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Experiments have demonstrated that a moderate amount of Be added to Zr57.5Cu38.3Al4.2 amorphous alloy enhances the plasticity of the alloy. In particular, Zr54Cu36Al4Be6 alloy exhibited 19% of strain to fracture along with a strength exceeding 2 GPa. Energy dispersive x-ray spectroscopy conducted on the Zr54Cu36Al4Be6 alloy exhibited the presence of compositional modulation, indicating that nm-scale phase separation had occurred at local regions. In this study, the role played by the nm-scale phase separation on the plasticity was investigated in terms of structural disordering, structural softening and shear localization in order to better understand the structural origin of the enhanced plasticity shown by the developed alloy.

keyword : amorphous alloy, phase-separation, structural disordering, shear Localization, plasticity

Deformation behavior of pure aluminum during equal channel angular pressing (ECAP) was simulated using a three-dimensional version of the finite element method in conjunction with a constitutive model based on the dislocation density and cell evolution. The three-dimensional finite element analyses for the prediction of microstructural features, such as the variation of the dislocation density and the cell size with the number of ECAP, are reported. The calculated stress and strain and their distributions are also investigated for the route Bc ECAP processed pure aluminum. The results of finite element analyses are found to be in good agreement with experimental results for the dislocation cell size. Due to the accumulation of strain throughout the workpiece and an overall trend to saturation in cell size, a decrease of the difference in cell size with the number of passes (1~4) was predicted.

keyword : equal channel angular pressing, microstructure based constitutive model, dislocation cell model, three dimensional finite element method

This paper deals with cyclic stress and strain responses during isothermal low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) loadings on Nb and Mo containing 15Cr stainless steel, which is used for exhaust manifolds in automobiles. The test temperatures (Ti) of the isothermal LCF were 600 and 800℃. The minimum temperature of the TMF test was 100℃ and the maximum temperaures (Tp) were varied between 500 and 800℃. In both loading conditions, weak cyclic softening is observed at Ti=Tp=800℃, but the transition to strong cyclic hardening is completed with the temperature decrease below Ti=600~700℃ for LCF and Tp=500~600℃ for TMF. The stress-strain hysteresis loops in the TMF loading show a significant stress relaxation during compressive (heating) half cycle at Tp>500℃, which develops tensile mean stress during cycling. Due to the stress relaxation, the TMF test sample reveals much lower dislocation density than the isothermally fatigued sample at the same temperature with Tp. A detailed correlation between fatigue microstructure and cycling deformation behavior is discussed.

keyword : heat resistant ferritic stainless steels, thermo-mechanical fatigue, Low cycle fatigue, cyclic deformation, fatigue microstructure, exhaust manifolds

The major drive for the application of low-temperature plasma treatment in nitrocarburizing of austenitic stainless steels lies in improved surface hardness without degraded corrosion resistance. The low-temperature plasma nitrocarburizing was performed in a gas mixture of N2, H2, and carbon-containing gas such as CH4 at 450℃. The influence of the processing time (5~30h) and N2 gas composition (15~35%) on the surface properties of the nitrocarburized layer was investigated. The resultant nitrocarburized layer was a dual-layer structure, which was comprised of a N-enriched layer (γN) with a high nitrogen content on top of a C-enriched layer (γC) with a high carbon content, leading to a significant increase in surface hardness. The surface hardness reached up to about 1050 HV0.01, which is about 4 times higher than that of the untreated sample (250 HV0.01). The thickness of the hardened layer increased with increasing treatment time and N2 gas level in the atmosphere and reached up to about 25 μm. In addition, the corrosion resistance of the treated samples without containing Cr2N precipitates was enhanced than that of the untreated samples due to a high concentration of N on the surface. However, longer treatment time (25% N2, 30 h) and higher N2 gas composition (35% N2, 20 h) resulted in the formation of Cr2N precipitates in the N-enriched layer, which caused the degradation of corrosion resistance.

keyword : Low-temperature plasma nitrocarburizing, expanded austenite, austenitic satinless steel, Low-temperature plasma nitriding

The bipolar plates are not only the major part of the polymer electrolyte membrane fuel cell (PEMFC) stack in weight and volume, but also a significant contributor to the stack costs. Stainless steels are considered to be good candidates for bipolar plate materials of the PEMFC due to their low cost, high strength and easy machining, as well as corrosion resistance. In this paper, 316L stainless steel with and without nitrogen ion implantation were tested in simulated PEMFC environments for application as bipolar plates. The results showed that the nitride formed by nitrogen ion implantation contributed the decrease of the interfacial contact resistance without degradation of corrosion property. The combination of excellent properties indicated that nitrogen ion implanted stainless steel could be potential candidate materials as bipolar plates in PEMFC. Current efforts have focused on optimizing the condition of ion implantation.

keyword : polymer electrolyte membrane fuel cell, bipolar plate, 316L stainless steel, nitrogen ion implantation, interfacial contact resistance

Cu based amorphous (Cu54Zr22Ti18Ni6) powders were deposited onto Al 6061 substrates by cold spray process with different powder preheating temperatures (below glass transition temperature: 350℃, near glass transition temperature: 430℃ and near crystallization temperature: 500℃). The microstructure and macroscopic properties (hardness, wear and corrosion) of Cu based amorphous coating layers were also investigated. X-ray diffraction results showed that cold sprayed Cu based amorphous coating layers of 300~350 μm thickness could be well manufactured regardless of powder preheating temperature. Porosity measurements revealed that the coating layers of 430℃ and 500℃ preheating temperature conditions had lower porosity contents (0.88%, 0.93%) than that of the 350℃ preheating condition (4.87%). Hardness was measured as 374.8 Hv (350℃), 436.3 Hv (430℃) and 455.4 Hv (500℃) for the Cu based amorphous coating layers, respectively. The results of the suga test for the wear resistance property also corresponded well to the hardness results. The critical anodic current density (i(c)) according to powder preheating temperature conditions of 430℃, 500℃ was lower than that of the sample preheated at 350℃, respectively. The higher hardness, wear and corrosion resistances of the preheating conditions of near Tg and Tx, compared to the properties of below Tg, could be well explained by the lower porosity of coating layer.

keyword : Cu based amorphous, cold spray deposition, powder preheating temperature, amorphous coating, porosity, wear resistance, corrosion resistance

It is well known that the temperature and the flow pattern of the crystal-melt interface affect the qualities of the single crystal in the Czochralski process. Thus the temperature profile in the growth system is very important information. This work focuses on controlling the temperature of the silicon melt with a thermal gradient of the crucible. Therefore, the side heater is divided into three parts and an extra heater is added at the bottom for thermal gradient. The temperature of the silicon melt can be strongly influenced and controlled by the electric power of each heater.

keyword : Czochralski method, single crystal, silicon, computer simulation

The purpose of this study is to identify the effect of electrolyte compositions on electrodeposited copper foil. First of all, the polyimide substrate was pretreated with plasma. Finally, copper foil was deposited on a Cu/Ni/Polyimide substrate using the electroplating technique. As the quantity of Cu increased, preferred orientations changed into (111). Increasing sulfuric acid, on the other hand, brought down the preferred orientation of (111). The lowest sheet resistance, surface roughness, and fine adhesion were detected when the ratio of Cu2+ and H2SO4 is 50:50(g/l).

keyword : polyimide, electrodeposition, electrolyte, surface morphology, texture, peel strength

The surface morphology and the surface roughness of n-type SiC induced by wet-treatment using 45% KOH and buffered oxide etchant (BOE-1HF: 6H2O) were investigated by atomic force microscopy (AFM). While Si-face of SiC could be etched by alkali solutions such as KOH, acidic solutions such as BOE were hardly able to etch SiC. When the rough SiC samples were used, the surface roughness of etched sample was decreased after wet-treatment regardless of etchant, due to the planarization the of surface by widening of scratches formed by mechanical polishing. It was observed that the initial etching was affected by the energetically unstable sites, such as dangling bond and steps. However, when a relatively smooth sample was used, the surface roughness was rapidly increased after treatment at 180℃ for 1 hr and at room temperature for 4 hr by using KOH solution, resulting from the nano-sized structures such as pores and bumps. This indicates that porous SiC surface can be achieved by using purely chemical treatment.

keyword : wet etch, n-type SiC, morphology, Si-face

Dense 5 Cu0.6Fe0.4-Al2O3 composite was consolidated from mechanically synthesized powders by high frequency induction heating method within 2 min. Consolidation was accomplished under the combined effects of a induced current and mechanical pressure. Dense 5 Co0.6Fe0.4-Al2O3 with relative density of up to 95% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. Fracture toughness and hardness of the composite are 7.6 MPa·m1/2 and 844 kg/mm2 respectively.

keyword : nanomaterial, composite, nanopowder, Fe-Al2O3, Cu-Al2O3