• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.24-29
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• 2002

It was observed that exchange bias field was increased with smooth surface and better ${\gamma}$-FeMn formation. Sputtering conditions were varied for the control of the surface roughness and ${\gamma}$-FeMn formation. From the results of Cu deposition as underlayer, it was found that ${\gamma}$-FeMn formation was closely related with the thickness of underlayer. After heat treatment, exchange bias field was increased over three times. This improvement was likely that the crystallites of ${\gamma}$-FeMn were well formed. In Co/Cu/Co/FeMn spin valve structure, magnetoresistance was increased over 1.4 times through the heat treatment. This was due to the disappearance of Co/Cu intermixed dead layer and removal of defect, and this was examined by AES analysis.

• Investigative Magnetic Resonance Imaging
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• v.19 no.2
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• pp.76-87
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• 2015

Purpose: There is an ongoing search for a stent material that produces a reduced susceptibility artifact. This study evaluated the effect of manganese (Mn) content on the MRI susceptibility artifact of ferrous-manganese (Fe-Mn) alloys, and investigated the correlation between MRI findings and measurements of Fe-Mn microstructure on X-ray diffraction (XRD). Materials and Methods: Fe-Mn binary alloys were prepared with Mn contents varying from 10% to 35% by weight (i.e., 10%, 15%, 20%, 25%, 30%, and 35%; designated as Fe-10Mn, Fe-15Mn, Fe-20Mn, Fe-25Mn, Fe-30Mn, and Fe-35Mn, respectively), and their microstructure was evaluated using XRD. Three-dimensional spoiled gradient echo sequences of cylindrical specimens were obtained in parallel and perpendicular to the static magnetic field (B0). In addition, T1-weighted spin echo, T2-weighted fast spin echo, and $T2^*$weighted gradient echo images were obtained. The size of the low-intensity area on MRI was measured for each of the Fe-Mn binary alloys prepared. Results: Three phases of ${\alpha}^{\prime}$-martensite, ${\gamma}$-austenite, and ${\varepsilon}$-martensite were seen on XRD, and their composition changed from ${\alpha}^{\prime}$-martensite to ${\gamma}$-austenite and/or ${\varepsilon}$-martensite, with increasing Mn content. The Fe-10Mn and Fe-15Mn specimens comprised ${\alpha}^{\prime}$-martensite, the Fe-20Mn and Fe-25Mn specimens comprised ${\gamma}+{\varepsilon}$ phases, and the Fe-30Mn and Fe-35Mn specimens exhibited a single ${\gamma}$ phase. The size of the low-intensity areas of Fe-Mn on MRI decreased relative to its microstructure on XRD with increasing Mn content. Conclusion: Based on these findings, proper conditioning of the Mn content in Fe-Mn alloys will improve its visibility on MR angiography, and a Mn content of more than 25% is recommended to reduce the magnetic susceptibility artifacts on MRI. A reduced artifact of Fe-Mn alloys on MRI is closely related to the paramagnetic constitution of ${\gamma}$-austenite and/or ${\varepsilon}$-martensite.

• Journal of the Korean Magnetics Society
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• v.4 no.4
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• pp.347-354
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• 1994

The structural change and magnetic properties of mechanically milled Fe-N and Mn-Al alloy powders have been investigated by XRD, TEM, VSM, $M\"{o}ssbauer$ spectroscopy and inelastic neutron scattering measurements. During milling of ${\gamma}'-Fe_{4}N$ powders, and fcc ${\gamma}'-Fe_{4}N$ phase is transformed to a bct ${\alpha}'-Fe(N)$ phase by stress-induced martensitic transformation, being accompanied by an initial increase in saturation magnetization. During annealing the bct ${\alpha}'-Fe(N)$ nanocrystalline phase which is obtained by mechanical grinding for a long time, an ${\alpha}'-Fe_{16}N_{2}$ phase partially appears as an intermediate phase at 673~773 K, causing an increase in saturation magnetization. During milling of Mn-45, 70 and 85 at.% Al mixed powders, Al atoms are partially solubilized into an ${\alpha}-Mn$ phase. The Al supersaturated ${\alpha}-Mn-type$ phases change from paramagnetic to ferromagnetic : the saturation magnetization is 11 emu/g for the as-milled Mn-70 at.% Al powders. Moreover, by removing almost all Al atoms from the as-milled Mn-85 at.% Al powders using chemical leaching, the saturation magnetization increases up to 36 emu/g. The above bct ${\alpha}'-Fe(N)$ and ferromagnetic ${\alpha}-Mn$ type alloys are the magnetic materials found for the first time, by using the present mechanochemical process.

• Korean Journal of Materials Research
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• v.9 no.9
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• pp.937-942
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• 1999

Fe계 합금의 적층결함에너지를 감소시키는 것으로 알려진 Mn이 Fe-20Cr-1C-Si 경면처리 합금의 변형유기 상변태거동과 상온 및 고온 마모저항성에 미치는 영향에 대하여 조사하였다. 15ksi의 접촉응력에 대하여 0~25wt.% Mn을 첨가한 시편은 모두 상온에서 마모손실량이 적은 우수한 마모저항성을 보였는데 Mn 첨가량이 5wt.% 이하인 시편의 경우 마모표면에서 ${\gamma}$$\longrightarrow$$\alpha$\`변형유기 상변태가 발생한 반면 15wt.% 이상 Mn을 첨가한 시편에서는 ${\gamma}$$\longrightarrow$$\varepsilon$변형유기 상변태가 발생하는 것으로 나타났다. 25$0^{\circ}C$까지 고온 마모시험결과 ${\gamma}$$\longrightarrow$$\alpha$\`변형유기 상변태가 발생한 5wt.% 이하 Mn 첨가시편은 Mn 첨가량이 증가할수록 마모손실량이 증가하는 것으로 보아 Mn 첨가는 ${\gamma}$$\longrightarrow$$\alpha$\`변형유기 상변태에 있어서 고온 마모저항성을 저하시키는 것으로 생각되며 이는 Mn이 ${\gamma}$$\longrightarrow$$\alpha$\`변형유기 상변태의 M(sub)d 온도를 감소시키기 때문으로 생각된다. 반면에 ${\gamma}$$\longrightarrow$$\varepsilon$변형유기 상변태가 일어난 15wt.% 이상 Mn 첨가 시편의 경우 Mn 첨가량 증가에 따른 고온 마모손실량의 차이가 없는 것으로 보아 ${\gamma}$$\longrightarrow$$\varepsilon$변형유기 상변태는 ${\gamma}$$\longrightarrow$$\alpha$\`변형유기 상변태에 비해 온도의 존성이 적은 것으로 생각된다.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.4
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• pp.243-251
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• 1996

Dilatometric experiment and thermodynamic calculation have been performed to determine $M_s$, $A_s$ and driving forces for ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation of Fe-Mn alloys. The transformation temperatures($M_s$, $A_s$, $T_o) were decreased with increasing manganese content and were newly formulated as a function of manganese content. Driving force for ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation was increased from -75J/mole to -105J/mole with increasing manganese content from 15wt.% to 25wt.%. Transformation temperature hysteresis($A_s-M_s$) was also increased from 50K to 80K with increasing mangenese content from 15wt.% to 25wt.%. The small driving force(-75J/mole~-105J/mole) and small ${\Delta}T$(50K~80K) for ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation indicated that Fe-Mn alloys behave like thermoelastic martensitic alloys : We would like to call them semi-thermoelastic martensitic alloys.

• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.235-240
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• 1994

The electric and magnetic properties of Mg1.9-2xMn0.05Fe4xO4+${\gamma}$+2wt% Al2O3, and its microstructure have been investigated as a function of ferrite composition (x=0.45, 0.5, 0.55). The microstructure turned out to be independent on the ferrite composition. The resistivity was decreased with increasing Fe contents, whereas the Curie temperature decreased. Saturation magnetization was varied from 1741 to 2022 G with composition, and squareness ratio (SR), coercive force (BHc) were decreased and increased with increasing Fe contents respectively, so the sample which SR and BHc were 0.97 Oe and 1.49 Oe can be attainable at x=0.45.

• 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.

• Korean Journal of Metals and Materials
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• v.47 no.12
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• pp.787-796
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• 2009

The fracture toughness improvement of Ni-Mn-Ga-Fe ferromagnetic shape memory alloys containing ductile particles was explained by direct observation of microfracture processes using an in situ loading stage installed inside a scanning electron microscope (SEM) chamber. The Ni-Mn-Ga-Fe alloys contained a considerable amount of ductile particles in the grains after the homogenization treatment at $800{\sim}1100^{\circ}C$. ${\gamma}$ particles were coarsened and distributed homogeneously along {$\beta}$ grain boundaries as well as inside {$\beta}$ grains as the homogenization temperature increased. The in situ microfracture observation results indicated that ${\gamma}$ particles effectively acted as blocking sites of crack propagation, and provided stable crack growth that could be confirmed by the R-curve analysis. This increase in fracture resistance with increasing crack length improved overall fracture properties of the alloys containing ${\gamma}$ particles.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.12-18
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• 1996

Austenite(${\gamma}$) grain size, ${\varepsilon}$ martensite volume fraction and damping capacity of Fe-17%Mn alloy have been investigated as a function of solution treatment temperature of $600^{\circ}C$ to $1100^{\circ}C$. With increasing the solution temperature, ${\gamma}$ grain size, ${\varepsilon}$ martensite content and damping capacity are increased, while the hardness is decreased. When ${\gamma}$ grains are small, ${\varepsilon}$ plates grow in only one direction in each ${\gamma}$ grain. However, if the ${\gamma}$ grains are large in accordance with high solution treating temperature, several ${\varepsilon}$ variants with different orientations are formed and intersected each other in each ${\gamma}$ grain. In spite of small ${\varepsilon}$ martensite content, the damping capacity of the specimen which was annealed at $700^{\circ}C$, followed by subzero treatment at $-196^{\circ}C$, is almost equal to that of the specimen annealed at $1000^{\circ}C$ and subsequently quenched to room temperature. From this result it is suggested that the damping capacity of Fe-17%Mn alloy having fine ${\gamma}$ grains is mainly attributed to the movement of ${\gamma}/{\varepsilon}$ interface without the operation of other damping sources such as ${\varepsilon}/{\varepsilon}$ boundaries and stacking faults in ${\varepsilon}$ reported previously.

• Journal of KSNVE
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• v.9 no.4
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• pp.720-729
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• 1999

Coventional methods for reducing vibration in engineering designs (i.e. by stifferning or detuning) may be undesirable in conditions where size or weight must be minimized, or where complex vibration spectra exist. Some alloys with a combination of high damping capacity and good mechanical properties can provide attractive techanical and economical solutions to problems involving seismic, shock and vibration isolation. Although several non ferrous damping alloys have been developed, none of those materials are applied in any industrial factor due largely to high production cost. To meet these requirement, we have developed a new Fe-Mn high damping alloy. In previous studies, we have reported that an Fe-17%Mn alloy exhibits the highest damping capacity(Specific Damping Capacity:SDC, 30%) among Fe-Mn binary system, and proposed that the boundaries of various types such as $\varepsilon$-martensite variant boundaries, stacking faults in $\varepsilon$-martensite, stacking faults in austenitic and ${\gamma}$$\gamma /\varepsilon$ interfaces give rise to a high damping capacity. The Fe-17%Mn alloy also has advantages of good mechanical properties(T.S. 70 kg/nm$^2$ and low cost over other damping alloys(1/4 times the cost of non-ferrous damping alloy). Thus, the Fe-17%Mn high damping alloy can be widely applied to household appliances, automobiles, industrial facilities and power plant components. In this paper, the overall properties of the Fe-17%Mn high damping alloy is introduced, and its applicability to containment spray pump in the power plant is discussed.