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- 저자 : Gbadebo Moses Owolabi (검색결과 1 건)
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Dynamic Failure Investigation in Ultrafi ne Grained AA2219: Mechanical and Microstructural Analysis
Amin Azimi,Gbadebo Moses Owolabi,Nikhil Kumar,Grant Warner 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.4
In this study, the high strain rate behavior of ultrafi ne grained (UFG) AA2219 alloy processed via multi axial forging atcryogenic temperature was investigated. Room temperature forged sample was used as a reference to determine the eff ectsof signifi cant grain size refi nement on the dynamic response of the materials. The initial microstructure characterizationindicated that severe plastic deformation in the cryogenically process alloy resulted in its grain size reduction to ~ 270 nmand the second phase breakage to fi ner particles. The results of the dynamic impact tests show that the strain hardening andthermal softening are substantially less signifi cant in the UFG materials, whereas the maximum fl ow stress and the strain ratesensitivity increased. Furthermore, the grain size reduction led to the absorption of higher portion of the deformation energyand an increase in the toughness of the fabricated UFG material when compared to the conventionally forged samples. Thisimprovement is approximately 56% at a strain rate of 4000 s −1 obtained via the grain structure refi nement. Microstructureanalysis of the post-deformed samples revealed two fully transformed adiabatic shear bands (ASBs) in the coarser grainedmaterial due to intense localized strain and thermal instability during the impact tests which caused the pushing off of thesecond phases and cracks formation inside the ASBs. However, low-intensity deformed ASBs and a notable enhancementin crack initiation strength were observed by morphology and fi nal confi guration of the post-deformed UFG samples. Inaddition, no considerable hardness variations were experienced in the impacted UFG material due to the saturation of grainsize during the cryogenically forging process. In contrary to the UFG alloys, signifi cant hardness increase was observed inthe deformed coarse grained material which was associated with softening in the adjacent regions providing a zone proneto cracks initiation.
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