• Journal of the Korean Society for Heat Treatment
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• v.13 no.4
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• pp.265-271
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• 2000

The microstructural change and transformation characteristics with cooling rate i.e. wheel speed were investigated in 82.8wt%Cu-12.8wt%Al-4.3wt%Ni SMA ribbons fabricated by melt-spinning. The thickness and width of ribbon were decreased with increasing wheel speed, while the uniformity of it was improved. At same wheel speed, the grain size of the contact surface of ribbon was smaller than that of free surface. The mean grain size was decreased with increasing wheel speed, resulted in obtaining grains with $3{\mu}m$ in mean diameter in the wheel speed of 30 m/s. However, micro-voids and cracks at grain boundary could be observed at higher wheel speed. $M_s$ and $A_s$ temperatures were decreased, and $M_s{\sim}M_f$ and $A_s{\sim}A_f$ temperature ranges were broadened with increasing wheel speed. All the ribbons were retained the ordered $D0_3$ due to rapid cooling, the volume fraction of it was increased with increasing wheel speed.

• Journal of Integrative Natural Science
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• v.2 no.4
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• pp.233-236
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• 2009

This study was undertaken to measure the electrochemical corrosion of amorphous $Zr_{65}Al_8Ni_{15}Cu_{12}$ (at.%) alloy ribbon under various conditions, including 0.4 mM HCl solution, and for various values of the pH and the immersion time. The corrosion potentials($E_{corr}$) for the amorphous $Zr_{65}Al_8Ni_{15}Cu_{12}$ alloy in 0.4 mM HCl decreased with increasing temperature; the corrosion current density($I_{corr}$) increased with increasing temperature in general. The polarization resistance($R_p$) was inversely proportional to the corrosion rate. While pH=7, 9, 11 was not as sensitive as pH=3, 5, pH=3 was more sensitive for amorphous $Zr_{65}Al_8Ni_{15}Cu_{12}$ alloy than other pHs specially. The change of mass in the 70 mM $H_2SO_4$ solution with immersion time was the greatest in the first 100 h.

• Korean Journal of Materials Research
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• v.1 no.3
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• pp.145-150
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• 1991

Crystallization and embrittlement of $Fe_{78}B_{13}Si_{9}$ amorphous alloy was investigated by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. The crystallization comprizes two exothermic processes. In the first crystallization stage, $\alpha$-(Fe, Si) dendrites are formed from the amorphous state, and in the second crystallization, $Fe_2B$ compounds are formed. An abrupt decrease of the fracture strain of the ribbon started from amorphous started annealed at about $340^{\circ}C$

• Proceedings of the KIEE Conference
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• 1990.07a
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• pp.236-238
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• 1990

For improving magnetic properties of the amorphous Fe-B-Si alloy, we annealed in a magnetic field oriented in the plane of the ribbon longitudinal to its long axis. By field annealing, coercive force and total core loss are reduced from 0.04 Oe to 0.02 Oe, and from 0.25 watt/kg to 0.15 watt/kg respectively comparing with non-field annealed specimen. These reductions were caused by the formation of $180^{\circ}$ domains parallel to the annealing field due to the induced anisotorpy.

• Journal of Magnetics
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• v.2 no.4
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• pp.130-134
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• 1997

The amorphous Co-based alloy Co66Fe4Ni1B15Si14 (Metglas 2714A) is a suitable magnetic core material for high frequency operation. Appreciable reduction of the coercive force can be achieved by proper heat treatment. In this study, samples annealed at wide temperature range were analyzed using differential scanning calorimetry, high frequency B-H loop tester, X-ray diffractometer and resistivity meter. The results show that coercive force at 10 kHz decreases with in-creasing annealing temperature up to 773 K, but dramatically increases above this temperature. The squareness shows that the magnetic anisotropy on longitudinal direction of the as-cast state remains up to 773 K. Above this temperature, it decreases down to 0.5 that represents random distribution of magnetic domains. The crystallization abruptly occurs between 781 K and 783 K.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.2
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• pp.111-117
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• 1994

Effect of rapidly solidfid 6.5wt%Si-Fe alloy annealed in the sulfur atmosphere were studied. The ribbons Which were showed with random structure at the received state, were developed into(110) texture in the heat treatment of the vacuum atmosphere, into (100)texture in the sulfur atmosphere. After the ribbon was continuously annealed in the vacuum atmosphere for 3 min. at $1100^{\circ}C$, and sulfur atmosphere for 1hr at $1175^{\circ}C$, grain size of (100)plane was grew to 4-8mm and the coercive force was decreased to 2-4A/m remarkably.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.1
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• pp.35-40
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• 2008

Ni-based amorphous alloy ribbon was prepared by a single-roller melt-spinning technique. Palladium coating was found to enhance significantly the absorption/desorption behavior of hydrogen in amorphous alloy. The hydrogen permeability of a Pd-coated $(Ni_{60}Nb_{40}){_{100-X}}$TaX(x=5, 10) amorphous alloy was examined in the temperature range of $623{\sim}773K$, comparable with those of $Pd_{60}-Cu_{40}$ alloys. The permeated hydrogen flux was increased with increasing the temperature and the difference of hydrogen pressure between the feed side and permeates side of the membrane. The Ni-based amorphous alloys were characterized by X-ray diffractometry(XRD) and differential scanning calorimetry(DSC). The morphology of surface and roughness was observed by using scanning electron microscopy(SEM) and atomic force microscopy(AFM).

• Journal of Korea Foundry Society
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• v.28 no.1
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• pp.31-36
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• 2008

Ti-Ni-Cu alloys are very attractive shape memory alloys for applications as actuators because of a large transformation elongation and a small transformation hysteresis. Rapidly solidified Ti-Ni alloy ribbons have been known to have the shape memory effect and superelasticity superior to the alloy ingots fabricated by conventional casting. In this study, solidification structures and shape memory characteristics of $Ti-Ni_{30}-Cu_{20}$ alloy ribbons prepared by melt spinning were investigated by means of DSC and XRD. Operating parameters to fabricate the amorphous ribbons were the wheel velocity of 55 m/s and the melt spinning temperature of $1500^{\circ}C$. The crystallization temperature was measured to be $440^{\circ}C$. The crystallized ribbons exhibited very fine microstructure after annealing at $440^{\circ}C$ for 10 minutes and $460^{\circ}C$ for 5 minutes and was deformed up to about 6.8% and 6.23% in ductile manner, respectively. Stress-strain curve of the ribbon exhibited a flat stress-plateau at 64 MPa and this is associated with the stress-induced a B2-B19 martensitic transformation. During cycle deformation with the applied stress of 220 MPa, transformation hysteresis and elongation associated with the B2-B19 transformation were observed to be $4.3^{\circ}C$ and 3.6%.

• Journal of Magnetics
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• v.1 no.1
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• pp.24-30
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• 1996

The relationship between effective permeability and the remanence ratio of an Fe-based amorphous alloy (Metglas 2605S3A) is investigated over a wide frequency range, in an effort to understand magnetization behavior of the alloy. In the frequency range from 1 to 200 kHz, the permeability is maximum at the remanence ratio of 0.4-0.5 and, at frequencies over 500 kHz, the correlation with negative coefficients emerges indicating that the permeability decreases with the remanent ratio, except for the ribbon coated with an insulating layer of MgO which exhibits both high values of the effective permeability and remanence ratio. It is considered from the correlation results that the boundary at which the dominant magnetization mechanism changes from domain wall motion to spin rotation is near 500 kHz. The core loss is also investigated as a function of annealing time when the samples are annealed at a fixed temperature of $435^{\circ}C$. The core loss in most cases decreases with the annealing time, the degree of the loss may consist of the hysteresis loss and anomalous eddy current loss. The two loss components are considered to be of similar magnitudes at low frequencies while, at high frequencies, the dominant contribution to the total loss is the anomalous loss.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.655-659
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• 1998

The effect of quenching speed of melt-spinning on intrinsic coercivity ($_iH_c$$) of annealed ribbons and the crystallization behavior from amorphous $Nd_{14.73}Fe_{78.67}B_{6.60}$ alloy have been studied. We have found that the intrinsic coecivity for annealed melt-spun ribbon is reduced with increasing of quenching rate. $\alpha$-Fe and $Fe_3B$ were formed as intermediate phases prior to the formation of $Nd_2Fe_{14}B$ phase during crystallization. The $Fe_3B$ is disappeared with crystallization of $Nd_2Fe_{14}B$ phase. But the $\alpha$-Fe phase is retained in fully crystallized ribbon by annealing. The intrinsic coercivity loss of annealed ribbon with increasing of quenching speed is believed to be due to existence of soft magnetic phase $\alpha$-Fe in annealed ribbons.