• The Journal of Advanced Prosthodontics
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• v.5 no.4
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• pp.471-478
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• 2013

PURPOSE. The aim of the study was to evaluate the effect of annealing on the nanostructure and hardness of Co-Cr metal ceramic samples that were fabricated with a direct metal laser sintering (DMLS) technique. MATERIALS AND METHODS. Five groups of Co-Cr dental alloy samples were manufactured in a rectangular form measuring $4{\times}2{\times}2$ mm. Samples fabricated by a conventional casting technique (Group I) and prefabricated milling blanks (Group II) were examined as conventional technique groups. The DMLS samples were randomly divided into three groups as not annealed (Group III), annealed in argon atmosphere (Group IV), or annealed in oxygen atmosphere (Group V). The nanostructure was examined with the small-angle X-ray scattering method. The Rockwell hardness test was used to measure the hardness changes in each group, and the means and standard deviations were statistically analyzed by one-way ANOVA for comparison of continuous variables and Tukey's HSD test was used for post hoc analysis. P values of <.05 were accepted as statistically significant. RESULTS. The general nanostructures of the samples were composed of small spherical entities stacked atop one another in dendritic form. All groups also displayed different hardness values depending on the manufacturing technique. The annealing procedure and environment directly affected both the nanostructure and hardness of the Co-Cr alloy. Group III exhibited a non-homogeneous structure and increased hardness ($48.16{\pm}3.02$ HRC) because the annealing process was incomplete and the inner stress was not relieved. Annealing in argon atmosphere of Group IV not only relieved the inner stresses but also decreased the hardness ($27.40{\pm}3.98$ HRC). The results of fitting function presented that Group IV was the most homogeneous product as the minimum bilayer thickness was measured (7.11 ${\AA}$). CONCLUSION. After the manufacturing with DMLS technique, annealing in argon atmosphere is an essential process for Co-Cr metal ceramic substructures. The dentists should be familiar with the materials that are used in clinic for prosthodontics treatments.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.5
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• pp.545-566
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• 1999

The use of pure titanium and titanium alloys have been increased recently in fixed, removable prosthodontics and implant fields as a framework. But when they were used for superstructures of implant or metal framework of removable prosthesis, welding is necessary to reconnect the fracture site to control the casting distortions. To overcome the difficulties in soldering the titanium due to high oxidation property, much effort have been devoted. In this study, some of mechanical properties were compared between pure titanium and Ti-6Al-4V alloy by using after welding, electron beam welding technique and tungsten arc welding. Mechanical properties such as tensile strength, yield strength, elongation and microhardness were measured. And, in order to compare the effect of welding site and surrounding metal tissue according to the welding condition, SEM photographs were taken and element distribution was observed by Wave Dispersion Spectroscopy. Through analyses of the data, following results were obtained; 1. In items such as tensile strength, yield strength and elongation according to the welding techniques of pure titanium, only tungsten arc welded group showed significant lower value than other groups(P<0.05). 2. In items such as tensile strength and yield strength according to the welding techniques of Ti-6Al-4V alloy, control group and tungsten arc welded group showed significant difference among all the groups(P<0.05). 3. Ti-6Al-4V alloy exhibited significantly greater elongation than control group when the laser welding method and electron beam welding method were used, and elongation showed increasing tendency. 4. Pure titanium specimens exhibited increasing tendency of microhardness regardless of the weld-ing technique applied, and especially tungsten arc welded group demonstrated a great increase of microhardness than parent metal. 5. There was no hardness change in laser welded group and electron beam welded group of Ti-6Al-4V alloy, but in tungsten arc welded group, hardness changed greatly from parent metal to weld seam. 6. Through the metallographic examination and scanning electron microscopy, laser welding caused central fusion and recristallizations were formed and tungsten arc welding caused localized fusion to 0.3-0.7mm from the surface.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.5
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• pp.526-536
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• 2006

Statement of problem : Use of fiber composite technology as well as development of nonmetal implant prosthesis solved many problems due to metal alloy substructure such as corrosion. toxicity, difficult casting, expensiveness and esthetic limit. After clinical and laboratory test, we could find out that fiber-reinforced composite prostheses have good mechanical properties and FRC can make metal-free implant prostheses successful. Purpose : The purpose of this study is to evaluate the flexural strength of implant fixed prosthesis using fiber reinforced composite. Material and methods : 2-implant fixture were placed in second premolar and second molar area in edentulous mandibular model, and their abutments were placed, and bridge prostheses using gold, PFG, Tescera, and Targis Vectris were fabricated. Tescera was made in 5 different designs with different supplements. Group I was composed by 3 bars with diameter 1.0mm and 5 meshes, 2 bars and 5 meshes for Group II, 1 bar and 5 meshes for Group III, and only 5 meshes were used for Group IV. And Group V is composed by only 3 bars. Resin (Tescera) facing was made to buccal part of pontic of gold bridge. All of gold and PFG bridges were made on one model, 5 Targis Vectris bridges were also made on one model, and 25 Tescera bridges were. made on 3 models. Each bridge was attached to the test model by temporary cement and shallow depression was formed near central fossa of the bridge pontic to let 5 mm metal ball not move. Flexual strength was marked in graph by INSTRON. Results : The results of the study are as follows. The initial crack strength was the highest on PFG. and in order of gold bridge Tescera I, Tescera II, Targis vectris, Tescera IV, Tescera III, and Tescera V. The maximum strength was the highest on gold bridge, and in order of PFG, Tescera I, Tescera IV Tescera II, Targis vectris, Tescera III, and Tescera V. Conculsions : The following conclusions were drawn from the results of this study. 1. Flextural strength of implant prosthesis using fiber reinforced composite was higher than average posterior occlusal force. 2. In initial crack strength, Tescera I was stronger than Tescera V, and weaker than PFG. 3. Kinds and number of auxillary components had an effect on maximum strength, and maximum strength was increased as number of auxillary components increased. 4 Maximum strength of Tescera I was higher than Targis vectris, and lower than PFG.

• The Journal of the Korean dental association
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• v.22 no.5 s.180
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• pp.439-446
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• 1984

The purpose of this study was observe the effects of excessive occlusal force on gingival fibroblasts and collagen fibers of dog. The experiment was performed in 5 dogs. 1 dog was used as control and 4 dogs as experimental group. In experimental group, high Sun Platinum casting metal crowns with 2.0mm thick were placed artificially onto the upper right third premolars to create the traumatic occlusion. After 3, 7, 15, 30 experimental days, the specimens were examined under electron microscope. The following results were observed: 1. In 3, 7, 15 day groups, swelling of the mitochondria in the fibroblast was observed. 2. In 7, 14, day groups, dilation of the endoplasmicreticulum in the fibroblast was observed. 3. There were no remarkable changes in the nucleus of the fibroblasts and collagen fibers. 4. In 30 day group, the changes of the mitochondria and the ER in the fibroblast were recovered to have the similar appearance with that of the control group.

• Journal of Korea Foundry Society
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• v.22 no.5
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• pp.265-270
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• 2002

A novel jewelry master pattern manufacturing process which reduce manufacturing steps by employing a Duraform rapid prototyping mold and a low melting alloy has been suggested. The novel process follows the steps of 'jewelry 3D CAD design ${\rightarrow}$ Durafrom RP mold ${\rightarrow}$ low melting alloy master pattern' while the previous process follows more complicated steps of 'jewelry idea sketch ${\rightarrow}$ detailed drawing ${\rightarrow}$ wax carving ${\rightarrow}$ flask ${\rightarrow}$ silver master pattern.' An upper and a lower part of molds have been manufactured of Duraform powder, of which melting point is $190^{\circ}C$. A maser pattern was manufactured by pouring a low melting alloy of Pb-Sn-Bi-Cd, so called Woods Metal, of which melting point is $70^{\circ}C$, into the mold. The master pattern is a shape of a disk of 20mm diameter that contains various design factors. The variations of dimensions, surface roughness, surface pore ratio were measured by an optical microscope, a surface roughness profilometer, and a Rockwell hardness tester. The pattern made of were maeasured by an optical microscope, a surface roughness profilometer, and a Rockwell hardness tester. The pattern made of low melting alloy has sufficient surface hardness, and surface pore ratio to be used as the jewelry master pattern.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.175-180
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• 2004

Improving furnace efficiency is a high priority need for aluminum, glass, steel and other metal casting industries. Oxy-fuel combustion is considered to be one of the most effective method to improve thermal efficiency and reduce $NO_x$, SOx and $CO_2$ emissions for high temperature furnaces. The characteristics of an oxy-fuel flame, in particular its shape, radiation profile and exhaust gas composition are considerably different to those of an air-fuel burner. For this reason, a new approach is needed regarding factors such as burner design, power input levels, number and positioning strategies of burners and also control philosophies. In this paper will discuss the latest developments of high performance oxy-fuel combustion reheating furnace system. This high performance oxy-fuel combustion system will be shown to be technologically superior to other types of combustion systems in the areas of fuel efficiency, emissions and productivity.

• Advances in materials Research
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• v.2 no.1
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• pp.37-49
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• 2013

The transition metal salt doped solid polymer electrolyte [TSPE] were prepared with HPMC as a host polymer. The virgin and doped films were prepared by solution-casting method and investigated using wide angle X-ray scattering method. Micro structural parameters like lattice strain (g%), stacking/twin faults, the average number of unit cells counted in a direction perpendicular to the Bragg's plane (hkl) spacing of (hkl) planes dhkl, crystallite size Ds, distortion width, standard deviation were determined by whole pattern powder fitting (WPPF) method, which is an extension of single order method. It is found that the crystallite size decreases with the increase in the content of $FeCl_3$. This decrease is due to increase in localized breaking of polymer network which also accounts for the amorphous nature of the material. The filler inorganic salt $FeCl_3$ acts as plasticizer. FTIR study also confirms and justifies the interaction between the polymer and in-organic salt in the matrix. Physical properties like mechanical stability and Ac conductivity in these films are in conformity with the X-ray results.

• Journal of the Korean Society of Industry Convergence
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• v.21 no.1
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• pp.29-36
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• 2018

Low pressure casting process for unidirectional carbon fiber reinforced aluminum (UD-CF/Al) composites which is an infiltration route of molten Al into porous UD-CF preform has been a cost-effective way to obtain metal matrix composites (MMCs) but, easy to cause non-uniform fiber distribution as CF clustering. Such clustered CFs have been a problem to decrease the density and thermal conductivity (TC) of composites, due to the existence of pores in the clustered area. To obtain high thermal performance composites for heat-sink application, the relationship between fiber distribution and porosity has to be clearly investigated. In this study, the CF distribution was evaluated with quantification approach by using two-dimensional spatial distribution method as local number 2-dimension (LN2D) analysis. Note that the CFs distribution in composites sensitively changed by sizes of Cu bridging particles between the CFs added in the UD-CF preform fabrication stage, and influenced on only $LN2D_{var}$ values.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.1
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• pp.64-68
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• 2014

This paper introduces the use of a crown-shaped (CR) lens to effectively diffuse the light from a light-emitting diode (LED) without any loss in the light intensity, in contrast to polymer-bulb-type diffusers. The diffusion lens was designed based on the Snell's law, which describes the physical path of a ray passing through the boundary between different media. CR lenses were fabricated by polydimethylsiloxane (PDMS) casting and UV-embossing processes, which used a pre-designed metal mold and UV-curable resin, respectively. Through experiments and optical evaluations, it was verified that the newly proposed CR lens not only decreased the vertical light strength and glare effect from an LED light source but also improved the diffusion characteristics while maintaining the quality of the LED's light intensity.

• Applied Microscopy
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• v.26 no.2
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• pp.235-241
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• 1996

Amophization and decomposition behaviour in $Mg_{62}Cu_{26}Y_{12}$ alloy prepared by melt spinning method and wedge type metal mold casting method have been investigated by a detailed transmission electron microscopy. Amorphous phase has formed in melt-spun ribbon. In the case of the wedge type specimen, however, the amorphous phase has formed only around the tip area within about 2 mm thickness. The remaining part of the wedge type specimen consists of crystalline phases, $Mg_{2}Cu\;and\;Cu_{2}Y$. The supercooling for crystallization behaviour of the amorphous $Mg_{62}Cu_{26}Y_{12}$ alloy, ${\Delta}T_x$ has been measured to be about 60 K. Such a large undercooling of the crystallization bahaviour enables formation of the amorphous phase in the $Mg_{62}Cu_{26}Y_{12}$ alloy under the cooling rate of $10^{2}K/s$. The amorphous $Mg_{62}Cu_{26}Y_{12}$ has decomposed into crystalline phases, $Mg_{2}Cu\;and\;Cu_{2}Y$ after heat treatment at $170^{\circ}C\;and\;250^{\circ}C$.