• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 1997.04a
• /
• pp.34-34
• /
• 1997

The effect of alloying mode and porosity on the axial tension-tension fatigue behavior of a P/M steel of nominal composition Fe-4w/o Ni-1.5w/o Cu-O.5w/o Mo-O.5w/o C has been evaluated. Alloying modes utilized were elemental powder mixing, partial alloying(distaloy) and prealloying by water atomization; in each case the carbon was introduced as graphite prior to sintering. Powder compacts were sintered($1120{\circ}C$/30 min.) in 7Sv/o $H_2$/25v/o $N_2$ to densities in the range 6.77-7.2 g/$cm^3$. The dependence of fatigue limit response on alloying mode and porosity was interpreted in terms of the constituent phases and the pore and fracture morphologies associated with the three alloying modes. For the same nominal composition, the three alloying modes resulted in different sintered microstructures. In the elemental mix alloy and the distaloy, the major constituent was coarse and fine pearlite, with regions of Ni-rich ferrite, Ni-rich martensite and Ni-rich areas. In contrast, the prealloy consisted primarily of martensite by with some Ni-rich areas. From an examination of the fracture surfaces following fatigue testing it was concluded that essentially all of the fracture surfaces exhibited dimpled rupture, characteristic of tensile overload. Thus, the extent of growth of any fatigue cracks prior to overload was small. The stress amplitude for the three alloying modes at 2x$l0^6$ was used for the comparison of fatigue strengths. For load cycles <3x$l0^5$, the prealloy exhibited optimum fatigue response followed by the distaloy and elemental mix alloy, respectively. At load cycles >2x$l0^6$, similar fatigue limits were exhibited by the three alloys. It was concluded that fatigue cracks propagate primarily through pores, rather than through the constituent phases of the microstructure. A decrease in pore SIze improved the S-N behavior of the sintered steel.

• International Journal of Precision Engineering and Manufacturing
• /
• v.5 no.1
• /
• pp.19-26
• /
• 2004

The growth of solid particles in TiC-XC-2vo1.% and TiC-XC-30vo1.% Ni alloys, (where X=Zr, W or Mo) was fitted to the equation of the form $d^3$-${do}^3$=Kt during the liquid phase sintering at 1,673K. Also, the grain growth behavior decreased markedly with the addition of ${MO}_2$C or WC and increased with the addition of zrC. The contiguity was greater in the alloys with a smaller growth rate constant and especially, decreased by increasing the Ni content in the TiC-${MO}_2$C-Ni alloy. In addition, the effect of the addition of carbide on the grain growth of 2 vo1.% Ni alloys was found to be similar to that of 30vo1.% Ni alloys. Consequently, the grain growth mechanism cannot be explained by the usual solution / reprecipitation process, but can be explained in terms of a new growth velocity equation, which includes the effects of contiguous carbide grain boundaries in restricting the overall grain growth, as well as the area of the solid / liquid interface in the alloy.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.6
• /
• pp.1353-1356
• /
• 2009

This study examined the adsorption of CO on a Mo(110) surface by Thermal Desorption Spectroscopy (TDS) and synchrotron-radiation based photoemission spectroscopy (SRPES). CO desorption was observed at approximately 400 K ($\alpha$-CO) and > 900 K ($\beta$-CO). When CO was exposed to Mo(110) at 100 K, it showed a tilted structure at low CO coverage and a vertical structure after saturation of the tilted CO. After heating the CO-precovered sample to 900 K, a broad peak at 12 eV below the Fermi level was identified in the valence level spectra, which was assigned to either the 4$\sigma$-molecular orbital of CO, or 2s of dissociated carbon. TDS results of the $\beta$-CO showed a first order desorption. These results are in a good agreement with the observations of CO adsorption on W(110) surfaces.

• Bulletin of the Korean Chemical Society
• /
• v.2 no.2
• /
• pp.37-41
• /
• 1981

The elution behaviors of molybdate and tungstate through anion exchange column have been investigated in the various concentration of hydrochloric and perchloric acid. A discussion is made to evaluate the existing these equilibrium and constant according to acidity. In both acids of 0.01-2.0 M concentration range, the existing equilibrium for molybdate and its constant calculated at $20^{\circ}C$ is $10^{18.9}$ for $Mo_8O_2^{4-} + 20H^+ {\rightleftharpoons} 8MoO_2^{2+} + 10H_2O$. In the 3-3.5 M hydrochloric acid it is 0.16 for $MoO_2Cl_2 + Cl^- {\rightleftharpoons} MoO_2Cl^{3-}$ and for the case of tungstate, in the both acids of 0.01-1.0 M concentration range $10^{6.6}$ for $W_{12}O_{39}^{6-} + 6H^+ {\rightleftharpoons} 12WO_3{\cdot}3H_2O$. In higher concentration than 1.0 M both acids the following equilibrium seems to be existed. $12WO_3{\cdot}3H_2O {\rightleftharpoons} 12WO_3 + 3H_2O$

• Journal of Magnetics
• /
• v.7 no.3
• /
• pp.106-114
• /
• 2002

To reduce the grain size and the media noise in a typical CrMo/CoCrPtB longitudinal media, a sputtering process which includes the exposure of oxygen onto the surface of CrW$_x$ (x=0, 25, 50, 75, 100 at.%) and CrTi$_{15}$ seedlayers with the thickness of 0.5 nm have been utilized. The main results are: (1) the media grain size and the media noise are reduced when using CrW$_x$ (x=0, 25, 50 at.%) seedlayers, and not reduced when using CrTils or CrW$_x$ (x=75, 100 at.%) seedlayers, (2) AES and RHEED results suggest that W seedlayer, which has the highest melting point, forms layer-like film with very small and dense island grain, due to its high free surface energy and low mobility. On the other hand, CrW$_{50}$ and Cr seedlayers, which have lower melting point than W seedlayer, form island film, (3) to effectively reduce the media grain size and improve the media signal to noise ratio, it is essential to utilize a very thin Cr-based seedlayer with high affinity for oxygen and which forms island-like structure, such as CrW$_{50}$ seedlayer.

• Journal of Fisheries and Marine Sciences Education
• /
• v.24 no.2
• /
• pp.234-245
• /
• 2012

This study aims to analyze the factors of the extra-curricula area in personal school performance record and propose the practical strategies for entrance examination affairs on this area. To address this goal, we have applied a SWOT analysis with related documents and research results. We found out five strengths: (S1) Link the students' experience to right people for the university, (S2) Quantitative Indicators, (S3) Qualitative Indicators, (S4) Link to other evaluation factors, and (S5) Analysis of Human Resource. The weakness included: (W1) Fairness, (W2) Reliability, (W3) Difficulties to set standards, (W4) Difficulties to set environments, and (W5) Lack of systemic experience of an evaluation. We also discovered five opportunities (O1) Recognition of public education, (O2) The need of national support, (O3) The importance of autonomy, (O4) Specialization, and (O5) Networks. Finally, threat factors consisted of: (T1) Frequent change of educational policy, (T2) Increasing of private education, (T3) Lack of information and preparation time, and (T4) The accuracy and reliability of personal school records. Based on these results, we suggested practical strategies with these four dimensions: S-O, W-O, S-T, and W-T.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2007.05a
• /
• pp.193.1-193.1
• /
• 2007

• 한국초전도학회:학술대회논문집
• /
• v.13
• /
• pp.13-13
• /
• 2003

• Proceedings of the Petrological Society of Korea Conference
• /
• 2009.05a
• /
• pp.56-56
• /
• 2009

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.545.2-545.2
• /
• 2006