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The effects of initial microstructures controlled by thermo-mechanical treatment on tensile properties at 950 ℃ were investigated in Alloy 617. Proprietary direct aging combined with a controlled cooling rate led successfully to the transition of serrated grain boundaries (GBs) with a proportion of over 80%. It was newly found that at an initial stage of the transition, the serrated GBs formed without the presence of carbide or a γ` phase in the solid-solution-strengthened Alloy 617. The serrated GBs with stable planar M23C6 carbides enhanced the uniform elongation while the strength was maintained due to higher resistance to GB cavitational cracking. The fine intragranular carbides, which precipitated substantially through preliminary 5% cold work treatment, were responsible for the strong hardening effect by inhibiting dislocation movement. Based on the results, we propose the initial microstructure for better tensile properties at 950 ℃. (Received January 6, 2014)

keyword : alloys, thermomechanical processing, grain boundary, serration, tensile test

Minute quantities of boron less than other added elements are able to improve various mechanical properties. To know the effect of boron on the properties of steel, it is necessary to accurately and precisely analyze it. It is easy to analyze boron in final products like thick plates and automotive steel sheets by OES, but it is impossible to analyze it in a sample like the ferro-alloy. An accurate analysis is also very difficult by ICP-OES because there is a matrix disturbance by the Fe element in the sample. In this work, instead of the existing specific procedures that are time-consuming for a matrix separation, we wanted to develop a quick and accurate method for analyzing boron by ICP-OES with the standard addition method. Three samples in this work, NCS HC 17204, NCS HC 23204 and JSS 174-7, were selected and used according to the boron content. When all the samples were analyzed using a wavelength of 182.583 nm of ICP-OES, we found that the analytic values corresponded to the certified values of CRM as follows. The certified value of NCS HC 17204 is 0.0042% and the analytic value was 0.0043%. The certified value of NCS HC 23204 is 0.0053% and the analytic value was 0.0052%. The certified value of JSS 174-7 is 0.0076% and the analytic value was 0.0080%. (Received January 15, 2014)

keyword : metals, determination of boron, standard addition method, ICP-OES, ferro-alloy

The aim of this paper was to analyze the cause of surface cracks and pit corrosion on 316L pipe. An End Grain Attack (EGA) as a kind of pit mechanism was conducted on the pipe surface. The early stage of the EGA may come from under-deposit of caustic-water formation compositions like Na+, K+, Ca+, and Mg+ etc. The under-deposit corrosion is caused by the corrosion layer on the pipe surface followed by crevice corrosion due to accumulation of Cl-or S-composition between the corrosion layer and the pipe surface. In the early stage, the EGA occurred in all grain boundaries beneath the under-deposit corrosion. In the later stage of EGA, almost all the early attacked grain boundaries stopped at a limited depth of about 10 μm. Meanwhile, only the smallest number of the attacked boundaries progressed into the pipe as pit corrosion and resulted in leak failure. (Received February 24, 2014)

keyword : 316L pipe, pit corrosion, under-deposit, end grain attack

A sapphire single crystal growth process by the Vertical-Horizontal Gradient Freezing (VHGF) method was studied by a numerical analysis technique. The heater power was controlled in order to follow the given arbitrary target heater temperature profile through the whole series of the process. Due to the influence of radiation heat transfer, the heater had spatial temperature deviation in spite of the fact that the heater power was imposed uniformly through its whole body. As a structural feature of the VHGF method, temperature at the lower part of crucible was lower than that at the upper part of crucible because it was cooler at the bottom of the furnace. Thus, the movement of the solid/liquid interface was driven in the bottom-to-top direction. (Received February 4, 2014)

keyword : oxides, crystal growth, solidification, computer simulation, VHGF

Carbonation of a synthesized CaO-Al2O3-MgO-SiO2 ladle refining slag has been kinetically studied using a thermo-gravimetric analyzer (TGA). The effects of extended basicity (CaO/Al2O3), temperature, and the crystal phase ratio were considered. The carbonation ratio and the initial reaction rate increased with basicity. However, for the same basicity of the slag, a decreasing crystal phase ratio seemed to accelerate the carbonation reaction due to the higher reactivity of the O2-ions within the slag. The carbonation ratio and the initial reaction rate were also found to increase with temperature in the range between 973 K and 1073 K, where the temperature effect was clearly observed at the onset of the reaction. Parameters were set to identify the carbonation mechanism and their values were calculated via regression analysis. The activation energy for carbonation was calculated to be 129.9 kJ/mol at C/A=1.0 and 109.0 kJ/mol at C/A=1.2. (Received February 24, 2014)

keyword : carbonation, slag, basicity, thermogravimetric analyzer, kinetics

Intermetallic-based materials are interesting for high temperature structural applications because of their good mechanical properties and enhanced oxidation resistance. In this study microstructural examination of the Nb-Si-B alloys at Nb-rich compositions was performed. The Nb-rich corner of the Nb-Si-B system is very attractive because the constituent phases are Nb (a ductile and tough phase with a high melting temperature) and T2 (a very hard intermetallic compound with favorable oxidation resistance), which make a good combination for high temperature structural materials. At compositions lower than 82 at%Nb the microstructure shows the T2 primary phase and eutectic (T2+Nb), while the Nb primary phase and eutectic were formed at higher compositions. Hardness tests (Rockwell A-scale and micro Vickers) were carried out to estimate the optimal composition for good mechanical properties. (Received January 13, 2014)

keyword : intermetallics, solidification, microstructure, hardness test, T2 phase

Separation of Zr (IV) and Hf (IV) is very important in the production of these metals for nuclear reactor applications. In this study, the effect of the concentration ratio of Zr to Hf on the selective extraction of Hf using PC88A was investigated in the sulfuric concentration range from 0.5 to 4 M. Hf was selectively extracted over Zr from sulfuric acid solution even at the metal concentration ratio of 100. As the concen- tration of sulfuric acid increased, the extraction percentage of Zr decreased while the separation factor increased. The addition of LIX63 to PC88A enhanced the extraction of Zr and the separation factor was decreased compared to single PC88A. Our results showed that it is possible to develop a process to separate Zr and Hf by selective extraction of Hf from sulfuric acid solution by using PC88A. (Received April 8, 2014)

keyword : metals, solvent extraction, separation

The present investigation provides an electromagnetic shielding composition that comprises Ag-coated Ni-Zn ferrite microspheres dispersed in silicon rubber matrix. Shielding effectiveness is analyzed for both the far-field and the near-field on the basis of electromagnetic shielding theory. Ni-Zn ferrite spheres that were 50 μm size on average were prepared by spray drying and sintering at 1130 ℃. Ag layer was plated on the ferrite spheres by electroless plating. Conductive Ni-Zn ferrite spheres with uniform Ag layer were obtained through plating using a high concentration of Ag precursor. The most sensitive material parameters of the rubber composites containing the ferrite spheres with Ag plating are the high values of the real and imaginary parts of the complex permittivity. The space charge polarization between the conductive particles in the rubber matrix results in high values of the dielectric constant and dielectric loss. Due to the high dielectric constant of the composites, a high value of the shielding effectiveness is predicted for the electric field. However, the shielding effectiveness for the magnetic field is not very high due to the small magnetic permeability of the ferrite spheres. (Received January 22, 2014)

keyword : composites, magnetic properties, powder processing, computer simulation, electromagnetic shielding

The changes to thermal expansion and mechanical properties by cold working were investigated in the Fe-29%Ni-17%Co (wt%) low thermal expansion alloy. The Fe-29%Ni-17%Co alloy was cold rolled gradually and prepared for plating with reduction ratios of 0%, 20%, 40%, 60%, and 80%. The effect of annealing on the property was also studied. Thermal expansion was measured from 25 ℃ to 600 ℃ using a vacuum differential dilatometer. We found that the thermal expansion coefficient (α30~400) slightly decreased (at a reduction ratio of 20%) and then remarkably increased (above reduction ratios of 40%) with increasing reduction ratios of cold rolling. The thermal expansion coefficient (α30~400) sharply decreased after heat treatment. Yield and tensile strengths continuously increased and elongation decreased by cold rolling. Microstructural observation and XRD analysis results showed that the α phase significantly increased as the reduction ratio increased. The slight decrease of the thermal expansion coefficient below a reduction ratio of 20% could be explained by the destruction of short-range ordering and decrease in grain size. The significant increase in the thermal expansion coefficient with cold rolling attributed to the appearance of the α phase. The correlation between the microstructural cause and invar effect of the low thermal expansion behavior is also discussed. (Received April 7, 2014)

keyword : alloys, cold working, microstructure, X-ray diffraction, low thermal expansion

In order to clarify the effect of Nb addition on the deformation properties of a sintered TiC matrix solid solution at high temperature, we made a study using a compression test at temperatures from 983 to 2223 K and at the strain rates from 2.1×10-4 to 5.2×10-2/s. Further, X-ray photoelectron spectroscopic (XPS) measurements were carried out. We found that solid solution hardening in the Nb added TiC matrix was smaller than that in a Mo added TiC matrix solid solution, though the size misfit parameter in the Nb added TiC matrix was larger than that in Mo added TiC matrix, which had an extremely high strength, being 15 to 20 times higher than TiC. The work softening phenomenon was for the first time clearly observed in the present investigation. This phenomenon shows the presence of a frictional resistance to dislocation motion. The deformation equation of state at the yield stress can be expressed by εp=A (σy/G)mexp (-Q/RT) where m=9 and Q=112 kJ/mol in the low temperature range at and below 1083 K and where m=10 and Q=343 kJ/mol in the high temperature range at and above 1873 K. The XPS measurement suggests that dislocationsolution atom interaction resulting from a change in electronic structure should be effective for solution hardening. (Received April 10, 2014)

keyword : composites, sintering, mechanical properties, compression test, solid solution