• Applied Microscopy
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• v.48 no.4
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• pp.117-121
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• 2018

The multiple length scale analysis of previously designed Fe-Mn-Al-C based low-density model alloys reveals the difference in ordered ${\kappa}-carbide$, $(Fe,Mn)_3AlC_x$, between Fe-25Mn-16Al-5.2C (at%) alloy and Fe-3Mn-10Al-1.2C (at%) alloy. For the former alloy composition consisting of fully austenite grains, ${\kappa}-carbide$ showed majorly cuboidal and minorly pancake morphology and its chemical composition was not changed through aging for 24 h and 168 h at $600^{\circ}C$. Meanwhile, for the isothermally annealed ferritic alloy system for 1 hr at 500 and $600^{\circ}C$, the dramatic change in the chemical composition of needle-shape ${\kappa}-carbide$, $(Fe,Mn)_3(Fe,Al)C_x$, was found. Here we address that the compositional fluctuations in the vicinity of the carbides are significantly controlled by abutting phase, either austenite or ferrite. Namely, the cooperative ordering of carbon and Al is an important factor contributing to carbide formation in the high-Mn and high-Al alloyed austenitic steel, while the carbon and Mn for the low-Mn and high Al alloyed ferritic steel.

• Journal of the Korean Magnetics Society
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• v.9 no.6
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• pp.296-300
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• 1999

Cross-shape structures of spin tunneling junctions were fabricated using DC magnetron sputtering and metal masks. The film structures were $substrate/Ta/NiFe/FeMn/NiFe/CoFe/Al_2O_3/CoFe/NiFe$ and $substrate/Ta/NiFe/CoFe/ Al_2O_3/CoFe/NiFe/FeMn/NiFe$. Fabrication conditions of insulating layer ($Al_2O_3$) and thickness and sputtering power of each film layer were varied, and maximum magnetoresistance ratio of 24.3 % was obtained. Magnetic characteristic variations in the above mentioned two structures and two types of substrates (Corning glass 7059 and Si(111)) were compared. Annealing of the junctions was performed to find out magnetic characteristic variations expected from the device fabrication. Magneoresistance Ratio were observed to maintain as-deposited value up to 150 $^{\circ}C$ annealing and then to drop rapidly after 180 $^{\circ}C$ annealing.

• Journal of the Korean Magnetics Society
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• v.8 no.6
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• pp.362-368
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• 1998

The magnetic properties, thermal stability and anti-corrosion properties of $Cr_86Al_14$ spin valves multilayers were studied. It was found that the magnetic properties of $Cr_86Al_14$ spin valves depend on the thickness of antiferromagnetic, ferromagnetic and non-ferromagnetic layers. Exchange coupled field ($H_{ex}$) and magnetoresistance ratio (%) showed the largest value of 20 Oe, 2 % in $glass/Cr_{86}Al_{14}(600 $\AA$)/Ni_{81}Fe_{19}(50$\AA$)/Cu(40 $\AA$)/Ni_{81}Fe_{19}(40 $\AA$)$ spin valves. The $H_{ex}$ MR ratios (%) of CrAl and FeMn spin valves were decreased with increasing annealing temperatures and were lost at 150 $^{\circ}C$, 250 $^{\circ}C$ respectively. Based on these result, it was elucidated that CrAl is more thermally stable than FeMn. It was also shown that there was no change of $H_{ex}$ MR ratios in CrAl, while FeMn was changed and lost 15 days later in corrosion resistance test under 35 $^{\circ}C$, 90 % humidity condition. FeMn was found to be pitted and peeled off 15 days later by SEM micrographic analysis.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.3
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• pp.158-162
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• 2000

The high temperature oxidation behavior and the surface defect in Fe-25Mn-1.5A1-0.5C steel was investigated by XRD (X-ray Diffractin) and electron microscopy. The intra- and inter-granular oxides were formed by the selective oxidation of manganese and aluminum, which were identified to MnAl2O4 phase. Aluminum nitride (AlN) was formed in front of these oxides. The ${\gamma}$-matrix was transformed to ${\alpha}$- and ${\varepsilon}$- phases by the selective oxidation of manganese. The surface defect, micro-scab was induced by the difference of the high temperature ductility between the matrix and the inter-granular oxide.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1703-1707
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• 2018

Ferromagnetic ${\tau}-phase$ $Mn_{54}Al_{46}C_{2.44}$ particles were synthesized, and its composites with commercial $Sm_2Fe_{17}N_3$ and synthesized $Fe_{65}Co_{35}$ powders were fabricated. Smaller grain size than the single domain size of the $Mn_{54}Al_{46}C_{2.44}$ without obvious grain boundaries and secondary phases is the origin for the low intrinsic coercivity. It was confirmed that the magnetic properties of the $Mn_{54}Al_{46}C_{2.44}$ can be enhanced by magnetic exchange coupling with the hard magnetic $Sm_2Fe_{17}N_3$ and soft magnetic $Fe_{65}Co_{35}$. The high degrees of the exchange coupling were verified by calculating first derivative curves. Thermo-magnetic stabilities of the composites from 100 to 400 K were measured and compared. It was demonstrated that the $Mn_{54}Al_{46}C_{2.44}$ based composites containing $Sm_2Fe_{17}N_3$ and $Fe_{65}Co_{35}$ could be promising candidates for future permanent magnetic materials with the proper control of purity, magnetic properties, etc.

• Corrosion Science and Technology
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• v.21 no.1
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• pp.53-61
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• 2022

Alloys of Fe-(5.3-29.8)%Mn-(1.1-1.9)%Al-(0.4-0.5)%C were oxidized at 550 ℃ to 650 ℃ for 20 h to understand effects of alloying elements on oxidation. Their oxidation resistance increased with increasing Mn level to a small extent. Their oxidation kinetics changed from parabolic to linear when Mn content was decreased and temperature was increasing. Oxide scales primarily consisted of Fe₂O₃, Mn₂O₃, and MnFe₂O₄ without any protective Al-bearing oxides. During oxidation, Fe, Mn, and a lesser amount of Al diffused outward, while oxygen diffused inward to form internal oxides. Both oxide scales and internal oxides consisted of Fe, Mn, and a small amount of Al. The oxidation of Mn and carbon transformed γ-matrix to α-matrix in the subscale. The oxidation led to the formation of relatively thick oxide scales due to inherently inferior oxidation resistance of alloys and the formation of voids and cracks due to evaporation of manganese, decarburization, and outward diffusion of cations across oxides.

• Journal of the Korean Magnetics Society
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• v.9 no.6
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• pp.291-295
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• 1999

$NiFe/Co/Al_2O_3/Co/IrMn$ tunneling junctions were grown on (100)Si wafer and their spin-valve tunneling magnetoresistance (TMR) was studied. The tunneling junctions were grown by using a 5-gun RF/DC magnetron sputter. $Al_2O_3$ barrier layer was formed by exposing Al layer to oxygen atmosphere at 6$0^{\circ}C$ for 72 hours. Strong exchange coupling interaction is observed between the ferromagnetic Co and the antiferromagnetic IrMn of Co/IrMn bilayer when IrMn is 100$\AA$ thick. $NiFe(183\;{\AA})/Co(17\;{\AA})/Al_2O_3(16\;{\AA})/Co(100\;{\AA})/IrMn(100\;{\AA})$ tunneling junction shows best TMR ratio of about 10% in the applied magnetic field range of $\pm$20 Oe. The TMR ratio is improved about 23% and electrical resistance is decreased about 34% when annealed at 200 $^{\circ}C$ for 1 hour in magnetic field of 330 Oe, parallel to the bottom electrode. With increasing the active area of junction the TMR ratio increases while electrical resistance decreases.

• Journal of Magnetics
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• v.10 no.3
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• pp.99-102
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• 2005

Modification in exchange bias of a NiFe/FeMn/NiFe trilayer, on introduction of a nonmagnetic Al layer at the top FeMn/NiFe interface, is investigated in multilayers prepared by rf magnetron sputtering. The introduction of Al layer leads to vanishing of bias of the top NiFe layer. But the bias for the bottom NiFe layer increases steadily with increasing Al layer thickness and attains bias (230 Oe) which is greater than that of the trilayer without the Al layer (150 Oe). When the top NiFe layer thickness is varied, exchange bias has highest value at 12 nm thickness for 1 nm thicknes of Al layer. Ion beam etching of the top NiFe layer also leads to an enhancement in bias for the bottom NiFe layer.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.274-282
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• 1998

The effect of Al addition on the fatigue properties of austenitic Fe-25Mn-Al-0.5C steels was studied. When Al was not added to the Fe-25Mn 0.5C steel, the strain induced ${\varepsilon}$ martensites, deformation twins and slip bands were formed during fatigue deformation. When 2wt% of Al was added to the steel, the deformation twins and slip bands were formed during fatigue deformation. When 5wt% of Al was added, only slip bands were formed. In low cycle fatigue test, the alloys containing 0wt% and 2wt%Al showed the cyclic hardening due to ${\varepsilon}$ martensites and deformation twins, resulting in shorter fatigue lives than the alloy containing 5wt%Al. In fatigue crack propagation test, the alloy without Al showed the highest crack propagation rate. The fracture surface of the alloy without Al was flat, whereas that of the alloy with 2% or 5%Al was rough. The ${\Delta}K_{th}$, values of the alloys with 0%, 2% and 5%Al were 16, 17.5, and $20.5MPam^{1/2}$, respectively.

• Korean Journal of Materials Research
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• v.27 no.6
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• pp.318-324
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• 2017

In this study, two Fe-30Mn-0.2C-(1.5Al) high-manganese steels with different surface conditions were hydrogen-charged under high temperature and pressure; then, tensile testing was performed at room temperature in air. The yield strength of the 30Mn-0.2C specimen increased with decreasing surface roughness(achieved via polishing), but that of the 30Mn-0.2C-1.5Al specimen was hardly affected by the surface conditions. On the other hand, the tendency of hydrogen embrittlement of the two high-manganese steels was not sensitive to hydrogen charging or surface conditions from the standpoints of elongation and fracture behavior. Based on the EBSD analysis results, the small decrease in elongation of the charged specimens for the Fe-30Mn-0.2C-(1.5Al) high-manganese steels was attributed to the enhanced dislocation pile-up around grain boundaries, caused by hydrogen.