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홍순익,권훈,윤상훈,이건배 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.10
The tempered martensite embrittlement (TME) has been analyzed in terms of impact toughness, fracture behavior, and microstructures in the 4140 steel and the 4340 steel with the Ni addition. On isothermal tempering, THE was detected by the continuous decreases in impact toughness, at 200 and 250℃ for 1-400 h. On isochronal tempering for 1 h, the THE troughs with the minimum at 300℃ in the 4140 steel and at 350℃ in the 4340 steel were observed. The presence of coarse carbides at the impurity-weakened grain boundaries led to the intergranular TME. As the impact toughness decreased in the TME region, the intergranular area extended. The intergranular fracture was mostly observed at the low level near or below about 5 J. THE in the 4340 steel was presented by a slower process, as compared to the 4140 steel. This may be caused by the delay of the formation of coarse boundary-carbides and by the high intrinsic toughness with the Ni-addition, requiring the coarser boundary-carbides for the activation of brittle intergranular fracture.
홍순익,정진희,김형섭 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.4
The mechanical properties of heavily drawn bundled Cu-Nb filamentary microcomposite was examined as a function of Nb content. In order to predict the variation of the yield strength with Nb content, the interfilamentary spacing was calculated as a function of Nb content based on the assumption that Nb filaments are distributed regularly along the sides of a triangular unit cell in the transverse section. The yield stress consists of the substructure strengthening component due to elongated grains, subgrains and/or cells, the phase boundary strengthening term associated with the Hall-Petch type interaction between dislocations and phase boundaries and precipitate strengthening component. The contributions from phase boundary strengthening σ_(P.B.)(Cu-Nb), and precipitate strengthening σ_(ppt), increases with increasing Nb content. However, the contribution from substructure strengthening, σ_(sub)(Cu-Nb), decreases with increasing Nb content since more grain or subgrain boundaries are absorbed at Cu/Nb phase boundaries with increasing Nb content. The good agreement between the prediction and the experimental data suggests that the increase of the strength in Cu-Nb filamentary microcomposite with increasing Nb content results mostly from an increasing volume fraction of Nb filaments, which act as barriers to plastic flow.
가공공정으로 제조된 Cu-Cr 계 미세복합재료의 기계적 전기적 특성
홍순익,송재숙 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.7
The strength and electrical conductivity of Cu-7Cr-0.9Ag-0.3Fe and Cu-7Cr-0.9Co-0.4Fe microcomposite plates obtained by cold rolling combined with intermediate heat treatments have been investigated. During cold working the primary and secondary dendrite arms were aligned along the rolling direction and elongated into filaments and also coarse Cr particles were found to be distributed uniformly in the matrix after thermo-mechanical deformation processing. The ultimate tensile strength and the conductivity of the Cu-Cr based microcomposites containing Ag were higher than those of Cu-Cr microcomposites containing Co. The strength of Cu-Cr composites was dependent on the spacing of the fine Cr filaments and volume fraction of the coarse Cr particles in accordance with a rule of mixture. The fracture surfaces of all the specimens showed ductile-type fracture.
Cu-Nb 미세복합재료의 미세구조의 안정성 및 강화기구 (1) : 미세구조의 안정성 Microstructural Stability
홍순익,임문수 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.12
The microstructural stability of Cu-Nb filamentary microcomposites wires fabricated by the bundling process were examined using TEM(Transmission Electron Microscope). The cross sectional shape of most Nb filaments in bundled wires appear straight with slight curvature. Nb filaments were distributed rather randomly and extremely irregular or heavily kinked Nb filaments were distributed to the cylinderization of Nb filaments during bundling process at high temperature. No flaws were observed near interface regions between subelemental wires and copper sheath, suggesting excellent bonding was promoted by copper sheath. Nb atoms were dissolved and numerous Nb precipitate were found to be formed in copper channels during bundling process. Twins were occasionally observed to have a twin relationship, indicating Nb filaments are strong barriers to twin propagation.
Cu-Nb 미세복합재료의 미세구조의 안정성 및 강화기구 : (2) 강화기구 (2) Strengthening Mechanism
홍순익,안장호 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.5
In this study, the deformation and fracture behavior of the Cu-Nb microcomposites fabricated by the bundling and drawing process was investigated. The yield strength of a Cu-20% Nb microcomposite was predicted by modifying the model of Verhoeven et al. It was assumed that the substructural strengthening in pure Cu and Nb phase fully contribute to the yield strength of Cu-Nb microcompoaite, σ_(Cu-Nb), at low draw strains (η $lt; 5.5). At high drawing strains (η $gt; 5.5) where the microstructural scale of the Cu matrix is limited by Nb filaments, the contribution of the partial grain boundaries (connecting the edge of Nb filaments) to the strength was assumed to be proportional to (λ/W_(Nb))^½ The good agreement between the yield stress predicted in this study and the experimental data at drawing strains between 6 and 9.5 supports the suggestion of the present study that the effectiveness of substructure strengthening of Cu and Nb in heavily deformed Cu-Nb microcomposites is much lower than that expected from the yield strength of heavily deformed Cu and Nb. The yield stress of the Cu-Nb microcomposite fabricated by the bundling and drawing process was found to be in good agreement with the predicted yield stress of the present model. At drawing strains above 10, Nb filaments reached a thickness of approximately 10 ㎚ and there after further working resulted in random rupture of the filaments rather than continued plastic deformation and thinning, which may result in the slower increase of the strength than the predicted values with drawing strain.