Advanced Materials Research Vols. 26-28

Abstract: In flexible display, reliability of the thin film/polymer interface is an important issue because adhesion strength dissimilar materials is often inherently poor, and residual stresses arising from thermal mismatches or pressure exerted by vaporized moisture often lead to delaminations of interfaces. In the present study we deposited various thin films such as silicon nitride (SiNx), aluminum metal layer, and indium tin oxide on polyether sulphone (PES) substrate. The film adhesion was determined by micro-scratch test. The adhesion strength, presented by the critical load, Lc, when the film starts to delaminate, was determined as a function of plasma pretreated on PES substrate.

Abstract: Carbon steel is the most popular engineering material, usually consisted of ferrite and cementite phases. Internal stress state of the steel under thermal or mechanical loading is strongly affected by the amount and morphology in the cementite phase. With this aim, a computational model which applies the finite element method at the microscale was used in present study. Effects of volume fraction and particle size of the spheriodal cementite on the internal stress states in carbon steels under the mechanical and thermal loadings are investigated. To verify the reliability of the computational simulations, the residual stresses in the constituent phases are measured by means of X-ray stress diffraction technique. The computational simulations fit well with the experimental data, and the microstructure-based model is validated.

Abstract: Field instrumentation for a recycled waste concrete geobag wall was performed to investigate the performance of the geobag wall, and uniaxial compression tests for a recycled waste concrete geobag were executed in the laboratory. The strength of a recycled waste concrete geobag, the lateral earth pressure of a geobag wall, the horizontal deflection of a geobag wall, and the deformation of the backfill in a geobag wall are evaluated in this study. Based on the results of analysis bylaboratory tests and measurements, the recycled waste concrete geobag wall displacement was within the recommended allowable range for mechanically stabilized earth walls. Furthermore, the recycled waste concrete in geobag wall provided stability, construction ease, and good performance.

Abstract: The mechanical properties of as-cast and hot-forging duplex stainless steel samples with the same compositions were characterized by nanoindentation. The effect of surface treating method and working state of the sample on the nanoindentation results of ferrite and austenite were discussed. The results show that the Young’s modulus and hardness of ferrite and austenite may be affected by the treating method of sample surface. The difference of Young’s modulus average of ferrite or austenite between as-cast and hot-forging duplex stainless steel samples is not great, but the hardness average of ferrite or austenite in hot-forging sample is obviously higher than those of as-cast sample. The difference of hardness between ferrite and austenite in the same sample is not great, but the young’s modulus of ferrite is higher than that of austenite.

Abstract: Deteriorated environment resulting from fossil fuel usage as well as foreseeable conventional energy depletion lead to the exploration of alternative fuel materials especially the renewable ones. In this work, characterization of synthetic fuel material formed by pelletization of Jatropha (physic nut) waste using glycerol waste as a binder was carried out in order to investigate the feasibility of utilizing these waste materials as another renewable energy source. Synthetic fuel materials of Jatropha residue mixed with 0-40% glycerol waste were formed to length of about 13 mm and diameter of about 11 mm under pressure of 7 MPa in a hydraulic press. Their thermal conversion properties were studied by using single particle reactivity testing scheme at temperature of 500-900°C under partial oxidation atmosphere. The burning started with a relative short drying phase, followed with a longer pyrolysis time and thereafter the dominated char combustion time which took around 81-89% of total conversion time. The average total conversion time varied from 741 sec to 1873 sec depended mainly on reaction temperature. Higher glycerol content resulted in char with lower density and less shrinkage. Changes in diameter were not strongly depended on glycerol contents. The results suggested that Jatropha residue mixed with glycerol may be utilized as quality solid fuel.

Abstract: Welding residual stress has important influence on the performance of engineering components. In this paper, the residual stress and FWHM were measured by X-ray diffraction method to investigate characteristics for P92 steel welds. The aim of the study is to estimate the residual stress and FWHM distribution characteristics. A compressive residual stress distributed as a function of depth has a different pattern in welds and base metal. A large tensile residual stress occurs welds and near the HAZ, but approaches gradually zero as away from the welding center. Residual stress and FWHM undergo rapid relaxation after PWHT. Also, FWHM is a scalar quantity without any directional difference and is proportional to hardness on the whole.

Abstract: The purpose of this study is to find out the AE characteristics and fracture mechanisms through AE signal analysis for the weldment, PWHT specimen and basemetal of the pressure vessel steel. Charpy sized specimens were taken from the multi-passed weld block. Specimens were given to four point bend and AE tests. Lots of AE signals were emitted from the weldment compared with the basemetal and PWHT specimen. Besides, amplitude for the weldment was the largest, followed by PWHT specimen and basemetal and more AE counts for the weldment were emitted in the process of deformation. Lots of microcracks around the notch for the weldment were formed so that more AE signals were produced. In addition, second phase particle such as MgO for the basemetal acts as AE source. However, in case of weldment, debonding mechanisms between matrix and hard oxides which are formed during welding in air attributed to the emission of AE signals and softened particles for the PWHT specimen cause to produce the low level AE signals.

Abstract: The residual stress in axial direction of the steel wires has been measured by using a method based on the combination of the focused ion beam (FIB) milling and digital image correlation (DIC) program. The residual stress is calculated from the measured displacement field before and after the introduction of a slot along the steel wires. The displacement is obtained by the digital correlation analysis of high-resolution scanning electron micrographs, while the slot is introduced by FIB milling with low energy beam. The experimental procedures are described and the feasibilities are demonstrated in steel wires fabricated with different conditions.

Abstract: The influence of nitriding type and condition on the thermal crack propagation behavior of hot work die steel was investigated. Thermal fatigue tests were carried out using a special apparatus, which is consisted of induction heating and water spray cooling unit. The sum of crack length per unit specimen length, Lm is proposed as an index representing the susceptibility to crack propagation. The Lm values of the gas and ion nitrided specimens were lower than that of as-heat treated specimen. But in the case of maximum and average crack length of nitrided specimen was higher than those of as-heat treated specimen. The nitrogen diffusion layer still remained although the oxide scale was formed and fell off during thermal fatigue test. After 1000 cycles of the thermal fatigue test, the interior region of nitrided specimen showed lower hardness by softening. In particular, ion nitrided specimens of relatively less softening condition showed reduction both the depth and number of cracks compared with the other surface conditions.

Abstract: Transformation of uniformly strained GexSi1-x layers into GeSi dots of 3 ~ 7 nm which are compositionally ordered by one or concurrently two sets of {111} planes was carried out for the first time under non-equilibrium conditions induced by 1.25 MeV electron irradiation at Tc ≥ 200 oC in the high voltage electron microscope (JEM-ARM1300S). This microscope installed in the KBSI is characterized by an excellent point-to-point resolution of 0.12 nm allowing obtaining detailed information on chemical ordering at specific parameters of defocus (-800 Å) and crystal thickness (200~250 Å) determined by extensive HRTEM image simulation for the ordered dots.