• Journal of Korea Foundry Society
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• v.22 no.6
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• pp.288-292
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• 2002

Ni-base amorphous alloys were manufactured using melt-spinning and Cu-mold die casting methods. Amorphous formability, the supercooled liquid region before crystallization and mechanical properties were examined. The reduced glass transition temperature and the supercooled liquid region of $Ni_{51} Nb_{20} Zr_9 Ti_9 Co_8 Cu_3$alloy were 0.621 and 46 K respectively. $Ni_{51} Nb_{20} Zr_9 Ti_9 Co_8 Cu_3$ alloy was produced in the rod shape 3mm diameter using the Cu-mold die casting. Hardness, compression strength, elongation and elastic modulus of the alloy were 850 DPN, 2.75 GPa, 1.8% and 150 GPa respectively. Moreover, compression strength of 2.75 GPa was the highest value in the amorphous bulk alloy produced up to now.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.264-269
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• 2000

Nickel-based heat resisting alloys are commonly used for high temperature applications such as in aircraft engines and gas turbines. In this paper, the machinability of Nickel-based heat resisting alloy was investigated with respect to the wear and the chip formation by tool type and cutting condition. Relationship between three types of tool and chip formation was experimentally investigated. Among the three types of tool tested, coated tools(CVD, PVD) are available for the difficult-to-cut-materials such as Nickel-based heat resisting alloy and etc..

• Journal of Powder Materials
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• v.27 no.1
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• pp.8-13
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• 2020

In this study, we investigated the effects of precipitates and oxide dispersoids on the high-temperature mechanical properties of oxide dispersion-strengthened (ODS) Ni-based super alloys. Two ODS Ni-based super alloy rods with different chemical compositions were fabricated by high-energy milling and hot extrusion process at 1150 ℃ to investigate the effects of precipitates on high-temperature mechanical properties. Further, the MA6000N alloy is an improvement over the commercial MA6000 alloy, and the KS6000 alloy has the same chemical composition as the MA6000 alloy. The phase and microstructure of Ni-based super alloys were investigated by X-ray diffraction and scanning electron microscopy. It was found that MC carbide precipitates and oxide dispersoids in the ODS Ni-based super alloys developed in this study may effectively improve high-temperature hardness and creep resistance.

• Journal of Power System Engineering
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• v.9 no.4
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• pp.90-95
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• 2005

The wire-arc process is a low-cost thermal spray method simply utilizes electrical energy to melt the feedstock wire. It is more userful for field applications, especially to coat large surface area. In this paper, a special Fe-based alloy coatings by using the wire-arc process were developed. Nanoscale composite coatings were achieved either during spraying or through a post heat treatment. As-sprayed Fe-based alloy coatings had been an amorphous matrix structure, after heating to $700^{\circ}C$ for 10 minutes a solid state transformation occurred in the some fraction of amorphous matrix which resulted in the formation of nanostructured recrystallized phase. Scanning electron microscopy (SEM) and field emotional scanning electron microscope(FE-SEM) were applied to analyze the microstructure of the coatings. Additionally hardness and bend resistance of the Fe-based alloy coatings were examined, and these results were compared with those of partially stabilized zirconia(PSZ) coatings by using the plasma spray process.

• Journal of Power System Engineering
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• v.21 no.1
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• pp.43-49
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• 2017

This work aims to investigate on the low cycle fatigue life assessment, which is adopted on the strain-life relationship, or better known as the Coffin-Manson relationship, and also the strain energy density-based model. The low cycle fatigue test results of Alloy 617 weldments under $900^{\circ}C$ have been statistically estimated through the Coffin-Manson relationship according to the provided strain profile. In addition, the strain energy density-based model is proposed to represent the energy dissipated per cycle as fatigue damage parameter. Based on the results, Alloy 617 weldments followed the Coffin-Manson relationship and strain energy density-based model well, and they were compatible with the experimental data. The predicted lives based on these two proposed models were examined with the experimental data to select a proper life prediction parameter.

• Transactions of Materials Processing
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• v.20 no.2
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• pp.160-166
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• 2011

Weight reduction while maintaining functional requirements is one of the major goals in the automotive industry. The use of lightweight magnesium alloys offers great potential for reducing weight because of the low density of these alloys. However, the formability and the surface quality of the final magnesium alloy product for auto-body structures are not acceptable without a careful optimization of the design parameters. In order to overcome some of the main formability limitations in the stamping of magnesium alloys, a new approach, the so-called "hybrid technology", has been recently proposed for body-in-white structural components. Within this approach, necessary level of mechanical joining can be obtained through the use of lightweight material-steel adhesion promoters. This paper presents the development process of an automotive hybrid hood assembly using magnesium alloy sheets. In the first set of material pairs, the selected materials are magnesium alloy AZ31B alloy and steel(SGCEN) as inner and outer panels, respectively. In order to optimize the design of the inner panel, the stamping process was analyzed with the finite element method (FEM). Laser welding by CW Nd:YAG were used to join the magnesium alloy sheets. Based on the simulation results and mechanical test results of the joints, the determination of die design variables and their influence on formability were discussed. Furthermore, a prototype based on the proposed design was manufactured and the static stiffness test was carried out. The results demonstrate the feasibility of the proposed hybrid hood with a weight reduction of 25.7%.

• Korean Journal of Materials Research
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• v.20 no.2
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• pp.60-64
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• 2010

This study looked at high performance copper-based alloys as LED lead frame materials with higher electrical-conductivity and the maintenance of superior tensile strength. This study investigated the effects on the tensile strength, electrical conductivity, thermal softening, size and distribution of the precipitation phases when Cr was added in Cu-Fe alloy in order to satisfy characteristics for LED Lead Frame material. Strips of the alloys were produced by casting and then properly treated to achieve a thickness of 0.25 mm by hot-rolling, scalping, and cold-rolling; mechanical properties such as tensile strength, hardness and electrical-conductivity were determined and compared. To determine precipitates in alloy that affect hardness and electrical-conductivity, electron microscope testing was also performed. Cr showed the effect of precipitation hardened with a $Cr_3Si$ precipitation phase. As a result of this experiment, appropriate aging temperature and time have been determined and we have developed a copper-based alloy with high tensile strength and electrical-conductivity. This alloy has the possibility for use as a substitution material for the LED Lead Frame of Cu alloy.

• Journal of the Korean institute of surface engineering
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• v.49 no.1
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• pp.62-68
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• 2016

A chromium-free Ce-based conversion coating formed by immersion in a solution containing cerium chloride and nitric acid on AZ31 magnesium alloy has been studied. The effects of acid pickling on the morphology and the corrosion resistance of the cerium conversion coating were investigated. The corrosion resistance of the conversion coating prepared on AZ31 Mg alloy after organic acid pickling was better than that of inorganic acid pickling. The morphology of the conversion-coated layer was observed using optical microscope and SEM. Results show that the conversion coatings are relatively uniform and continuous, with thickness 1.0 to $1.1{\mu}m$. The main elements of the conversion coating of AZ31 Mg alloy are Mg, O, Al, Ce and Zn by EDS analysis. The electrochemical polarization results showed that the Ce-based conversion coating could reduce the corrosion activity of the AZ31 Mg alloy substrates in the presence of chloride ions.

• Korean Journal of Materials Research
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• v.31 no.12
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• pp.690-696
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• 2021

The purpose of this study is to develop a zirconium-based alloy with low modulus and magnetic susceptibility to prevent the stress-shielding effect and the generation of artifacts. Zr-7Cu-xSn (x = 1, 5, 10, 15 mass%) alloys are prepared by an arc melting process. Microstructure characterization is performed by microscopy and X-ray diffraction. Mechanical properties are evaluated using micro Vickers hardness and compression test. The magnetic susceptibility is evaluated using a SQUID-VSM. The average magnetic susceptibility value of the Zr-7Cu-xSn alloy is 1.176 × 10^-8 cm³g^-1. Corrosion tests of zirconium-based alloys are conducted through polarization test. The average Icorr value of the Zr-7Cu-xSn alloy is 0.1912 ㎂/cm². The elastic modulus value of 14 ~ 18 GPa of the zirconium-based alloy is very similar to the elastic modulus value of 15 ~ 30 GPa of the human bone. Consequently, the Sn added zirconium alloy, Zr-7Cu-xSn, is very interesting and attractive as a biomaterial that reduces the stress-shielding effect caused by differences of elastic modulus between human bone and metallic implants. In addition, this material has the potential to be used in metallic dental implants to effectively eliminate artifacts in MRI images due to low magnetic susceptibility.

• Advances in materials Research
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• v.1 no.3
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• pp.205-219
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• 2012

Co-Re alloy development is prompted by the search for new materials for future gas turbines which can be used at temperatures considerably higher than the present day single crystal Ni-based superalloys. The Co-Re based alloys are designed to have very high melting range. Although Co-alloys are used in gas turbine applications today, the Co-Re system was never exploited for structural applications and basic knowledge on the system is lacking. The alloy development strategy therefore is based on studying alloying additions on simple model alloy compositions of ternary and quaternary base. Various strengthening possibilities have been explored and precipitation hardening through fine dispersion of MC type carbides was found to be a promising route. In the early stages of the development we are mainly dealing with polycrystalline alloys and therefore the grain boundary embrittlement needed to be addressed and boron addition was considered for improving the ductility. In this paper recent results on the effect of boron on the strength and ductility and the stability of the fine structure of the strengthening TaC precipitates are presented. In the beginning the alloy development strategy is briefly discussed.