A DSC scan of a Cu-33.5Zn-4Sn (mass%) alloy shows two exothermic peaks at around 250 and 300 C. The first peak is associated with the precipitation of 1 -plates with M9R structure, and the second peak is associated with the formation of precipitates. For the first peak, the 1 -plates start to nucleate at grain boundaries and grow dendritically upon heating. The primary and secondary arms of the dendritic 1 -plates grow in two preferred directions, namely, [110] B2 and [100] B2 of the 0 matrix. However, the stacking faults in the two arms are parallel and differ from those with the structure of the twin-accommodating variants. As the thickness and number of 1 -plates increase, the hardness of the alloy increases significantly; however, the recovery strain reduces dramatically. Additionally, the precipitates nucleate heterogeneously at the interface between the 1 -plate and the 0 matrix on heating above 300 C. The volume fraction of the precipitates increases with temperature, resulting in a reduction in the ductility of the alloy and a complete loss of its shape memory effect.
This study investigates the relationship between the morphology and the fracture behavior of upper bainite in JIS SK5 steel. The cleavage crack path was found to lie on f001g , f112g or f123g using electron backscatter diffraction (EBSD) from the fracture surface. Additionally, most of the bainite sheaf boundaries were found to be high-angle boundaries. If the cleavage planes are presumed to lie uniquely on f001g , then most of the deviations of the angles between two K-S variants in a given austenite grain are high-angle deviations. According to TEM diffraction analysis, the orientation relationship of cementite/bainitic ferrite satisfies the Bagaryatskii relation, and the habit plane of cementite precipitated in the bainite sheaf locates on ð0 1 11Þ k ð100Þ . Cementite does not significantly affect the propagation of a cleavage crack. Hence, cleavage cracking deflects at grain boundaries or bainite sheaf boundaries, but only reinitiates at the cementite/bainitic ferrite interface.
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