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나노인덴테이션과 주사탐침현미경을 이용한 박막 재료의 특성평가
김봉섭,윤존도,김종국,Kim, Bong-seob,Yun, Jon-do,Kim, Jong-kuk 한국재료학회 2003 한국재료학회지 Vol.13 No.9
Surface and mechanical properties of thin films with submicron thickness was characterized by nanoindentation with Berkovich and Vickers tips, and scanning probe microscopy. Nanoindention was made in a depth range of 15 to 200 nm from the surface by applying tiny force in a range from 150 to $9,000 \mu$N. Stiffness, contact area, hardness, and elastic modulus were determined from the force-displacement curve obtained. Reliability was first tested by using fused quartz, a standard sample. Elastic modulus and hardness values of fused quartz measured were the same as those reported in the literature within two percent of error. Mechanical properties of ITO thin film were characterized in a depth range of 15∼200nm. As indentation depth increased, elastic modulus and hardness decreased by substrate effect. Ion beam deposited DLC thin films were indented in a depth range of 40∼50 nm. The results showed that the DLC thin film using benzene and bias voltage 0∼-50 V has elastic modulus and hardness value of 132 and 18 GPa respectively. Pure DLC thin films showed roughnesses lower than 0.25 nm, but silicon-added DLC thin films showed much higher roughness values, and the wavy surface morphology.
Al6061 Bulk재에서 압축시험에 의한 상온가공성 분석 및 마찰인자 측정
김국주,박종수,윤존도 경남대학교 신소재연구소 2003 신소재연구 Vol.15 No.2
부피성형(bulk forming)은 가공속도, 소재 회수를 및 가공 후의 조직 미세와 등의 유리한 점이 많아 대량 생산에 적합한 가공 방식이다. 그러나 금형형상과 가공조건들이 적절하지 못할 경우 형상오차 및 연성파괴 등의 성형결함이 발생하게 된다. 이 성형결함 없이 성형될 수 있는 한계를 부피 성형한계(bulk forming limit)라고 하는데, 이것은 가공성(workability)과 의미가 비슷하다. 가공성은 공정종류 금형과 소재사이의 마찰, 변형속도 등에 의해 좌우되므로 예측하기 어렵다. 따라서 본 실험에서는 가공성을 Al6061의 소재에서 가공온도, 마찰 및 변형을 속도에 따른 성형한계도(forming limit diagram)로 작성하여 정량화하고자 하였다. 또 압축시험에서 금형과 소재사이의 마찰효과에 의한 베럴링(barreling) 현상이 생기므로 신빙성 있는 실험결과를 얻기 힘들다. 따라서, 각 마찰조건에서 링 압축시험을 통한 마찰인자를 구해서 압축시험으로 구한 측정웅력을 보정하여 유동웅력(flow stress)을 구하는데 사용하고자 한다. Bulk forming process is widely used for a large plastic deformation in a metal industry, which has a lot of advantages at processing speed, raw material utilization, fine microstructure, etc. But if die shape and process conditions are selected improperly, forming defects can be found due to geometric errors and ductile fracture. Bulk forming limit is defined as it is deformed without these defects which is similar to the workability. Prediction of workability is difficult because of dependence on a type of processes, friction of die and material, deformation rate, etc. Therefore, in this study, forming limit diagram is made depending on forming temperature, friction and strain rate to analyze the workability of A16061 bulk material. Also, it is difficult in measuring of reliable result exactly because the barreling is caused by interfacial friction between die and material at the compression test. So, friction factor is measured at the different friction conditions by ring compression test and then flow stress will be calculated from the measured stress by compression test.