• Transactions of Materials Processing
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• v.16 no.5 s.95
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• pp.406-411
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• 2007

The microstructure and the hardness of interstitial free steel processed by equal channel angular pressing (ECAP) was investigated experimentally. ECAP processing of route A and route C was compared with regard to grain refinement by transmission electron micrographs. Micro hardness evolution was correlated with the gram structure produced by ECAP. Especially, the effects of the ECAP processing temperature and the number of processing passes were discussed in terms of grain refinement.

• Geomechanics and Engineering
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• v.16 no.2
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• pp.177-185
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• 2018

The subsidence mechanism of ground surface is a complex phenomenon when multiple seam coal mining operations are carried out. Particularly, the coal mining beneath karstic formations causes a very special form of subsidence. The subsidence causes elasto-plastic deformation of the karstic layers and the collapse of cavities leads to dolinization and/or sinkhole formation. In this study, a sinkhole with a depth of 90 m and a width of 25 m formed in Gelik district within the coal-basin of Zonguldak (NW, Turkey) induced by multiple seam coal mining operations in the past has been presented as a case-history together with two-dimensional numerical simulations and InSAR monitoring. The computational results proved that the sinkhole was formed as a result of severe yielding in the close vicinity of the faults in contact with karstic formation due to multiple seam longwall mining at different levels.

• Journal of Powder Materials
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• v.13 no.6 s.59
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• pp.427-431
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• 2006

Mg-4.3Zn-0.7Y (at%) alloy powders were prepared using an industrial scale gas atomizer, followed by warm extrusion. The powders were almost spherical in shape. The microstructure of atomized powders and those extruded bars was examined using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscope (EDS) and X-ray Diffractometer (XRD). The grain size of the powders was coarsen as the initial powder size increased. After the extrusion, the grain size became fine due to the severe plastic deformation during the extrusion with the ratio of 10:1. Both the ultimate strength and elongation were enhanced with the decrease of initial particle size.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.58-59
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• 2012

Surface hardening mechanism of H13 steel was investigated when ion niriding after shot peening process was applied. Severe plastic deformation induced nanocrystallized grains at surface region. Higher nitrogen concentration was achieved in ion nitrided specimen with shot peening treatment than in single nitrided specimen. The elemental mapping on chromium and nitrogen by TEM-EELs showed chromium dissolved in matrix enhanced bulk nitrogen diffusion at surface region. Higher nitrogen diffusion also caused lattice distortion. Nano-sized grains, higher nitrogen concentration, and lattice diffustion contributed to the surface hardening.

• Journal of Powder Materials
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• v.11 no.3
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• pp.233-241
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• 2004

In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve both full density and grain refinement of Al-20 wt% Si powders without grain growth, which was considered as a bottle neck of the bottom-up method using the conventional powder metallurgy of compaction and sintering. ECAP (Equal channel angular pressing), one of the most promising method in SPD, was used for the powder consolidation. The powder ECAP processing with 1, 2, 4 and 8 passes was conducted for 10$0^{\circ}C$ and 20$0^{\circ}C$ It was found by microhardness, compression tests and micro-structure characterization that high mechanical strength could be achieved effectively as a result of the well bonded powder contact surface during ECAP process. The SPD processing of powders is a viable method to achieve both fully density and nanostructured materials.

• Journal of Mechanical Science and Technology
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• v.19 no.7
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• pp.1441-1448
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• 2005

Fine grained AZ31 and AZ61 magnesium alloys produced by equal channel angular pressing (ECAP) were tested for investigating tensile and fatigue properties, including microstructure, monotonic tensile flow, fatigue life and crack growth rate. For the two alloys, the yield stress of the ECAPed sample was lower than that of the unECAPed (=as received) sample, because of the fact that the softening effect due to texture anisotropy overwhelmed the strengthening effect due to grain refinement. Grain refinement of the AZ31 and AZ61 alloys through ECAP was found not to be significantly effective in increasing fatigue strength.

• Korean Journal of Metals and Materials
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• v.50 no.10
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• pp.785-792
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• 2012

A new flip chip structure consisting of interlocking joints locally surrounded by non-conductive adhesive was investigated in order to improve the contact resistance characteristics and prevent the parasitic capacitance increase. The average contact resistance of the interlocking joints was substantially reduced from $135m{\Omega}$ to $79m{\Omega}$ by increasing the flip chip bonding pressure from 85 MPa to 185 MPa. Improvement of the contact resistance characteristics at higher bonding pressure was attributed not only to the increased contact area between Cu chip bumps and Sn pads, but also to the severe plastic deformation of Sn pads caused during formation of the interlocking-joint structure. The parasitic capacitance increase due to the non-conductive adhesive locally surrounding the flip chip joints was estimated to be as small as 12.5%.

• Advances in materials Research
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• v.7 no.2
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• pp.105-118
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• 2018

Magnesium and its alloys are attracted towards all engineering applications like automotive, marine, aerospace etc. due to its inherent high strength to weight ratio. But, extensive use of Mg alloys is limited to the current scenario because of low wear and corrosion resistance behavior. However, equal channel angular press is one of the severe plastic deformation technique which has been effective method to improve the wear and corrosion resistance by achieving fine grain structure. In this study, the effect of grain refinement on wear and corrosion resistance of AZ80 Mg alloys were investigated. The wear behavior of the coarse and fine-grained Mg alloys was examined through $L_9$ orthogonal array experiments in order to comprehend the wear behavior under varies control parameters. It was shown that ECAPed alloy increased the wear and corrosion resistance of the Mg alloy through the formation of fine grain and uniform distribution of secondary ${\beta}-phase$. Also, the performance of AZ80 Mg alloy for these changeswas discussed through SEM morphology.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.4
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• pp.89-95
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• 2005

Thrust cut off(TCO) system is installed at the port of a rocket motor case forward dome. The snap ring and the closure are escaped sequentially by pulling out a wedge under internal pressure. The hydraulic structural tests of TCO and numerical simulations were performed, and both results were compared to understand the deformation behavior of TCO. By increasing splines symmetrically, the sealing capacity of TCO can be improved significantly. The escape pressure of TCO increases according to the increase of friction coefficient and there is a critical friction coefficient beyond which the snap ring can not be nearly escaped even after forced escape of wedge. Under low friction coefficient the snap ring is contracted to radial direction and easily escaped. But, under high friction coefficient, the snap ring can not be escaped from the port even after severe plastic deformation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.952-962
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• 2015

In this study, multilayered rings with a large outer diameter have been developed using a hot ring rolling process. The ring rolling process has been analyzed by rigid plastic finite element analyses (FEA) using the AFDEX2D and AFDEX3D/HEXA/RING simulators, where the finite element meshes received severe plastic deformation are remeshed into a fine mesh-size using a dual-mesh system. According to the simulated results, the design variables of the multilayered rings were determined and real tests were conducted to check the validity of the simulation results. By adopting the hot ring rolling process, the input weight of raw materials was reduced by 40% against the conventional hot forging process and that the recovery rate was increased by 24%. The measurement of the averaged roundness was satisfied within 0.5 mm for both the inner and outer diameters. Moreover, the hot ring rolling processes yielded 1.49 Cpk for the outer-diameter and 0.84 Cpk 0.84 for the inner-diameter.