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이성학,김낙준,오진근,이의휘 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.10
The effects of microstructural factors on high-cycle fatigue properties and fatigue crack propagation behavior of welded regions of a cast Ti-6Al-4V alloy were investigated in this study. High-cycle fatigue test and fatigue crack propagation test were conducted for the welded regions, which were processed by two different welding methods, i.e., tungsten inert gas (TIG) welding and electron beam (EB) welding, and then the test data were analyzed in relation to microstructures, tensile properties, and fatigue fracture mode. The base metal was composed of Widmansta¨tten structure, while the EB and TIG welds consisted of basket-weave type structure having thin α platelets. The high-cycle fatigue results indicated that fatigue strength of the EB weld was lower than that of the base metal or the TIG weld because of the existence of coarse pores formed during welding, although it had highest yield strength. In the case of the fatigue crack propagation, the EB weld composed of very thin α platelets had the faster crack propagation rate than the base metal or the TIG weld. The effective microstructural factor determining the fatigue crack propagation rate was found to be the width of α platelets because it was well matched with the reversed plastic zone size calculated at near-threshold ΔK.
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정밀주조된 Ti-6Al-4V 합금 판재의 피로성질에 미치는 판재 두께의 영향
吳振根,李玎求,金洛俊,李星鶴,李義徽 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.7
Effects of plate thickness on high-cycle fatigue properties and fatigue crack propagation behavior of investment-cast Ti-6Al-4V alloy plates having Widmansta¨tten structure were investigated in this study. High-cycle fatigue test and fatigue crack propagation test were conducted on three cast plates having different thickness, and then the test data were analyzed in relation with microstructures, tensile properties, and fatigue fracture mode. The high-cycle fatigue results indicated that fatigue strength of the three cast plates was quite similar because of their similar tensile strength. In the case of the fatigue crack propagation, the thicker cast plate composed of thinner α platelets had the slightly faster crack propagation rate than the other plates. The effective microstructural factor determining the fatigue crack propagation rate was found to be the thickness of a platelets because it was well matched with the reversed cyclic plastic zone size calculated in the threshold ΔK regime.
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정밀주조된 A356 Al 합금의 미세조직과 기계적 성질과 미치는 HIPping의 영향
김낙준,이민하,김재중,김경훈,이성학,이의휘 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.2
The effects of HIPping on high-cycle fatigue properties of investment cast A356 Al alloys were investigated in this study. Tensile and high-cycle fatigue tests were conducted for cast alloys, two of which were HIPped, and then the test data were analyzed in relation with microstructures, tensile and fracture properties, and fatigue fracture mode. Eutectic Si particles were homogeneously dispersed in the matrix of the cast A356 Al alloys, but there were many large pores formed as cast defects. The high-cycle fatigue results indicated that fatigue strength of the HIPped alloys was higher than that of the non-HIPped alloys because of the significant reduction in volume fraction of pores by HiPping. In the non-HIPped specimens, fatigue cracks initiated at large pores adjacent to the specimen surface and then propagated down to several hundreds micrometers depth while coalescing with other large pores. On the other hand, the HIPped specimens, where pores did not affect the fatigue substantially, fatigue cracks propagated along eutectic Si particles formed at solidification cell boundaries, thereby showing improved fatigue strength by 40∼50% over the non-HIPped specimens.
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오진근(Jinkeun Oh),김낙준(Nack J. Kim),이성학(Sunghak Lee),이의휘(Eui W. Lee) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
The effects of microstructural factors on high-cycle fatigue properties of welded regions of an investment cast Ti-6AI-4V alloy were investigated in this study. High-cycle fatigue were conducted for the welded regions, which were processed by two different welding methods, i.e. tungsten inert gas (TIG) welding and electron beam (EB) welding, and then the test data were analyzed in relation with microstructures, tensile properties, and fatigue fracture mode. The base metal was composed of a Widmanstatten structure, which was then transformed to a basket-weave structure having thin a platelets after welding and annealing. The high-cycle fatigue results indicated that fatigue strength of the EB weld was lower than that of the base metal or the TIG weld because of the existence of coarse micropores formed during welding, although it had highest yield strength.
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