformation and fracture characteristics of these films. The aged high hydrogen films have better characteristics such as thermal and mechanical stability than low hydrogen films.

Abstract: In this study, we investigated indentation behavior by varying the tip radius in a finite element model. We measured the tip radius and shape of the nano-indenter by SPM (scanning probe microscope) and compared them with the simulation results. The tip radius of cube corner indenter was measured to be 39nm, in agreement with the common tip radius of such indenters, which range from 20~50nm.

Abstract: Cast austenitic stainless steel piping pump, valve casings and elbows are susceptible to reductions in toughness and ductility because of long term exposure at the operating temperatures in the LWR (light water reactor). In this study, the three classes of thermally aged CF-8A cast austenitic stainless steel specimens were prepared using an artificially accelerated aging method for 0, 2,679 and 3,572 hours at 400oC. An indentation technique was applied to evaluate of the thermal aging of CF-8A cast austenitic stainless steel. We have performed indentation tests (automated ball indentation and nano-indentation) and EDS (energy dispersive spectroscopy) in order to characterize the micro-structural changes of the phase with aging. The fracture toughness of aged CF-8A cast stainless steel was determined by standard fracture toughness tests and automated ball indentation techniques.

Abstract: Nano-indentation test is used widely to determine the fracture toughness of brittle materials and to provide information on important material properties such as the Young’s modulus and hardness. In this study, using nano-indentation testing, atomic force microscope (AFM), and finite element method (FEM), we performed the indentation fracture toughness and fracture strength measurement for a (100) single crystalline silicon at different load states. In addition, the loads of the phase transformation events during unloading were estimated by the load-depth curves. The phase transformation load and micro-crack propagation events at pop-out during the unloading process depended on the maximum applied indentation load.