• Korean Journal of Metals and Materials
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• v.56 no.11
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• pp.805-812
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• 2018

High pressure die casting is one of the precision casting methods. It is highly productivity and suitable for manufacturing components with complex shapes and accurate dimensions. Recently, there has been increasing demand for efficient heat dissipation components, to control the heat generated by devices, which directly affects the efficiency and life of the product. Die cast aluminum alloys with high thermal conductivity are especially needed for this application. In this study, the influence of elements added to the die cast aluminum alloy on its thermal conductivity was evaluated. The results showed that Mn remarkably deteriorated the thermal conductivity of the aluminum alloy. When Cu content was increased, the tensile strength of cast aluminum alloy increased, showing 1 wt% of Cu ensured the minimum mechanical properties of the cast aluminum. As Si content increased, the flow length of the alloy proportionally increased. The flow length of aluminum alloy containing 2 wt% Si was about 85% of that of the ALDC12 alloy. A heat dissipation component was successfully fabricated using an optimized composition of Al-1 wt%Cu-0.6 wt%Fe-2 wt%Si die casting alloy without surface cracks, which were turned out as intergranular cracking originated from the solidification contraction of the alloy with Si composition lower than 2 wt%.

• Journal of the Korean institute of surface engineering
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• v.51 no.5
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• pp.277-290
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• 2018

In this study, Pd-Ni-Ag alloy hydrogen separation membranes were fabricated by Pd/Ag/Pd/Ni/Pd multi-layer sputter deposition on the modified MIM(Metal Injection Molding)-PSS(Porous Stainless Steel) support and followed heat treatment. Nickel, used as an alloying element in Pd alloy membranes, is inexpensive and stable material in a hydrogen isotope environment at high temperature up to 1123 K. Hydrogen perm-selectivity of Pd-Ni-Ag alloy membranes is affected not only by composition of membrane films but also by other factors such as surface properties of PSS support, microstructure of membrane films and inter-diffused impurities from PSS support. In order to clarify the effect of surface Ni composition on hydrogen perm-selectivity of Pd-Ni-Ag alloy membranes, the other effects were significantly minimized by the formation of dense and homogeneous Pd-Ni-Ag alloy membranes. Hydrogen permeation test showed that hydrogen permeability decreased from $7.6{\times}10^{-09}$ to $1.02{\times}10^{-09}mol/m{\cdot}s{\cdot}Pa^{0.5}$ as Ni composition increased from 0 to 16 wt% and the selectivity for $H_2/N_2$ was infinite.

• Journal of the Korean institute of surface engineering
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• v.55 no.6
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• pp.460-468
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• 2022

Due to its high electrical conductivity, low contact resistance, good weldability and high corrosion resi-stance, gold is widely used in electronic components such as connectors and printed circuit boards (PCB). Gold ion salts currently used in gold plating are largely cyan-based salts and non-cyanic salts. The cya-nide bath can be used for both high and low hardness, but the non-cyanide bath can be used for low hardness plating. Potassium gold cyanide (KAu(CN)₂) as a cyanide type and sodium gold sulfite (Na₃[Au(SO)₃]₂) salt as a non-cyanide type are most widely used. Although the cyan bath has excellent performance in plating, potassium gold cyanide (KAu(CN)₂) used in the cyan bath is classified as a poison and a toxic substance and has strong toxicity, which tends to damage the positive photoresist film and make it difficult to form a straight side-wall. There is a need to supplement this. Therefore, it is intended to supplement this with an eco-friendly process using sodium sulfite sodium salt that does not contain cyan. Therefore, the main goal is to form a gold plating layer with a controllable hardness using a non-cyanide gold plating solution. In this study, the composition of a non-cyanide gold plating solution that maintains hardness even after annealing is generated through gold-palladium alloying by adding thallium, a crystal regulator among electrolysis factors affecting the structure and hardness, and changes in plating layer structure and crystallinity before and after annealing the correlation with the hardness.

• Korean Journal of Metals and Materials
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• v.48 no.2
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• pp.122-132
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• 2010

Higher strength and fracture toughness of reactor pressure vessel steels can be obtained by changing the material specification from that of Mn-Mo-Ni low alloy steel (SA508 Gr.3) to Ni-Mo-Cr low alloy steel (SA508 Gr.4N). However, the operation temperature of the reactor pressure vessel is more than $300^{\circ}C$ and the reactor operates for over 40 years. Therefore, we need to have phase stability in the high temperature range in order to apply the SA508 Gr.4N low alloy steel for a reactor pressure vessel. It is very important to evaluate the temper embrittlement phenomena of SA508 Gr.4N for an RPV application. In this study, we have performed a Charpy impact test and tensile test of SA508 Gr.4N low alloy steel with changing impurity element contents such as Mn and P. And also, the mechanical properties of these low alloy steels after longterm heat treatment ($450^{\circ}C$, 2000hr) are evaluated. Further, evaluation of the temper embrittlement by fracture analysis was carried out. Temper embrittlement occurs in KL4-Ref and KL4-P, which show a decrease of the elongation and a shifting of the transition curve toward high temperature. The reason for the temper embrittlement is the grain boundary segregation of the impurity element P and the alloying element Ni. However, KL4-Ref shows temper embrittlement phenomena despite the same contents of P and Ni compared with SC-KL4. This result may be caused by the Mn contents. In addition, the behavior of embrittlement is not largely affected by the formation of $M_3P$ phosphide or the coarsening of Cr carbides.

• Journal of Korea Foundry Society
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• v.44 no.2
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• pp.31-39
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• 2024

Dendrite boundaries and γ/γ' structure of a second generation single crystalline superalloy CMSX-4 almost disappeared during solution treatment above 1310℃. γ' size in the dendrite core was uniform and fine, however, that in the interdendritic region was coarse and nonuniform. With increasing solutionizing temperature and time, γ' size in the interdednritic region became fine and segregation of alloying elements between dendrite core and interdendritic region diminished. Segregation of solid solution strengthening elements such as W, Co, Re in the dendrite core was not fully removed through the heat treatments, especially that of Re still remained to some extent. Tensile properties at room temperature at which does not cause precipitaion of harmful phases, were improved with increasing solutionizing temperature and time.

• Journal of Powder Materials
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• v.13 no.5 s.58
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• pp.327-335
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• 2006

In the development of new hydrogen absorbing materials for a next generation of metal hydride electrodes for rechargeable batteries, metastable Mg-Ni-based compounds find currently special attention. Amor phous-nanocrystalline $Mg_{63}Ni_{30}Y_7$ and $Mg_{50}Ni_{30}Y_{20}$ alloys were produced by mechanical alloying and melt-spinning and characterized by means of XRD, TEM and DSC. On basis of mechanically alloyed Mg-Ni-Y powders, complex hydride electrodes were fabricated and their electrochemical behaviour in 6M KOH (pH=14,8) was investigated. The electrodes made from $Mg_{63}Ni_{30}Y_7$ powders, which were prepared under use of a SPEX shaker mill, with a major fraction of nanocrystalline phase reveal a higher electrochemical activity far hydrogen reduction and a higher maximum discharge capacity (247 mAh/g) than the electrodes from alloy powder with predominantly amorphous microstructure (216 mAh/g) obtained when using a Retsch planetary ball mill at low temperatures. Those discharge capacities are higher that those fur nanocrystalline $Mg_2Ni$ electrodes. However, the cyclic stability of those alloy powder electrodes was low. Therefore, fundamental stability studies were performed on $Mg_{63}Ni_{30}Y_7$ and $Mg_{50}Ni_{30}Y_{20}$ ribbon samples in the as-quenched state and after cathodic hydrogen charging by means of anodic and cathodic polarisation measurements. Gradual oxidation and dissolution of nickel governs the anodic behaviour before a passive state is attained. A stabilizing effect of higher fractions of yttrium in the alloy on the passivation was detected. During the cathodic hydrogen charging process the alloys exhibit a change in the surface state chemistry, i.e. an enrichment of nickel-species, causing preferential oxidation and dissolution during subsequent anodization. The effect of chemical pre-treatments in 1% HF and in $10\;mg/l\;YCl_3/1%\;H_2O_2$ solution on the surface degradation processes was investigated. A HF treatment can improve their anodic passivation behavior by inhibiting a preferential nickel oxidation-dissolution at low polarisation, whereas a $YCl_3/H_2O_2$ treatment has the opposite effect. Both pre-treatment methods lead to an enhancement of cathodically induced surface degradation processes.

• Korean Journal of Materials Research
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• v.2 no.6
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• pp.428-435
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• 1992

AISI 4600 Iron powder was mixed with 0~1.0% phosphor as F$e_2$P powder and/or 0~0.8% carbon as graphite powder in rotating mixer. Mixed powder was pressed 800MPa in double-punch mould. Compacts were sintered at 115$0^{\circ}C$for 30 min. in vacuum or mixed hydrogen and nitrogen gas. Sintered compacts were ground and polished, and etched by 2% nital etchant. The microstructure was observed by image analyzer and optical microscope. Density and microhardness were tested by ASTM B3l2 and Microvickers hardness tester. The results obtained were as follows : (1) As the amount of F$e_2$P powder increased, sintered microstructure showed more densified effect and the grain size was larger. (2) The shape of pore was rounded and the number of pore was decreased by F$e_2$P addition. But mean pore size was larger with F$e_2$P content. (3) Simultaneous alloying addition of F$e_2$P and graphite brought about larger grain growth than respective addition. (4) Sintering atmosphere did not affect the microstructure. (5) Hardness of sintered compact increased with phosphrous and carbon content.

• Korean Journal of Materials Research
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• v.21 no.7
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• pp.357-363
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• 2011

In this paper, high temperature oxidation behavior of newly developed alloys, Ti-6Al-4Fe and Ti-6Al-1Fe, is examined. To understand the effect of Fe on the air oxidation behavior of the Ti-Al-Fe alloy system, thermal oxidation tests are carried out at $700^{\circ}C$ and $800^{\circ}C$ for 96 hours. Ti-6Al-4V alloy is also prepared and tested under the same conditions for comparison with the developed alloys. The oxidation resistance of the Ti-Al-Fe alloy system is superior to that of Ti-6Al-4V alloy. Ti-6Al-4V shows the worst oxidation resistance for all test conditions. This is not a result of the addition of Fe, but rather it is due to the elimination of V, which has deleterious effects on high temperature oxidation. The oxidation of the Ti-Al-Fe alloy system follows the parabolic rate law. At $700^{\circ}C$, Fe addition does not have a noticeable influence on the amount of weight gain of all specimens. However, at $800^{\circ}C$, Ti-6Al-4Fe alloy shows remarkable degradation compared to Ti-6Al-1Fe and Ti-6Al. It is discovered that the formation of $Al_2O_3$, a diffusion resistance layer, is remarkably hindered by a relative decrease of the ${\alpha}$ volume fraction. This is because Fe addition increases the volume fraction of ${\beta}$ phase within the Ti-6Al-xFe alloy system. Activities of Al, Ti, and Fe with respect to the formation of oxide layers are calculated and analyzed to explore the oxidation mechanism.

• Transactions of the Korean hydrogen and new energy society
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• v.10 no.1
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• pp.27-40
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• 1999

By hydrogen induced planetary ball milling process, $Mg_2NiH_x$ hydrogen absorbing materials were successfully alloyed mechanically at room temperature, using pure Mg and Ni chips. The Mg & Ni chips were mixed by 45:55 weight ratio and Mechanical Alloying(M.A.) was carried out : the hydrogen pressure induced in the jar was varied from 1 to 20 bars and the M.A. times were 24 and 48 hours. The XRD results revealed that the homogeneous $Mg_2NiH_x$ was incresed with the hydrogen pressure increasing, and that $MgH_x$ was detected by unalloyed Ni chips. The shape and size of the mechanically alloyed particles didn't depend on the induced hydrogen pressure. The results of TGA showed that the hydrogen quantities of $Mg_2NiH_x$ has 1.1~3.9 wt%.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.195-195
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• 2016

Titanium and its alloys are widely used as implants in orthopedics, dentistry and cardiology due to their outstanding properties, such as high strength, high level of hemocompatibility and enhanced biocompatibility. Hence, recent works showed that the synthesis of new Ti-based alloys for implant application involves more biocompatible metallic alloying element, such as, Nb, Hf, Zr and Mo. In particular, Nb and Hf are one of the most effective Ti ${\beta}-stabilizer$ and reducing the elastic modulus. Plasma electrolyte oxidation (PEO) is known as excellent method in the biocompatibility of biomaterial due to quickly coating time and controlled coating condition. The anodized oxide layer and diameter modulation of Ti alloys can be obtained function of improvement of cell adhesion. Silicon (Si) and magnesium (Mg) has a beneficial effect on bone. Si in particular has been found to be essential for normal bone and cartilage growth and development. In vitro studies have shown that Mg plays very important roles in essential for normal growth and metabolism of skeletal tissue in vertebrates and can be detected as minor constituents in teeth and bone. The aim of this study is to research Si and Mg doped hydroxyapatite film formation by plasma electrolytic oxidation. Ti-29Nb-xHf (x= 0, 3, 7 and 15wt%, mass fraction) alloys were prepared Ti-29Nb-xHf alloys of containing Hf up from 0 wt% to 15 wt% were melted by using a vacuum furnace. Ti-29Nb-xHf alloys were homogenized for 2 hr at $1050^{\circ}C$. Each alloy was anodized in solution containing typically 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophosphate at room temperature. A direct current power source was used for the process of anodization. Anodized alloys was prepared using 270V~300V anodization voltage at room. A Si and Mg coating was produced by RF-magnetron sputtering system. RF power of 100W was applied to the target for 1h at room temperature. The microstructure, phase and composition of Si and Mg coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.