Eco-Materials Processing & Design VII

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Authors: Seong Joo Lim, Kyoung Hoan Na, C.H. Lee
Abstract: The rotary swaging process for producing solid bars, tubes or wires is often used to obtain the chipless forming process compared with the conventional process such as the machining and welding operation. Furthermore, machined chip, dust particles, harmful gas, and surface contamination to be commonly generated at hot working during the conventional process could be eliminated as the swaging process is applied and conducted at room temperature. Experiments for swaged product were performed to analyze the influence of the swaging process on the mechanical properties and dimensional precision in terms of surface roughness, surface hardness, and deviation of formed dimension. The changes of dimensional precision in swaged product are also checked out and considered for various process parameters such as the forming speed and the reduction in the outer diameter. Based on the experimental results, the surface roughness is improved under the swaging process. The weight of rod shift is reduced by about 15 % from 223.5 g to 190.2 g. Thus the number of operations to produce the final product under the conventional process is larger than that under the swaging process to be able to omit the machining and welding operation, etc. This paper demonstrates that a rotary swaging process turns out to be an environment-friendly forming process or chipless forming process without the machined chip.
Authors: Seong Joo Lim, Geun An Lee, Ha Guk Jeong, Seo Gou Choi, C.H. Lee
Abstract: In automotive industries, components have replaced steel with aluminum alloys since the automotive parts that used aluminum alloys have the ability to improve the environment by lower weights and recycling of waste materials. In this study, experiments were carried out to investigate the characteristics of the developed aluminum alloys according to the forming temperature and speed. The microstructure of forged product in hot forging process was also investigate. The results revealed that the grain size of aluminum alloys was grown according to the forming temperature and speed. Three-dimensional finite element analyses were also carried out to investigate the forming load, deformed shape, and the stress distribution of the workpiece in the hot forging process. The deformed shape of the workpiece was consistent with the trend of experimental results.
Authors: Dae Hyun Song, C.W. Lee, K.Y. Nam, S.W. Lee, Yong Ho Park, Kyung Mok Cho, Ik Min Park
Abstract: The effect of Al content on the castability, tensile and creep properties of Mg-xAl-Zn alloy was investigated. The molten Mg-(3~11)Al-Zn alloys of 700°C were poured into the mould designed to estimate castability. Tensile and creep tests were performed for the alloys. The results show that the castability increased with higher Al content. Creep resistance decreased while tensile strength improved with increasing Al amount. Our microstructure study revealed that morphology of Mg17Al12 is the main factor determining the tensile and creep properties of as cast Mg-xAl-Zn alloys. The final purpose of this study is to develop the heat resistant Mg alloys to be applied in transportation systems such as automobile. Further research will be conductedon the effect of heat treatment and additional alloying elements on the microstructure and properties of Mg-xAl alloys.
Authors: Hyoung Wook Lee, Geun An Lee, Duk Jae Yoon, Seo Gou Choi, Nak Kyu Lee, Hye Jin Lee, Sung Min Bae
Abstract: A micro-alloyed non-heat-treated material does not need post heat treatment processes such as quenching and tempering after the forming process in production stages. This material can be called a green material since it can reduce industrial costs and harmful pollutants generated from post heat treatments. In this paper, near-net-shape forming processes were studied in order to make an automotive part using a micro-alloyed material. The cold forging technique using a former was utilized for the main shaping, and the cold incremental forming technique using a cross wedge rolling machine was adopted for the enhancement of strength and the final shaping of the part. In order to get more adequate process, the cross wedge rolling process is compared to the swaging process for the micro-alloyed steel and general carbon steels through experiments.
Authors: Jun Ki Chung, Sung Yeal Bae, Sung Gap Lee, Chan Park, Sang Im Yoo, Cheol Jin Kim
Abstract: We fabricated bi-axially textured pure Ni and Ni–5at.%W (Ni-5W) alloy tapes for the application of rechargeable battery cathode and coated superconductor, where the controlled microstructure of the substrate plays a critical role. The sintered Ni or Ni-W rods were cold-rolled into the thin tapes of 80 ~ 100 µm thickness, and the tapes were heat-treated for texture development with a line focused infrared heater. The temperature was maintained at 800 ~ 1050 °C, using a 1kW double ended linear halogen lamp in 96%Ar-4%H2 atmosphere. The (2 0 0) texture of Ni tape was successfully formed through optimization of the recrystallization infrared heating condition for the cold rolled Ni tapes. The full width half maximum of the Ni tapes was less than 10o, and the grain size was 20 ~ 40 µm. Focused IR-heating resulted in a better texture development and smaller grain size compared to the conventional resistive heating because of the steep temperature gradient.
Authors: Tae Hyun Nam, Shin Goo Hur, Jae Hwa Lee, Gyu Bong Cho
Abstract: Shape memory characteristics and superelasticity of an equiatomic Ti-Ni alloy with surface sulfide layers were investigated by means of thermal cycling tests under constant load, tensile tests, and scanning electron microscopy. Martensitic transformation start temperature (Ms) increased by sulfidation, which is ascribed to a compressive stress imposed by surface sulfide layers. Surface sulfide layers were found to make transformation elongation be small when their thickness was less than 5 ㎛. This is ascribed to the fact that the surface sulfide layers were not detached from substrates and constrained martensitic transformation. When thickness of the surface sulfide layers was 35 ㎛, transformation elongation was not affected by them because they were detached during transformation. Superelastic recovery decreased by the sulfide layers when their thickness was about 5 ㎛, while it did not change when the thickness was about 35 ㎛.
Authors: Gyu Bong Cho, Bong Ki Lee, Won Chul Sin, Tae Hyun Nam
Abstract: Si film electrodes for Li micro-film batteries were fabricated on a Cu substrate and a Ni/Cu film. In the structural properties, Si film had an amorphous structure, while the crystallinity of Ni buffer film was improved after annealing. FE-SEM observation demonstrated differences in surface morphologies of Si films fabricated with different methods. In the electrochemical properties, the Ni-inserted film showed the largest initial charge and discharge capacity, and the cell with annealed Si/Ni/Cu film showed good cycleability. It is believed that the insertion of Ni film as a buffer film improved the charge and discharge capacity owing to the enhancement of adhesion between Si film and Cu substrate.
Authors: Kwon Yeong Lee, Chang Seon Hwang, Seon Jin Kim, Gyung Guk Kim, Ji Hui Kim, Chong Seung Yoon
Abstract: The sliding wear behavior of a steam generator in a nuclear power plant (Inconel 600) was investigated at 225, 250 and 300°C. Effects of wear parameters such as sliding distance and contact stress were examined with SUS 304 (austenitic). In the prediction of the wear volume by Archard wear equation, the standard error range was calculated to be ±0.53×10-9 m3 and the reliability to be 71.9 % for the combination of Inconel 600 and SUS 304. The error range was considered to be relatively broad because the wear coefficient in Archard equation was assumed to be constant. However, the wear volume turned out to increase parabolically with the sliding distance owing to the combination of strain hardening of the wear surface and the oxidative wear. Based on the experimental results, the wear coefficient was modified as a function of the rotating sliding distance. The calculation with the modified wear equation showed that, although the error range was not significantly narrowed, the reliability increased from 71.9 to 78.1 %.
Authors: Ji Hui Kim, Kwang Su Na, Seon Jin Kim
Abstract: The cavitation erosion behavior of Fe-Cr-C-Si-xNi (x = 1, 2 and 3 wt.%) alloys were investigated for 50 hours using a 20 kHz vibratory cavitation erosion test equipment. 1 wt.% Ni added Fe-based hardfacing alloy showed excellent cavitation erosion resistance, comparable to the stellite 6. Above 1 wt.% Ni, however, the erosion resistance deteriorated quickly. It is conjectured that Ni addition above 1 wt.%, which has been shown to increase the stacking fault energy (SFE), resulted in reduction of the work hardening rate during the erosion test. Therefore, the enhanced cavitation erosion resistance of the 1 wt.% Ni alloy over the 2 and 3 wt.% Ni alloys could be explained in terms of the SFE, Ms temperature and work hardening.
Authors: M.H. Kim, S.H. Lee, H.N. Lim, Jung Mann Doh, H.G. Baik

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