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| 1 | Evaluation of dynamic development of grain structure during friction stir welding of pure copper using a quasi in situ method显示文摘By employing a quasi in situ method, we investigated the dynamic evolution of the grain structure con-sidering the material flow, strain, and strain rate in the friction stir welding of pure copper. The tool' stop action' and rapid cooling were employed and a brass foil was used as a marker to show the material flow path. The grain structure along the material flow path was characterised using electron backscatter diffraction. Static recrystallization occurs for the work-hardened base material in the preheating stage in front of the tool In the acceleration flow stage, grains are significantly refined by plastic deforma-tion, discontinuous dynamic recrystallization, annealing twinning during the strain-induced boundary migration and slight continuous dynamic recrystallization. In the deceleration flow stage, due to a strain reversal, the grain first coarsens, and is thereafter refined again. Finally, the hot-deformed material in the shoulder-affected zone is ‘frozen’ directly whereas that in the probe-affected zone undergoes signif-icant annealing;thus, the recrystallized microstructure and 45°-rotated cube texture are obtained in the probe-affected zone. | X.C.Liu Y.F.Sun T.Nagira K.Ushioda H.Fujii | 2019 | Journal of Materials Science & Technology2019，35，7： | 3 |
| 2 | Friction stir spot welding of SPCC low carbon steel plates at extremely low welding temperature显示文摘Friction stir spot welding (FSSW) was applied to 2.0 mm thick steel plate cold-rolled commercial (SPCC) low carbon steel plates at a very low rotation speed that ranged from 5 to 50rpm, which was much lower than that generally used for the conventional FSSW technique. Due to the very low heat input, the welding processes could therefore be completed at a peak welding temperature below 160℃. As a result, a significantly refined microstructure with an average grain size of about 0.41μm was formed in the stir zone of the joints and the JI {0-11 }<-211> and J2{1-1O}<-1-12> shear textures were the dominant components, which are different from the D1{11-2}<111> and D2{-1-12}<111> shear textures formed in the conventional FSSW joints. In addition, no heat affected zone could be detected along the crosssectional plane of the joints. Although a few void-like non-bonded areas were still observed along the interface between the upper and lower steel plates, the shear tensile loads of the joints increased to about 10.0 kN when welded at a condition of 8t, 20rpm and 30 s, and the joints fractured through the plug failure mode. | Y.F.Sun H.Fujii Y.Sato Y.Morisada | 2019 | Journal of Materials Science & Technology2019，35，5： | 2 |
| 3 | Shock compression and spallation damage of high-entropy alloy Al_(0.1)CoCrFeNi显示文摘Shock compression and spallation damage of a face-center cubic phase high-entropy alloy(HEA)Al_(0.1)CoCrFeNi were investigated via plate impact experiments along with free surface velocity measurements.Postmortem samples were characterized with transmission electron microscopy and electron backscatter diffraction.The Hugoniot equation of state and spall strength at different impact strengths were determined.There exists a power-law relation between spall strength and strain rate.The spall strength of Al_(0.1)CoCrFeNi HEA is about 50%higher than those of previously studied HEAs and comparable to those widely applied structural stainless steels at the same shock stress.Dislocation glide and stacking faults are the important deformation mechanisms in the Al_(0.1)CoCrFeNi HEA.Nanotwins are only observed at high shock stress.Damage in the Al_(0.1)CoCrFeNi HEA is ductile in nature.Voids are nucleated preferentially in grain interiors,and the intragranular voids show a strong dependence on grain boundary misorientation and peak stress. | N.B.Zhang J.Xu Z.D.Feng Y.F.Sun J.Y.Huang X.J.Zhao X.H.Yao S.Chen L.Lu S.N.Luo | 2022 | Journal of Materials Science & Technology2022，，33： | 0 |
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