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Experiments have demonstrated that the addition of a moderate amount of V to Fe52Co(20-x)B20Si4-Nb4Vx amorphous alloy enhances the plasticity of the alloy. In particular, Fe52Co17.5B20Si4Nb4V2.5 alloy withstood a maximum of 8.3% strain prior to fracture along with a strength exceeding 4.7 GPa. Energy dispersive x-ray spectroscopy conducted on the Fe52Co17.5B20Si4Nb4V2.5 alloy exhibited evidence of compositional modulation, indicating that nm-scale phase separation had occurred at local regions. In this study, the role played by nm-scale phase separation on the plasticity was investigated in terms of structural disordering 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

This study aimed at investigating quasi-static and dynamic torsional deformation behavior of three API X70 and X80 linepipe steels. Quasi-static and dynamic torsional tests were conducted on these steels. having different grain sizes and volume fractions of acicular ferrite and polygonal ferrite, using a torsional Kolsky bar. The test data were then compared via microstructures and adiabatic shear band formation. The dynamic torsional test results indicated that the steels rolled in the single phase region had higher maximum shear stress than the steel rolled in the two phase region, because the microstructures of the steel rolled in the single phase region were composed mainly of acicular ferrites. In the X80 steel rolled in the single phase region. the increased dynamic torsional properties could he explained by a decrease in the overall effective grain size due to the presence of acicular ferrite having smaller effective grain size. The possibility of adiabatic shear hand formation was analyzed from the energy required for void initiation and variation in effective grain size.

keyword : API X 70 and X80 pipeline steel, quasi-static torsional deformation, dynamic torsional deformation, adiabatic shear band, effective grain size

This paper investigates the influence of aging time on creep properties via a small punch creep test and evaluates the microstructural change of P122 steel at 600℃. The area fraction of precipitates was quantitatively analyzed to identify the relationship between the creep rupture life and precipitates. The coarsening behavior of precipitates along the grain boundaries was also investigated for various aging times. It is found that this coarsening behavior led to a loss of solution hardening and resulted in a hardness drop and a reduction of creep life.

keyword : P122, ultra super critical power plant, creep, small punch, martensite, precipitates, aging, coarsening, Laves phase, prior austenite grain boundary, sub-grain

High temperature high cycle and low cycle fatigue deformation behavior of automotive heat resistant aluminum alloys (A356 and A319 based) were investigated in this study. The microstructures of both alloys were composed of primary Al-Si dendrite and eutectic Si phase. However, the size and distribution for eutectic Si phase varied: a coarse and inhomogeneous distributed was observed in alloy B (A319 based). A brittle intermetallic phase of α-Fe Al12(Fe,Mn)3Si2 was detected only in B alloy. Alloy B exhibited high fatigue life only under a high stress amplitude condition in the high cycle fatigue results, whereas alloy A showed high fatigue life when stress was lowered. With regard to the low-cycle fatigue result (250℃) showing higher fatigue life as ductility increased. alloy A demonstrated higher fatigue life under all of the strain amplitude conditions. Fractographic observations showed that large porosities and pores near the outside surface could he the main factor in the formation of fatigue cracks. In alloy n. micro-cracks were formed in both the brittle intermetallic and coarse Si phases. These micro-cracks then coalesced together and provided a path for fatigue crack propagation. From the observation of the differences in microstructure and fractography of these two automotive alloys. the authors attempt to explain the high-temperature fatigue deformation behavior of heat resistant aluminum alloys.

keyword : Heat resisting aluminum, casting, cylinder head, high temperatue, high cycle fatigue, Low cycle fatigue, tensile property

In order to investigate the effects of tempering temperature and heat-treatment path on the microstructural and mechanical properties of ASTM Gr.92 steels, foul samples with different tempering temperatures and heat-treatment paths were prepared. Three experimental steels showed tempered martensitic microstructures. but the sample tempered at 8l0℃ was presumed to retain partially untempered martensitic microstructures due to a lower α+γ phase regime. M23C6. V(C,N), and Nb(C.N) precipitates were observed in all samples. In addition, Cr2N was observed to be precipitated finely and uniformly by isothermal heat-treatment. The lath width and precipitate size increased with an increase of the tempering temperature. In particular, the lath width and precipitate size in the isothermal heat-treated samples were much smaller than those of the tempered-only specimens. Because of a fine and uniform precipitate, a reduction of lath width would enhance precipitation hardening, and it was shown that mechanical propertiesincluding the hardness and tensile properties of the steels were improved by isothermal heat-treatment.

keyword : sodium-cooled, fast reactor, SFR, fuel cladding, ferritic/matensitic steel, heat-treatment, microstructures, tensile properties

This study investigated how the surface of Al-12wt.%Si alloy is modified by the plasma electrolytic oxidation process (PEO). The PEO process was performed in an electrolyte with sodium hexametaphosphate as a conducting salt. and the effect of ammonium metavanadate on variations in the morphology of electrochemically generated oxide lavers on the alloy surface was investigated. It is difficult to form a uniform passive oxide layer on Al alloys with a high Si content due to the differences in the oxidation behavior of the silicon-rich phase and the aluminum-rich phase. The oxide layer covered the entire surface of the Al-12wt%Si alloy uniformly when ammonium metavanadate was added to the electrolyte. The oxide laver was confirmed as a mixture of V203 and V2O5 by XPS analysis. In addition, the oxide layer obtained by the PEO process with ammonium metavanadate exhibited a black color. Application of this surface modification method is expected to solve the problem of the lack of uniformity in the coloring of oxide layers caused by different oxidation behaviors during: a surface treatment.

keyword : Al-Si alloy, plasma electrolytic axidation, vanadium, surface modification

Nanosized surface structures of Cu powders were investigated at the atomic scale by field-emission transmission electron microscope techniques. The nanoscale surface oxide layer on the Cu powder was analyzed to be the CU2O phase by electron diffraction pattern and electron energy-loss spectroscopy. In addition, it was found from high-resolution transmission electron microscopy study that there are formed no surface oxide layers on the surface of alkanethiol coated Cu powders.

keyword : Cu powder, surface oxidation, field-emission transmission electron microscope, high-resolution transmission electron microscopy, electron energy Loss spectroscopy

Leaching and solvent extraction experiments have been performed to develop a hydrometallurgical process for the recovery of nickel and cobalt from nickel laterite ore with high magnesium content. Most of the nickel and magnesium in the laterite ore dissolved at leaching conditions of 80℃ and 100 g/L sulfuric acid concentration. while half of the cobalt and iron were leached at the same conditions. Solvent extraction experiments were carried out with D2EHPA and saponifed D2EHPA from a synthetic solution containing Ni, Co, and Mg. The extraction percentage of Co, Mg. and Ni by D2EHPA was very low in a pH range of 4.4 to 7.3. while the extraction percentage sharply increased by using saponified D2EHPA. The stripping percentage of the metals from the saponified D2EHPA increased with sulfuric acid concentration and reached 99.9% at 1 M H2SO4 solution.

keyword : Ni Laterite ore, Leaching, solvent extraction, stripping D2EHPA

The use of advanced high-strength steels (AHSS) in automotive applications has steadily increased over the past few years. Two different failure modes are generally observed in shear-tension tests for resistance spot welds of AHSS. interfacial fractures and full button pullout. Despite high load-carrying capacity. the resistance spot welds in AHSS cue prone to interfacial fractures. To improve the load carrying ability of welds during shear-lap and cross tension tests. the tip surface of the electrode was grooved in a round shape. The electrode tip surface was modified so as to concentrate the current now in the central and circumferential portion of the electrode force. The results showed that the interfacial fracture was suppressed in welds using the modified electrode. In a comparison of failure mode during mechanical tests. the welds made with the modified electrode showed a higher tendency to fail via full button pullout fracture.

keyword : resistance spot, welding, advanced high strength steel, modified electrode tip

Annealing characteristics of an oxygen free copper (OFC) processed by differential speed rolling (DSR) were investigated in detail. An OFC sample with a thickness of hum was rolled to 35% reduction at ambient temperature without lubrication, varying the differential speed ratio from 1.0:1 to 2.2:1, and then annealed for 0.5h at various temperatures from 100 to 400℃. Different recrystallization behavior was observed depending on the differential speed ratio, especially in the case of annealing at 200℃ Complete recrystallization occurred in the specimens annealed at temperatures above 250℃ regardless of the differential ratios. The hardness distribution in the thickness direction of the rolled OFC sheets varied depending on the differential speed ratios. These annealing characteristics were explained by the magnitude of shear strain introduced during rolling.

keyword : Differential speed rolling, oxygen free copper, annealing, strain, hardness