• Journal of Korea Foundry Society
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• v.33 no.3
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• pp.113-121
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• 2013

The effects of Zn and Mg amounts on the solidification characteristics, microstructure, thermal conductivity and tensile strength of Al-Zn-Mg-Fe alloys were investigated for the development of high thermal conductivity aluminium alloys for die casting. Zn and Mg amounts in Al-Zn-Mg-Fe alloys had a little effect on the liquidus / solidus temperature, the latent heat for solidification and the fluidity of Al-Zn-Mg-Fe alloys. Thermo-physical modelling of Al-Zn-Mg-Fe alloys by JMatPro program showed $MgZn_2$, AlCuMgZn and Al3Fe phases on microstructure of their alloys. Increase of Zn and Mg amounts in Al-Zn-Mg-Fe alloys resulted in gradual reduction of the thermal conductivity of their alloys. Increase of Mg amounts in Al-2%Zn-Mg-Fe alloys had little effect on the tensile strength of their alloys, but increase of Mg amounts in Al-4%Zn-Mg-Fe alloys resulted in steep increase of the tensile strength of their alloys.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.48.2-48.2
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• 2010

The effect of additives as rare-earth in dielectric materials has been studied to meet the development trend in electronics on the miniaturization with increasing the capacitance of MLCCs (multi-layered ceramic capacitors). It was reported that the addition of rare-earth oxides in dielectrics would contribute to enhance dielectric properties and high temperature stability. Especially, dysprosium and thulium are well known to the representative elements functioned as selective substitution in barium titanate with perovskite structure. The effects of these additives on microstructure and electric properties were studied. The 0.8 mol% Dy doped $BaTiO_3$ and the 1.0 mol% Tm doped $BaTiO_3$ had the highest electric properties as optimized composition, respectively. According to the increase of rare-earth contents, the growth of abnormal grains was suppressed and pyrochlore phase was formed in more than solubility limits. Furthermore, the effect of two rare-earth elements co-doped $BaTiO_3$ on the dielectric properties and insulation resistance was investigated with different concentration. The dielectric specimens with $BaTiO_3-Dy_2O_3-Tm2O_3$ system were prepared by design of experiment for improving the electric properties and sintered at $1320^{\circ}C$ for 2h in a reducing atmosphere. The dielectric properties were evaluated from -55 to $125^{\circ}C$ (at $1KHz{\pm}10%$ and $1.0{\pm}0.2V$) and the insulation resistance was examined at 16V for 2 min. The morphology and crystallinity of the specimens were determined by microstructural and phase analysis.

• Korean Journal of Materials Research
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• v.27 no.10
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• pp.524-529
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• 2017

The effect of strain aging on the tensile properties of API X70 linepipe steel was investigated in this study. The API X70 linepipe steel was fabricated by controlled rolling and accelerated cooling processes, and the microstructure was analyzed using optical and scanning electron microscopes and electron backscatter diffraction. Strain aging tests consisting of 1 % pre-strain and thermal aging at $200^{\circ}C$ and $250^{\circ}C$ were conducted to simulate U-forming, O-forming, Expansion(UOE) pipe forming and anti-corrosion coating processes. The API X70 linepipe steel was composed of polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite whose volume fraction was dependent on the chemical composition and process conditions. As the thermal aging temperature increased, the steel specimens showed more clearly discontinuous type yielding behavior in the tensile stress-strain curve due to the formation of a Cottrell atmosphere. After pre-strain and thermal aging, the yield and tensile strengths increased and the yield-to-tensile strength ratio decreased because yielding and aging behaviors significantly affected work hardening. On the other hand, uniform and total elongations decreased after pre-strain and thermal aging since dislocation gliding was restricted by increased dislocation density after a 1 % pre-strain.

• Journal of Welding and Joining
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• v.31 no.3
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• pp.66-75
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• 2013

In this study, the effect of coating thickness($20{\mu}m$ and $30{\mu}m$) on microstructure and tensile properties in Yb:YAG disk laser welds of Al-Si-coated boron steel (1.2mmt) was investigated. In the case of as welds, the quantity of ferrite was found to be higher in base metal than that in HAZ (Heat Affected Zone) and fusion zone, indicating, fracture occurrs in base metal, and the fracture position is unrelated to the coating thickness. Furthermore, yield strength, tensile strength of base metal and welded specimens showed similar behavior whereas elongation was decreased. On the other hand, base metal and HAZ showed existence of martensite after heat treatment, the fusion zone indicated the presence of full ferrite or austenite and ferrite during heat treatment ($900^{\circ}C$, 5min), After water cooling, austenite was transformed to martensite, and the quantity of ferrite in fusion zone was higher as compared with in base metal, resulting in sharply decrease of yield strength, tensile strength and elongation, which leads to fracture occured at fusion zone. In particular, results showed that because the concentration of Al was higher in 30um coating layer specimen than that of 20um coating specimen, after heat treatment, producing a higher quantity of ferrite was higher after heat treatment in the fusion zone; howevers, it leads to a lower tensile property.

• Journal of the Korean Vacuum Society
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• v.13 no.4
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• pp.150-156
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• 2004

Boron nitride thin films were deposited on Si(100) substrate by RF (Radio-frequency) UBM (Unbalanced Magnetron) sputtering system. The effect of working pressure and substrate bias voltage on microstructure and compressive stress of boron nitride thin films has been investigated. In high working pressure, the alignment of hBN laminates increased with substrate bias voltage, in low working pressure, however, it was high in low substrate bias voltage. Compressive stress evolution and surface morphology of deposited BN films are closely related with the alignment of hBN laminates. The cBN phase without high compressive stress could be nucleated on hBN thin film by controlling the alignment of hBN laminates.

• Korean Journal of Materials Research
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• v.16 no.4
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• pp.235-240
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• 2006

We investigated the effect of ZnO filler on the microstructure of $BaO-B_2O_3-ZnO-P_2O_5$ glass system to find an etching mechanism of barrier ribs. The sintering behavior of composites heated in the temperature range $560-600^{\circ}C$ was studied by volumetric shrinkage rate and microstructure. The etching test was carried out in $HNO_3$ solution at $50^{\circ}C$ for 10 min. The volumetric shrinkage of sintered sample decreased with the increased firing temperature because of the formation of two crystals. Glass and ZnO filler react forming the $BaZn_2(PO_4)_2$ crystal phases during the sintering process. Etching phenomenon of sintered samples by $HNO_3$ showed that the $BaZn_2(PO_4)_2$ crystal phase was strongly leached compared to glass matrix, crystal phases and fillers. Therefore, the control of interface by condition of sintering is so important to achieve etching effect in barrier ribs.

• Korean Journal of Materials Research
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• v.5 no.8
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• pp.1005-1112
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• 1995

The Effects of 0~9% stretching on the microstructure and mechanical properties have been investigated in Al-Li-Cu-Mg alloys. Stretching made T$_1$(Al$_2$CuLi) precipitates finer and more uniform, however, had no effect on the size of $\delta$'. The number of sheared $\delta$'precipitates distributed in the matrix were reduced. The 6% stretching improved the yield strength of the alloys aged at 15$0^{\circ}C$ for 120 hours from 328~342 MPa to 466~488MPa, however, decreased the elongation from 9.7~10.4% to 5.7%.

• Journal of Powder Materials
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• v.23 no.4
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• pp.303-306
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• 2016

An optimum route to synthesize Ti-Mo system powders is investigated by analyzing the effect of the heat treatment atmosphere on the formation of the reaction phase by dehydrogenation and hydrogen reduction of ball-milled $TiH_2-MoO_3$ powder mixtures. Homogeneous powder mixtures with refined particles are prepared by ball milling for 24 h. XRD analysis of the heat-treated powder in a hydrogen atmosphere shows $TiH_2$ and $MoO_3$ peaks in the initial powders as well as the peaks corresponding to the reaction phase species, such as $TiH_{0.7}$, TiO, $MoO_2$, Mo. In contrast, powder mixtures heated in an argon atmosphere are composed of Ti, TiO, Mo and $MoO_3$ phases. The formation of reaction phases dependent on the atmosphere is explained by the partial pressure of $H_2$ and the reaction temperature, based on thermodynamic considerations for the dehydrogenation reaction of $TiH_2$ and the reduction behavior of $MoO_3$.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.20 no.1
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• pp.23-29
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• 1984

Nowdays, the high strength aluminum alloys are broadly used for structural purpose, but the practical strengthening method by aging treatment are not much available. So that, in this study, in order to investigate the effect of aging treatment for strengthening on the fracture characteristics of the domestic high strength Al alloy (A2024BE), the variations of the aging temperature and time were taken after solution treatment. By microstructural examination, and by SEM fractographs of the fractures, the effects of aging temperature and time were investigated, considering on the fracture behaviour. The results obtained are as follows: 1) It was confirmed by microstructural investigation that the aging temperature of $190^{\circ}C$ and the aging time of 12hours were optimal to get more sound microstructure with distribution of uniform precipitation. 2) By step aging treatment, the proper aging time for obtaining the similar microstructure without any microstructural defects could be shortened in half the normal aging time. 3)By examining the SEM fractographs of the fracture surface, it was found that, regardless of the aging treatment time and temperature, all were intergranular ductile fractures, but the aging treatment at $190^{\circ}C$ for 12 hours resulted in dimple-type-transgranular and intergranular-ductile-frature.

• Journal of Periodontal and Implant Science
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• v.41 no.3
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• pp.135-142
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• 2011

Purpose: The present study was performed to evaluate the effect of erbium-doped: yttrium, aluminium and garnet (Er:YAG) laser irradiation on sand-blasted, large grit, acid-etched (SLA) implant surface microstructure according to varying energy levels and application times of the laser. Methods: The implant surface was irradiated by the Er:YAG laser under combined conditions of 100, 140, or 180 mJ/pulse and an application time of 1 minute, 1.5 minutes, or 2 minutes. Scanning electron microscopy (SEM) was used to examine the surface roughness of the specimens. Results: All experimental conditions of Er:YAG laser irradiation, except the power setting of 100 mJ/pulse for 1 minute and 1.5 minutes, led to an alteration in the implant surface. SEM evaluation showed a decrease in the surface roughness of the implants. However, the difference was not statistically Significant. Alterations of implant surfaces included meltdown and flattening. More extensive alterations were present with increasing laser energy and application time. Conclusions: To ensure no damage to their surfaces, it is recommended that SLA implants be irradiated with an Er:YAG laser below 100 mJ/pulse and 1.5 minutes for detoxifying the implant surfaces.