• Journal of the Korean Society for Heat Treatment
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• v.16 no.4
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• pp.211-215
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• 2003

In this work, a new way of measuring the volume fraction of e martensite in Fe-based alloys has been proposed. Since the specific volume of ${\varepsilon}$ martensite, depending on alloy composition, is smaller than that of austenite i.e ${\gamma}$ phase, volume expansion takes place during ${\varepsilon}{\rightarrow}{\gamma}$ reverse transformation. As the amount of the volume expansion is proportional to the product of specific volume difference times the volume fraction of ${\varepsilon}$ martensite, the volume fraction of ${\varepsilon}$ martensite can be calculated by measuring the volume expansion and the specific volume difference. Such a relationship was confirmed in Fe-21Mn and Fe-32Mn-6Si alloys which undergo ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation on cooling and by cold rolling, respectively. It was also found that the former has isotropic ${\varepsilon}$ martensite while the latter has anisotropic ${\varepsilon}$ martensite.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.3-6
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• 2003

This paper describes the interface stability of Ta-Mo alloy metal on $SiO_2$ Alloy was formed by co-sputtering method, and the alloy composition was varied by controlling Ta and Mo sputtering power. When the atomic composition of Ta was about 91%, the measured work function was 4.2eV that is suitable for NMOS gate. To identify interface stability between Ta-Mo alloy metal and $SiO_2$, C-V, FE-SEM(Field Emission-SEM), and XRD(X-ray diffraction) were performed on the samples annealed with rapid thermal processor between $600^{\circ}C$ and $900^{\circ}C$. Even after $900^{\circ}C$ rapid thermal annealing, excellent interface stability and electrical properties were observed. Also, thermodynamic analysis was studied to compare with experimental results.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.233-238
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• 2010

Hot-dipped Al-Mg-Si coatings to alternate Zn and Zn alloy coatings for steel were examined on metallographic structure, corrosion resistance, sacrificial ability, formation and growth of inter-metallic compounds, and mechanical properties. Near the eutectic composition of quasi-binary system of Al-$Mg_2Si$, very fine eutectic structure of ${\alpha}$-Al and $Mg_2Si$ was obtained and it showed excellent corrosion resistivity and sacrificial ability for a steel in sodium chloride solutions. Formation and growth of Al-Fe inter-metallic compounds at the interface of substrate steel and coated layer was suppressed by addition of Si. The inter-metallic compounds layer was usually brittle, however, the coating layer did not peel off as long as the thickness of the inter-metallic compounds layer was small enough. During sacrificial protection of a steel, amount of hydrogen into the steel was more than ten times smaller than that of Zn coated steel, suggesting to prevent hydrogen embrittlement. Al-Mg-Si coating is expected to apply for several kinds of high strength steels.

• Transactions of Materials Processing
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• v.24 no.1
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• pp.44-51
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• 2015

The current study seeks to examine the effects of V and C additions on the mechanical and low thermal expansion properties of a high strength invar base alloy. The base alloy (Fe-36%Ni-0.9%Co-2.75%Mo-0.7Cr-0.23Mn-0.17Si-0.3%C, wt.%) contains $Mo_2C$ carbides, which form as the main precipitate. In contrast, alloys with additions of 0.4%V+0.3%C (alloy A) or 0.4%V+0.45%C (alloy B) contain $Mo_2C$+[V, Mo]C carbides. The average thermal expansion coefficients of these high strength invar based alloys were measured in the range of $5.16{\sim}5.43{\mu}m/m{\cdot}^{\circ}C$ for temperatures of $15{\sim}230^{\circ}C$. Moreover, alloy B showed lower thermal expansion coefficient than the other alloys in this temperature range. For the mechanical properties, the [V, Mo]C improved hardness and strengths(Y.S. and T.S.) of the high strength invar base alloy. T.S.(tensile strength) and Y.S.(yield strength) of hot forged alloy B specimen were measured at 844.6MPa and 518.0MPa, respectively. The tensile fractography of alloy B exhibited a ductile transgranular fracture mode and voids were initiated between the [V, Mo]C particles and the matrix. Superior properties of high strength and low thermal expansion coefficient can be obtained by [V, Mo]C precipitation in alloy B with the addition of 0.4%V and 0.45%C.

• Journal of Korea Foundry Society
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• v.3 no.3
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• pp.174-180
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• 1983

The matrix changes and graphite formation in high manganese cast iron (Fe-12Mn-3.5C) are studied with increasing nickel and silicon content. Also, the decomposition of carbides and graphite precipitation are studied by adequate heat treatment.The results obtained in this work are as follows. 1. In high manganese cast iron, fine flakes graphite appeared by adding 5 wt% nickel and A-type flakes graphite can be obtained by adding 7 wt% nickel. 2. Nodular graphite are obtained by graphite spheroidizing treatment with same melt. 3. In high manganese cast iron containing 7 wt% nickel, full austenitic matrix with nodular graphite can be achieved by water quenching after 10 hours' solution heat treatment at $1050^{\circ}C$ in case of containing 2.0 wt% silicon, and 6 hours' at the same temperature in case of containing 2.5 wt% silicon.

• Applied Microscopy
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• v.47 no.1
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• pp.50-54
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• 2017

The microstructure, the crystallization behavior, and magnetic properties of FeSi-based soft magnetic alloys (FINEMET) were investigated using transmission electron microscopy, X-ray diffraction, and coercive force measurements. The amorphous $Fe_{73.28}Si_{13.43}B_{8.72}Cu_{0.94}Nb_{3.63}$ alloys particles, prepared in $10^{-4}$ torr by gas atomization process, were heat treated at $530^{\circ}C$, $600^{\circ}C$, and $670^{\circ}C$ for 1 hour in a vacuum of $10^{-2}$ torr. Nanocrystalline Fe precipitation was first formed followed by the grain growth. Phase formation and crystallite sizes was compared linked to its magnetic behavior, which showed that excellent soft magnetic property can directly be correlated with its microstructure.

• Korean Journal of Materials Research
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• v.9 no.9
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• pp.926-931
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• 1999

The microstructure, wettability, shear strength and aging effect of Sn-3.5Ag/Cu and Alloy42 lead-frame solder joints were measured for comparison. In the case of Sn-3.5Ag/Cu, $Ag_3Sn and Cu_6Sn_5$ phases in the matrix Sn and $1~2\mu\textrm{m}$ thick $Cu_6Sn_5$ phase at the interface of solder/lead-frame were formed. In the case of Sn-3.5Agl Alloy42, only AgJSn phase of low density in the matrix Sn and $0.5~1.5\mu\textrm{m}$ thick $FeSn_2$, phase at the interface of solder/leadframe were formed. Comparing to Cu, Alloy42 showed wider area of spread and smaller contact angle, thus better wet­tability. But shear strength and ductility of Alloy 42 solder joints were only 33% and 75% of those of Cu, respectively After aging at $180^{\circ}C$ for 1 week, $\xi-Cu_3Sn$ layer on $\eta-Cu_6Sn_5$ layer was formed on Cu lead-frame, while coarsened cir­cular $Ag_3Sn$ phase in the matrix and thickened $FeSn_2$, at the interface were formed on Alloy42 lead- frame.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.864-873
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• 1995

Amorphous $Fe_{73.5}Cu_{1}Nb_{3}Si_{16.5}B_{6}$ ribbons were annealed for different time at $500^{\circ}C$ and $552^{\circ}C$, just before and after the exothermic reaction in DSC curve. The development of nanocrystalline phase was investigated by means of $M\"{o}ssbsuer$ spectroscopy. The crystalline phase consists mainly of $DO_{3}Fe-Si$. Though slight in amount (5%), another ferromagnetic phase which could be presumed $t-Fe_{3}B$ was detected Si content of $DO_{3}Fe-Si$, Si/(Fe+Si), was 0.218 under the heat treatment at $500^{\circ}C$ for 60 min and 0.222 at $552^{\circ}C$ for 10 min. Since then both of those values decreased with time until 120 min and finally these two values remained constant at 0.210. The variation in Si content with annealing time results in the variation in the hyperfine field and the isomer shift. The increase in the mean hyperfine fields and the decrease in the mean isomer shifts of Fe-Si are caused by the increase in Si content. The volume fractions of residual amorphous phase rapidly decrease during the early stage of annealing and come nearer to saturation after 120 min both at $500^{\circ}C$ and $552^{\circ}C$. The decrease in the mean hyperfine field of residual amorphous. in spite of slight changes in the volume fractions of Fe-Si and of residual amorphous after 120 min. is caused by the increase in the content of Nb and B in residual amorphous phase. The saturated volume fraction of the crystalline phase was 81% for $500^{\circ}C$ (180 min) and 77% for $552^{\circ}C$ (960 min), different from expectation.

• Transactions of Materials Processing
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• v.8 no.5
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• pp.482-490
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• 1999

7000 series Al alloy with good mechanical properties has been focused with tendency to reduce the components weight of aircraft and automobile. However, it is difficult to manufacture a sound extruded product because of segregation, grain growth, casting defect, surface defect, decreasing extrudability and so on. The objective of this study is to manufacture a new 7000 al alloy more than the extrudability of A7N01 and A7003 through controlling the weight (%) Mg, Zn, Si. Hot extrusion experiments on the axisymmetric rod are performed in 500℃ and also performed analysis of the same process using unmerical analysis method, a coupled rigid-thermoviscoplastic finite element method. Extrusion limit diagram was obtained for the developed alloy by FE-simulation in order to define the relationship of extrusion speed and initial billet temperature.

• Journal of the Korean Magnetics Society
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• v.14 no.5
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• pp.186-191
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• 2004

The variation of magnetic properties with insulating materials(glass frits, talc and polyamide) in compressed powder cores composed of Fe$\sub$73.5/Cu$_1$Nb$_3$Si$\sub$15.5/B$\sub$7/ nanocrystalline alloy powders(size: 250～850 $\mu\textrm{m}$) and 3 wt% insulators has been investigated. Larger permeability was obtained at the frequency lower than 300～400 kHz for the powder cores including ceramic insulators(glass frits and talc) as compared to the cores with polyamide, while at higher frequency than 1 MHz the permeability of the former cores decreased rapidly. Further the cores with ceramic insulators showed larger core loss and smaller peak quality factor attained at lower frequency. On the contrary, the powder cores with polyamide exhibited high stability of permeabilities up to several MHz and superior core-loss and quality-factor properties. Moreover the dc bias property was better in the wide field range for the cores having polyamide. The enhanced magnetic properties of polyamide-added cores were attributed to the more sufficient electrical insulation between magnetic particles, where the higher insulation state was considered to be obtained from the larger volume fraction of polyamide in the powder cores.