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SiC 입자강화 Al-14Fe 복합재료의 고온변형 특성
유연철,전정식,이준선 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.3
Continuous hot torsion tests of 10vol%SiC_P/Al-14Fe composites were performed in the range of 350∼530℃ and 1.15×10^(-3)∼1.15×10^(-1)/sec. Flow curves of the hot torsion tests were analysed with respect to the characteristics of work hardening rate θ, dynamic recrystallization (DRX) and constitutive equation. The critical strain (ε_c) for DRX initiation was determined from changes in slope of the strain hardening rate -effective stress (θ-σ) curves, and it was decreased with increasing temperature and strain rate. Although the SiC particles helped the initiation of DRX, they also retarded dynamic recrystallization progress. Relationship between critical strain and peak strain (ε_P) was found to be ε_c = 0.51 ε_P. The stress dependence on the strain rate (ε˙) and temperature (T) could be described by hyperbolic sine relationship, ε˙=2.21×[sinh(1.92×10^(-2)·σ)]^(4.7)exp(-193.5 kJ/RT). The microstructural development during hot deformation were interpreted by dynamically recrystallized structures which were composed of equiaxed grains, subgrains and dislocation tangles.
고병철,이지환,유연철,전정식,김경택 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.12
Tensile and wear-resistance properties were studied on SiC particle reinforced Al-12Si eutectic alloy(AC8A) composites. The Al-Si alloy was produced by gas atomization process and the composites were fabricated by powder metallurgy route. On hot extrusion process, at an extrusion ratio of 25 : 1 and at 500℃, the Si precipitates and SiC particles were not fractured. During tensile tests the Si precipitates which were Larger than 4㎛ were fractured and the degree of fracture of SiC particles was small. As the Vol.% of SiC increased the fracture sources of the composites were varied from internal cracks of Si precipitates or decohesion of interfaces between SiC and matrix to separation of SiC particles within agglomeration regions. After thermal expousure the width of wear was increased with increasing exposure temperature and time. The wear mode was varied from abrasive wear to delamination wear with increasing SiC volume fraction.
유연철,전정식,한형기 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.5
In order to investigate the microstructures of Al-(0.8, 1.3, 3)wt%Fe alloys, solidification processes were performed with water-cooled mold, air-cooled mold and in furnace. The intermetallic particles of these alloys were analyzed by X-ray diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy. The eutectic structure between Al and Al_6Fe particles was dominant and a few Al₃Fe particles were observed as cooling rate increased. With the increasing Fe contents and cooling rate, the formation of microcellular structures of Al grains largely containing globular or rod-liked Al_6Fe intermetallic precipitates were predominant. The crystallographic orientation relationships between Al matrix and particles were identified as [2(33) ̄]_(Al)//[(11) ̄0]_(Al₃Fe), ((311) ̄)_(Al)//(2(22) ̄)_(Al_6Fe), (011 ̄)_(Al)//(001)_(Al_bFe) and [1 ̄12]_(Al)//[010]_(Al₃Fe). The Al-Fe alloy exibited goad thermal stability and appreciable strength up to 450℃. The results indicate that high solidification rate is necessary to obtain high temperature strength Al-Fe alloy.
Al-(0.6, 1.3) wt % Fe 합금의 고온변형 및 조직에 관한 연구
이호인,유연철,전정식,한형기 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.2
High temperature dynamic softening characteristics related to microstructures have been examined for Al-(0.6, 1.3)wt%Fe alloys deformed in torsion at temperatures between 300℃ and 500℃, and at strain rates of 2.65×10^(-2)/sec to 1.2/sec. The flow stress as a function of strain rose to a maximum value then gradually decreased towards a steady state deformation. The effect of temperature on the flow stress was more pronounce than that of strain rate in this experimental range. The high temperature restoration mechanism was found to be dynamic recrystallization(DRX). From the relations between flow stresses and microstructures including intermetallic compounds at specific points on a flow curve, it can be assumed that the intermetallic compounds promoted dynamic recrystallization and prohibited grains from growing during the high temperature deformation. The relation between Zenner-Hollomon parameter, Z, and the microstructure was also studied and the equiaxied DRX grains were shown at low value of Z range.