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Shot-peening 표면처리된 Ti함유 스테인리스강의 응력균열부식
최한철(Han-Cheol Choe) 한국표면공학회 2004 한국표면공학회지 Vol.37 No.6
Stress corrosion cracking(SCC) characteristics of shot-peened stainless steel containing Ti (0.09 wt%-0.92 wt%) fabricated by the vacuum furnace were investigated using SCC tester and potentiostat. The homogenization and the sensitization treatment were carried out at 1050℃ for 1hr and 650℃ for 5 hr. The samples for SCC were shot-peened using Φ0.6 ㎜ steel ball for 4 min and 10 min. Intergranular and pitting corrosion characteristics were investigated by using EPR and CPPT. SCC test was carried out at the condition of 288℃, 90 kgf pressure, water with 8 ppm dissolved oxygen, and 8.3×10??/s strain rate. After the corrosion and SCC test, the surface of the tested specimen was observed by the optical microscope, TEM and SEM. Specimen with Ti/C ratio of 6.14 showed high tensile strength at the sensitization treatment. The tensile strength decreased with the increase of the Ti/C ratio. Pitting and intergranular corrosion resistance increased with the increase of Ti/C ratio. Stress corrosion cracking strength of shot-peened specimen was higher than that of non shot-peened specimen. Stress corrosion cracking strength decreased with the increase of the Tile ratio.
임상에서 사용된 치과용 Ni-Ti합금 파일의 피로파괴현상
최한철 ( Han Cheol Choe ),배성철 ( Seong Chul Bae ),고영무 ( Yeong Mu Ko ),황호길 ( Ho Keel Hwang ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 대한금속·재료학회지 Vol.44 No.6
The purpose of this study was to investigate the fatigue fracture phenomena of clinically used dental Ni-Ti alloy files. ProTaper(R)(Maillfer, Dentsply, Ballaigues, Switzerland) were used, respectively, for experiment. In order to observe the fatigue surface of clinically used file, the fractured files were classified into three groups: fractured files at the upper, middle and lower part after clinical use. The fractured surface and chemical composition were studied with energy dispersive X-ray spectroscopy(EDS) and field emission scanning electron microscope(FE-SEM) to analyze elements on the surface of fractured file. Fatigue fracture crack of Ni-Ti file was initiated and propagated at defects such as scratch formed by machine under repeated load. Fractured surface of Ni-Ti file showed the brittle fracture behavior at the exterior and ductile fracture behavior at the interior of specimen. The ductile fracture behavior appeared predominantly at the lower part of Ki-Ti file compared with at the upper part of Ni-Ti file.
최한철 ( Han Cheol Choe ),홍국선 ( Kook Sun Hong ),고영무 ( Yeong Mu Ko ),김병옥 ( Byung Ock Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 대한금속·재료학회지 Vol.44 No.6
The aim of this investigation was to analyze surface of clinically failed dental implant fixture in order to determine possible causes of failure. The failed implants were classified into three groups; 3 and 5 month used implant, 19 and 60 month used implant, and fractured implant, after implantation for 33 month and 120 month in patient jaws. The topography and surface chemical composition were studied with energy dispersive x-ray spectroscopy(EDS) and field emission scanning electron microscope(FE-SEM) to analyze elements on the surface of flank and bottom of thread. Evaluations were performed at the upper, middle and lower implant fixture. From surface observation of 3 and 5 month used implant, contaminants were detected in the middle and lower part of implants. Overall, foreign elements such as silicon, carbon, oxygen, zinc, sulfur, zirconium, and chloride were detected in failed implants. From surface observation of 19 and 60 month used implant, the corrosion was accelerated at the bottom of thread that was accumulated chloride. Corrosion products showed in the bottom of thread including dissolution elements, such as Au, Cu, Ag, from suprastructure of dental implant system. From surface observation of fatigue fractured implants, the crack were nucleated in the bottom of thread and the crack of corrosion fatigue was predominantly propagated. The corrosion products including chloride were found opposite side of starting point of corrosion fatigue crack. We could find the fatigue striation and estimate the dimple fracture of implants.
치과보철용 Ni-Cr-Ti소결체합금의 이온용출과 생체적합성
최한철(Han-Cheol Choe),김승희(Seung-Hui Kim) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.5
In this study, ion release and biocompatibility of sintered Ni-Cr-Ti alloy for dental prosthodontics have been researched by corrosion and cell culture test. The microstructures of the alloys were observed by optical microscope, and corrosion behavior was investigated using potentiostat (Model PARSTAT 2273, EG&G, USA). Cell culture was carried out using hGf cell in DMEM (Welgene Inc., South Korea) supplemented with 10% fetal bovine serum (FBS) (Welgene Inc., South Korea) and antibiotic antimycotic solution (Welgene Inc., South Korea). After corrosion and cell culture test, surface morphologies were observed by field-emission scanning electron microscopy. For wettability behaviors, contact angles were measured by wettability test. As the content of Ti increased, the number of pit decreased and the corrosion resistance was improved from anodic polarization test, also, polarization resistance of samples containing Ti remarkably improved as compared with the alloy not containing Ti. The sintered alloy showed a low contact angle due to the pores formed on the surface. The addition of Ti element showed that the cell survival rate was better than that of the control group.
Nb함유 스테인리스강의 표면특성에 미치는 플라즈마질화의 영향
최한철(Han-Cheol Choe) 한국표면공학회 2004 한국표면공학회지 Vol.37 No.2
In order to develop the corrosion and wear resistance of stainless steels, effects of plasma-nitriding on the surface characteristics of stainless steels containing Nb were investigated by utilizing a potentiostat. It was found that plasma nitriding at 350℃, compared with 500℃, produced a good corrosion resistance as nitriding time increased, whereas stainless steel containing low Nb content showed that pitting potential and corrosion potential decreased.
최한철(Han-Cheol Choe),고영무(Yeong-Mu Ko) 한국표면공학회 2004 한국표면공학회지 Vol.37 No.5
The defects of partial denture frameworks are mainly shrinkage porosity, inclusions, micro-crack, particles from investment, and dendritic structure. In order to investigate a good casting condition of partial denture frameworks, the three casting alloys and casting methods were used and detected casting defects were analyzed by using electrochemical methods. Three casting alloys (63Co-27Cr-5.5Mo, 63Ni-16Cr, 63Co-30Cr-5Mo) were prepared for fabricating partial denture frameworks with various casting methods; centrifugal casting (Kerr, USA), high frequency induction casting (Jelenko Eagle, USA), vacuum pressure casting (Bego, Germany). The casting temperature was 1,380℃ (63Co-27Cr-5.5Mo and 63Ni-16Cr) and 1,420℃ (63Co-30Cr-5Mo). The casting morphologies were analyzed using FE-SEM and EDX. The corrosion test of the dendritic structure was performed through potentiodynamic method in 0.9% NaCI solutions at 36.5℃ and corrosion surface was observed using SEM. The defects of partial denture frameworks improved in the order of centrifugal casting, high frequency induction casting, and vacuum pressure casting method, especially, pore defects were found at part of clasp in the case of centrifugal casting method. The structure of casting showed dendritic structure for three casting alloys. In the 63Co-27Cr-5.5Mo and 63Co-30Cr-5Mo, α-Co and ε-Co phases were identified at matrix and γ-Ni₂Cr second phase were shown in 63Ni-16Cr. Also, the corrosion resistance of cast structure increased in the order of vacuum pressure casting, high frequency induction casting, and centrifugal casting method.
최한철(Han-Cheol Choe),이호종(Ho-Jong Lee),정용운(Yong-Woon Jeong) 한국표면공학회 2005 한국표면공학회지 Vol.38 No.3
SKD11 steel has been widely used for tools, metallic mold and die for press working because of its favorable mechanical properties such as high toughness and creep strength as well as excellent oxidation resistance. The ion nitrided tool steel containing Mo results in improvement of corrosion resistance, strength at high temperature and pitting resistance, especially in Cl? contained environment. But the Mo addition causes a disadvantage such as lower oxidation resistance at elevated temperature. In this study, several effects of ion-nitriding on the oxdation characteristics for SKD11 steel with various oxidation temperature were investigated. SKD11 steels were manufactured by using vacuum furnace and solutionized for 1 hr at 0,050℃, Steel surface was ion nitrided at 500℃ for 1 hr and S hr by ion nitriding equipment. Ion nitrided specimen were investigated by SEM, OM and hardness tester. Oxidation was carried out by using muffle furnace in air at 500℃, 700℃ and 900℃ for 1 hr, respectively. Oxidation behavior of the ion nitrided specimen was investigated by SEM, EDX and surface roughness tester. The conclusions of this study are as follows: It was found that plasma nitriding for 5 hr at 500℃, compared with ion nitriding for 1 hr at 500℃, had a thick nitrided layer and produced a layer with good wear, corrosion resistance and hardness as nitriding time increased. Nitrided SKD11 alloy for 1 hr showed that wear resistance and hardness decreased, whereas surface roughness increased, compared with nitrided SKD11 alloy for 5 hr. The oxidation surface at 900℃ showed a good corrosion resistance.