Doh-Jae Lee

Fabrication and characterization of functionally graded nano‐micro porous titanium surface by anodizing

The purpose of this study was to fabricate and characterize nanotubular structure on machined titanium (MA) and resorbable blast media (RBM) treated titanium by anodizing. The anodized MA and RBM were characterized with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy disperse spectra, X-ray photoelectron spectra, and nano-indentation and scratch test. Highly ordered nanotubular layers of individually 100 nm in diameter and 500 nm in length approximately were formed regardless of the substrates. The nanotubular layers consisted mainly of amorphous TiO(2) with trace fluorine. The nanotubular surfaces on both the substrates significantly reduced water contact angles and elastic modulus compared with those prior to anodizing. The anodizing treatment significantly increased the surface roughness of the smooth MA, but significantly decreased the surface roughness of the roughened RBM. The critical delamination forces of the nanotubular layer were not obtained due to the limitation of surface roughness. The anodized RBM consisted of a nano-micro porous graded structure, or a nanotubular amorphous fluoride containing TiO(2) layer on top of micro-roughened titanium surface, which is expected to significantly improve the surface area that can be used to deliver drugs and growth factors and alleviate the interfacial elastic modulus mismatch as to enhance osseointegration when compared with conventional dental and orthopedic implant devices with smooth or acid etched surface.

Effect of metal chloride solutions on coloration and biaxial flexural strength of yttria-stabilized zirconia

The effect of three kinds of transition metal dopants on the color and biaxial flexural strength of zirconia ceramics for dental applications was evaluated. Presintered zirconia discs were colored through immersion in aqueous chromium, molybdenum and vanadium chloride solutions and then sintered at 1450 °C. The color of the doped specimens was measured using a digital spectrophotometer. For biaxial flexural strength measurements, specimens infiltrated with 0.3 wt% of each aqueous chloride solution were used. Uncolored discs were used as a control. Zirconia specimens infiltrated with chromium, molybdenum and vanadium chloride solutions were dark brown, light yellow and dark yellow, respectively. CIE L*, a*, and b* values of all the chromium-doped specimens and the specimens infiltrated with 0.1 wt% molybdenum chloride solution were in the range of values for natural teeth. The biaxial flexural strengths of the three kinds of metal chloride groups were similar to the uncolored group. These results suggest that chromium and molybdenum dopants can be used as colorants to fabricate tooth colored zirconia ceramic restorations.

Phase Stability and Interface Reactions in the Al-SiC System

The Al-SiC system has been used as a model system in an examination of phase stability in the presence of a liquid phase and microstructure development in metal-matrix composites. The Al-Si-C phase diagram has been calculated for temperatures between 500°C and 1500°C. The phases formed between Al(liquid) and SiC at 920°C have been determined experimentally, using analytical electron microscopy, in both fiber and particulate composites and compared with what is predicted from the equilibrium phase diagram. The morphologies and the spatial distributions of phases have also been examined in addition to the phase analysis. The only phases found were Al, Al 4 C 3 , SiC, and Si. Although Al 4 SiC 4 is calculated to be stable at 920°C, it was not found. The SiC grain structure was found to influence strongly the morphology of the Al 4 C 3 -SiC and Al-SiC interfaces.

Effect of thermal treatment on the atomic ordering of mechanically alloyed Al3Nb

Abstract The present study was carried out to investigate the effect of thermal treatment on the atomic ordering of mechanically alloyed Al 3 Nb. The partially disordered Al 3 Nb alloy is transformed into an ordered 10-nm sized Al 3 Nb after a following heat treatment. The value of Δ H order for ordering of Al 3 Nb intermetallics is more negative for faster heating rates and prolonged milling time. The average values of Δ H order correspond to about 35% of the Δ H necessary for Al 3 Nb phase formation. The activation energies for ordering of Al 3 Nb at 30 and 40 h of milling are relatively close to the isothermal grain growth enthalpy of nanocrystalline Al 3 Nb intermetallics.

Surface Characteristics of Oxide Film Prepared on CP Ti and Ti-10Ta-10Nb Alloy by Anodizing

In the present study, we investigated the formation of self-organized nanostructure oxide layers on CP Ti and Ti-10Ta-10Nb alloy in an electrolyte of 1M phosphoric acid and 1.5 wt% Hydrofluoric acid. The morphology of oxide film on substrate was observed using scanning electron microscopy and transmission electron microscopy The surface roughness of titanium oxide film was analyzed by atomic force microscopy and the crystalline of specimen was investigated using X-ray diffractometer. The results of this study showed that well-aligned titanium oxide nanotubes are formed with diameter of approx. 100nm and length of approx. 500nm with CP Ti. However, it is clear that TiTaNb alloy highly irregular structure with various diameters. Transmission electron microscope investigations show that the specimens were confirmed as amorphous. Such titanium oxide nanotubes are expected a well-adhered bioacitive surface layer on titanium substrate for orthopedics and dental implants.

Effects of oxide layers on surface defects during hot rolling processes

An oxide layer, which developed on the surface of a commercial hot rolling mill, was examined by forcibly stopping the roller between mill stands during activity. Liquid quartz was sprayed on the strip to prevent further oxide layer growth during cooling after stopping the hot-rolling mills. Then the thickness and shape of the oxide layer was examined in a cross-sectional view using an optical microscope. The thickness of the oxide layer increased through the 1st and 2nd passes of hot rolling, and then decreased through successive rolling, because the thickening rate by growth is larger than the thinning rate by deformation in high temperature. The temperature distributions of the oxide layer as well as the strip were predicted using the thermo-mechanical finite element method. As thermal conductivity of the oxide layer is low, the temperature deviation of the oxide layer increases and average temperature decreases as the thickness of the oxide layer increases, suggesting the increased formation of surface defects. With these results, a new cooling device was installed between the hot rolling mills to decrease the surface temperature and the thickness of the oxide layer, resulting in improved surface quality of the strip.

Characteristics of Ir-Re Thin Films on WC for Lens Glass Molding by Ion Beam Assisted DC Magnetron Sputtering

Ir-Re thin films with Ti interlayer were deposited onto the tungsten carbide substrate by ion beam assisted DC magnetron sputtering. The Ir-Re films were prepared with targets of having two atomic percent of 7:3 and 5:5. The microstructure and surface analysis of the specimen were conducted by using SEM, XRD and AFM. Mechanical properties such as hardness and adhesion strength of Ir-Re thin film also were examined. The interlayer of pure titanium was formed with 100 nm thickness. The film growth of Ir-30at.%Re was faster than that of Ir-50at.%Re in the same deposition conditions. Ir-Re thin films consisted of dense and columnar structure irrespective of the different target compositions. The values of hardness and adhesion strength of Ir-30at.%Re thin film coated on WC substrate were higher than those of Ir-50at.%Re thin film.

Effects of Nb Addition on Corrosion Resistance and Cytotoxicity Behavior of Ti Alloys

The corrosion resistance and cytotoxicity behavior of Ti alloys were studied as a function of Nb contents(3wt.%Nb, 20wt.%Nb, 40wt.%Nb). Ti-Nb alloys were melted by vacuum arc furnace and then rolled to 50% reduction ratio after homogenized at 105 for 24hrs. The corrosion resistance of Ti-Nb alloys were investigated by potentiodynamic polarization test in the 0.9% NaCl and 5% HCI solution. Biocompatibility of Ti-Nb alloys was evaluated by cytotoxicity test. The results can be summarized as follows 1) The microstructure change from equiaxial to acicular and the increased phase in Ti-Nb alloys were obtained as the Nb content increased. 2) For the corrosion test in the solution of 0.9% NaCl and 5% HCI, the corrosion behavior of Ti-Nb alloys was similar to ASTM grade 2 CP Ti. 3) For the cytotoxicity test, Ti-Nb alloys showed excellent biocompatibility compared to ASTM grade 2 CP Ti, 316L STS and Co-Cr alloys.

Biocompatibility of Ti-8wt.%Ta-3wt.%Nb alloy with Surface Modification

The alloys were prepared by a non-consumable vacuum arc melting and homogenized at for 24 hrs. Two kind of surface modifications were performed alkali treatment in 5.0M NaOH solution subsequent and heat treatment in vacuum furnace at , and were oxidizing treatment at the temperature range of 550 to for 30 minutes. After surface modification, these samples were soaked in SBF which consists of nearly the same ion concentration as human blood plasma. Cytotoxicity tests were performed in MTT assay treated L929 fibroblast cell culture, using indirect methods. A porous and thin activated layer was formed on Titanium and Ti-8Ta-3Nb alloy by the alkali treatment. A bone-like hydroxyapatite was nucleated on the activated porous surfaces during the in vitro test. However, Ti-8Ta-3Nb alloys showed better bioactive properties than Titanium. According to XRD results, oxide layers composed of mostly (rutile) phases. Cytotoxicity test also revealed that moderate oxidation treatment lowers cell toxicity and Ti-8Ta-3Nb alloy showed better results compared with Titanium.

Characteristics of TiAlN Film on Different Buffer Layer by D.C Magnetron Sputter

TiAlN films were deposited on WC-5Co substrates with different buffer layers by D.C. magnetron sputtering. The films were evaluated by microstructural observations and measuring of preferred orientation, hardness value, and adhesion force. As a process variable, various buffer layers were used such as TiAlN single layer, TiAlN/TiAl, TiAlN/TiN and TiAlN/CrN. TiAlN coating layer showed columnar structures which grew up at a right angle to the substrates. The thickness of the TiAlN coating layer was about 1.8 µm, which was formed for 200 minutes at 300 C. XRD analysis showed that the preferred orientation of TiAlN layer with TiN buffer layer was (111) and (200), and the specimens of TiAlN/TiAl, TiAlN/CrN, TiAlN single layer have preferred orientation of (111), respectively. TiAlN single layer and TiAlN/TiAl showed good adhesion properties, showing an over 80N adhesion force, while TiAlN/TiN film showed approximately 13N and the TiAlN/CrN was the worst case, in which the layer was destroyed because of high internal residual stress. The value of micro vickers hardness of the TiAlN single layer, TiAlN/TiAl and TiAlN/TiN layers were 2711, 2548 and 2461 Hv, respectively.