Chul-Ho Park

FERROELECTRIC PROPERTIES OF PZT/TiO2 STRUCTURE ACCORDING TO THE DEPOSITION CONDITION OF TiO2 INTERLAYER

ABSTRACT PZT thin films on the interlayer (TiO2) and Si substrate were fabricated by the r.f. magnetron-sputtering method. As a result of the EPMA analysis, we can conclude that the TiO2 thin film decrease Pb volatilization. TiO2 interlayer and PZT thin film were investigated by interface analysis of Glow Discharge Spectrometer (GDS) and observed to be independent layers respectively. Interlayer (TiO2) between PZT and Pt affected as seed layer of thin film and decreased crystallization temperature. Compared to the PZT thin films with TiO2 interlayer without post-annealing, the films with TiO2 interlayer annealed by RTA furnace showed prevailing ferroelectric properties.

Effects of High Current and Welding Wire Diameter on the Magnesium Vaporization and Mechanical Properties of Al5083 Arc Welds

Abstract The demand of LNG tank and the constituting material, i.e., the Al5083 thick plate, increased due to the rapid growth LNG market. To weld the Al5083 thick plate, the gas metal arc welding (GMAW) of high current is necessary to increase manufacturing productivity incurred by the multi pass welding. However, the arc welding vaporizes the volatile element such as magnesium (Mg). This phenomenon changes the Mg composition of the weld metal and the mechanical properties. The study investigated the weldability of Al5083 alloys after conducting high current GMAW. The Al5083 alloy was welded by using different size of welding wires and high current (800-950A). As the arc current increased from 800A to 950A, the mechanical strength decreased and the secondary dendrite arm spacing (SDAS) increased. Even though the arc current increased SDAS, the mechanical strength decreased due to the Mg loss in the weldment. The large diameter of welding wire decreased the dilution of the weld, therefore increasing the Mg content and the strength of the weld. For the reason, the content of Mg in welds was a major parameter to determine the mechanical property for the high current GMAW. For the arc current between 800A and 950A, the yield strength of the weldments showed a relationship with the weight percent of Mg content (X

Effect of post weld heat treatment on weldability of high entropy alloy welds

ABSTRACT The effect of post weld heat treatment (PWHT) temperature on laser beam welds in high-entropy alloys (HEAs) using a cold-rolled cantor system (CoCrFeMnNi) was investigated. Laser welding of low heat input was applied to reduce thermal distortion. The cold-rolled HEA welds indicated larger grain size and inferior tensile/hardness properties as compared to the base metal (BM). By applying PWHT, the welds showed superior hardness to the BM with no variation in the face-centred cubic phase and a decrease in the size and fraction of CrMn oxide inclusions. As the PWHT temperature increased (800–1000°C), the variation in the grain size decreased between the weld metal and heat-affected zone, thus resulting in approximately the same tensile strength and elongation of the transverse welds as compared to the BM.

Isothermal Phase Transformations and Stability of Retained Austenite during Quenching and Partitioning Process for 0.15C Steel

The microstructure and dilatation for 0.15C steels were investigated to define the phase transformation during the quenching and partitioning (Q&P) process. For the one step Q&P dilatation, the isothermal martensite/bainite transformation occurred because the holding temperature was between Ms and Mf. The isothermally transformed martensite/bainite and the athermally transformed martensite were produced by a loss of retained austenite. As the holding time increased, new martensite-start (Ms) temperature produced from the final quenching process decreased due to the carbon partitioning from the martensite to the retained austenite. This was the direct evidence of increment for the retained austenite stability. For the two step Q&P dilatation, the isothermal bainitic transformation occurred because the partitioning temperature was larger than the Ms and new Ms. The partitioning at 400℃ indicated the short incubation period for the bainite transformation than the 350℃ partitioning because the partitioning at 400℃ should acquire the larger thermal driving force for carbon partitioning than the 350℃ partitioning. A quick drop of Ms and short period of bainite incubation for the 400℃ partitioning steel were also the direct evidence of significant effects of carbon partitioning on the stability of retained austenite.

Scoring system for traumatic liver injury (SSTLI) in polytraumatic patients: a predictor of mortality

PurposeThe aim of this study was to examine prognostic factors in polytraumatic patients with liver injury and to develop a scoring system for traumatic liver injury (SSTLI) to predict mortality.MethodsThe medical records of 175 patients treated for traumatic liver injury from July 2009 to April 2013 were reviewed. The primary outcome variable was hospital mortality. All risk factors were analyzed by multivariate logistic regression analysis. The SSTLI was created based on the predictive power of each factor.ResultsAge, injury severity score (ISS), trauma and injury severity score, the shock index, and the volume of packed red blood cells transfused were strong predictors of mortality. We hypothesized that the SSTLI would use five clinical measures (total bilirubin, prothrombin time, serum creatinine, age, and ISS). Each measure was scored 0–1 (age and ISS) or 0–3 (total bilirubin, prothrombin time, and creatinine), with 3 indicating the most severe derangement. The receiver-operating characteristic curve of the SSTLI was significant at post-traumatic days 0, 1, 3, and 5 [area under the curve (AUC), 0.830; AUC, 0.912; AUC, 0.941; and AUC, 0.930, respectively]. A value of 5 points was the threshold for reliability dividing low-risk (<5) from high-risk (≥5) patients.ConclusionsThe SSTLI may be available to predict mortality in polytraumatic patients with liver injury, although external validation is needed before widespread implementation.

THE EFFECT OF THE DEPOSITION CONDITION OF THE PbO BUFFER LAYER ON THE INTERFACIAL CONDITION OF Pb1.1Zr0.53Ti0.47O3/PbO/Si STRUCTURES

ABSTRACT Pt/PZT/PbO/Si (MFIS) structure was deposited on the p-type (100) Si substrate by the r.f. magnetron sputtering method with Pb1.1Zr0.53Ti0.47O3 and PbO targets. From the X-ray photoelectron spectroscopy (XPS) results, we could confirm that the substrate temperature of PbO affects the chemical states of the interface between the PbO buffer layer and Si substrate, which results in the inter-diffusion of Pb and the formation of the intermediate phases (PbSiO3). And we could confirm that the partial pressure ratio during PbO deposition affects the interface condition of PbO/Si and the chemical state of Pb existing at the surface of the PZT thin film.

FERROELECTRIC PROPERTIES OF Pt/PbZr0.53Ti0.47O3/PbO/Si (MFIS) STRUCTURES ACCORDING TO THE SUBSTRATE TEMPERATURE DURING THE PBO BUFFER LAYER DEPOSITION

ABSTRACT PbO and PZT thin films were deposited on the p-type (100) Si substrate by the r.f. magnetron sputtering method with PbO and Pb1.1Zr0.53Ti0.47O3 targets for the application of the Metal-Ferroelectric-Insulator-Semiconductor (MFIS) structure. The MFIS structures with the PbO buffer layer show the good electric properties including a high memory window and a low leakage current density. The maximum value of the memory window is 2.0 V under the applied voltage of 9 V for the Pt/PZT (200 nm, 400°)/PbO (80 nm)/Si structures with the PbO buffer layer deposited at the substrate temperature of 300°.