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Fe-Ni-Co 저열팽창성 합금의 고온 변형 특성 및 열간가공에 따른 열팽창 거동 연구
이기안,박종혁,조봉현,남궁정,김문철 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.9
The high temperature deformation behavior and the effect of hot compression on the thermal expansion behavior of Fe-29Ni-17Co low thermal expansion Kovar alloy were investigated in the compressive temperature range of 900~1300℃ at the strain rate range of 25~0.01 sec.^(-1). The temperature (T) and strain rate (ε˙) dependence of the flow stress (σ_(0.7)) could be well described by hyperbolic sine law as ε˙= A [sinh(0.0084 σ)^(5.2018)] exp(-330.41/RT). Surface hot cracking and significant voids around grain boundary could be found at low temperature below 1000℃ and low strain rate (0.01 sec.^(-1)). Thermal expansion coefficient α_(30~400) generally increased with increasing compressive temperature. Moreover, α_(30~400) remarkably increased as strain rate decreased at high temperature above 1100℃. However the thermal expansion coefficient α_(30~400) of low compressive temperatures (900℃ and 1000℃) anomalously increased especially at high strain rates. Experimental results indicated that not only α phase appearance but also grain size had definite influence on the thermal expansion behavior with hot deformation. The correlation between microstructure and thermal expansion behavior of Kovar alloy were also discussed.
저열팽창성 Fe-29Ni-17Co 코바 합금의 고온균열 발생과 고온연성에 미치는 S 및 Mn의 영향
이기안,박종혁,조봉현,남궁정,김문철 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.12
The effect of S & Mn on the hot ductility of Fe-29Ni-17Co Kovar alloy and the mechanism of high temperature cracking occurrence were investigated. It has been found that the brittle intergranular fracture at high temperature cracking is closely associated with the sulfide along grain boundary. Experimental results showed, especially when the S content was high and the Mn content was free, that small cavities could be nucleated easily on FeS particles along grain boundary and propagated fast at high temperature. The hot ductility of Kovar alloy was drastically increased with the addition of Mn and it was also increased with decreasing S content. SEM and FE-SEM analyses showed that the Mn addition in this alloy could cause ductile intergranular fracture appearance below 1150℃ by the precipitation of MnS. It was proposed from the results that the addition of Mn and optimum S content (below 30 ppm) in Kovar alloy was necessary in order to reduce the hot cracking susceptibility.
β-CuZn 합금의 항복강도 이상거동에 미치는 변형률 속도와 온도의 영향
이기안,장영원,이종수 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.3
A series of tensile and load relaxation behaviors in B2 type β-CuZn alloy have been examined to clarify the strain rate & the temperature dependence of yield stress anomaly. It has been found in tensile tests that the region showing anomalous peak of yield stress moves to a higher stress and higher temperature region with increasing strain rate. The anomalous yielding region below peak temperature(T_p) revealed slightly positive strain rate dependence, while the region above T_p showed considerably positive strain rate dependence. The slip lines formed below peak temperatures (T_P) were clearly visible with naked eye(coarse slip lines), and became finer near T_p(fine slip lines), while they disappeared completely above T_p. Based on the different tendency of temperature and strain rate dependence of anomalous yielding as the above-mentioned results, two types of deformation modes were suggested and incorporated into the flow curve analysis, which was in accord well with the experimental results. The slightly positive strain rate dependence of yield stress anomaly indicated that the yield stress anomaly in β-CuZn alloy mainly seemed to be attributed to the vacancy hardening.
이기안,송재영,성정석,최유미,이정로,이석영,김창영,김연규,이명철 한국작물학회 2012 Journal of crop science and biotechnology Vol.15 No.4
Balloon flower (Platycodon grandiflorum A. DC) is widely distributed in South Korea and there are some local landraces that are cultivated as a vegetable crop or medicinal plant. Making use of the gene resources of wild-type and landraces is a way to increase the genetic diversity of the cultivars. However, few tools or information are available on an efficient identification system for maintaining and management of these landraces. To improve the genetic resources for balloon flower, 22 simple sequence repeat (SSR)markers, also known as microsatellite markers, were evaluated in a collection of 42 balloon flower landraces, 34 of which were from Korea and eight from China. All microsatellite markers produced the 107 alleles ranging from 2 to 10 with a mean of 4.864 alleles per each locus (NA). The values of observed heterozygosity (HO) and expected heterozygosity (HE) ranged from 0.00 to 0.667 (mean of 0.285) and from 0.024 to 0.741 (mean of 0.416), respectively. An average value of polymorphic information contents (PIC) were 0.382 with a range of 0.023 to 0.703. Results of population structure and phylogenetic and principal coordinate analysis (PCoA) indicated that P. grandiflorum germplasm formed two largely distinct clusters according to their origins and the genetic differentiation. There was a high level of genotypic diversity at broad geographic regions between Korea and China, but the low genetic differentiation was found within the collections from Korea. The results of the genetic diversity will be useful for the selection of the parents for developing balloon flower breeding and the multi-locus SSR markers developed herein will be a valuable resource for germplasm assessments, evaluation of genetic diversity, and population genetic studies of balloon flower. Balloon flower (Platycodon grandiflorum A. DC) is widely distributed in South Korea and there are some local landraces that are cultivated as a vegetable crop or medicinal plant. Making use of the gene resources of wild-type and landraces is a way to increase the genetic diversity of the cultivars. However, few tools or information are available on an efficient identification system for maintaining and management of these landraces. To improve the genetic resources for balloon flower, 22 simple sequence repeat (SSR)markers, also known as microsatellite markers, were evaluated in a collection of 42 balloon flower landraces, 34 of which were from Korea and eight from China. All microsatellite markers produced the 107 alleles ranging from 2 to 10 with a mean of 4.864 alleles per each locus (NA). The values of observed heterozygosity (HO) and expected heterozygosity (HE) ranged from 0.00 to 0.667 (mean of 0.285) and from 0.024 to 0.741 (mean of 0.416), respectively. An average value of polymorphic information contents (PIC) were 0.382 with a range of 0.023 to 0.703. Results of population structure and phylogenetic and principal coordinate analysis (PCoA) indicated that P. grandiflorum germplasm formed two largely distinct clusters according to their origins and the genetic differentiation. There was a high level of genotypic diversity at broad geographic regions between Korea and China, but the low genetic differentiation was found within the collections from Korea. The results of the genetic diversity will be useful for the selection of the parents for developing balloon flower breeding and the multi-locus SSR markers developed herein will be a valuable resource for germplasm assessments, evaluation of genetic diversity, and population genetic studies of balloon flower.