This study investigates the melting point and brazing properties of the aluminum (Al)-copper (Cu)-silicon (Si)-tin (Sn) alloy fabricated for low-temperature brazing based on the alloy design. Specifically, the Al-20Cu-10Si-Sn alloy is examined and confirmed to possess a melting point of approximately 520oC. Analysis of the melting point of the alloy based on composition reveals that the melting temperature tends to decrease with increasing Cu and Si content, along with a corresponding decrease as the Sn content rises. This study verifies that the Al-20Cu-10Si-5Sn alloy exhibits high liquidity and favorable mechanical properties for brazing through the joint gap filling test and Vickers hardness measurements. Additionally, a powder fabricated using the Al-20Cu-10Si-5Sn alloy demonstrates a melting point of around 515oC following melting point analysis. Consequently, it is deemed highly suitable for use as a low-temperature Al brazing material.

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.

In this research, a new medium-entropy alloy with an equiatomic composition of FeCuNi was designed using a phase diagram (CALPHAD) technique. The FeCuNi MEA was produced from pure iron, copper, and nickel powders through mechanical alloying. The alloy powders were consolidated via a high-pressure torsion process to obtain a rigid bulk specimen. Subsequently, annealing treatment at different conditions was conducted on the four turn HPT-processed specimen. The microstructural analysis indicates that an ultrafine-grained microstructure is achieved after post-HPT annealing, and microstructural evolutions at various stages of processing were consistent with the thermodynamic calculations. The results indicate that the post-HPT-annealed microstructure consists of a dual-phase structure with two FCC phases: one rich in Cu and the other rich in Fe and Ni. The kernel average misorientation value decreases with the increase in the annealing time and temperature, indicating the recovery of HPT-induced dislocations.

This study mainly treats a new type of the bracing friction damper system, which is able to minimize structural damage under earthquake loads. The slotted bolt holes are placed on the shear faying surfaces with an intention to dissipate considerable amount of friction energy. The superelastic shape memory alloy (SMA) wire strands are installed crossly between two plates for the purpose of enhancing recentering force that are able to reduce permanent deformation occurring at the friction damper system. The smart recentering friction damper system proposed in this study can be expected to reduce repair cost as compared to the conventional damper system because the proposed system mitigates the inter-story drift of the entire frame structure. The response mechanism of the proposed damper system is firstly investigated in this study, and then numerical analyses are performed on the component spring models calibrated to the experimental results. Based on the numerical analysis results, the seismic performance of the recentering friction damper system with respect to recentering capability and energy dissipation are investigated before suggesting optimal design methodology. Finally, nonlinear dynamic analyses are conducted by using the frame models designed with the proposed damper systems so as to verify superior performance to the existing damper systems.

기존의 전자 기판에서 땜납으로 사용되고 있는 Sn-Pb계 합금을 대체하기 위한 새로운 합금을 개발하기 위하여 열역학을 이용한 상평형계산을 통해 얻은 다원계 상태도를 바탕으로 적정한 녹는점과 용융구간을 가지는 Sn-Bi-In-Zn계 솔더합금을 설계하였다. 설계된 합금을 제작하여 XRD, DSC및 EDX로 분석하여 상의 확인,조성분석 및 고상점과 액상점 등의 녹음 거동을 확인하였다. 또한 열처리에 따른 미세구조의 변화를 관찰하였고, 이러한 조직변화가 기계적 성질에 미치는 영향을 경도실험과 인장실험을 통해 연구하였다.