The purpose of this study was to analyze microstructural changes and evaluate the mechanical properties of TWIP steel subjected to variations in heat treatment, in order to identify optimal process conditions for enhancing the performance of TWIP steel. For this purpose, a homogenization heat treatment was conducted at 1,200 °C for 2 h, followed by hot rolling at temperature exceeding 1,100 °C and cold rolling. Annealing heat treatment is achieved using a muffle furnace in the range of 600 °C to 1,000 °C. The microstructure characterization was performed with an optical microscope and X-ray diffraction. Mechanical properties are evaluated using micro Vickers hardness, tensile test, and ECO index (UTS × Elongation). The specimens annealed at 900 °C and 1,000 °C experienced a significant decrease in hardness and strength due to decarburization. Consequently, the decarburization phenomenon is closely related to the heat treatment process and mechanical properties of TWIP steel, and the effect of the microstructure change during annealing heat treatment.

The purpose of this study is to develop a zirconium-based alloy with low modulus and magnetic susceptibility to prevent the stress-shielding effect and the generation of artifacts. Zr-7Cu-xSn (x = 1, 5, 10, 15 mass%) alloys are prepared by an arc melting process. Microstructure characterization is performed by microscopy and X-ray diffraction. Mechanical properties are evaluated using micro Vickers hardness and compression test. The magnetic susceptibility is evaluated using a SQUIDVSM. The average magnetic susceptibility value of the Zr-7Cu-xSn alloy is 1.176 × 108 cm3g1. Corrosion tests of zirconiumbased alloys are conducted through polarization test. The average Icorr value of the Zr-7Cu-xSn alloy is 0.1912 A/cm2. The elastic modulus value of 14 ~ 18 GPa of the zirconium-based alloy is very similar to the elastic modulus value of 15 ~ 30 GPa of the human bone. Consequently, the Sn added zirconium alloy, Zr-7Cu-xSn, is very interesting and attractive as a biomaterial that reduces the stress-shielding effect caused by differences of elastic modulus between human bone and metallic implants. In addition, this material has the potential to be used in metallic dental implants to effectively eliminate artifacts in MRI images due to low magnetic susceptibility.

목적: 본 연구는 –2.00D 이하의 난시를 가진 사람에게 콘택트렌즈 처방 시 구면등가대등법에 의한 구면 콘택트렌즈가 토릭 콘택트렌즈와 비교하여 시력, 자각적 만족도의 차이가 어느 정도인지 확인하고자 하였다. 방법: 전신질환 및 안과적 수술경험이 없고 실험의 취지를 이해하고 동의한 교정시력 1.0 이상의 남녀 6명을 대상으로 하였다. 구면과 토릭콘택트렌즈는 동일한 재질과 베이스커브의 콘택트렌즈를 사용하였으며, 콘택트렌즈 피팅을 위해 문진, 전안부검사, 각막곡률검사, 굴절검사, 피팅 평가 등을 실시한 후 교정시력과 착용 후 자각적 만족도(건조감, 이물감, 흐림, 눈부심, 두통, 가려움증, 충혈 등) 조사를 실시하였다. 결과: 난시도수에 따라 그룹A(-1.00D 미만), 그룹B(-1.00D ~ -2.00D)으로 나누어 등가구 면콘택트렌즈 처방결과 착용 시간이 길어짐에 따라 시력교정에 대한 만족도 낮았으나, 토릭 소프트콘택트렌즈의 경우 착용 시간에 상관없이 만족도가 매우 높게 조사되었다. 또한 등가 구면 콘택트렌즈의 처방 교정시력은 그룹 A(난시도수 -1.00D미만)의 경우 교정시력의 만족 도가 낮게 나타났으며, 그룹 B(난시도수 -1.00D~-2.00D)의 처방 교정시력에서는 등가구 면 처방된 콘택트렌즈에 비해 시력 향상과 높은 만족도를 보였다. 결론: 두 그룹 모두 구면 소프트콘택트렌즈와 토릭 소프트콘택트렌즈에서 시력향상에 유의한 차이를 보였으나, 자각적 만족도를 함께 비교한 결과 토릭 소프트콘택트렌즈를 처방할 경우 시력 향상과 안정피로 개선에 도움이 되기 때문에 난시 콘택트렌즈처방에서 토릭 소프트콘택트렌즈를 처방이 우선되어야 할 것으로 생각된다.

Microstructural and mechanical characteristics of Al-6Si-2Cu alloy for lightweight automotive parts were investigated. The test specimens were prepared by gravity casting process. Solution heat treatments were applied to as-cast alloys to improve mechanical properties. The microstructure of the gravity casting specimen presents a typical dendrite structure, having a secondary dendrite arm spacing (SDAS) of 37μm. In addition to the Al matrix, a large amount of coarsened eutectic Si, Al2Cu intermetallic phase, and Fe-rich phases were identified. After solution heat treatment, single-step solution heat treatments were found to considerably improve the spheroidization of the eutectic Si phase. Two-step solution treatments gave rise to a much improved spheroidization. The mechanical properties of the two-step solution heat treated alloy have been shown to lead to higher values of properties such as tensile strength and microhardness. Consequentially, the microstructural and mechanical characteristics of Al alloy have been successfully characterized and are available for use with other basic data for the development of lightweight automotive parts.