• 한국도로학회논문집
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• 제20권4호
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• pp.1-6
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• 2018

PURPOSES : The objective of this study is to evaluate of the effect of thermal segregation reduction in asphalt paving using material transfer vehicles (MTVs). METHODS : Asphalt paving using MTVs was carried out, and the paved surface temperature was measured using an infrared camera. The amount of thermal segregation was estimated from temperature variations. RESULTS : The transportation of hot mix asphalt (HMA) using dump trucks caused temperature segregation that persisted in the paving surface if an MTV was not used. The average temperature variation was 8.58% in paved surfaces where an MTV was not used. However, the temperature variation was 3.10%, 2.86%, and 4.53% for the base layer, inter-layer, and surface layer, respectively, when an MTV was used. CONCLUSIONS : The use of an MTV in asphalt paving reduces thermal segregation approximately 2.3 times in an asphalt mat via a remixing process and also allows for a smoother work process because the paver never needs to stop to receive HMA. However, MTV equipment without pre-heating devices requires careful temperature control during the warm up process at the MTV during construction in the winter.

• 소성∙가공
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• 제12권2호
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• pp.94-101
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• 2003

For the optimal net shape forging of S semi-solid materials (SSM), it is important to predict the deformation behavior and defects of materials. Among these defects, liquid segregation is detrimental to produce products with good mechanical properties. Moreover, to apply a numerical method to thixoforging, it is very important to prevent a liquid segregation during forming process. The liquid segregation phenomena in deformation behavior of semi-solid material with variation of test specimen size were studied. The SSM compression tests were performed by dynamic material test system with a furnace. Stress-strain curves and microstructures of SSM were investigated, and Porosities were analyzed to evaluate the effects of experiment parameters on liquid segregation.

• 한국도로학회논문집
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• 제9권4호
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• pp.135-147
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• 2007

아스팔트 포장에서의 골재분리(segregation)는 혼합물 내의 굵은골재와 잔골재가 고르게 분포하지 않은 결과이며, 균열, 레블링(raveling), 박리(stripping)와 같은 조기 파손을 야기한다. 그러나 소성변형에 대한 골재분리의 효과는 아직까지 제대로 규명되지 못하고 있다. 본 연구에서 수행된 실험 및 분석 결과, 아스팔트 포장의 소성변형은 혼합물의 골재분리보다는 혼합물 내의 골재 구조에 더 큰 영향을 받음을 알 수 있었다. 또한 굵은골재의 체적이 증가함에 따라 혼합물의 소성변형 저항성은 증가하였다. 그러나 이러한 현상은 낮은 공극율을 갖는 혼합물에서는 잘 일치하였지만, 높은 공극율을 갖는 혼합물에서는 골재의 체적 증가 보다는 공극율 자체가 소성변형에 더 큰 영향을 줌을 알 수 있었다. 즉, 공극율 10%를 기준으로, 이를 초과하는 혼합물은 굵은 골재의 체적이 큼에도 불구하고 소성변형 저항성은 크게 감소함을 알 수 있었다.

• 한국주조공학회지
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• 제21권6호
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• pp.343-349
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• 2001

The effect of cooling rate on the solidification microstructure and segregation behavior of 7075 and 7050 aluminum alloy was investigated. Samples were solidified with cooling rates from 0.3 to $17^{\circ}K/sec$. Using the cooling curves of each sample, liquidus, eutectic and intermetallic reaction temperatures were estimated. The microstructures were characterized in terms of dendrite arm spacing and eutectic volume fraction. The segregation behavior of each alloying element of these alloys in various cooling rates was discussed.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.664-667
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• 2001

Segregation of binary particle systems in a horizontally gyrated bed has been experimentally studied to recover the heavy metals from municipal waste incineration (MWI) ash. Differences in density and size had less effect on segregation. Effective segregation took place under the centrifugal effect of 1 or less for any particle size ratio. Zn, Cu and Pb were concentrated in the upper side of bed by the horizontal vibration. However, there was less change in concentration for other metals such as Mg, Al and Fe etc. The separation system with the horizontal gyrating separator proved to be an effective method for the pretreatment of recovering Zn, Cu and Pb from incineration residues.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.167-170
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• 1997

For the optimal net shape forging of semi-solid materials (SSM), it is important to predict the deformation for variation of strain rate. It should be necessruy to conduct a formation of stress-strain curve in semi-solid alloys for analysis of the thixoforming process. Particularly, important problem to application of computer aided engineering in SSM processing is to prevent a segregation of liquid component during compression process. The liquid segregation is studied as multistage change of the strain rate and test piece size to prevent the liquid segregation during the compression process. The compression test for semi-solid aluminium alloy with a controlled solid fraction is performed by dynamic material test system with a furnace. Moreover morphology of structure and fraction of pore are investigated through compression test.

• 한국주조공학회지
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• 제13권1호
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• pp.71-80
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• 1993

Squeeze casting has advantages to improve mechanical properties of nonferrous castings without losing high productivity. Sound pore free structure makes it possible to be subjected to heat treatment and welding. This process became popular to produce lighter automobile parts alternating cast iron parts. It has, however, two disadvantages of segregation and scattered structure due to the solidified layers in sleeve. In this study segregation behavior of squeeze cast Al-7%Si-0.3%Mg alloy bars was investigated using HVSC machine under various injection conditions. Degree of segregation decreased with injection pressure and effect of injection velocity on it was small. Segregation mode of solute was strongly governed by solidification mode and flow pattern.

• Journal of Welding and Joining
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• 제12권2호
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• pp.87-96
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• 1994

Correlation between microstructural features and segregation of elements (Si, Mn, P and S) near the mid of thickness in the base metal and the synthetic HAZ was investigated. Furthermore, the relationship between the degree of center segregation and weld cold cracking susceptibility in the thickness direction was also conducted by evaluating the effect of P concentration on the critical applied stress. The results obtained are as follows: 1) Pearlite band, containing the MnS type inclusion and a locally transformed structure with a higher hardness, was observed in the center segregation region. 2) By the weld thermal cycle, center segregation region was transformed to the white band which had a higher hardness than that of base metal due to a greater hardenability of concentrated Mn, P etc.. 3) Weld cold cracking susceptibility in the thickness direction was mainly dependent on the concentration of impurity elements rather than on the number of the segregated particles near the mid of thickness. 4) During welding, the higher concentrated region was easily changed into white band. Therefore, it could be predicted that the initiation and propagation of a cold crack would be promoted by increasing the restraint stress and hydrogen content.

• Metals and materials international
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• 제24권6호
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• pp.1262-1274
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• 2018

The inhibition of gravity segregation has been a long-standing challenge in fabrication and applications of homogeneous immiscible alloys. Therefore, the effect of rare-earth La on the gravity segregation of Al-Bi immiscible alloys was investigated to understand the homogenization mechanism. The results showed that the addition of La can completely suppress the gravity segregation. This is attributed to the nucleation of Bi-rich liquid phase on the in-situ produced $LaBi_2$ phase and the change of the shape of $LaBi_2@Bi$ droplets. In addition, a novel strategy is developed to prepare the homogeneous immiscible alloys through the addition of rare-earth elements. This strategy not only is applicable to other immiscible alloys, but also is conducive to finding more elements to suppress the gravity segregation. This study provided a useful reference for the fabrication of the homogeneous immiscible alloys.

• 한국재료학회지
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• 제31권7호
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• pp.409-419
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• 2021

The effect of solidification rate on micro-segregation in investment casting of IN738LC superalloy was studied. In Ni-based superalloys, the micro-segregation of solute atoms is formed due to limited diffusion during cast and solidification. The microstructure of cast Ni-based superalloys is largely divided into dendrite core of initial solidification and interdendrite of final solidification. In particular, mosaic shaped eutectic γ/γ' and carbides are formed in the interdendrite of the final solidification region in some cases. The micro-segregation phenomena formed in regions of dendrite core and interdendrite including eutectic γ/γ' and carbides were analyzed using OM, SEM/EDS and micro Vickers hardness. As a result of analysis, the lack of (Cr, W) and the accumulation of Ti were measured in the eutectic γ/γ', and the accumulation of (Cr, Mo) and the lack of Ti were measured in the interdendrite between dendrite and eutectic. Carbides formed in interdendritic region were composed of (Ti, W, Mo, C). The segregation applied to each microstructure is mainly due to the formation of γ' with Ni₃(Al,Ti) composition. The Ni accumulation accompanied by Cr depletion, and the Ti accumulated in the eutectic region as a γ' forming elements. The Mo tends to diffuse out from the dendrite core to the interdendrite, and the W diffuse out from the interdendrite to the dendrite core. Therefore, the accumulation of Mo in the interdendrite and the deficiency of W occur in the eutectic region located in the interdendrite. Heat treatment makes the degree of the micro-segregation decrease due to the diffusion during solid solution. This study could be applied to the heat treatment technology for the micro-segregation control in cast Ni-based superalloys.