• Korean Journal of Materials Research
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• v.11 no.1
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• pp.8-14
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• 2001

Microstructural evolution and creep failure behavior of GTD 111 have been studied. Solidification and precipitation behaviors of the alloy during casting have been analyzed by microstructural observations. It has been found that MC carbides solidify just before the $\gamma$/$\gamma$' eutectic solidification. The ηphase was found to be formed by transformation of Ti-rich $\gamma$'phase. PFZ has formed in the vicinity of the transformed $\eta$ phase. A few MC particles, which have been identified as TaC, precipitated within the PFZ. Creep failure along grainboundary was dominant at and above $871^{\circ}C$. Creep failure above$ 871^{\circ}C$ was caused by the propagation of surface cracks and internal cracks. Creep crack has initiated at the microporosities embedded on the grainboundary. The $\eta$phase and PFZ have been found to be little or no effect on creep crack initiation.

• Journal of Conservation Science
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• v.29 no.4
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• pp.355-366
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• 2013

Diverse scientific analyses, including microstructure, ICP-AES, SEM-EDS, and P-XRF(Bench Top type and Gun type), were carried out on 6 bronze artefacts which handed from generation to generation. Also, we attempted to study applicability for authenticity of the bronze artefacts using scientific analyses based on the specific element. The results of ICP-AES analysis showed that the bronze were formed from an alloy of Cu, Sn, Pb with trace elements such as Ag, As, Co, Fe, but there were not Zn found. The result of P-XRF are 10~25% lower in Cu and 10~20% higher in Sn than that of ICP-AES. This is because of destannification that the compound of $SnO_2$ are present on the surface. The results of SEM-EDS represented that there is lead segregation. It was difficult to study applicability for authenticity of bronze artefact according to the microstructures and chemical components of the bronze artefacts. Therefore, as bronze artefacts have shown different corrosion materials depending on the buried environment and conserving environment, identifying the authenticity would be possible on the basis of the additional researches on the corrosion and comparative research of ancient art.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.1
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• pp.120-131
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• 2005

Statement of problem. More than 70% of patients who need the implant supported restoration are parially edentulous. The principles of design for implant supported fixed partial denture in mandibular posterior region are many and varied. Jurisdiction for their use is usually based on clinical evaluation. There are several areas or interest regarding the design of implant supported fixed partial denture in mandibular posterior region. 1) Straight and tripod configuration in implant placement, 2) Two restoration types such as individualized and splinted restorations. Purpose. The purpose of this study was to compare the amount and distribution of stress around the implant fixtures placed in the mandibular posterior region with two different arrangements and to evaluate the effects of splinting using the photoelastic stress analysis. Material & methods. 1) Production of study model: Mandibular partially edentulous model was waxed-up and duplicated with silicone and two models were poured in stone. 2) Fixture installation and photoelastic model construction: Using surveyor(Ney, USh), 3 fixtures(two 4.0 $\times$13 mm, one 5.0$\times$10 mm, Lifecore, USA) were insta)led in straight & tripod configurations. Silicone molds were made and poured in photoelastic resin (PL-2. Measurements group, USA). 3) Prostheses construction: Four 3-unit bridges (Type III gold alloy, Dongmyung co., Korea) were produced with nonhexed and hexed UCLA abutments and fitted with conventional methods. The abutments were tightened with 30 Ncm torque and the static loads were applied at 12 points of the occlusal surface. 4) Photoelastic stress analysis : The polarizer analyzer system with digital camera(S-2 Pro, Fujifilm, Japan) was used to take the photoelastic fringes and analysed using computer analysis program. Results. Solitary hexed UCLA restoration developed different stress patterns between two implant arrangement configurations, but there were no stress transfer to adjacent implants from the loaded implant in both configurations. However splinted restorations showed lesser amount of stresses in the loaded implants and showed stress transfer to adjacent implants in both configurations. Solitary hexed UCLA restoration with tripod configuration developed higher stresses in anterior and middle implants under loading than implants with straight configurations. Splintied 3 unit fixed partial dentures with tripod configuration showed higher stress development in posterior implant under loading but there were no obvious differences between two configurations. Conclusions. The tripod configuration of implant arrangement didn't show any advantages over the straight configuration. Splinting of 3 unit bridges with nonhexed UCLA abutments showed less stress development around the fixtures. Solitary hexed UCLA restoration developed tilting of implant fixture under offset loads.

• Corrosion Science and Technology
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• v.11 no.1
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• pp.1-8
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• 2012

The development of martensitic grades which can be processed in continuous galvanizing lines requires the reduction of the oxides formed on the steel during the hot dip process. This reduction mechanism was investigated in detail by means of High Resolution Transmission Electron Microscopy (HR-TEM) of cross-sectional samples. Annealing of a martensitic steel in a 10% $H_2+N_2$ atmosphere with the dew point of $-35^{\circ}C$ resulted in the formation of a thin $_{C-X}MnO.SiO_{2}$ (x>1) oxide film and amorphous $_{a-X}MnO.SiO_{2}$ oxide particles on the surface. During the hot dip galvanizing in Zn-0.13%Al, the thin $_{C-X}MnO.SiO_{2}$ (x>1) oxide film was reduced by the Al. The $_{a-X}MnO.SiO_{2}$ (x<0.9) and $a-SiO_{2}$ oxides however remained embedded in the Zn coating close to the steel/coating interface. No $Fe_{2}Al_{5-X}Zn_{X}$ inhibition layer formation was observed. During hot dip galvanizing in Zn-0.20%Al, the $_{C-X}MnO.SiO_{2}$ (x>1) oxide film was also reduced and the amorphous $_{a-X}MnO.SiO_{2}$ and $a-SiO_{2}$ particles were embedded in the $Fe_{2}Al_{5-X}Zn_{X}$ inhibition layer formed at the steel/coating interface during hot dipping. The results clearly show that Al in the liquid Zn bath can reduce the crystalline $_{C-X}MnO.SiO_{2}$ (x>1) oxides but not the amorphous $_{a-X}MnO.SiO_{2}$ (x<0.9) and $a-SiO_{2}$ oxides. These oxides remain embedded in the Zn layer or in the inhibition layer, making it possible to apply a Zn or Zn-alloy coating on martensitic steel by hot dipping. The hot dipping process was also found to deteriorate the mechanical properties, independently of the Zn bath composition.

• Journal of Conservation Science
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• v.27 no.1
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• pp.1-11
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• 2011

For the silver artifacts in the Koryo Dynasty excavated from Neungnae-ri Ganghwa island, the metallographic section analysis and hardness and chemical analysis were conducted. After making samples in the similar ratio of the composition concentration, the changes of the microstructure were checked according to the working method and temperature. The results show that those silver artifacts are Au-Cu alloys with 2 to 6 % of Cu. From the results it is judged that Cu was artificially alloyed with them to keep the proper hardness and identified that they were gilded by the amalgamation process seeing that mercury was included at the guilt layer. Also the porous texture on the surface of them could be formed at over $400^{\circ}C$, therefore, it is assumed the hot working or heat treatment at over $400^{\circ}C$ were performed. In silver artifacts made by the relief and repousse, they have the similar composition analysis to other 7 artifacts but the hardness is lower than pure silver. Consequently from differences in the hardness, it can be inferred that the low hardness of silver artifacts is concerned with manufacturing techniques.

• Restorative Dentistry and Endodontics
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• v.12 no.1
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• pp.39-49
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• 1986

The purpose of this study was to observe characteristic properties through the polarization curves and SEM images from 4 different types of amalgam obtained by using the potentiostats (Princeton EG & G) & SEM (Jeol/35), and to investigate the degree of corrosion on the oxidation peak of the each phase of amalgam. After each amalgam alloy and Hg was triturated as the direction of the manufacturer by means of the mechanical amalgamator (Shofu Co.), the triturated mass was inserted into the cylindrical metal mold which was 12mm in diameter and 10.0mm in height and was condensed by using routine manner. The specimen was removed from the mold and stored at room temperature for about 24 hours. The standard surface preparation was routinely carried out. Anodic polarization measurement was employed to confirm the corrosion behaviour of the amalgams in a 0.9% saline solution (P.H: 6.8-7.0) at $37^{\circ}C$. The initial rest potential (corrosion potential) was determined after 30 minutes of immersion of specimen in electrolyte, and the potential scan was begun at the point of 100mV cathodic from the corrosion potential. The scan rate was 0.17mV/sec. in the study to observe the degree of corrosion of each phase. SEI and EPMA images on the determined oxidation peaks of each amalgam were observed. The results were as follows: 1. In the four anodic polarization curves, low copper amalgams have three oxidation peaks and high copper amalgams have two oxidation peaks, -270mV, +26mV and +179mV(SEC) in the low copper lathe cut, and -300mV, +39mV and +163mV(SEC) in the low copper spherical. -4mV and +154mV(SEC) in the Dispersalloy, and +17mV and +180mV(SEC) in the Tytin as high copper amalgams. 2. ${\gamma}_2$ phase in the low copper amalgam and ${\eta}$ phase in the high copper amalgam were the most corrodible phases and Ag-Cu eutectic in high copper amalgam was the most slowly corroded phase. 3. Low copper amalgam was more susceptible in corrosion than high copper amalgam.

• Journal of Korea Foundry Society
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• v.11 no.6
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• pp.475-481
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• 1991

In this study the fabrication technology and mechanical properties of AC8A/$Al_2O_3$ Composites by squeeze casting process were investigated to develope for application as the piston materials that require good friction, wear resistance, and thermal stability. AC8A/$Al_2O_3$ composistes without a porosity and the break of preform were fabricated at the melt temperature of $740^{\circ}C$, the preform temperature of $500^{\circ}C$, and mold temperature of $400^{\circ}C$ under the applied pressure of $1200kg/cm^2$ as the results of the observation of microstructures. As the results of this study, the tensile strength of AC8A/$Al_2O_3$ composites was not increased linearly with $Al_2O_3$ volume fraction and so it seemed not to agree with the rule of mixture, which had been used often in metal matrix composite. Also the tensile strength after thermal fatigue test was little different from that before the test. Consequently it was thought that AC8A/$Al_2O_3$ composites fabricated under our experimental conditions had a good thermal stability and subsequently a good interface bonding. Wear rate(i.e., volume loss per unit sliding distance) of AC8A/$Al_2O_3$ composites was decreased with $Al_2O_3$ volume fraction and the sliding speed at both room temperature and $250^{\circ}C$ and so there was a good correlation between wear rate and hardness. Also the wear rate of AC/8A20% $Al_2O_3$ composities was obtained the value of $1.65cm^3/cm$ at sliding speed of 1.14m/sec as compared with about $3.0\;{\times}10^{-8}cm^3/cm$ hyereutectie Al-Si alloy(Al-16%Si-2%Cu-1%Fe-1%Ni), which applied presently for piston materials. The wear behavior of $Al_2O_3$ composites was observed to a type of abrasive wear by the SEM view of wear surface.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.6
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• pp.717-723
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• 2007

Statement of problem. Unreasonable distal cantilevered implant-supported prosthesis can mask functional problems of reconstruction temporarily, but it can cause serious strain and stress around its supported implant and surrounding alveolar bone. Purpose. The purpose of this study was to evaluate strain of implants supporting distal cantilevered fixed prosthesis with two different cantilevered length under distal cantilevered static load. Material and methods. A partially edentulous mandibular test model was fabricated with auto-polymerizing resin (POLYUROCK; Metalor technologies, Stuttgart, Swiss) and artificial denture teeth (Endura; Shofu inc., Kyoto, Japan). Two implants-supported 5-unit screw-retained cantilevered fixed prosthesis was made using standard methods with Type III gold alloy (Harmony C&B55; Ivoclar-vivadent, Liechtenstein, Germany) for superstructure and reinforced hard resin (Tescera; Ivoclar-vivadent, Liechtenstein, Germany) for occlusal material. Two strain gauges (KFG-1-120-C1-11L1M2R; KYOWA electronic instruments, Tokyo, Japan) were then attached to the mesial and the distal surface of each standard abutment with adhesive (M-bond 200; Tokuyama, Tokyo, Japan). Total four strain gauges were attached to test model and connected to dynamic signal conditioning strain amplifier (CTA1000; Curiotech inc., Paju, Korea). The stepped $20{\sim}100$ N in 25 N increments, cantilevered static load 8mm apart (Group I) or 16mm apart (Group II), were applied using digital push-pull gauge (Push-Pull Scale & Digital Force Gauge, Axis inc., Seoul, Korea). Each step was performed ten times and every strain signal was monitored and recorded. Results. In case of Group I, the strain values were surveyed by $80.7{\sim}353.8{\mu}m$ in Ch1, $7.5{\sim}47.9{\mu}m/m$ in Ch2, $45.7{\sim}278.6{\mu}m/m$ in Ch3 and $-212.2{\sim}718.7{\mu}m/m$ in Ch4 depending on increasing cantilevered static load. On the other hand, the strain values of Group II were surveyed by $149.9{\sim}612.8{\mu}m/m$ in Ch1, $26.0{\sim}168.5{\mu}m/m$ in Ch2, $114.3{\sim}632.3{\mu}m/m$ in Ch3, and $-323.2{\sim}-894.7{\mu}m/m$ in Ch4. Conclusion. A comparative statistical analysis using paired sample t-test about Group I Vs Group II under distal cantilevered load shows that there are statistical significant differences for all 4 channels (P<0.05).

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.4
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• pp.317-324
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• 2008

The objective of this study was to test effects of (1) where the occlusal contact points locate on a full veneer crown, and (2) which direction the contact forces are directed to, on the stresses within the luting cement layer that might suffer microfracture. A total of 27 finite element models were created for a mandibular first molar, combining 9 different locations of the occlusal contact points and 3 different loading directions. Type 3 gold alloy was used for crown material with a chamfer margin, and the luting cement material was glass ionomer cements in uniform thickness of $75{\mu}m$. Modeled crowns were loaded at 100 N. Different patterns in the cement stress were observed in the vicinity of the buccal and lingual margins. Whereas, the peak stress in buccal margin occurred approximately 0.5 mm away from the external surface, the highest stress in lingual margin was observed at approximately 1 mm. Significantly different distribution of stresses was recorded as a function either of the location of the occlusal contact points or of the loading direction. Higher stresses were produced by more obliquely acting load, and when the loaded point was in the vicinity of the cusp tip.

• Korean Journal of Materials Research
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• v.10 no.10
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• pp.703-708
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• 2000

As the engine design changes to get high efficiency and performance of commercial diesel engine, surface w wear of the earn follower becomes an important issue as applied load increasing at the contact face between cam follower and cam. We developed the ceramic cam follower made of sili$\infty$n nitride ceramic which was more wear resistant than the cast iron or sintered metal cam follower. Ceramic cam follower was made by direct brazing of thin ceramic disk to steel body using an active brazing alloy without the interlayer. In-situ crowning(R), resulted from the difference of thermal expansion coefficient between ceramic and carbon steel after direct brazing without any stress-relieving inter]ayer, could be controlled. When a earbon steel was heated above $A_{c1}$ point and then c$\infty$led, the expansion curve represented a hysteresis. Appropriate crowning was achieved below the $A_{c1}$ point(about $723^{\circ}C$) and crowning increased with brazing temperature exponentially above the $A_{c1}$ point. Optimum brazing temperature range was from 700 to $720^{\circ}C$. We developed successfully the ceramic cam follower having appropriate crowning and being inexpensive. Also we could successfully control the crowning of ceramic earn follower by hysteresis behavior of thermal expansion of earbon steel during direct brazing process.