• Journal of Powder Materials
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• v.28 no.6
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• pp.491-496
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• 2021

The process optimization of directed energy deposition (DED) has become imperative in the manufacture of reliable products. However, an energy-density-based approach without a sufficient powder feed rate hinders the attainment of an appropriate processing window for DED-processed materials. Optimizing the processing of DED-processed Ti-6Al- 4V alloys using energy per unit area (E_eff) and powder deposition density (PDD_eff) as parameters helps overcome this problem in the present work. The experimental results show a lack of fusion, complete melting, and overmelting regions, which can be differentiated using energy per unit mass as a measure. Moreover, the optimized processing window (E_eff = 44~47 J/mm² and PDD_eff = 0.002~0.0025 g/mm²) is located within the complete melting region. This result shows that the Eeff and PDDeff-based processing optimization methodology is effective for estimating the properties of DED-processed materials.

• Korean Journal of Materials Research
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• v.21 no.7
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• pp.384-390
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• 2011

Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. $Ti_2O$, CaO, $CaTiO_3$, and $Ti_xP_y$ phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.4
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• pp.675-686
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• 1996

Today, dental implants are an acceptable alternative, capable of providing bone-anchored fixed prostheses for improved quality of life and self esteem for many patients. Research advances in dental implantology have led to the development of several different types of materials, and it is anticipated that continued research will likewise lead to advanced dental implant materials. Currently used pure titanium has relatively low hardness and strength which possibly limits its ability to resist the functional loads as a dental implant. Ti-6Al-4V also has potential problems such as corrosion resistance, bone biocompatibility etc. The carefully selected Zr, Nb, Ta, Pd, In constituents could improve mechanical strength, corrosion resistance, and biocompatibility compared to that of currently used implant metals. On the basis of the totality of the data from our study, it can be concluded that new titanium alloys containing Zr, Nb, Ta, Pd, In are able to provide improved mechanical properties, corrosion resistance and biocompatibility to warrant further investigation of it's potential as new biomaterials for dental implants.

• Transactions of the Korean hydrogen and new energy society
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• v.16 no.3
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• pp.244-252
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• 2005

It is very interesting and important in the academic point of view and in practical use the hydrogen-induced phase separation(HIPS) which appears during hydrogen heat treatment. Since hydrogen can be removed very fast by pumping it out the hydrogen-induced new lattice phase which can not be obtained without hydrogen can be preserved as meta-stable state. In this study it has been investigated whether the HIPS appear in Pd-Al, Pd-Co, Pd-Cr, Pd-Ti, Pd-V and Pd-Zr alloys and discussed thermodynamic representation of the HIPS. The Pd alloys were arc-melted under argon atmosphere and remelted 4 or 5 times for homogenization. The alloys were annealed at 600$^{\circ}C$ under vacuum for 24 hrs and then subjected to pressure-composition isotherm measurements at 100$^{\circ}C$. The hydrogen heat treatment(HHT) of samples was carried out at 600$^{\circ}C$ under hydrogen pressure of 70 bar for 6 days and PC isotherms at 100$^{\circ}C$ were measured. By comparing the PC isotherms measured before and after HHT, occurrence of phase separation was determined. The experimental results showed that the HIPS appeared only in Pd-0.05Co alloy. For Pd-Co alloys with various composition the PC isotherms were measured. By adopting Park-Flanagan model for ternary thermodynamics the Gibbs free energy change for Pd-Co-H solid solution was calculated and subsequently with this the HIPS in Pd-Co alloy was explained fairly.

• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.3 s.22
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• pp.51-55
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• 2005

In this paper, a near net shape technology using superplasticity and diffusion bonding characteristics was presented for application to various components of aircraft and missiles. Due to these special characteristics of some aerospace alloys, it is possible to produce complex components to shape very near final dimension with enhanced design freedom, reduced material usage, and overall saving of weight and cost. The high pressure vessel for a space launcher was fabricated with Ti-6Al-4V alloy by superplastic forming and diffusion bonding process and the failure characteristics are compared with conventionally fabricated vessel spin formed and TIG welded. The structural integrity of the superplastic forming and diffusion bonding process was successfully demonstrated.

• Transactions of the Korean hydrogen and new energy society
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• v.11 no.1
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• pp.43-49
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• 2000

The heat transportation from a complex of industry to a rural area needs more efficient method because the distance between them is usually more than 10km. Conventional heat transportation using steam or hot water via pipe line has limits in transportation distance (about 3~5 km) because of the heat loss and frictional loss in the pipe line. Metal hydride can absorb or discharge hydrogen through exothermic or endothermic reaction. After releasing hydrogen from metal hydride by means of the waste heat from industry, we can transport this hydrogen to urban area via pipe line. In urban areas, other metal alloy reacts with this hydrogen to form metal hydride and produces heat for heating. Cool heat is also obtained if it is possible to use metal hydride with low reaction temperature. Therefore, metal hydride can be used as a media for transportation and storage of heat. $MmNi_{4.5}Al_{0.5}Zr_{0.003}$, $LaNi_5$, $Zr_{0.9}Ti_{0.1}Cr_{0.6}Fe_{1.4}$, $MmNi_{4.7}Al_{0.1}Fe_{0.1}V_{0.1}$ alloys were selected for this purpose and the properties of those metal hydrides were discussed. The design and control techniques were proposed and discussed for this heat transportation system using metal hydride.

• Korean Journal of Metals and Materials
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• v.49 no.12
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• pp.983-988
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• 2011

Failure analyses of the screws in spinal fixation devices were carried out. The fractured screws were retrieved from a patient who had spinal surgery in the thoracic vertebrae from number 10 to 15. The failure occurred one month after the removal of the braces. Microstructures and fracture surfaces were examined by optical and scanning electron microscopy. The microstructures of the screws corresponded to annealed Ti-6Al-4V bar. However, in the vicinity of the screw surface, there was an insufficient number of fine precipitates. Fracture surfaces showed typical fatigue failure modes. Regarding the fact that no machining defects were detected, fatigue crack initiation might have been caused by the lack of precipitates near the screw surfaces. Only the fourth of five fixed screws was severely stress-concentrated by the action of the spinal bones, while the stress of the 4th screw was decreased to half of its acceptable level when the screw was supplemented by one more, which might have been fixed in the 6th vertebra under the 5th position by the switching of its position. The stress simulation was conducted by ANSYS with 3D CAD of PRO/E in order to understand the stress concentration behavior and to provide an effective spinal surgery guide.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.78-78
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• 2017

Pure Titanium and alloy have been widely used in dental implants and orthopedics due to their excellent mechanical properties, biocompatibility and corrosion resistance. However, due to the biologically inactive nature of Ti metal implants, it cannot bind to the living bone immediately after transplantation into the body. In order to improve the bone bonding ability of titanium implants, many attempts have been made to alter the structure, composition and chemical properties of titanium surfaces, including the deposition of bioactive coatings. The PEO method has the advantages of short experiment time and low cost. These advantages have attracted attention recently. Recently, many metal ions such as silicon, magnesium, zinc, strontium, and manganese have received attention in this field due to their impact on bone regeneration. Silicon (Si) in particular has been found to be essential for normal bone and cartilage growth and development. Zinc (Zn) plays very important roles in bone formation and immune system regulation and promotes bone metabolism and growth. Manganese (Mn) is an essential trace metal found in all tissues and is required for normal amino acid, lipid, protein and carbohydrate metabolism. The objective of this work was research on the corrosion behavior of Si, Zn and Mn-doped hydroxyapatite on the PEO-treated surface. Anodized alloys was prepared at 270V~300V voltage in the solution containig Zn, Si, and Mn ions. Ion release test was carried out using potentidynamic and AC impedance method in 0.9% NaCl solution. The surface characteristics of PEO treated Ti-6Al-4V alloy were investigated using XRD, FE-SEM, AFM and EDS.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.77-77
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• 2017

Titanium and its alloys offer attractive properties in a variety of applications. These are widely used for the field of biomedical implants because of its good biocompatibility and high corrosion resistance. Titanium anodizing is often used in the metal finishing of products, especially those can be used in the medical devices with dense oxide surface. Based on SAE/AMS (Society of Automotive Engineers/Aerospace Material Specification) 2488D, it has the specification for industrial titanium anodizing that have three different types of titanium anodization as following: Type I is used as a coating for elevated temperature forming; Type II is used as an anti-galling coating without additional lubrication or as a pre-treatment for improving adherence of film lubricants; Type III is used as a treatment to produce a spectrum of surface colours on titanium. In this study, we have focused on Type II anodization for the medical (dental and orthopedic) application, the anodized surface was modified with gray color under alkaline electrolyte. The surface characteristics were analyzed with Focused Ion Beam (FIB), Scanning Electron Microscopy (SEM), surface roughness, Vickers hardness, three point bending test, biocompatibility, and corrosion (potentiodynamic) test. The Ti-6Al-4V alloy was used for specimen, the anodizing procedure was conducted in alkaline solution (NaOH based, pH>13). Applied voltage was range between 20 V to 40 V until the ampere to be zero. As results, the surface characteristics of anodic oxide layer were analyzed with SEM, the dissecting layer was fabricated with FIB method prior to analyze surface. The surface roughness was measured by arithmetic mean deviation of the roughness profile (Ra). The Vickers hardness was obtained with Vickers hardness tester, indentation was repeated for 5 times on each sample, and the three point bending property was verified by yield load values. In order to determine the corrosion resistance for the corrosion rate, the potentiodynamic test was performed for each specimen. The biological safety assessment was analyzed by cytotoxic and pyrogen test. Through FIB feature of anodic surfaces, the thickness of oxide layer was 1.1 um. The surface roughness, Vickers hardness, bending yield, and corrosion resistance of the anodized specimen were shown higher value than those of non-treated specimen. Also we could verify that there was no significant issues from cytotoxicity and pyrogen test.

• Toxicological Research
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• v.23 no.4
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• pp.331-339
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• 2007

Titanium or titanium alloy is a widely used implant material according to its certified biocompatibility, sufficient strength and ready availability. The purpose of this study was to evaluate the relative biocompatibility of titanium and titanium alloy specimens (Ti-29Nb-13Ta, TiNb and Ti-6Al-4V, Ti64) using in vivo and in vitro methods. For in vivo experiment, the specimens were implanted in the abdominal subcutaneous region of female mice for 2 and 4 weeks. The reaction of connective tissue to specimens was evaluated histologically. The specimens were encapsulated by fibrous connective tissue consisting of fibroblast, fibrocyte and other cells including neutrophil, macrophage, giant multinucleated cell and unidentified cells. Some newly formed blood vessels were located in the fibrous capsule surrounding the implant. Cell types and the thickness of fibrous capsules were examined quantitatively. Most of cell types located in the fibrous capsule were fibroblasts and fibrocytes. The average thickness of fibrous capsules for the TiNb specimens was much thinner than that of the titanium alloy, Ti64. The thickness of the fibrous capsule around all titanium specimens decreased at 4 weeks compared to 2 weeks post-implantation. The biocompatibility of titanium and titanium alloy specimens were also investigated in in vitro method using alkaline phosphatase from MG-63 cells. Alkaline phosphatase activity of the TiNb specimen showed higher activity than the titanium alloy, Ti64. In conclusion, the TiNb alloy with thin capsule thickness in vivo and high alkaline phosphatase activity in vitro will be of considerable use in biomedical applications.