http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
(TiB+TiC) 입자강화 Ti기 복합재료의 접촉하중에 따른 내마모 특성
최봉재,Choi, Bong-Jae 한국주조공학회 2017 한국주조공학회지 Vol.37 No.4
The aim of this research is to evaluate the wear properties of (TiB+TiC) paticulate reinforced titanium matrix composites (TMCs) by in-situ synthesis. Different particle sizes (1500, $150{\mu}m$) and contents (0.94, 1.88 and 3.76 mass% for Ti, 1.98 and 3.96 mass% for the Ti6Al4V alloy) of boron carbide were added to pure titanium and to a Ti6Al4V alloy matrix during vacuum induction melting to provide 5, 10 and 20 vol.% (TiB+TiC) particulate reinforcement amounts. The wear behavior of the (TiB+TiC) particulate reinforced TMCs is described in detail with regard to the coefficient of friction, the hardness, and the degree of reinforcement fragmentation during sliding wear. The worn surfaces of each sliding wear condition are shown for the three types of wear studied here: transfer layer wear, particle cohesion wear and the development of abrasive areas. The fine reinforcements of TMCs were easily fragmented from the Ti matrix as compared to coarse reinforcements, and fragmented debris accelerated the decrease in the wear resistance.
Al 합금 다이캐스팅 용 타이타늄 기지 복합재료 슬리브의 내용손성 및 내마모성 평가
최봉재 ( Bong Jae Choi ),성시영 ( Si Young Sung ),김영직 ( Young Jig Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.2
The main purpose of this study was to evaluate the endurance against Al alloy melts and wear resistance of an in-situ synthesized titanium matrix composite (TMC) sleeve for aluminum alloy die-casting. The conventional die-casting shot sleeve material was STD61 tool steel. TMCs have great thermal stability, wear and oxidation resistance. The in-situ reaction between Ti and B4C leads to two kinds of thermodynamically stable reinforcements, such as TiBw and TiCp. To evaluate the feasibility of the application to a TMCs diecasting shot sleeve, the interfacial reaction behavior was examined between Al alloys melts with TMCs and STD61 tool steel. The pin-on-disk type dry sliding wear test was also investigated for TMCs and STD61 tool steel.
논문 : 침입형 및 치환형 화합물을 함유한 Ti 정밀주조용 Al2O3 주형의 α-case 계면반응 거동
최봉재 ( Bong Jae Choi ),이슬 ( Seul Lee ),김영직 ( Young Jig Kim ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.7
The newly developed α-case controlled mold material for Ti investment castings was suggested in this research. The Al2O3 mold containing interstitial TiO2 and substitutional Ti3Al was manufactured by the reaction between Al2O3 and Ti. It is obvious that as the TiO2 and Ti3Al content in the mold surface were increased, the depth of the interfacial reaction was significantly reduced. In addition, substitutional Ti5Si3 in the mold surface owing to the reaction between Ti and SiO2 from the binder was effective for α-case reduction. Therefore, the α-case reduction was accomplished by the diffusion barrier effect of interstitial TiO2, substitutional Ti3Al and Ti5Si3.
반응생성 합성에 의한 (TiB+TiC) 입자강화 Ti기 복합재료의 미세조직 및 인장특성 평가
최봉재 ( Bong Jae Choi ),김영직 ( Young Jig Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.8
The aim of this study is to evaluate the microstructure and tensile property of in-situ (TiB+TiC) particulate reinforced titanium matrix composites (TMCs) synthesized by the investment casting process. Boron carbide (1,500 μm and 150 μm) was added to the titanium matrix during vacuum induction melting, which can provide the in-situ reaction of 5Ti+B4C→4TiB+TiC. 0.94, 1.88 and 3.76 wt% of B4C were added to the melt. The phases identification of the in-situ synthesized TMCs was examined using scanning electron microscopy, an X-ray diffractometer, an electron probe micro-analyzer and transmission electron microscopy. Tensile properties of TMCs were investigated in accordance with the reinforcement size and volume fraction. The improvement of tensile property of titanium matrix composites was caused by load transfer from the titanium matrix to the reinforcement and by grain refinement of titanium matrix and reinforcements. (Received April 2, 2010)
SD계 흰쥐에서 마황 추출물의 아급성 경구 독성 시험 연구
최동기 ( Dong Gi Choi ),심경준 ( Kyung Jun Shim ),최봉재 ( Bong Jae Choi ),박수연 ( Soo Yeon Park ),장문석 ( Mun Seog Chang ),박성규 ( Seong Kyu Park ) 대한본초학회 2008 大韓本草學會誌 Vol.23 No.4
Objectives: Ephedrae herba, also known as Ma-huang, is a traditional Korean medicinal herb. It has been used to treat asthma, nose and lung congestion, and fever with anhidrosis for centuries. Recently, Ma-huang was used as a source of ephedrine in many dietary supplements for weight reduction in the United States. The objective of this study was to investigate the subacute toxicity of ephedrae herba extract in rats. Methods: SPF Sprague-Dawley male rats were administered orally with ephedrae herba extract for 4 weeks as several doses(0, 125, 250, 500, 1,000, and 2,000 mg/kg). We examined number of deaths, clinical signs, body weights and gross findings for experimental period. Results: No dead animals were found during the experimental period. In addition, no differences were found between control and treated groups in clinical signs, hematology, serum biochemistry, and other findings. Conclusions: In conclusion, above data suggest that no observed adverse effect level of ephedrae herba extract in SD rats might he over 2,000 mg/kg/day in this study.
Ni기 초내열 합금 LESS 1의 합금설계 및 평가: 1. 합금 설계 및 고온 상 안정성 평가
윤정일 ( Jeong Il Youn ),강병일 ( Byung Il Kang ),최봉재 ( Bong Jae Choi ),김영직 ( Young Jig Kim ) 한국주조공학회 2013 한국주조공학회지 Vol.33 No.5
The alloys required for fossil power plants are altered from stainless steel that has been used below 600oC to Ni-based alloys that can operate at 700oC for Hyper Super Critical (HSC) steam turbine. The IN740 alloy (Special Metals Co. USA) is proposed for improved rupture strength and corrosion resistance at high temperature. However, previous studies with experiments and simulations on stable phases at about 700oC indicated the formation of the eta phase with the wasting of a gamma prime phase, which is the most important reinforced phase in precipitation hardened Ni alloys, and this resulted in the formation of precipitation free zones to decrease the strength. On the basis of thermodynamic calculation, the new Ni-based superalloy named LESS 1 (Low Eta Sigma Superalloy) was designed in this study to improve the strengthening effect and structure stability by depressing the formation of topologically close packed phases, especially sigma and eta phases at high temperature. A thermal exposure test was carried out to determine the microstructure stability of LESS 1 in comparison with IN740 at 800oC for 300 hrs. The experimental results show that a needle-shaped eta phase was formed in the grin boundary and it grew to intragrain, and a precipitation free zone was also observed in IN740, but these defects were entirely controlled in LESS 1.