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Quantitative Analysis of Cryomilled Nanocrystalline Ti-6Al-4V Alloy Powder by X-Ray Diffraction

Oh M., Yu H. K., Lee J.-H., Oh M. C., Jung S.-H., Ahn B.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 3

1439--1442

EN

A nanocrystalline Ti alloy powder was fabricated using cryomilling. The grain size and lattice strain evolution during cryomilling were quantitatively analyzed using X-ray diffraction (XRD) based on the Scherrer equation, Williamson-Hall (W-H) plotting method, and size-strain (S-S) method assuming uniform deformation. Other physical parameters including stress and strain have been calculated. The average crystallite size and the lattice strain evaluated from XRD analysis are in good agreement with the result of transmission electron microscopy (TEM).

2

Microstructural Characterization Of Laser Heat Treated AISI 4140 Steel With Improved Fatigue Behavior

Oh M. C., Yeom H., Jeon Y., Ahn B.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1331--1334

EN

The influence of surface heat treatment using laser radiation on the fatigue strength and corresponding microstructural evolution of AISI 4140 alloy steel was investigated in this research. The AISI 4140 alloy steel was radiated by a diode laser to give surface temperatures in the range between 600 and 800°C, and subsequently underwent vibration peening. The fatigue behavior of surface-treated specimens was examined using a giga-cycle ultrasonic fatigue test, and it was compared with that of non-treated and only-peened specimens. Fatigue fractured surfaces and microstructural evolution with respect to the laser treatment temperatures were investigated using an optical microscope. Hardness distribution was measured using Vickers micro-hardness. Higher laser temperature resulted in higher fatigue strength, attributed to the phase transformation.

3

High Temperature Deformation Flow Of A ZK60A Magnesium Alloy After Extrusion

Kawasaki M., Lee H. J., Oh M. C., Ahn B.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1327--1330

EN

Flow behavior of a ZK60A magnesium alloy after continuous casting and subsequent extrusion was examined in tension at a range of strain rates of 3.0×10-6 − 1.0×10-2 s-1 at temperatures of 473-623K. The results demonstrated that the alloy exhibited a maximum elongation of ~250% at 523K when tested at an initial strain rate of 1.0×10-5 s-1 and strain rate sensitivity, m, of ~0.3-0.4 and the activation energy of ~94 kJ/mol were calculated under the testing conditions. The detailed investigation suggested that the high temperature flow of the ZK60A alloy having submicrometer grains demonstrates quasi-superplastic flow behavior controlled by a dislocation viscous glide process.

4

De-Lubrication Behavior Of Novel EBS Based Admixed Lubricant In Aluminum P/M Alloy

Oh M. C., Seok H., Kim H. J., Ahn B.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1427--1431

EN

The objective of the present research is to develop a novel lubricant for Al-Cu-Mg P/M alloy and to address the effects of the lubricant and compaction pressure on sintered properties. A lubricant mixture consisting of Ethylene Bis Stearamide, Zn-Stearate, and fatty acid was newly developed in this study, and the de-lubrication behavior was compared with that of other commercial lubricants, such as Ethylene Bis Stearamide, Zn-Stearate, and Al-Stearate. Density and transverse rupture strength of sintered materials with each lubricant were examined, respectively. The microstructural analysis was conducted using optical microscope.