• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1997년도 추계학술대회 논문집
• /
• pp.895-898
• /
• 1997

These days, most of new materials, which is in use widely as cutting process materials have a characteristic in common. That is hard cutting. So, it happens that hardness by cutting temperature. And hardness on cutting process has an effect on tool wear or life shortness of tools. To solve these problems hot-machining is proposed. When a material is heated, organization of material is soften. So cutting process becomes easy. When such a hot-machining method applies on drilling process and then heated material is processed, cutting force is less than usual drilling process cutting force. In this paper, when a material is heated, cutting force on drilling process is measured. It is decided that the best suitable temperature area. And it suggest that the better hot-machining condition as surface accuracy is measured.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
• /
• pp.323-325
• /
• 1995

An Inductively Coupled Plasma(ICP) was employed to prepare the Diamond-Like Carbon film with $CH_4$ gas. We observed the changes of mechanical, optical properties and internal stress of the films according to the variation of discharge power and negative-self bias. When weak magnetic field is applied, the properties of film are observed to change drastically. In magnetized case, the micro-hardness and the internal stress increase up to critical point and droped down in marked contrast to unmagnetized case. It suggests that large amount of ion flux exists due to high dissociation rate of the reactive radicals in plasma with magnetic field as reported elsewhere. As a result of FT-IR absorption measurement it could be confirmed that the $CH_x$ bonding and the micro-hardness and the internal stress decreased with the increase of negative-self bias.

• 대한기계학회논문집
• /
• 제13권2호
• /
• pp.229-235
• /
• 1989

본 연구에서는 편면도금 강판과 복합조직 고장력 강판간의 이종 용접재의 피로거동을 연구하고져 한다. 즉 유한요소법으로 응력분포를 조사하고 그 결과와 피로균열발생 위치를 비교 검토해 보고자 한다.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
• /
• pp.1065-1066
• /
• 2006

The aging behavior of sintered Al composites with various ceramic contents was investigated. 2xxx series blended powder was used as the starting powder. Ceramic contents were 0wt.% and 5wt.%. The blended powders were compacted at 250MPa. The sintering process was performed at $620^{\circ}C$ for 60min in a $N_2$ atmosphere. Each part was solution-treated at $518^{\circ}C$ for 60min and aged at $180^{\circ}C$. The Rockwell hardness at the peak aging time increased with ceramic contents. However, the peak aging time at maximum hardness was reduced with increased ceramic contents.

• 한국표면공학회지
• /
• 제32권3호
• /
• pp.224-234
• /
• 1999

An attempt was made to characterize the relationship between pretreatment processes, electrolysis conditions and behaviors of the plated gold layer. In order to investigate the effect of pretreatment processes on plating, rest potential measurements of various pretreated stainless steels and a.c.-impedance spectroscopy tests were carried out in the strike plating solution. Characteristics of plated gold layers and adhesions between plated gold layers and stainless steel substrates were examined by scratching tests and micro-Vickers hardness tests. The result shows that the strike plating enhanced the adhesion of interface, the cathodic electro-activation pretreatment process improving both corrosion resistance and adhesion strength. The preferred orientations of plated gold layers were examined by the X-ray diffraction technique. As the current density increases, [111] preferred orientation of plated gold layers was found to become well developed.

• Corrosion Science and Technology
• /
• 제20권5호
• /
• pp.242-248
• /
• 2021

Unforeseen failures of boilers in power plants may affect the continuation of electricity generation. Main failures in boilers are influenced by the tube material, tube position, boiler service temperature and pressure, and chemical composition of the feed water and coal. This investigation was intended to find answers on the causes and mechanism of failure of the fire-side boiler water-wall tubes, due to perforation and corrosion. The tube conformed to the material requirements in terms of its chemical composition and hardness. Microscopic examination showed ferrite and pearlite indicating no changes in its microstructure due to the temperature variation. SEM test showed a single layer and homogenous film density particularly on the area far from perforation. However, layers of corrosion product were formed on the nearby perforation area. EDX showed that there were Na, Ca, S, and O elements on the failed surface. XRD indicated the presence of Fe₂O₃ oxide. The failure mechanism was identified as a result of significant localized wall thinning of the boiler water wall-tube due to oxidation.

• 한국작물학회지
• /
• 제58권4호
• /
• pp.408-415
• /
• 2013

본 연구는 동아시아 및 동남아시아에서 수집한 들깨, 차조기 그리고 이들 잡초형 계통들에 대하여 10개의 양적 및 질적 형질들을 이용하여 형태적 변이성을 조사하였다. 그 결과 분석에 이용된 형질들 중에서 종자크기와 종자경도는 재배형 들깨와 재배형 차조기 그리고 들깨의 재배형과 잡초형 계통들을 식별하는 유용한 형질로 밝혀졌으며, 반면에 재배형 및 잡초형 차조기의 계통들은 조사한 대부분의 형질들에서 뚜렷한 차이를 나타내지 않았다. 주성분분석 결과에서 분석에 이용된 10개의 형질들 중에서 꽃색(QL6), 엽표면색(QL3), 종자크기(QN2), 종자경도(QL1), 종자색(QL2), 줄기색(QL7), 엽이면색(QL4) 등은 1축 위에서 음의 방향에 기여하였고, 개화일수(QN1)와 잎모양(QL5), 모용빈도(QL8) 등은 1축 위에서 양의 방향에 기여하였다. 특히, 이들 형질들 중에서 꽃색(QL6), 엽표면색(QL3), 종자크기(QN2), 종자경도(QL1) 그리고 모용빈도(QL8) 등은 들깨 재배형와 차조기의 재배형 그리고 들깨의 재배형 및 잡초형 계통들을 식별하는데 유용한 형질들이었다. 그러나 차조기의 재배형 및 잡초형 계통들은 대부분의 형질들에서 명확하게 구분되지가 않았다. 아직까지 동아시아 및 동남아시아에서 들깨와 차조기의 야생종은 알려져 있지는 않지만, 들깨와 차조기 작물의 잡초형 계통들은 재배형 들깨와 재배형 차조기 작물의 기원을 이해하는데 분류학적으로 중요한 위치에 있는 것으로 생각된다.

• 한국버섯학회지
• /
• 제8권3호
• /
• pp.109-115
• /
• 2010

팽이버섯의 자실체 특성이 재배사 환경인자중 습도변화에 따라 어떤 변화를 보이는지를 조사하기위해 농촌진흥청 버섯과에 보존된 8개 균주에 대해 형태적 특징, 경도, 색깔 등을 조사하였다. 형태적 특징에서 백색계통 버섯의 대길이는 습도 낮아지면서 증가하는 경향을 보이나 갈색계통은 균주에 따라 각기 다른 상관관계를 보이고 있어 습도가 절대적인 지배요인은 아닌 것으로 판단된다. 갓직경은 습도와 상관관계가 없으며, 대굵기 및 갓두께는 품종에 따라 약간의 차이를 보이고 있다. 품종에 있어서는 대길이가 가장 긴 품종은 ASI 4051, ASI 4031 이고, 짧은 품종은 ASI 4103 이며, 갓직경은 ASI 4103 가장 크고, 갓두께는 ASI 4103이 가장 두꺼우며, 가장 얇은 것은 ASI 4065이고, 대굵기는 ASI 4103이 가장 굵으며, ASI 4153이 가장 가늘었다. 백색계통은 습도가 낮아지면 ASI 4021를 제외한 균주는 L값이 증가하는 경향이나 ASI 4021은 정도의 차이는 있으나 갓과 대가 명도(L)값은 감소된다. 그러나 채도(a, b) 값은 습도처리에 따른 차이가 작아 어떤 평가를 내리기가 곤란하였다. 갈색계통은 습이 낮아지면 명도 L 이 증가하는 경향이며, 채도(a, b) 값은 습도에 따른 차이가 크기 않아 명확한 결론을 내리기는 곤란하지만, 갓의 a 값은 습도 증가에 따라 증가하는 경향을 보이고, 갓의 b값은 a 값과는 다르게 감소하는 경향을 보이고 있다. 품종별 특성을 보면 대부분 대보다 갓 색이 밝은 색을 보인다. 습도 조건에 따른 경도의 차이는 어떤 일정한 상관관계를 보이지 않았으나, 갓보다 대의 경도가 높으며, 품종에 따라 각기 다른 정도를 나타낸다. 가장 높은 경도를 보이는 것은 ASI 4021 이며, 가장 약하게 나타난 것은 ASI 4166 품종이었다. 계통 간에는 갈색 보다 백색이 높을 것으로 나타났다. 이 결과 습도조건 보다는 품종 및 계통에 따른 차이가 확실히 보이고 있다.

• 열처리공학회지
• /
• 제32권5호
• /
• pp.212-223
• /
• 2019

This study is to investigate the relationship between microstructural factors and tensile properties after aging heat treatment of the 15-5PH stainless steel at the temperature range of $450^{\circ}C$, $500^{\circ}C$ and $550^{\circ}C$ for various time. For the aging time of 2 hours, hardness showed maximum at $450^{\circ}C$ and then decreased with increasing aging temperature. While, hardness decreased gradually during aging $450^{\circ}C$, $500^{\circ}C$ and $550^{\circ}C$ from 1 hour to 5 hours but the hardness nearly unchanged until the 100 hours after 5 hours aging. When aging at $450^{\circ}C$, Cu atoms preferentially aggregated at the prior austenite grain boundaries and martensite lath boundaries, and Cu concentration at those boundaries was nearly unchanged even after aging for 100 hours. Therefore it was suggested that the coherency is still maintained after 100 hours aging at $450^{\circ}C$. Aging at $500^{\circ}C$ and $550^{\circ}C$ results in an increase in the concentration of Ni at the martensite lath boundaries and prior austenite grain boundaries, resulting in the formation of reversed austenite. Especially, when aged at $550^{\circ}C$ for 100 hours, the concentration of Ni remarkably increased at those boundaries, and thus the microstructure of herring bone shape was appeared. Considering the migration of Ni atom to the lath boundaries and prior austenite grain boundaries, Ni atoms contributed greatly to the formation of reversed austenite. On the other hand, it was found that Cu atoms hardly moving to those boundaries may not be contributed to the formation of reversed austenite. When aging at $450^{\circ}C$, the coarsening of the precipitated Cu atoms proceeded very slowly with increasing aging time, therefore the decrease in strengths were small but the reduction area was considerably increased due to the softening of the matrix. At the aging temperature of $500^{\circ}C$ and $550^{\circ}C$, the strengths decreased and the elongation and reduction area increased due to the appearance of the reversed austenite. Especially, the increase of reduction area was remarkable.

• 한국해양공학회지
• /
• 제16권6호
• /
• pp.60-64
• /
• 2002

This paper describes the machining characteristics of the MoSi$_2$--based composites through the process of electric discharge drilling with various tubular electrodes. In addition to hardness characteristics, microstructures of Nb/MoSi$_2$laminate composites were evaluated from the variation of fabricating conditions, such as preparation temperature, applied pressure, and pressure holding time. MoSi$_2$-based composites have been developed in new materials for jet engines of supersonic-speed airplanes and gas turbines for high-temperature generators. These high performance engines may require new hard materials with high strength and high temperature-resistance. Also, with the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material. The tool electrode is almost -unloaded, because there is n direct contact between the tool electrode and the work piece. By combining a non-conducting ceramic with more conducting ceramic, it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and MoSi$_2$ powder was an excellent strategy to improve hardness characteristics of monolithic MoSi$_2$. However, interfacial reaction products, like (Nb, Mo)SiO$_2$and Nb$_2$Si$_3$formed at the interface of Nb/MoSi$_2$, and increased with fabricating temperature. MoSi$_2$composites, with which a hole drilling was not possible through the conventional machining process, enhanced the capacity of ED-drilling by adding MbSi$_2$, relative to that of SiC or ZrO$_2$reinforcements.