• Journal of the Korean Society for Heat Treatment
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• v.25 no.3
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• pp.126-133
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• 2012

Semi-solid forming of the high melting point alloys such as steel is a promising near-net shape forming process for decreasing manufacturing costs and increasing the quality of the final products. This paper presents the microstructure characteristics of SKH51 (high speed tool steel) during heating and holding in the mushy zone between $1233^{\circ}C$ and $1453^{\circ}C$, which has been measured by differential scanning calorimetry (DSC). The results of heating/holding experiments showed that the grain size and the liquid fraction increased gradually with temperature up to $1350^{\circ}C$. The drastic grain growth occurred at heating above $1380^{\circ}C$. The strain-induced melt-activated (SIMA) process has been applied to obtain globular grains in the billet materials. Working by mechanical upsetting and successive heating of SKH51 into the temperatures in the mushy zone resulted in globular grains due to recrystallization and partial melting.

• Electrical & Electronic Materials
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• v.7 no.4
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• pp.331-340
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• 1994

Polysilicon on insulator has been recrystallized by zone melting recrystallization method with graphite strip heaters. Experiments are performed with non-seed SOI structures. When the capping layer thickness of Si$\_$3/N$\_$4//SiO$\_$2/ is 2.0.mu.m, grain boundaries are about 120.mu.m spacing and protrusions reduced. After the seed SOI films are annealed at 1100.deg. C in NH$\_$3/ ambient for 3 hours, the recrystallized silicon surface has convex shape. After ZMR process, the tensile stress is 2.49*10$\^$9/dyn/cm$\^$2/ and 3.74*10$\^$9/dyn/cm$\^$2/ in the seed edge and seed center regions. The phenomenon of convex shape and tensile stress difference are completely eliminated by using the PSG/SiO$\_$2/ capping layer. The characterization of SOI films are showed that the SOI films are improved in wetting properties. N channel SOI MOSFET has been fabricated to investigate the electrical characteristics of the recrystallized SOI films. In the 0.7.mu.m thickness SOI MOSFET, kink effects due to the floating substrate occur and the electron mobility was calculated from the measured g$\_$m/ characteristics, which is about 589cm$\^$2//V.s. The recrystallized SOI films are shown to be a good single crystal silicon.

• Korean Journal of Materials Research
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• v.21 no.12
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• pp.673-678
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• 2011

With an increased production of Printed Circuit Boards (PCBs) in electronic equipment, the consumption of solder alloys is growing globally. Recently, increasing importance of recycling solder scrap has been recognized. Generally, solder scrap contains many impurities such as plastics and other metals. Hazardous components must be eliminated for recycling solder scrap. The present work studied pretreatment for reuse of solder scrap alloys. An experiment was conducted to enhance the cleanliness of solder scrap melt and eliminate impurities, especially lead. Physical separation with sieving and magnetic force was made along with pyrometallurgical methods. A small decrease in lead concentration was found by high temperature treatment of solder scrap melt. The impurities were removed by filtration of the solder scrap melt, which resulted in improvement of the melt cleanliness. A very low concentration of lead was achieved by a zone melting treatment with repeated passage. This study reports on a pretreatment process for the reuse of solder scrap that is lead free.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.290-294
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• 1997

In this study, the welded residual stresses test was carried out with pure titanium and TIG welded material using in chemical plants an airplane frames etc.. The relationship between process parameters and residual stresses is complex since a number of factors are involved. Extensive studies have been carried out to determine the effects of various process parameters on residual stress. The result of micro-hardness about butt welded spacemen was measured of low hardness value in the melting metal zone. The residual stress of welded zone on the Titanium plate by the sectioning method and finite element method was high measured in the spacemen of high current and voltage. Also, compressive residual stress in the range of distance about 15∼20mm from the middle of the deposited metal area is very change. The result of impact test about butt welded spacemen of pure titanium plate was measured of very difference in the welded bead, heat affect zone and base metal, and be measured of high impact value in the heat affect zone. The measure result of welded residual stresses about pure titanium is high measured hen nominal steel plate. The V-Type butt welded spacemen, that of the measurement result on the welded residual stress is high measure then X-Type butt welded spacemen.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.2
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• pp.68-72
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• 2004

Sm-doped YBCO high $T_c$ superconductor was directionally grown by zone melt growth process in air atmosphere. Cylindrical green rods of $(Sm/Y)_{1.8}Ba_{2.4}Cu_{3.4}O_{7-x}$[(Sm/Y)1.8] oxides were fabricated by cold isostatic pressing (CIP) method using rubber mold. Based on the variation of melting temperature and growth rate, the microstructure and superconducting properties were systematically measured by using optical micrographs, TEM and SQUID magnetometer. In this study optimum melting temperature and growth rate were $1085^{\circ}C$ and 3.5 mm/hr respectively. Nonsuperconducting $(Sm/Y)_2BaCuO_5$ inclusions of (Sm/Y)1.8 superconductor were uniformly distributed within the superconducting (Sm/Y) $Ba_2Cu_3O^{7-x}$ matrix. The directionally melt-textured (Sm/Y)1.8 superconductor showed an onset $T_c$ $\geq$ 90K and sharp superconducting transition.

• Journal of the Korean institute of surface engineering
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• v.38 no.6
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• pp.227-233
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• 2005

Electrochemical characteristics of welded stainless steels containing Ti have been studied by using the electrochemical techniques in 0.5 M $H_2SO_4$+0.01 M KSCN solutions at $25^{\circ}C$. Stainless steels with 12 mm thick-ness containing $0.2{\~}0.9 wt\%$ Ti were fabricated with vacuum melting and following rolling process. The stainless steels were solutionized for 1hr at $1050^{\circ}C$ and welded by MIG method. Samples were individually prepared with welded zone, heat affected zone, and matrix for intergranular corrosion and pitting test. Optical microscope, XRD and SEM are used for analysing microstructure, surface and corrosion morphology of the stainless steels. The welded zone of the stainless steel with lower Ti content have shown dendrite structure mixed with $\gamma$ and $\delta$ phase. The Cr-carbides were precipitated at twin and grain boundary in heat affected zone of the steel and also the matrix had the typical solutionized structure. The result of electrochemical measurements showed that the corrosion potential of welded stainless steel were Increased with higher Ti content. On the other hand, reactivation($I_r$), passivation and active current($I_a$) density were decreased with higher Ti content. In the case of lower Ti content, the corrosion attack of welded stainless steel was remarkably occurred along intergranular boundary and ${\gamma}/{\delta}$ phase boundary in heat affected zone.

• Journal of the Semiconductor & Display Technology
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• v.11 no.4
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• pp.7-12
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• 2012

Extrusion is one of the most important operations in the polymer-processing industry. Development of models for extrusion and computer tools offer a route to developing reliable and optimized process designs. The models are based on the analysis of physical phenomena encountered during the process. Balance equations for mass, momentum and energy are fundamental to the problem. A predictive computer model has been developed for the single screw extruders with conventional screws of different geometry. The model takes into account melting zones of the extruder and describes an operation of the extruder system, making it possible to predict mass flow rate of the polymer, pressure and velocity profiles along the extruder screw channel. The simulation parameters are the material and rheological properties of the polymer; the screw pitch, and screw speed.

• Journal of Welding and Joining
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• v.34 no.5
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• pp.26-32
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• 2016

In this study, Hot-wire laser welding (HWLW) without keyhole which deposits filler material by feeding hot wire into the process zone has been performed to increase process performance. From the analysis of High Speed Imaging (HSI), for higher voltage, the process is prone to arc formation and drop transfer, which is disagreeable transfer mode. It is necessary that arc formation and drop (globular) transfer should be avoided by lower voltage. Therefore, continuous wire melting and transfer mode is preferred when adopting this process. The HWLW technique has high potential in terms of performance, precision, robustness and controllability for thick section of narrow gap.

• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.4
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• pp.159-166
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• 2003

Microstructures and mechanical properties of VIM/VAR/VAR-processed Ni-based Alloy718 ingot were investigated. Vacuum arc remelting(VAR) results in chill grain zone, columnar grain zone, and equi-axed grain zone in the ingot due to the difference in local solidification processes. Different grain structures of the remelting ingot result in the different hot workability for the given cogging conditions. Experimental results on microstructural inhomogeniety and material flow behavior under billet cogging conditions were presented, and their potential effects on the billet cogging process are discussed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.6
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• pp.128-133
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• 2011

In this study, the steel material for shipbuilding(LR-A class) was used, and FCAW was taken advantage of 3G attitude and they are welded by different welding ways. As a result of analyzing wave with welding monitoring system, the stable values are obtained which are the first floor(electronic current 164~182 A, voltage 24 V), the second floor(electronic current 174~190 A, voltage 22~25 V), the third floor(electronic current 158~188 A, voltage 22~25 V), and fourth floor(electronic current 172~184 A, voltage 22~25 V), at this time, the stable wave standard deviation and changing coefficient could be obtained. When the welding testing through nondestructive inspection was analyzed know defect of welding, there was no defect of welding in A, D, E, but some porosities in B, and slag conclusion near the surface in C, because the length of arc was not accurate, and the electronic current and voltage was not stable. After observing the change of heat affect zone through micro testing, each organization of floor formed as Grain Refinement, so welding part was fine, the distance of heat affect zone is getting wider up to change the values of the electronic current and voltage. As a result of degree of hardness testing, the hardness orders were the heat affect zone(HAZ), Welding Zone(WZ), and Base Metal(BM). When the distribution of degree of hardness is observed. B is the highest degree of hardness The reason why heat effect zone is higher than welding zone and base metal, welding zone is boiled over melting point($1539^{\circ}C$) and it starts to melt after the result of analysis through metal microscope, so we can know that delicate tissue is created at the welding zone. Therefore, in order to get the optimal conditions of the welding, the proper current of the welding and voltage is needed. Furthermore the precise work of welding is required.