• Archives of Metallurgy and Materials
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• v.64 no.3
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• pp.863-867
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• 2019

The effects of carbon content on the austenite stability and strain-induced transformation of nanocrystalline Fe-11% Ni alloys were investigated using X-ray analysis and mechanical tests. The nanocrystalline FeNiC alloy samples were rapidly fabricated using spark plasma sintering because of the extremely short densification time, which not only helped attain the theoretical density value but also prevented grain growth. The increased austenite stability resulted from nanosized crystallites in the sintered alloys. Increasing compressive deformation increased the volume fraction of strain-induced martensite from austenite decomposition. The kinetics of the strain-induced martensite formation were evaluated using an empirical equation considering the austenite stability factor. As the carbon content increased, the austenite stability was enhanced, contributing to not only a higher volume fraction of austenite after sintering, but also to the suppression of its strain-induced martensite transformation.

• Archives of Metallurgy and Materials
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• v.66 no.4
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• pp.971-975
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• 2021

This study investigates the effects of grain boundary structures on mechanical properties of nanocrystalline Al-0.7Mg-1.0Cu alloy using nanoindentation system. Grain boundary structure transforms to high angle grain boundaries from low angle ones with increase of heat treatment temperature and the transformation temperature is about 400℃. Young's modulus and hardness are higher in sample with low angle grain boundaries, while creep length is larger in sample with high angle ones. These results indicate that progress of plastic deformation at room temperature is more difficult in sample with low angle ones. During compression test at 200℃, strain softening occurs in all samples. However, yield strength in sample with low angle grain boundaries is higher twice than that with high angle ones due to higher activation energy for grain boundary sliding.

• Journal of Powder Materials
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• v.12 no.6 s.53
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• pp.433-440
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• 2005

The hydrogen sorption speed of $Zr_{57}V_{36}Fe_7$ nanocrystalline and amorphous alloys was evaluated at room temperature. Nanocrystalline alloys of $Zr_{57}V_{36}Fe_7$ were prepared by planetary ball milling. The hydrogen sorption speed of nanocrystalline alloys was higher than that of the amorphous alloy. The enhanced sorption speed of nanocrystalline alloys was explained in terms of surface oxygen stability which has been known to retard the activation of amorphous alloys. The retardation can be reduced by formation of nanocrystals, which results in the observed increase in sorption properties.

• Journal of Powder Materials
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• v.6 no.4
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• pp.277-285
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• 1999

Mechanical properties of nanocrystalline Al-5at.%Ti alloy were investigated through high temperature compression test. Al-5at.%Ti nanocrystalline metal powders, which had finer and more equiaxed shape than those produced at room temperature, were produced by mechanical alloying at low temperature. The powders were successfully consolidated to 99fo of theoretical density by vacuum hot pressing. XRD and TEM analysis revealed that $Al_3Ti$ intermetallic compounds formed inside powders and pure Al region with coarse grains formed between powders, especially at triple junction. Mechanical properties in terms of hardness and strength were improved by grain size refinement, but ductility decreased presumably due to the formation of the weak interfaces between Al pool and powders.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.483-486
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• 1995

Soft magnetic properties of Fe-based (Fe,Co)-B-Al-M (M=Nb, Mo or Ta) nanocrystalline alloy have been investigated. The alloy obtained directly form the rapid solidification process. Microstructure of the alloy is a mixtu re of ultrafine bcc Fe(Co) nanocrystallines and a small amount of retained amorphous phase. Heat treatment of as-prepared alloys improves soft magnetic properties in high frequency range. ${(Fe_{.85}Co_{.15})}_{70}B_{18}Al_{10}Ta_{6}$ alloy alloy annealed at $500^{\circ}C$ for 1 h shows the most improved soth magnetic properties among the alloy examined. Average grain size of the nanocystalline is about 10 nm.

• Journal of Powder Materials
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• v.28 no.3
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• pp.246-252
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• 2021

The effect of sintering conditions on the austenite stability and strain-induced martensitic transformation of nanocrystalline FeCrC alloy is investigated. Nanocrystalline FeCrC alloys are successfully fabricated by spark plasma sintering with an extremely short densification time to obtain the theoretical density value and prevent grain growth. The nanocrystallite size in the sintered alloys contributes to increased austenite stability. The phase fraction of the FeCrC sintered alloy before and after deformation according to the sintering holding time is measured using X-ray diffraction and electron backscatter diffraction analysis. During compressive deformation, the volume fraction of strain-induced martensite resulting from austenite decomposition is increased. The transformation kinetics of the strain-induced martensite is evaluated using an empirical equation considering the austenite stability factor. The hardness of the S0W and S10W samples increase to 62.4-67.5 and 58.9-63.4 HRC before and after deformation. The hardness results confirmed that the mechanical properties are improved owing to the effects of grain refinement and strain-induced martensitic transformation in the nanocrystalline FeCrC alloy.

• Korean Journal of Materials Research
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• v.14 no.3
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• pp.181-185
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• 2004

The mechanical properties of a bulk amorphous alloy ($Zr_{41.2}$ $Ti_{13.8}$ /$Cu_{10}$ $Ni_{10}$ $Be_{22.5}$ /at.%) before and after an annealing treatment were investigated. For the bulk amorphous alloy, the compressive strength was about 2.0 GPa, irrespective of the strain rates in the range of $10^{-4}$ to $10^3$$ sec^{-1}$ . Fine-sized nanocrystalline particles (10～100 nm) were precipitated homogeneously in the bulk amorphous matrix after the annealing treatments. Compared to the bulk amorphous materials, these composite materials, composed of the nanocrystalline phases and a bulk amorphous matrix had much different mechanical properties. The strength and strain of coposite materials measured by a compressive test showed a peak-maximum values at 7 vol.% of the nanocrystalline phases. The values in higher volume fraction of the crystalline phases in the amorphous matrix were decreased, as measured by both quasi-static and high strain rate. The decrease in fracture strength is due to presence of the dispersed large-crystalline phases in the amorphous matrix.

• Journal of Magnetics
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• v.19 no.4
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• pp.327-332
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• 2014

The effect of minor element additions (Ca, Al) on microstructural change and magnetic properties of Fe-Nb-Cu-Si-B alloy has been investigated, in this paper. The Fe-Si-B-Nb-Cu(-Ca-Al) alloys were prepared by arc melting in argon gas atmosphere. The alloy ribbons were fabricated by melt-spinning, and heat-treated under a nitrogen atmosphere at $520-570^{\circ}C$ for 1 h. The soft magnetic properties of the ribbon core were analyzed using the AC B-H meter. A differential scanning calorimetry (DSC) was used to examine the crystallization behavior of the amorphous alloy ribbon. The microstructure was observed by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). The addition of Ca increased the electrical resistivity to reduce the eddy current loss. And the addition of Al decreased the intrinsic magnetocrystalline anisotropy $K_1$ resulting in the increased permeability. The reduction in the size of the ${\alpha}$-Fe precipitates was observed in the alloys containing of Ca and Al. Based on the results, it can be concluded that the additions of Ca and Al notably improved the soft magnetic properties such as permeability, coercivity and core loss in the Fe-Nb-Cu-Si-B base nanocrystalline alloys.

• Journal of Surface Science and Engineering
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• v.49 no.1
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• pp.1-13
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• 2016

This review deals with one of the surface modification techniques, chemical conversion coating and particularly cerium-based conversion coatings (CeCC) as a promising substitute for chromium and phosphate conversion coating on magnesium and its alloys. The CeCCs are commonly considered environmentally friendly. The effects of surface preparation, coating thickness, bath composition, and e-paint on the corrosion behavior of CeCCs have been studied on the AZ31 magnesium alloy. This review also correlates the coating microstructural, morphological, and chemical characteristics with the processing parameters and corrosion protection. Results showed that the as-deposited coating system consists of a three layer structure (1) a nanocrystalline MgO transition layer in contact with the Mg substrate, (2) a nanocrystalline CeCC layer, and (3) an outer amorphous CeCC layer. The nanocrystalline CeCC layer thickness is a function of immersion time and cerium salt used. The overall corrosion protection was crucially dependent on the presence of coating defects. The corrosion resistance of AZ31 magnesium alloy was better for thinner CeCCs, which can be explained by the presence of fewer and smaller cracks. On the other hand, maximum corrosion protection was achieved when AZ31 magnesium samples with thin CeCCs are e-painted. The e-paint layer further restricts and hinders the movement of chloride and other aggressive ions present in the environment from reaching the magnesium surface.

• Journal of Surface Science and Engineering
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• v.36 no.6
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• pp.455-460
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• 2003

Microstructural and magnetic properties of nanocrystalline Fe-46 wt%Ni and Fe-36 wt%Ni alloys were investigated. Alloys were prepared by the electrodeposition process. The electrolytes were iron sulfate/nickel chloride-based and iron chloride/nickel sulfamate-based solutions. Fe-46 wt%Ni alloy was FCC structure with grain size of 10 nm, but FCC and BCC phases were found in Fe-36 wt%Ni alloy and its grain size was smaller. Effective permeability of Fe-36 wt%Ni alloy was higher than that of Fe-46 wt%Ni alloy in the high frequency range because of large electrical resistivity and small eddy current loss resulted from grain size decrease. Up to $300^{\circ}C$ of annealing temperature, grain growth of Fe-Ni alloys slowly occured. Conversely, annealing above $450^{\circ}C$ led to a drastic grain growth. In that case, effective permeability was decreased at the temperature lower than $300^{\circ}C$ but at $300^{\circ}C$ or higher effective permeability was increased. At the high frequency of 1 MHz, electrodeposited Fe-Ni alloys had higher effective permeability with an decrease in the grain size.