• Oral Biology Research
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• v.42 no.4
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• pp.187-197
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• 2018

Chemical agents such as minocycline (MC) and citric acid (CA) were suggested in the treatment of contaminated implant surface. In this study, MC-HCl treatment was performed to enhance surface characteristics of titanium alloy surface. The purpose of this study was to assess the characteristics and the biocompatibility of Ti-6Al-4V surface treated by MC. Alpha-beta titanium alloy (Ti-6Al-4V) samples were prepared and they were divided into 6 groups according to chemical concentration and treatment time. These groups include 1) group I, non-treated smooth titanium alloy; 2) group II, MC 1.5 mg/mL for 1 hour; 3) group III, MC 1.5 mg/mL for 24 hours; 4) group IV, MC 15 mg/mL for 10 minutes; 5) group V, MC 100 mg/mL for 5 minutes; 6) group VI, pH1 CA for 3 minutes. The analysis of the surface characteristics of MC-treated titanium alloy was executed using scanning electron microscopy, roughness test, and X-ray photoelectron spectroscopy (XPS). Cell adhesion and MTT assay was done using MC3T3 cell. Titanium surfaces treated with MC indicated a more smoothened surface microstructure. For group II and III, the new peaks of rutile TiO2 were found. Group II and V have more basic group of Ti-OH form in XPS. In MTT assay, all MC-treated groups showed significantly higher cell viability compared to control. The surface roughness, crystal structure, surface hydrophilicity, cell viability of smooth titanium surface was improved by MC treatment. Compared with the control experiment and CA-treated group, smooth titanium surface treated with MC showed improved surface characteristics and cell biocompatibility.

• Transactions of Materials Processing
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• v.28 no.1
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• pp.34-42
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• 2019

In this study, various alloying elements (Cr, Sr, Ca, Cd) were added to improve the mechanical properties of ADC12 fabricated by a die casting process. The effect of alloying elements on the microstructure and mechanical properties were investigated. The phase analysis results of the modified ADC12 alloy with conventional ADC12 alloy, showed the similar characteristics of Al matrix, Si phase, $CuAl_2$ phase and the Fe intermetallic phase. As a result of the microstructure observation, the secondary dendrite arm spacing (SDAS) was shown to have decreased after the addition of the alloying elements. The eutectic Si phase, which existed as flake form in the conventional ADC12 alloy, was modified finely as a fiber form in the modified ADC12 alloy. It was observed that the $CuAl_2$ phase as the strengthening phase was relatively finely distributed in the modified ADC12 alloy. The Fe intermetallic appeared as a Chinese script shaped $Al_6$ (Mn,Fe) which is detrimental to mechanical properties in conventional ADC12 alloy. On the other hand, in the modified ADC12 alloy, polyhedral ${\alpha}-Al_{15}Si_2$ $(Fe,Mn,Cr)_3$ was observed. The tensile properties were improved in the modified ADC12 alloy. The yield strength and tensile strength increased by 12.4% and 10.0%, respectively, in the modified ADC12 alloy, and the elongation was also seen to have been increased. As a result of the pin on disk wear test, the wear resistance properties were also improved by up to about 7% in the modified ADC12 alloy. It is noted that the wear deformation microstructures were also observed, and it was found that the fine eutectic Si and strengthening phases greatly improved abrasion resistance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.39-42
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• 2008

Alloy 718 nozzle component was manufactured by hot working and electron beam welding process. In this process, domestic 718 materials were applied and evaluated. Hot compression tests were carried out at a lot of process conditions and microstructural evaluation was investigated. Using the results, FEM simulations were performed in order to optimize the hot working process. After hot working, forged work-pieces were machined and welded by electron beam. Final nozzle component were heat treated and their microstructure and mechanical properties were investigated.

• Journal of Welding and Joining
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• v.15 no.4
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• pp.42-62
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• 1997

Resistance spot welding has been widely used in the sheet metal joining processes because of its high productivity and convenience. Recently, automobile industries are trying to replace partly steel sheets with aluminum alloy sheets. Among currently produced aluminum alloys, Al alloy sheets of Al-Mg-Si(6000 series) are being tested. Especially, 6000 series are the most probable substitute in view of strength and weldability. In this paper, an attempt was made to apply resistance spot welding to joining of dissimilar sheet metals (KS6383+SCPZn or KS6383+SHCP). An effort was made to balance heating rate in the Al alloy with that in the steel sheets by increasing electrode tip diameter. Although resistance spot welding of Al alloy sheet and sheet metals does not produce desirable nugget, it proved to have reasonable strength if optimal weld condition is found by tensile-shear strength and fatigue life test. Since spot weld joints in automobile are always experiencing repeated load, spot welding methodology proposed in this paper is found to be not suitable to automobile body manufacturing.

• Journal of Powder Materials
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• v.11 no.1
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• pp.34-42
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• 2004

The effect of extrusion temperature on the microstructure and mechanical properties were studied in He-gas atomized $Al_{81-(x＋y)}Si_{19}Ni_xCe_y$ alloy powders and their extruded bars using SEM, tensile testing and thermal expansion testing. The extruded bar of $Al_{73}Si_{19}Ni_7Ce_1$ alloy consists of a mixed structure in which fine Si particles with a particle size below 20∼500nm and very fine $Al_3Ni,\;Al_3Ce$ compounds with a particle size below 200nm are homogeneously dispersed in Al martix with a grain size below 500nm. With increasing extrusion temperature, the microstructural scale was decreased. The ultimate tensile strength of the alloy bars has incresed with decreasing extrusion temperature from 500 to 35$0^{\circ}C$ and $Al_{73}Si_{19}Ni_7Ce_1$ alloy extreded at 35$0^{\circ}C$ shows a highest tensile strength of 810 MPa due to the fine namostructure. The addition of Ni and Ce decreased the coefficients of thermal expansion and the effects of extression temperature on the thermal expansion were not significant.

• Journal of Welding and Joining
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• v.3 no.2
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• pp.42-51
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• 1985

The dynamic fracture toughness, fracture characteristics, impact tension and tensile properties of Al-Mg-Si T5 alloy and Al-Zn-Mg T6 alloy respectively welded with filler metal of Alcan 4043 were investigated. The dynamic fracture toughness values were obtained rapidly and simply for the specimen of small size by using instrumented Chirpy impact testing machine. the testing temperatures of the specimen were a range of room temperature and-196.deg. C. The results obtained in this experiment are summarized as follows. With decreasing the testing temperatures, dynamic tensile stress and fracture load were increased, on the other hand the deflection and impact value showed decreasing tendency in order of base metal>HAZ>weld. Changes of total absorbed energy were more influenced by the crack propagation energy than the crack initiation energy. At the low temperatures, the unstable rapid fracture representing the crack propagation appeared for the specimens of Charpy press side notched in Al-Zn-Mg alloy, but it was difficult to obtain the unstable rapid fracture in Al-Mg-Si alloy. Because of the development of plastic zone at the notch root, it was difficult to obtain thevalid $K_{1d}$ value in Al-Mg-Si alloy. Therefore the fatigue cracked specimens were effective in both Al-Mg-Si and Al-Zn-Mg alloys. With decreasing the impact testing temperatures, specimens underwent a transition from dimple-type transgranular fracture to lamella surface-type intergranular fracture because of the precipitate at the grain boundaries, impurities and crystal structure of the precipitates.s.

• Korean Journal of Materials Research
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• v.13 no.2
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• pp.133-136
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• 2003

Sn-2.5Cu alloy layers were deposited on the Alloy 42 lead-frame substrates by the electroplating method, and their microstructures, adhesion strength, and electrical resistivity were measured to evaluate the applicability of Sn-Cu alloy as a surface finishing material of electronic parts. The Sn-2.5Cu layers were electroplated in the granular form, and composed of pure Sn and Cu$_{6}$Sn$_{5}$ intermetallic compound. Surfaces of the electroplated Sn-2.5Cu layers were rather rough and also the thickness variance was large. The adhesion strength of the Sn-2.5Cu electroplated layers was highly comparable to that of the electroplated Cu alloy layer and the electrical conductivity was about 10 times higher than the pure Sn. After the 20$0^{\circ}C$ 30 min. annealing of the electroplated Sn-2.5Cu layers, the surface roughness was reduced, and adhesion strength and conductivity were improved. These results showed the Sn-Cu alloys can be used as an excellent surface finishing material.ial.

• Corrosion Science and Technology
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• v.22 no.4
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• pp.221-231
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• 2023

Interest in aluminum alloys for the hydrogen valves of fuel cell electric vehicles (FCEVs) is growing due to the reduction in fuel efficiency by the high weight. However, when an aluminum alloy is used, deterioration in mechanical characteristics caused by hydrogen embrittlement and wear is regarded as a problem. In this investigation, the aluminum alloy used to prevent hydrogen embrittlement was subjected to surface treatments by performing hard anodizing and plasma ion nitriding processes. The hard anodized Al alloy exhibited brittleness in which the mechanical characteristics rapidly deteriorated due to porosity and defects of surface, resulting in a decrease in the ultimate tensile strength and modulus of toughness by 15.58 and 42.51%, respectively, as the hydrogen charging time increased from 0 to 96 hours. In contrast, no distinct nitriding layer in the plasma ion-nitrided Al alloy was observed due to oxide film formation and processing conditions. However, compared to 0 and 96 hours of hydrogen charging time, the ultimate tensile strength and modulus of toughness decreased by 7.54 and 13.32%, respectively, presenting excellent resistance to hydrogen embrittlement.

• Journal of the Korean institute of surface engineering
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• v.42 no.6
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• pp.260-266
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• 2009

The anodic oxidation behaviour of a cast component of AC2A Al alloy with machined surface and ascast surface was investigated in sulfuric acid solution. The anodized specimen showed relatively uniform and thick anodic oxide films on the as-cast surface, while non-uniform and very thin oxide films were formed on the machined surface. Non-anodized as-cast surface was observed to be covered with thick oxide scales and showed a number of second-phase particles containing Si, while non-anodized machined surface showed no oxide scales and relatively very small number of Si particles. Thus, the very limited growth of anodic oxide films on the as-cast surface was attributed to the presence of thick oxide scales and Si-containing second-phase particles on its surface.

• Nuclear Engineering and Technology
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• v.53 no.7
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• pp.2323-2333
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• 2021

The paper proposes a technique for reconstructing the true hardening curve of isotropic materials from ring tensile tests. Neutron irradiated 42XNM alloy tensile properties were investigated. The calculation of the true hardening curve for tensile and compression tests of standard cylindrical samples was performed at the first step. After that, the FEM-model was developed and validated using the ring tension and compression tests (with the hardening curve defined in step 1). Finally, the true hardening curve was calculated by selecting the FEM-model parameters and its validation by ring sample tests in different states using an iterative method. For these samples, experimental and calculated gauge length values were obtained, and the corresponding material's constants were estimated.