• Journal of the Mineralogical Society of Korea
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• v.22 no.1
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• pp.1-11
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• 2009

Fine-grained peridotite xenoliths are rarely trapped in the basaltic rocks from the southeastern part of Jeju Island. Based on textural characteristics of the constituent phases showing uniform-sized, fine-grained tabular to mosaic grains with rare porphyroclastic relics, the studied samples can be defined as fine-grained, foliated porphyroclastic peridotites (FPP). Almost no significant difference among the FPPs in textures and major element compositions implies that the FPPs were derived from a structural domain, experiencing similar deformation events and deformation patterns. Moreover, the bimodal distribution with kink-banded porphyroclasts ($2{\sim}3mm$) and stain-free neoblasts ($200{\sim}300{\mu}m$), straight to gently curved grain boundaries with triple junctions, interstitial melt pockets, and microstructures for migrating grain boundary suggest that the studied samples went through dynamic recrystallization (${\pm}$ static recrystallization) in the presence of melt/fluid movement along foliation planes. No notable difference between the FPP and common protogranular xenoliths in major element compositions and geochemical evolution also implies that the FPP and protogranular xenoliths were from a similar horizon. Thus, the textural and geochemical characteristics of the FPPs reflects deformation events occurred at a localized and narrow zone within the lithospheric mantle beneath the Jeju Island. Although further detailed studies are necessary to define deformation events, the most possible process which could trigger deformation in the FPP in the rigid upper mantle was the ascending basaltic magma forming high-stress deformation zones. The suggested high-stress deformation zones in the lithosphere beneath the Jeju Island may be produced by paleo-faulting events related to the ascent of basalt magma before Jeju Island was formed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.107-110
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• 2007

It has been reported that the permanent strain could happen during recrystallization and grain growth even under the externally applied stress which is much lower than yield stress. In this study, we performed dilatometry experiments under the various compressive stresses and measured the amount of recrystallization and grain growth induced permanent strain. A new constitutive equation based on the concept of boundary migration induced plasticity was suggested to describe the recrystallization and grain growth induced plasticity. This equation was verified by comparing the calculated values with dilatometric experimental data under the various compressive stresses.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.427-430
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• 2007

Gas turbine disk components have been used by Ni-base superalloys which have high temperature strength for enduring stress induced by high speed rotation. This study introduced the overview of development strategy of precision forging of turbine disk and closed-die forging process for manufacturing good quality gas turbine disk. To make superior quality turbine disk, it is important to select optimal forging process conditions like preform shape, die shape and forging temperature etc. In this paper, closed-die forging process has been studied through the rigid-plastic finite element simulation. Proposed forging process can be used for the successful manufacturing of small-size gas turbine disk.

• Korean Journal of Materials Research
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• v.7 no.11
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• pp.942-950
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• 1997

NiAI기 산화물 분산강화(Oxide Dispersion Strengthende:ODS)합금을 기계적 합금화 (Mechanical Alloying: MA)방법으로 제조하였으며, 열간압축방법으로 성형하였다. 연이어 단순항온처리에 의한 정상결정립성장과 특성조건에서의 thermomechanical treatment 에 의한 이차재결정화를 유도하였다. 결정립 조대화된 ODSD MA NiAI의 creep 성질 및 이에 조대화된 미세조직은 creep 성질이 저하된 반면, 이차재결정화된 MA NiAI의 creep성질은 크게 향상되었다. 이 creep 성질의 향상은 이차재결정화의 특성인 급격한 결정립의 조대화, 분산상의 성장억제 및 grain aspect ratio의 증가에 기인한 것으로 사료되었다. 이차재결정화된 ODS MA NiAI의 creep또는 glide controlled dislocation creep임을 제시하지만, 전체 creep속도가 결정립 크기 및 grain aspect ratio의 영향을 크게 받은 것을 볼 때, 결정립계 미끄럼기구가 주 creep 기구와 조합되어 MA NiAI의 전체 creep기구에 영향을 준 것으로 추정할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.7
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• pp.1243-1250
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• 2003

In the present study, hot forging process for a lower arm connector of an automobile was investigated. An FEM code, DEFORM-3D, was used to analyze the process and the process parameters, such as temperature, strain and strain rate, were obtained. The microstructure of the connector was predicted by applying the Sellars and Yada microstructure evolution models to the process parameters. The method of microstructure prediction used in the present study seems to be effective for the quality assurance of a forged automotive product.

• Transactions of Materials Processing
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• v.10 no.4
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• pp.338-346
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• 2001

Evaluation of microstructural changes is important for process control during open die forging of heavy ingots. The control of forging parameters, such as shape of the dies, reduction, temperature and sequence of passes, is to maximize the forging effects and to minimize inhomogeneities of mechanical properties. The hot working die steel is produced by using the multistage open die forging. The structure is altered during forging by subsequent Precesses of plastic deformation, recrystallization and grain growth. A numerical analysis using an rigid visco-plastic finite element model was performed to predict microstructural evolution of hot working die steel.

• Transactions of Materials Processing
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• v.7 no.3
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• pp.197-206
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• 1998

This paper presents the prediction of dynamic recrystallization behavior during hot forging of Inconel 718. Another experiment of pancake forging was also carried out to examine the recrystallization ration dynamically recrystallizaed grain size, and grain growth in the forging. In experiments cylindrical billets were forged by two operations with variations of forging temperature, reduction ration of deformation. and preheating process at each forging step. Also the finite element program, developed here for the prediction using the metallurgical models was used for the analysis of to Inconel 718 upsetting and the results were compared with experimental ones.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.03a
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• pp.81-90
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• 1996

In this paper, a finite element based system is presented for the prediction of the distributions of the recrystallized grain sizes in the workpiece in hot forging. The system adopts fully coupled finite element thermo-mechanical model for predicting plastic deformatin and heat transfer occuring in the workpiece, and employsexisting metallurgical models relating the recrystallization behavior with the thermo-mechanical variables such as temperatures, strain, and strain rate. The system is applied to upsetting of cylindrical preform. The predicted grain sizes are compared with the measurements . It is further applied to forging of a complex-shaped product.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.136-141
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• 1998

재결정된 Zircaloy-4 합금을 35$0^{\circ}C$ 의 여러가지 알칼리 금속 수산화물 수용액에서 부식시켜 동일한 무게증가량을 갖도록 조절한 뒤, 1M H$_2$SO$_4$ 용액에서 그 시편에 대한 임피던스 특성을 분석하였다. LiOH, NaOH, KOH 순서로 알칼리 금속의 이온반경이 클수록 수소이온의 이동에 대한 임피던스가 증가함에 따라 산화막을 통한 수소이온의 흡수가 점차로 어려워졌다. 이것은 Zr$^4$$^{+}$와 이온반경이 비슷한 알칼리 금속 수용액 조건에서 얻은 부식시편은 open grain boundary 와 equiaxed microstructure의 산화막을 갖기 때문이었고, 반면에 Zr$^4$$^{+}$와 이온반경의 차이가 큰 알칼리 금속 수용액 조건에서 얻은 부식시편은 compact 한 columnar microstructure의 산화막을 갖기 때문인 것으로 생각된다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.25-25
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• 2003

마그네슘 합금은 결정구조가 HCP구조로 슬립면이 제한되어있어 상온에서의 가공이 용이하지 않다. 따라서 최근 마그네슘 합금의 미세 조직을 제어하기 위해 많은 연구가 수행되어 왔다. 본 연구에서는 구조용 재료 및 기능성 재료로 기대되는 마그네슘 합금(AZ3l)을 이용하여 주조로부터 압출·압연 과정으로의 연속적인 판재 성형공정을 실행하였다. 모든 공정에 대한 전형적인 기계적 특성을 평가하기 위하여 각 공정에서 재료의 인장실험을 실시하였으며 각 공정 후에 향상된 기계적 특성들을 규명하기 위하여 경도시험을 실시하였다 또한 각 공정에서의 대표적인 미세 조직을 관찰하여 결정립 미세화에 따른 기계적 물성의 향상을 확인하였다. 주조재, 압출판재, 압연판재의 인장강도는 189.3㎫, 257.9㎫ 그리고 234.㎫로 증가하였다가 다소 감소하지만, 연신율은 상대적으로 16.26%, 24.99% 그리고 27.16%의 50%에 가까운 주목할만한 증가를 나타낸다. 인장실험의 실험결과로부터 얻어진 가공경화지수로부터 대상 재료인 마그네슘 합금(AZ3l)에 대하여 DRX의 거동을 예측할 수 있었으며, 압출후 압연 판재의 경우 연한 재결정 조직으로 인하여 연신율의 대폭적인 증가를 확인 할 수 있었다.